~Cambridge Natural Science Manuals.~
                         =BIOLOGICAL SERIES.=

                GENERAL EDITOR:—ARTHUR E. SHIPLEY, M.A.
           FELLOW AND TUTOR OF CHRIST’S COLLEGE, CAMBRIDGE.

                            FOSSIL PLANTS.

                    ~London~: C. J. CLAY AND SONS,
                 CAMBRIDGE UNIVERSITY PRESS WAREHOUSE,
                            AVE MARIA LANE,
                                  AND
                             H. K. LEWIS,
                        136, GOWER STREET, W.C.

                    ~Glasgow~: 263, ARGYLE STREET.
                      ~Leipzig~: F. A. BROCKHAUS.
                  ~New York~: THE MACMILLAN COMPANY.
                      ~Bombay~: E. SEYMOUR HALE.

[Illustration: TREE STUMPS IN A CARBONIFEROUS FOREST. VICTORIA PARK,
  GLASGOW.]

                             FOSSIL PLANTS

                  FOR STUDENTS OF BOTANY AND GEOLOGY

                                  BY

                      A. C. SEWARD, M.A., F.G.S.
                     ST JOHN’S COLLEGE, CAMBRIDGE,
          LECTURER IN BOTANY IN THE UNIVERSITY OF CAMBRIDGE.

                          WITH ILLUSTRATIONS.

                                VOL. I.

                              CAMBRIDGE:
                       AT THE UNIVERSITY PRESS.
                                 1898
                       [_All Rights reserved._]

                             ~Cambridge~:
                     PRINTED BY J. AND C. F. CLAY,
                       AT THE UNIVERSITY PRESS.

                               PREFACE.

In acceding to Mr Shipley’s request to write a book on Fossil Plants
for the Cambridge Natural History Series, I am well aware that I have
undertaken a work which was considered too serious a task by one who
has been called a “founder of modern Palaeobotany.” I owe more than I
am able to express to the friendship and guidance of the late Professor
Williamson; and that I have attempted a work to which he consistently
refused to commit himself, requires a word of explanation. My excuse
must be that I have endeavoured to write a book which may render more
accessible to students some of the important facts of Palaeobotany, and
suggest lines of investigation in a subject which Williamson had so
thoroughly at heart.

The subject of Palaeobotany does not readily lend itself to adequate
treatment in a work intended for both geological and botanical
students. The Botanist and Geologist are not always acquainted
with each other’s subject in a sufficient degree to appreciate the
significance of Palaeobotany in its several points of contact with
Geology and recent Botany. I have endeavoured to bear in mind the
possibility that the following pages may be read by both non-geological
and non-botanical students. It needs but a slight acquaintance with
Geology for a Botanist to estimate the value of the most important
applications of Palaeobotany; on the other hand, the bearing of fossil
plants on the problems of phylogeny and descent cannot be adequately
understood without a fairly intimate knowledge of recent Botany.

The student of elementary geology is not as a rule required to concern
himself with vegetable palaeontology, beyond a general acquaintance
with such facts as are to be found in geological text-books. The
advanced student will necessarily find in these pages much with which
he is already familiar; but this is to some extent unavoidable in a
book which is written with the dual object of appealing to Botanists
and Geologists. While considering those who may wish to extend their
botanical or geological knowledge by an acquaintance with Palaeobotany,
my aim has been to keep in view the requirements of the student who
may be induced to approach the subject from the standpoint of an
original investigator. As a possible assistance to those undertaking
research in this promising field of work, I have given more references
than may seem appropriate to an introductory treatise, and there are
certain questions dealt with in greater detail than an elementary
treatment of the subject requires. In several instances references
are given in the text or in footnotes to specimens of Coal-Measure
plants in the Williamson cabinet of microscopic sections. Now that this
invaluable collection of slides has been acquired by the Trustees of
the British Museum, the student of Palaeobotany has the opportunity of
investigating for himself the histology of Palaeozoic plants.

My plan has been to deal in some detail with certain selected types,
and to refer briefly to such others as should be studied by anyone
desirous of pursuing the subject more thoroughly, rather than to cover
a wide range or to attempt to make the list of types complete. Of late
years there has been a much wider interest evinced by Botanists in
the study of fossil plants, and this is in great measure due to the
valuable and able work of Graf zu Solms-Laubach. His _Einleitung in
die Palaeophytologie_ must long remain a constant book of reference
for those engaged in palaeobotanical work. While referring to authors
who have advanced the study of petrified plants of the Coal period,
one should not forget the valuable services that have been rendered by
such men as Butterworth, Binns, Wilde, Earnshaw, Spencer, Nield, Lomax
and Hemingway, by whose skill the specimens described by Williamson and
others were first obtained and prepared for microscopical examination.

I am indebted to many friends, both British and Continental, for help
of various kinds. I would in the first place express my thanks to
Professor T. McKenny Hughes for having originally persuaded me to begin
the study of recent and fossil plants. I am indebted to Prof. Nathorst
of Stockholm, Dr Hartz of Copenhagen, Prof. Zeiller, Dr Renault and
Prof. Munier-Chalmas of Paris, Prof. Bertrand of Lille, Prof. Stenzel
and the late Prof. Roemer of Breslau, Dr Sterzel of Chemnitz, the
late Prof. Weiss of Berlin, the late Dr Stur of Vienna, and other
continental workers, as well as to Mr Knowlton of Washington, for
facilities afforded me in the examination of fossil plant collections.
My thanks are due to the members of the Geological and Botanical
departments of the British Museum; also to Mr E. T. Newton of the
Geological Survey, and to those in charge of various provincial
museums, for their never-failing kindness in offering me every
assistance in the investigation of fossil plants under their charge.
Prof. Marshall Ward has given me the benefit of his criticism on the
section dealing with Fungi; and my friend Mr Alfred Harker has rendered
me a similar service as regards the chapter on Geological History. I
am especially grateful to my colleague, Mr Francis Darwin, for having
read through the whole of the proofs of this volume. To Mr Shipley, as
Editor, I am under a debt of obligation for suggestions and help in
various forms. I would also express my sense of the unfailing courtesy
and skill of the staff of the University Press.

My friend Mr Kidston of Stirling has always generously responded to my
requests for the loan of specimens from his private collection. Prof.
Bayley Balfour of Edinburgh, Mr Wethered of Cheltenham and others have
assisted me in a similar manner. I would also express my gratitude
to Dr Hoyle of Manchester, Mr Platnauer of York, and Mr Rowntree of
Scarborough for the loan of specimens.

To Dr Henry Woodward of the British Museum I am indebted for the loan
of the woodblocks made use of in figs. 10, 47, 60, 66, and 101, and to
Messrs Macmillan for the process-block of fig. 25.

For the photographs reproduced in figs. 15, 34, 68, 102 and 103 I owe
an acknowledgment to Mr Edwin Wilson of Cambridge, and to my friend Mr
C. A. Barber for the micro-photograph made use of in fig. 40.

In conclusion I wish more particularly to thank my wife, who has drawn
by far the greater number of the illustrations, and has in many other
ways assisted me in the preparation of this Volume.

In Volume II the Systematic treatment of Plants will be concluded,
and the last chapters will be devoted to such subjects as geological
floras, plants as rock-builders, fossil plants and evolution, and other
general questions connected with Palaeobotany.

                                                        A. C. SEWARD.

  BOTANICAL LABORATORY, CAMBRIDGE.
            _March_, 1898.

                          TABLE OF CONTENTS.

                           PART I. GENERAL.

                              CHAPTER I.
                    =HISTORICAL SKETCH.= Pp. 1–11.

  Fossil plants and the Flood. Sternberg and Brongniart. The
      internal structure of fossil plants. English Palaeobotanists.
      Difficulties of identification.

                              CHAPTER II.
     =RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY.= Pp. 12–21.

  Neglect of fossils by Botanists. Fossil plants and distribution.
      Fossil plants and climate. Fossil plants and phylogeny.

                             CHAPTER III.
                   =GEOLOGICAL HISTORY.= Pp. 22–53.

  Rock-building. Calcareous rocks. Geological sections. Inversion of
      strata. Table of Strata:

  I. Archaean, 34–36. II. Cambrian, 36–37. III. Ordovician, 37–38.
  IV. Silurian, 38. V. Devonian, 39. VI. Carboniferous, 39–45.
  VII. Permian, 45–47. VIII. Trias., 47–48. IX. Jurassic, 48–49. X.
  Cretaceous, 50–51. XI. Tertiary, 51–53. Geological Evolution.

                              CHAPTER IV.
          =THE PRESERVATION OF PLANTS AS FOSSILS.= Pp. 54–92.

  Old surface-soils. Fossil wood. Conditions of fossilisation.
      Drifting of trees. Meaning of the term ‘Fossil.’ Incrustations.
      Casts of trees. Fossil casts. Plants and coal. Fossils in
      half-relief. Petrified trees. Petrified wood. Preservation of
      tissues. Coal-balls. Fossil nuclei. Fossil plants in volcanic
      ash. Conditions of preservation.

                              CHAPTER V.
               =DIFFICULTIES AND SOURCES OF ERROR IN THE
              DETERMINATION OF FOSSIL PLANTS.= Pp. 93–109.

  External resemblance. Venation characters. Decorticated stems.
      Imperfect casts. Mineral deposits simulating plants. Traces of
      wood-borers in petrified tissue. Photography and illustration.

                              CHAPTER VI.
                     =NOMENCLATURE.= Pp. 110–115.

  Rules for nomenclature. The rule of priority. Terminology and
      convenience.

                         PART II. SYSTEMATIC.

                             CHAPTER VII.
                      =THALLOPHYTA.= Pp. 116–228.
                                                                 =PAGE=
    I. =PERIDINIALES=                                            117–118

   II. =COCCOSPHERES AND RHABDOSPHERES=                          118–121

  III. =SCHIZOPHYTA=                                             121–138
      A. SCHIZOPHYCEAE (CYANOPHYCEAE)                            122–132
          _Girvanella_ 124–126.  Borings in shells 127–129.
            _Zonatrichites_ 129–130.

      B. SCHIZOMYCETES (BACTERIA)                                132–138
          _Bacillus Permicus_ 135–136. _B. Tieghemi_ and
            _Micrococcus Guignardi_ 136. Fossil Bacteria 137–138.

   IV. =ALGAE=                                                   138–205
      Scarcity of fossil algae. Fossils simulating Algae.
          Recognition of fossil algae. _Algites &c._

      A. DIATOMACEAE                                             150–156
          Recent Diatoms. Fossil Diatoms. _Bactryllium &c._

      B. CHLOROPHYCEAE                                           156–178
          _a._ SIPHONEAE                                         157–177
              α. =Caulerpaceae=                                  157–159
              β. =Codiaceae=                                     159–164
                _Codium_ 159–160. _Sphaerocodium_ 160.
                  _Penicillus_ 161. _Ovulites_ 161–164.
                  _Halimeda_ 164.
              γ. =Dasycladaceae=                                 164–177
                _Acetabularia_ 165–166. _Acicularia_ 166–169.
                  _Cymopolia_ 169–171. _Vermiporella_ 172–173.
                  _Sycidium_ 173. _Diplopora_ 174–175.
                  _Gyroporella_ 175. _Dactylopora_, Palaeozoic
                  and Mesozoic Siphoneae 175–177.
          _b._ CONFERVOIDEAE                                     177–178

      C.INCERTAE SEDIS                                           178–183
          Boghead ‘Coal.’ _Reinschia_ 180–181. _Pila_ 181–182.

      D. RHODOPHYCEAE                                            183–190
          CORALLINACEAE                                          183–190
              _Lithothamnion_ 185–189. _Solenopora_ 189–190.

      E. PHAEOPHYCEAE                                            191–202
          _Nematophycus_                                         192–202
          _Pachytheca_                                           202–204
          _Algites_                                              204–205

    V. =MYXOMYCETES (MYCETOZOA)=                                 205–206
        _Myxomycetes Mangini_ 206.

   VI. =FUNGI=                                                   207–222
        ASCOMYCETES. BASIDIOMYCETES.
            Pathology of fossil tissues. _Oochytrium Lepidodendri_
              216–217. _Peronosporites antiquarius_ 217–220.
              _Cladosporites bipartitus_ 220. _Haplographites
              cateniger_ 220. _Zygosporites_ 220–221. _Polyporus
              vaporarius_ 221.

  VII. =CHAROPHYTA=                                              222–228
        CHAREAE                                                  223–228
            _Chara_ 225–228. _C. Bleicheri_ 226. _C. Knowltoni_
              226–227. _C. Wrighti_ 227.

                             CHAPTER VIII.
                       =BRYOPHYTA.= Pp. 229–241.

     I. =HEPATICAE=                                              230–236
            _Marchantites_ 233–235. _M. Sezannensis_ 234–235.

    II. =MUSCI=                                                  236–241
            _Muscites_ 238–241. _M. polytrichaceus_ 239–240.
              Palaeozoic Mosses. _Muscites ferrugineus_ 241.

                              CHAPTER IX.
          =PTERIDOPHYTA (VASCULAR CRYPTOGRAMS).= Pp. 242–294.

    I. =EQUISETALES (RECENT)=                                    244–254
            EQUISETACEAE                                         244–254
                _Equisetum_ 246–254.

   II. =FOSSIL EQUISETALES=                                      254–294
      A. EQUISETITES                                             257–281
            _Equisetites Hemingwayi_ 263–264. _E.
              spatulatus_ 264–266. _E. zeaeformis_ 266. _E.
              arenaceus_ 268–269. _E. columnaris_ 269–270.
              _E. Beani_ 270–275. _E. lateralis_ 275–279. _E.
              Burchardti_ 279–280.
      B. PHYLLOTHECA                                             281–291
            _Phyllotheca deliquescens_ 283–284. _P.
              Brongniarti_ 286–287. _P. indica_ and _P.
              australis_ 287–289.
      C. SCHIZONEURA                                             291–294
            _S. gondwanensis_ 292–293.

                              CHAPTER X.
               =EQUISETALES (_continued_).= Pp. 295–388.

      D. CALAMITES                                               295–383

          I. =Historical sketch=                                 295–302

         II. =Description of the anatomy of Calamites=           302–364
          _a._ _Stems_                                           304–329
              _Arthropitys_, _Arthrodendron_, and
                _Calamodendron_.
          _b._ _Leaves_                                          329–342
              α. _Calamocladus_ (_Asterophyllites_) 332–336.
                _C. equisetiformis_ 335–336.
              β. _Annularia_ 336–342. _A. stellata_ 338–340.
                _A. sphenophylloides_ 341–342.
          _c._ _Roots_                                           342–349
          _d._ _Cones_                                           349–365
              _Calamostachys Binneyana_ 351–355. _C. Casheana_
                355–357. _Palaeostachya vera_ 358–360.
                _Calamostachys_, _Palaeostachya_ and
                _Macrostachya_ 361–364.

        III. =Pith-casts of Calamites=                           365–380
          _Calamitina_ 367–374. _Calamites_ (_Calamitina_)
            _Göpperti_ 372–374. _Stylocalamites_ 374–376. _C._
            (_Stylocalamites_) _Suckowi_ 374–376. _Eucalamites_
            376–379. _C._ (_Eucalamites_) _cruciatus_ 378–379.

         IV. =Conclusion=                                        381–383

      E. ARCHAEOCALAMITES                                        383–388
        _A. scrobiculatus_ 386–387.

                              CHAPTER XI.
                     SPHENOPHYLLALES. Pp. 389–414.

    I. =SPHENOPHYLLUM=                                           389–414
       A. =The anatomy of Sphenophyllum=                         392–406
          _a._ _Stems_                                           392–398
              _Sphenophyllum insigne_ and _S. plurifoliatum_
                397–398.
          _b._ _Roots_                                               399
          _c._ _Leaves_                                              399
          _d._ _Cones_                                           401–406
              _Sphenophyllostachys Dawsoni_ 402–405. _S.
                Römeri_ 405–406.

       B. =Types of vegetative Branches of Sphenophyllum=        407–412
          _Sphenophyllum emarginatum_ 407–408. _S.
            trichomatosum_ 408–409. _S. Thoni_ 410–411. _S.
            speciosum_ 411–412.

       C. =Affinities, Range and Habit of Sphenophyllum=         412–414

                        LIST OF ILLUSTRATIONS.

  FRONTISPIECE. TREE STUMPS IN A CARBONIFEROUS FOREST. Drawn from a
      photograph. (M. Seward.) PAGE 57.

  FIG.                                                              PAGE
    1. _Lepidodendron._ (M. S.)                                       10
    2. Geological section                                             29
    3. Table of strata                                            32, 33
    4. Geological section (coal seam)                                 44
    5. _Neuropteris Scheuchzeri_ Hoffm. (M. S.)                       45
    6. Submerged Forest at Leasowe. (M. S.)                           59
    7. Ammonite on coniferous wood. (M. S.)                           61
    8. Coniferous wood in flint. (M. S.)                              62
    9. Bored fossil wood. (M. S.)                                     62
   10. Section of an old pool filled up with a mass of _Chara_. (From
         block lent by Dr Woodward)                                   69
   11. _Equisetites columnaris_ Brongn. (M. S.)                       72
   12. _Stigmaria ficoides_ Brongn. (M. S.)                           73
   13. _Cordaites etc._ in coal. (M. S.)                              76
   14. Crystallisation in petrified tissues                           81
   15. _Lepidodendron._ (From a photograph by Mr Edwin Wilson
         of a specimen lent by Mr Kidston)                            82
   16. Cast of a fossil cell. (M. S.)                                 84
   17. Calcareous nodule from the Coal-Measures                       85
   18. _Lepidodendron_ from Arran. (M. S.)                            89
   19. _Trigonocarpon_ seeds in a block of sandstone. (M. S.)         91
   20. _Restio_, _Equisetum_, _Casuarina_ and _Ephedra_. (M. S.)      95
   21. _Polygonum equisetiforme_ Sibth. and Sm. (M. S.)               96
   22. _Kaulfussia æsculifolia_ Blume. (M. S.)                        97
   23. A branched Lepidodendroid stem (_Knorria mirabilis_ Ren.
         and Zeill.). (M. S.)                                        102
   24. Partially disorganised petrified tissue                       107
   25. Coccospheres and Rhabdospheres. (Lent by Messrs Macmillan)    119
   26. _Girvanella problematica_ Eth. and Nich. (M. S.)              124
   27. Fish-scale and shell perforated by a boring organism. (M. S.) 128
   28. _Bacillus Tieghemi_ Ren. and _Micrococcus Guignardi_ Ren.
         (M. S.)                                                     135
   29. _Laminaria_ sp.                                               140
   30. Rill-mark; trail of a seaweed; tracks of a Polychaet. (M. S.) 143
   31. _Chondrites verisimilis_ Salt. (M. S.)                        146
   32. _Lithothamnion mamillosum_ Gümb.; _Sycidium melo_ Sandb.;
         _Bactryllium deplanatum_ Heer; Calcareous pebble from a
         lake in Michigan. (M. S.)                                   155
   33. _Cymopolia barbata_ (L.); _Acicularia Andrussowi_ Solms;
         _Acicularia_ sp.; _A. Schencki_ (Möb.); _A. Mediterranea_
         Lamx.; _Ovulites margaritula_ Lamx.; _Penicillus
         pyramidalis_ (Lamx.) (M. S.)                                162
   34. _Acetabularia mediterranea_ Lamx. (Photograph by Mr Edwin
         Wilson)                                                     165
   35. _Diplopora_; _Gyroporella_; _Penicillus_; _Ovulites
         margaritula_ Lam.; _Confervites chantransioides_ (Born.)    174
   36. Torbanite; _Pila bibractensis_ and _Reinschia australis_      180
   37. _Lithothamnion_ sp.; _L. suganum_ Roth.; _Sphaerocodium
         Bornemanni_ Roth.                                           186
   38. _Solenopora compacta_ (Billings). (M. S.)                     189
   39. _Nematophycus Logani_ (Daws.)                                 196
   40. _Nematophycus Storriei_ Barb. (Photograph by Mr C. A. Barber) 199
   41. Cells of _Cycadeoidea gigantea_ Sew., _Osmundites Dowkeri_
         Carr and _Memecylon_ with vacuolated contents;
         _Peronosporites antiquarius_ Smith; _Zygosporites_          214
   42. Tracheids of coniferous wood attacked by _Trametes
         radiciperda_ Hart and _Agaricus melleus_ Vahl.              215
   43. _Oochytrium Lepidodendri_ Ren.; _Polyporus vaporarius_ Fr.
         var. _succinea_; _Cladosporites bipartitus_ Fel.;
         _Haplographites cateniger_ Fel. (M. S.)                     217
   44. Cells of fossil plants with fungal hyphae                     219
   45. _Chara Knowltoni_ Sew.; _Chara foetida_ A. Br. (_A_ and _B_,
         Mr Highley; _C–E_, M. S.)                                   224
   46. _Chara Bleicheri_ Sap.; _Chara_? sp.; _C. Wrighti_ Forbes.
         (M. S.)                                                     226
   47. _Chara Knowltoni_ Sew. (From block lent by Dr Woodward)       227
   48. _Tristichia hypnoides_ Spreng.; _Podocarpus cupressina_ Br.
         and Ben.; _Selaginella Oregana_ Eat. (M. S.)                231
   49. _Marchantites erectus_ (Leck.) (M. S.)                        233
   50. _Marchantites Sezannensis_ Sap. (M. S.)                       235
   51. _Muscites polytrichaceus_ Ren. and Zeill. (M. S.)             239
   52. _Equisetum maximum_ Lam.; _E. arvense_ L.                     246
   53. _Equisetum palustre_ L. (M. S.)                               247
   54. Plan of the vascular bundles in an _Equisetum_ stem; _E.
         arvense_ L.                                                 250
   55. _Equisetum variegatum_ Schl.; _E. maximum_ Lam.               252
   56. Calamitean leaf-sheath. (M. S.)                               260
   57. _Equisetites Hemingwayi_ Kidst. (Mr Highley)                  262
   58. _Equisetites spatulatus_ Zeill.; _E. zeaeformis_ (Schloth.);
         _Equisetites lateralis_ Phill.; _Equisetites columnaris_
         Brongn.; _Equisetum trachyodon_ A. Br. (M. S.)              265
   59. _Equisetites platyodon_ Brongn. (M. S.)                       267
   60. _Equisetites Beani_ (Bunb.). (From a block lent by Dr
         Woodward)                                                   271
   61. _Equisetites Beani_ (Bunb.). (M. S.)                          272
   62. _E. Beani_ (Bunb.). (M. S.)                                   274
   63. _E. lateralis_ Phill. (M. S.)                                 275
   64. _E. lateralis_ Phill. (M. S.)                                 278
   65. _E. Burchardti_ Dunk. (M. S.)                                 279
   66. _E. Yokoyamae_ Sew. (From a block lent by Dr Woodward)        280
   67. _Phyllotheca_? sp. (From a photograph by Mr Edwin Wilson)     285
   68. _Phyllotheca Brongniarti_ Zigno; _P. indica_ Bunb.;
         _Calamocladus frondosus_ Grand’Eury. (M. S.)                287
   69. _Schizoneura gondwanensis_ Feist. (M. S.)                     293
   70. Transverse section of a Calamite stem. (M. S.)                299
   71. Transverse section of a young Calamite stem                   305
   72. Longitudinal and transverse sections of _Calamites_           308
   73. Transverse section of a Calamite stem                         310
   74. Transverse section of _Calamites_ (_Arthropitys_) sp.         312
   75. Longitudinal section (tangential) of _Calamites_
         (_Arthropitys_) sp.                                         313
   76. Longitudinal section (tangential) of _Calamites_
         (_Arthropitys_) sp.                                         314
   77. Portion of a Calamite stem; partially restored. (M. S.)       316
   78.╮ Transverse and longitudinal (radial) sections of a thick     318
   79.╯   Calamite stem. (Mr Highley)                                319
   80. Transverse section of a Calamite showing callus wood          320
   81. Longitudinal section of a young Calamite                      321
   82. Pith-casts of _Calamites_ (_Stylocalamites_) sp. (M. S.)      323
   83. _Calamites_ (_Arthrodendron_) sp. Transverse and longitudinal
         sections                                                    327
   84. Transverse section of _Calamites_ (_Calamodendron_)
         _intermedius_ Ren.                                          328
   85. Leaves of a Calamite. (M. S.)                                 330
   86. Transverse section of a Calamite leaf                         331
   87. _Calamocladus equisetiformis_ (Schloth.) (Miss G. M.
         Woodward)                                                   334
   88. _Annularia stellata_ (Schloth.) (M. S.)                       339
   89. _Annularia sphenophylloides_ Zenk. (M. S.)                    340
   90. Pith-cast of a Calamite, with roots. (M. S.)                  343
   91. Transverse sections of Calamite roots                         345
   92. Root given off from a Calamite stem                           347
   93. _Calamostachys_ sp. (M. S.)                                   350
   94. _C. Binneyana_ (Carr.). (Mr Highley)                          352
   95. _C. Binneyana_ (Carr.)                                        354
   96. _C. Casheana_ Will.                                           356
   97. _Palaeostachya pedunculata_ Will. (M. S.)                     357
   98. _P. vera_ sp. nov.                                            359
   99. _Calamites_ (_Calamitina_) Göpp. (Ett.) (M. S.)               368
  100. _Calamites_ (_Calamitina_) _approximatus_ Brongn. From a
         photograph by Mr Kidston                                    370
  101. _Calamites_ (_Calamitina_) sp. (From a block lent by Dr
         Woodward)                                                   373
  102. _Calamites_ (_Eucalamites_) _cruciatus_ Sternb. (From a
         photograph by Mr Edwin Wilson)                              377
  103. _Archaeocalamites scrobiculatus_ (Schloth.). (From a
         photograph by Mr Edwin Wilson)                              385
  104. Diagrammatic longitudinal section of _Sphenophyllum_          393
  105. Transverse and longitudinal sections of _Sphenophyllum
         insigne_ (Will.) and _S. plurifoliatum_ Will. and Scott     394
  106. _Sphenophyllum plurifoliatum_ Will. and Scott. (From a
         photograph by Mr Highley)                                   398
  107. _Sphenophyllum_ strobilus, stem and root                      400
  108. Diagrammatic longitudinal section of a _Sphenophyllum_
         strobilus. (M. S.)                                          402
  109. _Sphenophyllum emarginatum_ (Brongn.) (M. S.)                 407
  110. _Sphenophyllum Thoni_ Mahr.; _S. trichomatosum_ Stur.
         (M. S.)                                                     410
  111. _Sphenophyllum speciosum_ (Royle). (M. S.)                    411

=Note.= The references in the footnotes require a word of explanation.
The titles of the works referred to will be found in the Bibliography
at the end of the volume. In this list the authors’ names are arranged
alphabetically and the papers of each author are in chronological
order. The numbers in brackets after the author’s name in the
footnotes, and before his name in the bibliographical list, refer to
the year of publication. Except in cases where the works were published
prior to 1800, the first two figures are omitted: thus Ward (84) refers
to a paper published by L. F. Ward in 1884. This system was suggested
by Dr H. H. Field in the _Biologisches Centralblatt_, vol. XIII.
1893, p. 753. (_Ueber die Art der Abfassung naturwissenschaftlicher
Litteraturverzeichnisse._)

                          =PART I. GENERAL.=

                              CHAPTER I.

                          HISTORICAL SKETCH.

  “But particular care ought to be had not to consult or take
  relations from any but those who appear to have been both long
  conversant in these affairs, and likewise persons of Sobriety,
  Faithfulness and Discretion, to avoid the being misled and
  imposed upon either by falsehood, or the ignorance, credulity,
  and fancifulness, that some of these people are but too obnoxious
  unto.” JOHN WOODWARD, 1728.

The scientific study of fossil plants dates from a comparatively recent
period, and palaeobotany has only attained a real importance in the
eyes of botanists and geologists during the last few decades of the
present century. It would be out of place, in a short treatise like
the present, to attempt a detailed historical sketch, or to give an
adequate account of the gradual rise and development of this modern
science. An excellent _Sketch of Palaeobotany_ has recently been drawn
up by Prof. Lester Ward[1], of the United States Geological Survey, and
an earlier historical retrospect may be found in the introduction to
an important work by an eminent German palaeobotanist, the late Prof.
Göppert[2]. In the well-known work by Parkinson on _The Organic Remains
of a Former World_[3] there is much interesting information as to the
early history of our knowledge of fossil plants, as well as a good
exposition of the views held at the beginning of this century.

[Sidenote: FOSSIL PLANTS AND THE FLOOD.]

As a means of bringing into relief the modern development of the
science of fossil plants, we may briefly pass in review some of the
earlier writers, who have concerned themselves in a greater or less
degree with a descriptive or speculative treatment of the records of a
past vegetation. In the early part of the present century, and still
more in the eighteenth century, the occurrence of fossil plants and
animals in the earth’s crust formed the subject of animated, not to
say acrimonious, discussion. The result was that many striking and
ingenious theories were formulated as to the exact manner of formation
of fossil remains, and the part played by the waters of the deluge in
depositing fossiliferous strata. The earlier views on fossil vegetables
are naturally bound up with the gradual evolution of geological
science. It is from Italy that we seem to have the first glimmering
of scientific views; but we are led to forget this early development
of more than three hundred years ago, when we turn to the writings
of English and other authors of the eighteenth century. “Under these
white banks by the roadside,” as a writer on Verona has expressed it,
“was born, like a poor Italian gipsy, the modern science of geology.”
Early in the sixteenth century the genius of Leonardo da Vinci[4]
compelled him to adopt a reasonable explanation of the occurrence of
fossil shells in rocks far above the present sea-level. Another Italian
writer, Fracastaro, whose attention was directed to this matter by
the discovery of numerous shells brought to light by excavations at
Verona, expressed his belief in the organic nature of the remains, and
went so far as to call in question the Mosaic deluge as a satisfactory
explanation of the deposition of fossil-bearing strata.

The partial recognition by some observers of the true nature of fossils
marks the starting point of more rational views. The admission that
fossils were not mere sports of nature, or the result of some wonderful
‘vis lapidifica,’ was naturally followed by numerous speculations
as to the manner in which the remains of animals and plants came
to be embedded in rocks above the sea-level. For a long time, the
‘universal flood’ was held responsible by nearly all writers for the
existence of fossils in ancient sediments. Dr John Woodward, in his
_Essay toward a Natural History of the Earth_, propounded the somewhat
revolutionary theory, that “the whole terrestrial globe was taken all
to pieces and dissolved at the Deluge, the particles of stone, marble,
and all solid fossils dissevered, taken up into the water, and there
sustained together with sea-shells and other animal and vegetable
bodies: and that the present earth consists, and was formed out of that
promiscuous mass of sand, earth, shells, and the rest falling down
again, and subsiding from the water[5].” In common with other writers,
he endeavoured to fix the exact date of the flood by means of fossil
plants. Speaking of some hazel-nuts, which were found in a Cheshire
moss pit, he draws attention to their unripened condition, and adds:
“The deluge came forth at the end of May, when nuts are not ripe.” As
additional evidence, he cites the occurrence of “Pine cones in their
vernal state,” and of some Coal-Measure fossils which he compares with
Virginian Maize, “tender, young, vernal, and not ripened[6].” Woodward
(1665–1728) was Professor of Physic in Gresham College; he bequeathed
his geological collections to the University of Cambridge, and founded
the Chair which bears his name.

Another writer, Mendes da Costa, in a paper in the _Philosophical
Transactions_ for 1758, speaks of the impressions of “ferns and
reed-like plants” in the coal-beds, and describes some fossils
(_Sigillaria_ and _Stigmaria_) as probably unknown forms of plant
life[7].

Here we have the suggestion that in former ages there were plants
which differed from those of the present age. Discussing the nature
of some cones (_Lepidostrobi_) from the ironstone of Coalbrookdale
in Shropshire, he concludes: “I firmly believe these bodies to be of
vegetable origin, buried in the strata of the Earth at the time of the
universal deluge recorded by Moses.” Scheuchzer of Zurich, the author
of one of the earliest works on fossil plants and a “great apostle
of the Flood Theory,” figures and describes a specimen as an ear of
corn, and refers to its size and general appearance as pointing to the
month of May as the time of the deluge[8]. Another English writer, Dr
Parsons, in giving an account of the well-known ‘fossil fruits and
other bodies found in the island of Sheppey,’ is disposed to dissent
from Woodward’s views as to the time of the flood. He suggests that the
fact of the Sheppey fruits being found in a perfectly ripe condition,
points to the autumn as the more probable time for the occurrence of
the deluge[9].

In looking through the works of the older writers, and occasionally
in the pages of latter-day contributors, we frequently find curiously
shaped stones, mineral markings on rock surfaces, or certain fossil
animals, described as fossil plants. In Plot’s _Natural History of
Oxfordshire_, published in 1705, a peculiarly shaped stone, probably a
flint, is spoken of as one of the ‘Fungi lethales non esculenti[10]’;
and again a piece of coral[11] is compared with a ‘Bryony root broken
off transversely.’ On the other hand, that we may not undervalue
the painstaking and laborious efforts of those who helped to lay
the foundations of modern science, we may note that such authors as
Scheuchzer and Woodward were not misled by the moss-like or dendritic
markings of oxide of manganese on the surface of rocks, which are not
infrequently seen to-day in the cabinets of amateurs as specimens of
fossil plants.

The oldest figures of fossil plants from English rocks which are drawn
with any degree of accuracy are those of Coal-Measure ferns and other
plants in an important work by Edward Lhwyd published at Oxford in
1760[12].

Passing beyond these prescientific speculations, brief reference may
be made to some of the more eminent pioneers of palaeobotany. The
Englishman Artis[13] deserves mention for the quality rather than the
quantity of his contributions to Palaeozoic botany; and among American
authors Steinhauer’s[14] name must hold a prominent place in the list
of those who helped to found this branch of palaeontology. Among
German writers, Schlotheim stands out prominently as one who first
published a work on fossil plants which still remains an important
book of reference. Writing in 1804, he draws attention to the neglect
of fossils from a scientific standpoint; they are simply looked upon,
he says, as “unimpeachable documents of the flood[15].” His book
contains excellent figures of many Coal-Measure plants, and we find in
its pages occasional comparisons of fossil species with recent plants
of tropical latitudes. Among the earlier authors whose writings soon
become familiar to the student of fossil plants, reference must be
made to Graf Sternberg, who was born three years before Schlotheim,
but whose work came out some years later than that of the latter.
His great contribution to Fossil Botany entitled _Versuch einer
geognostisch-botanischen Darstellung der Flora der Vorwelt_, was
published in several parts between the years 1820 and 1838; it was
drawn up with the help of the botanist Presl, and included a valuable
contribution by Corda[16]. In addition to descriptions and numerous
figures of plants from several geological horizons, this important work
includes discussions on the formation of coal, with observations on the
climates of past ages.

[Sidenote: STERNBERG AND BRONGNIART.]

Sternberg endeavoured to apply to fossil plants the same methods of
treatment as those made use of in the case of recent species. About
the same time as Sternberg’s earlier parts were published, Adolphe
Brongniart[17] of Paris began to enrich palaeobotanical science by
those splendid researches which have won for him the title of the
“Father of palaeobotany.” In Brongniart’s _Prodrome_, and _Histoire des
végétaux fossiles_, and later in his _Tableau des genres de végétaux
fossiles_, we have not merely careful descriptions and a systematic
arrangement of the known species of fossil plants, but a masterly
scientific treatise on palaeobotany in its various aspects, which
has to a large extent formed the model for the best subsequent works
on similar lines. From the same author, at a later date, there is at
least one contribution to fossil plant literature which must receive
a passing notice even in this short sketch. In 1839 he published an
exhaustive account of the minute structure of one of the well-known
Palaeozoic genera, _Sigillaria_; this is not only one of the best
of the earliest monographs on the histology of fossil species, but
it is one of the few existing accounts of the internal structure of
this common type[18]. The fragment of a Sigillarian stem which formed
the subject of Brongniart’s memoir is in the Natural History Museum
in the Jardin des Plantes, Paris. It affords a striking example of
the perfection of preservation as well as of the great beauty of the
silicified specimens from Autun, in Central France. Brongniart was
not only a remarkably gifted investigator, whose labours extend over
a period connecting the older and more crude methods of descriptive
treatment with the modern development of microscopic analysis, but
he possessed the power of inspiring a younger generation with a
determination to keep up the high standard of the palaeobotanical
achievements of the French School. In some cases, indeed, his
disciples have allowed a natural reverence for the Master to warp
their scientific judgement, where our more complete knowledge has
naturally led to the correction of some of Brongniart’s conclusions.
Without attempting to follow the history of the science to more recent
times, the names of Heer, Lesquereux, Zigno, Massalongo, Saporta and
Ettingshausen should be included among those who rendered signal
service to the science of fossil plants. The two Swiss writers,
Heer[19] and Lesquereux[20], contributed numerous books and papers
on palaeobotanical subjects, the former being especially well known
in connection with the fossil floras of Switzerland and of Arctic
lands, and the latter for his valuable writings on the fossil plants
of his adopted country, North America. Zigno[21] and Massalongo[22]
performed like services for Italy, and the Marquis of Saporta’s name
will always hold an honourable and prominent position in the list of
the pioneers of scientific palaeobotany; his work on the Tertiary and
Mesozoic floras of France being specially noteworthy among the able
investigations which we owe to his ability and enthusiasm[23]. In Baron
Ettingshausen[24] we have another representative of those students
of ancient vegetation who have done so much towards establishing the
science of fossil plants on a philosophical basis.

As in other fields of Natural Science, so also in a marked degree in
fossil botany, a new stimulus was given to scientific inquiry by the
application of the microscope to palaeobotanical investigation. In
1828 Sprengel published a work entitled _Commentatio de Psarolithis,
ligni fossilis genere_[25]; in which he dealt in some detail with
the well-known silicified fern-stems of Palaeozoic age, from Saxony,
basing his descriptions on the characteristics of anatomical structure
revealed by microscopic examination.

[Sidenote: THE INTERNAL STRUCTURE OF FOSSIL PLANTS.]

In 1833 Henry Witham of Lartington brought out a work on _The Internal
Structure of Fossil Vegetables_[26]; this book, following the much
smaller and less important work by Sprengel, at once established
palaeobotany on a firmer scientific basis, and formed the starting
point for those more accurate methods of research, which have yielded
such astonishing results in the hands of modern workers. In the
introduction Witham writes, “My principal object in presenting this
work to the public, is to impress upon geologists the advantage of
attending more particularly to the intimate organization of fossil
plants; and should I succeed in directing their efforts towards
the elucidation of this obscure subject, I shall feel a degree of
satisfaction which will amply repay my labour[27].”

On another page he writes as follows,—“From investigations made by
the most active and experienced botanical geologists, we find reason
to conclude that the first appearance of an extensive vegetation
occurred in the Carboniferous series; and from a recent examination
of the mountain-limestone groups and coal-fields of Scotland, and the
north of England, we learn that these early vegetable productions, so
far from being simple in their structure, as had been supposed, are
as complicated as the phanerogamic plants of the present day. This
discovery necessarily tends to destroy the once favourite idea, that,
from the oldest to the most recent strata, there has been a progressive
development of vegetable and animal forms, from the simplest to the
most complex[28].” Since Witham’s day we have learnt much as to the
morphology of Palaeozoic plants, and can well understand the opinions
to which he thus gives expression.

It would be difficult to overrate the immense importance of this
publication from the point of view of modern palaeobotany.

The art of making transparent sections of the tissues of fossil
plants seems to have been first employed by Sanderson, a lapidary,
and it was afterwards considerably improved by Nicol[29]. This most
important advance in methods of examination gave a new impetus to
the subject, but it is somewhat remarkable that the possibilities of
the microscopical investigation of fossil plants have been but very
imperfectly realised by botanical workers until quite recent years. As
regards such a flora as that of the Coal-Measures, we can endorse the
opinion expressed at the beginning of the century in reference to the
study of recent mosses—“Ohne das Göttergeschenk des zusammengesetzten
Mikroskops ist auf diesem Felde durchaus keine Ernte[30].” A useful
summary of the history of the study of internal structure is given
by Knowlton in a memoir published in 1889[31]. Not long after
Witham’s book was issued there appeared a work of exceptional merit
by Corda[32], in which numerous Palaeozoic plants are figured and
fully described, mainly from the standpoint of internal structure.
This author lays special stress on the importance of studying the
microscopical structure of fossil plants.

[Sidenote: ENGLISH PALAEOBOTANISTS.]

Without pausing to enumerate the contributions of such well-known
continental authors as Göppert, Cotta, Schimper, Stenzel, Schenk and
a host of others, we may glance for a moment at the services rendered
by English investigators to the study of palaeobotanical histology.
Unfortunately we cannot always extend our examination of fossil plants
beyond the characters of external form and surface markings; but in
a few districts there are preserved remnants of ancient floras in
which fragments of stems, roots, leaves and other structures have been
petrified in such a manner as to retain with wonderful completeness
the minute structure of their internal tissues. During the deposition
of the coal seams in parts of Yorkshire and Lancashire the conditions
of fossilisation were exceptionally favourable, and thus English
investigators have been fortunately placed for conducting researches on
the minute anatomy of the Coal-Measure plants. The late Mr Binney of
Manchester did excellent service by his work on the internal structure
of some of the trees of the Coal Period forests. In his introductory
remarks to a monograph on the genus _Calamites_, after speaking of
the desirability of describing our English specimens, he goes on to
say, “When this is done, we are likely to possess a literature on our
Carboniferous fossils worthy of the first coal-producing country[33].”
The continuation and extension of Binney’s work in the hands of
Carruthers, Williamson, and others, whose botanical qualifications
enabled them to produce work of greater scientific value, has gone far
towards the fulfilment of Binney’s prophecy.

[Sidenote: DIFFICULTIES OF IDENTIFICATION.]

In dealing with the structure of Palaeozoic plants, we shall be
under constant obligation to the splendid series of memoirs from
the pen of Prof. Williamson[34]. As the writer of a sympathetic
obituary notice has well said: “In his fifty-fifth year he began
the great series of memoirs which mark the culminating point of his
scientific activity, and which will assure to him, for all time, in
conjunction with Brongniart, the honourable title of a founder of
modern Palaeobotany[35].” If we look back through a few decades,
and peruse the pages of Lindley and Hutton’s classic work[36] on
the Fossil flora of Great Britain, a book which is indispensable
to fossil botanists, and read the description of such a genus as
_Sigillaria_ or _Stigmaria_; or if we extend our retrospect to an
earlier period and read Woodward’s description of an unusually good
specimen of a _Lepidodendron_, and finally take stock of our present
knowledge of such plants, we realise what enormous progress has been
made in palaeobotanical studies. Lindley and Hutton, in the preface
to the first volume of the Flora, claim to have demonstrated that
both _Sigillaria_ and _Stigmaria_ were plants with “the highest
degree of organization, such as _Cactaeae_, or _Euphorbiaceae_, or
even _Asclepiadeae_”; Woodward describes his _Lepidodendron_ (Fig. 1)
as “an ironstone, black and flat, and wrought over one surface very
finely, with a strange cancellated work[37].” Thanks largely to the
work of Binney, Carruthers, Hooker, Williamson, and to the labours
of continental botanists, we are at present almost as familiar with
_Lepidodendron_ and several other Coal-Measure genera as with the
structure of a recent forest tree. While emphasizing the value of the
microscopic methods of investigation, we are not disposed to take such
a hopeless view of the possibilities of the determination of fossil
forms, in which no internal structure is preserved, as some writers
have expressed. The preservation of minute structure is to be greatly
desired from the point of view of the modern palaeobotanist, but he
must recognise the necessity of making such use as he can of the
numberless examples of plants of all ages, which occur only in the form
of structureless casts or impressions.

[Illustration: FIG. 1. Four leaf-cushions of a _Lepidodendron_. Drawn
  from a specimen in the Woodward Collection, Cambridge. (Nat. size.)]

In looking through the writings of the earlier authors we cannot help
noticing their anxiety to match all fossil plants with living species;
but by degrees it was discovered that fossils are frequently the
fragmentary samples of extinct types, which can be studied only under
very unfavourable conditions. In the absence of those characters on
which the student of living plants relies as guides to classification,
it is usually impossible to arrive at any trustworthy conclusions as
to precise botanical affinity. Brongniart and other authors recognised
this fact, and instituted several convenient generic terms of a purely
artificial and provisional nature, which are still in general use. The
dangers and risks of error which necessarily attend our attempts to
determine small and imperfect fragments of extinct species of plants,
will be briefly touched on in another place.

                              CHAPTER II.

            RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY.

  “La recherche du plan de la création, voilà le but vers lequel nos
  efforts peuvent tendre aujourd’hui.” GAUDRY, 1883.

Since the greater refinements and thoroughness of scientific methods
and the enormous and ever-increasing mass of literature have inevitably
led to extreme specialisation, it is more than ever important to look
beyond the immediate limits of one’s own subject, and to note its
points of contact with other lines of research. A palaeobotanist is
primarily concerned with the determination and description of fossil
plants, but he must at the same time constantly keep in view the
bearing of his work on wider questions of botanical or geological
importance. From the nature of the case, we have in due measure to
adapt the methods of work to the particular conditions before us. It is
impossible to follow in the case of all fossil species precisely the
same treatment as with the more complete and perfect recent plants;
but it is of the utmost importance for a student of palaeobotany, by
adhering to the methods of recent botany, to preserve as far as he is
able the continuity of the past and present floras. Palaeontological
work has often been undertaken by men who are pure geologists, and
whose knowledge of zoology or botany is of the most superficial
character, with the result that biologists have not been able to avail
themselves, to any considerable extent, of the records of extinct forms
of life. They find the literature is often characterised by a special
palaeontological phraseology, and by particular methods of treatment,
which are unknown to the student of living plants and animals. From
this and other causes a purely artificial division has been made
between the science of the organic world of to-day and that of the past.

[Sidenote: NEGLECT OF FOSSILS BY BOTANISTS.]

Fossils are naturally regarded by a stratigraphical geologist
as records which enable him to determine the relative age of
fossil-bearing rocks. For such a purpose it is superfluous to inquire
into the questions of biological interest which centre round the
relics of ancient floras. Primarily concerned, therefore, with fixing
the age of strata, it is easy to understand how geologists have been
content with a special kind of palaeontology which is out of touch
with the methods of systematic zoology or botany. On the other hand,
the botanist whose observations and researches have not extended
beyond the limits of existing plants, sees in the vast majority of
fossil forms merely imperfect specimens, which it is impossible to
determine with any degree of scientific accuracy. He prefers to wait
for perfect material; or in other words, he decides that fossils must
be regarded as outside the range of taxonomic botany. It would seem,
then, that the unsatisfactory treatment or comparative neglect of
fossil plants, has been in a large measure due to the narrowness of
view which too often characterises palaeobotanical literature. This
has at once repelled those who have made a slight effort to recognise
the subject, and has resulted in a one-sided and, from a biological
standpoint, unscientific treatment of this branch of science. It must
be admitted that palaeobotanists have frequently brought the subject
into disrepute by their over-anxiety to institute specific names for
fragments which it is quite impossible to identify. This over-eagerness
to determine imperfect specimens, and the practice of drawing
conclusions as to botanical affinity without any trustworthy evidence,
have naturally given rise to considerable scepticism as to the value
of palaeobotanical records. Another point, which will be dealt with
at greater length in a later chapter, is that geologists have usually
shown a distinct prejudice against fossil plants as indices of
geological age; this again, is no doubt to a large extent the result of
imperfect and inaccurate methods of description, and of the neglect of
and consequent imperfect acquaintance with fossil plants as compared
with fossil animals.

The student of fossil plants should endeavour to keep before him the
fact that the chief object of his work is to deal with the available
material in the most natural and scientific manner; and by adopting
the methods of modern botany, he should always aim to follow such
lines as may best preserve the continuity of past and present types
of plants. Descriptions of floras of past ages and lists of fossil
species, should be so compiled that they may serve the same purpose to
a stratigraphical geologist, who is practically a geographer of former
periods of the Earth’s history, as the accounts of existing floras
to students of present day physiography. The effect of carrying out
researches on some such lines as these, should be to render available
to both botanists and geologists the results of the specialist’s work.

In some cases, palaeobotanical investigations may be of the utmost
service to botanical science, and of little or no value to geology.
The discovery of a completely preserved gametophyte of _Lepidodendron_
or _Calamites_, or of a petrified Moss plant in Palaeozoic rocks would
appeal to most botanists as a matter of primary importance, but for the
stratigraphical geologist such discoveries would possess but little
value. On the other hand the discovery of some characteristic species
of Coal-Measure plants from a deep boring through Mesozoic or Tertiary
strata might be a matter of special geological importance, but to the
botanist it would be of no scientific value. In very many instances,
however, if the palaeobotanist follows such lines as have been briefly
suggested, the results of his labours should be at once useful and
readily accessible to botanists and geologists. As Humboldt has said
in speaking of Palaeontology, “the analytical study of primitive
animal and vegetable life has taken a double direction; the one is
purely morphological, and embraces especially the natural history
and physiology of organisms, filling up the chasms in the series of
still living species by the fossil structures of the primitive world.
The second is more specially geognostic, considering fossil remains
in their relations to the superposition and relative age of the
sedimentary formations[38].”

[Sidenote: FOSSIL PLANTS AND DISTRIBUTION.]

To turn for a moment to some of the most obvious connections between
palaeobotany and the wider sciences of botany and geology. The records
of fossil species must occupy a prominent position in the data by
which we may hope to solve some at least of the problems of plant
evolution. From the point of view of distribution, palaeobotany is of
considerable value, not only to the student of geographical botany, but
to the geologist, who endeavours to map out the positions of ancient
continents with the help of palaeontological evidence. The present
distribution of plants and animals represents but one chapter in the
history of life on the Earth; and to understand or appreciate the facts
which it records, we have to look back through such pages as have been
deciphered in the earlier chapters of the volume. The distribution of
fossil plants lies at the foundation of the principles of the present
grouping of floras on the Earth’s surface. Those who have confined
their study of distribution to the plant geography of the present
age, must supplement their investigations by reference to the work of
palaeobotanical writers. If the lists of plant species drawn up by
specialists in fossil botany, have been prepared with a due sense of
the important conclusions which botanists may draw from them from the
standpoint of distribution, they will be readily accepted as sound
links in the chain of evidence. Unfortunately, however, if many of
the lists of ancient floras were made use of in such investigations,
the conclusions arrived at would frequently be of little value on
account of the untrustworthy determinations of many of the species.
In the case of particular genera the study of the distribution of
the former species both in time and space, that is geologically and
geographically, points to rational explanations of, or gives added
significance to, the facts of present day distribution. That isolated
conifer, _Ginkgo biloba_ L. now restricted to Japan and China, was in
former times abundant in Europe and in other parts of the world. It is
clearly an exceedingly ancient type, isolated not only in geographical
distribution but in botanical affinities, which has reached the last
stage in its natural life. The Mammoth trees of California (_Sequoia
sempervirens_ Endl., and _S. gigantea_ Lindl. and Gord.) afford other
examples of a parallel case. The Tulip tree of North America and China
and other allied forms are fairly common in the Tertiary plant beds
of Europe, but the living representatives are now exclusively North
American. Such differences in distribution as are illustrated by these
dicotyledonous forest trees in Tertiary times and at the present day,
have been clearly explained with the help of the geological record.
Forbes, Darwin, Asa Gray[39] and others have been able to explain many
apparent anomalies in the distribution of existing plants, and to
reconcile the differences between the past and present distribution
of many genera by taking account of the effect on plant life of the
glacial period. As the ice gradually crept down from the polar regions
and spread over the northern parts of Europe, many plants were driven
further south in search of the necessary warmth. In the American
continent such migration was rendered possible by the southern land
extension; in Europe on the other hand the southerly retreat was cut
off by impassable barriers, and the extinction of several genera was
the natural result.

The comparatively abundant information which we possess as to the
past vegetation of polar regions and the value of such knowledge to
geologists and botanists alike is in striking contrast to the absence
of similar data as regards Antarctic fossils. Darwin in an exceedingly
interesting letter to Hooker _à propos_ of a forthcoming British
Association address, referring to this subject writes as follows:—

“The extreme importance of the Arctic fossil plants is self-evident.
Take the opportunity of groaning over our ignorance of the Lignite
plants of Kerguelen Land, or any Antarctic land. It might do good[40].”

In working out any collection of fossil plants, it would be well,
therefore, to bear in mind that our aim should be rather to reproduce
an accurate fragment of botanical history, than to perform feats of
determination with hopelessly inadequate specimens. Had this principle
been generally followed, the number of fossil plant species would be
enormously reduced, but the value of the records would be considerably
raised.

[Sidenote: FOSSIL PLANTS AND CLIMATE.]

Our knowledge of plant anatomy, and of those laws of growth which
govern certain classes of plants to-day and in past time, has been very
materially widened and extended by the facts revealed to us by the
detailed study of Coal-Measure species. The modern science of Plant
Biology, refounded by Charles Darwin, has thrown considerable light
on the laws of plant life, and it enables us to correlate structural
characteristics with physiological conditions of growth. Applying the
knowledge gained from living plants to the study of such extinct types
as permit of close microscopic examination, we may obtain a glimpse
into the secrets of the botanical binomics of Palaeozoic times. The
wider questions of climatic conditions depend very largely upon the
evidence of fossil botany for a rational solution. As an instance
of the best authenticated and most striking alternation in climatic
conditions in comparatively recent times, we may cite the glacial
period or Ice-Age. The existence of Arctic conditions has been proved
by purely geological evidence, but it receives additional confirmation,
and derives a wider importance from the testimony of fossil plants. In
rocks deposited before the spread of ice from high northern latitudes,
we find indubitable proofs of a widely distributed subtropical flora in
Central and Northern Europe. Passing from these rocks to more recent
beds there are found indications of a fall in temperature, and such
northern plants as the dwarf Birch, the Arctic Willow and others reveal
the southern extension of Arctic cold to our own latitudes.

The distribution of plants in time, that is the range of classes,
families, genera and species of plants through the series of strata
which make up the crust of the earth, is a matter of primary importance
from a botanical as well as from a geological point of view.

Among the earlier writers, Brongniart recognised the marked differences
between the earlier and later floras, and attempted to correlate
the periods of maximum development of certain classes of plants
with definite epochs of geological history. He gives the following
classification in which are represented the general outlines of plant
development from Palaeozoic to Tertiary times[41].

    I. Reign of Acrogens    ╭ 1. Carboniferous epoch.
                            ╰ 2. Permian epoch.

   II. Reign of Gymnosperms ╭ 3. Triassic epoch.
                            ╰ 4. Jurassic epoch (including the Wealden).

  III. Reign of Angiosperms ╭ 5. Cretaceous epoch.
                            ╰ 6. Tertiary epoch.

Since Brongniart’s time this method of classification has been
extended to many of the smaller subdivisions of the geological epochs,
and species of fossil plants are often of the greatest value in
questions of correlation. In recent years the systematic treatment
of Coal-Measure and other plants in the hands of various Continental
and English writers has clearly demonstrated their capabilities
for the purpose of subdividing a series of strata into stages and
zones[42]. The more complete becomes our knowledge of any flora, the
greater possibility there is of making use of the plants as indices of
geological age[43].

[Sidenote: FOSSIL PLANTS AND PHYLOGENY.]

Not only is it possible to derive valuable aid in the correlation of
strata from the facts of plant distribution, but we may often follow
the various stages in the history of a particular genus as we trace
the records of its occurrence through the geologic series. In studying
the march of plant life through past ages, the botanist may sometimes
follow the progress of a genus from its first appearance, through the
time of maximum development, to its decline or extinction. In the
Palaeozoic forests there was perhaps no more conspicuous or common tree
than the genus long known under the name of _Calamites_. This plant
attained a height of fifty or a hundred feet, with a proportionate
girth, and increased in thickness in a manner precisely similar to
that in which our forest trees grow in diameter. The exceptionally
favourable conditions under which specimens of calamitean plants
have been preserved, have enabled us to become almost as familiar
with the minute structure of their stems and roots, as well as with
their spore-producing organs, as with those of a living species.
In short, it is thoroughly established that _Calamites_ agrees in
most essential respects with our well known _Equisetum_, and must
be included in the same order, or at least sub-class, as the recent
genus of _Equisetaceae_. As we ascend the geologic series from the
Coal-Measures, a marked numerical decline of _Calamites_ is obvious
in the Permian period, and in the red sandstones of the Vosges, which
belong to the same series of rocks as the Triassic strata of the
Cheshire plain, the true _Calamites_ is replaced by a large _Equisetum_
apparently identical in external appearance and habit of growth with
the species living to-day. In the more recent strata the Horse-tails
are still represented, but the size of the Tertiary species agrees
more closely with the comparatively small forms which have such a
wide geographical distribution at the present time. Thus we are able
to trace out the history of a recent genus of Vascular Cryptogams,
and to follow a particular type of organisation from the time of its
maximum development, through its gradual transition to those structural
characters which are represented in the living descendants of the
arborescent Calamites of the coal-period forests. The pages of such a
history are frequently imperfect and occasionally missing, but others,
again, are written in characters as clear as those which we decipher by
a microscopical examination of the tissues of a recent plant.

As one of the most striking instances in which the microscopic study
of fossil plants has shown the way to a satisfactory solution of
the problems of development, we may mention such extinct genera as
_Lyginodendron_, _Myeloxylon_ and others. Each of these genera will be
dealt with at some length in the systematic part of the book, and we
shall afterwards discuss the importance of such types, from the point
of view of plant evolution.

The botanist who would trace out the phylogeny of any existing class or
family, makes it his chief aim to discover points of contact between
the particular type of structure which he is investigating, and that of
other more or less closely related classes or families.

Confining himself to recent forms, he may discover, here and there,
certain anatomical or embryological facts, which suggest promising
lines of inquiry in the quest after such affinities as point to a
common descent. Without recourse to the evidence afforded by the plants
of past ages, we must always admit that our existing classification
of the vegetable kingdom is an expression of real gaps which separate
the several classes of plants from one another. On the other hand our
recently acquired and more accurate knowledge of such genera as have
been alluded to, has made us acquainted with types of plant structure
which enable us to fill in some of the lacunae in our existing
classification. In certain instances we find merged in a single species
morphological characteristics which, in the case of recent plants, are
regarded as distinctive features of different subdivisions. It has
been clearly demonstrated that in _Lyginodendron_, we have anatomical
peculiarities typical of recent cycads, combined with structural
characteristics always associated with existing ferns. In rare cases,
it happens that the remarkably perfect fossilisation of the tissues of
fossil plants, enables us not only to give a complete description of
the histology of extinct forms, but also to speak with confidence as to
some of those physiological processes which governed their life.

[Sidenote: GEOLOGICAL HISTORY.]

So far, palaeobotany has been considered in its bearings on the
study of recent plants. From a geological point of view the records
of ancient floras have scarcely less importance. In recent years,
facts have been brought to light, which show that plants have played
a more conspicuous part than has usually been supposed as agents of
rock-building. As tests of geologic age, there are good grounds for
believing that the inferiority of plants to animals is more apparent
than real. This question, however, must be discussed at greater length
in a later chapter.

Enough has been said to show the many-sided nature of the science of
Fossil Plants, and the wide range of the problems which the geologist
or botanist may reasonably expect to solve, by means of trustworthy
data afforded by scientific palaeobotanical methods.

                             CHAPTER III.

                          GEOLOGICAL HISTORY.

  “But how can we question dumb rocks whose speech is not clear[44]?”

In attempting to sketch in briefest outline the geological history
of the Earth, the most important object to keep in view is that of
reproducing as far as possible the broad features of the successive
stages in the building of the Earth’s crust. It is obviously
impossible to go into any details of description, or to closely
follow the evolution of the present continents; at most, we can only
refer to such facts as may serve as an introduction of the elements
of stratigraphical geology to non-geological readers. For a fuller
treatment of the subject reference must be made to special treatises on
geology.

For the sake of convenience, it is customary in stratigraphical geology
as also in biology, to make use of our imperfect knowledge as an aid
to classification. If we possessed complete records of the Earth’s
history, we should have an unbroken sequence, not merely of the various
forms of life that ever existed, but of the different kinds of rocks
formed in the successive ages of past time. As gaps exist in the chain
of life, so also do we find considerable breaks in the sequence of
strata which have been formed since the beginning of geologic time. The
danger as well as the convenience of artificial classification must be
kept in view. This has been well expressed by Freeman, in speaking of
architectural styles,—“Our minds,” he says, “are more used to definite
periods; they neglect or forget transitions which do indeed exist[45].”
The idea of definite classification is liable to narrow our view of
uniformity and the natural sequence of events.

[Sidenote: ROCK-BUILDING.]

Composing that part of the earth which is accessible to us,—or as it is
generally called the earth’s crust,—there are rocks of various kinds,
of which some have been formed by igneous agency, either as lavas or
beds of ashes, or in the form of molten magmas which gradually cooled
and became crystalline below a mass of superincumbent strata. With
these rocks we need not concern ourselves.

A large portion of the earth’s crust consists of such materials as
sandstones, limestones, shales, and similar strata which have been
formed in precisely the same manner as deposits are being accumulated
at the present day. The whole surface of the earth is continually
exposed to the action of destructive agencies, and suffers perpetual
decay; it is the products of this ceaseless wear and tear that form the
building materials of new deposits.

The operation of water in its various forms, of wind, changes of
temperature, and other agents of destruction cannot be fully dealt with
in this short summary.

A river flowing to the sea or emptying itself into an inland lake,
carries its burden of gravel, sand, and mud, and sooner or later, as
the rate of flow slackens, it deposits the materials in the river-bed
or on the floor of the sea or lake.

Fragments of rock, chipped off by wedges of ice, or detached in other
ways from the parent mass, find their way to the mountain streams,
and if not too heavy are conveyed to the main river, where the larger
pieces come to rest as more or less rounded pebbles. Such water-worn
rocks accumulate in the quieter reaches of a swiftly flowing river, or
are thrown down at the head of the river’s delta. If such a deposit
of loose water-worn material became cemented together either by the
consolidating action of some solution percolating through the general
mass, or by the pressure of overlying deposits, there would be formed
a hard rock made up of rounded fragments of various kinds of strata
derived from different sources. Such a rock is known as a CONGLOMERATE.
The same kind of rock may be formed equally well by the action of the
sea; an old sea-beach with the pebbles embedded in a cementing matrix
affords a typical example of a coarse conglomerate. Plant remains are
occasionally met with in conglomerates, but usually in a fragmentary
condition.

From a conglomerate composed of large water-worn pebbles, to a fine
homogeneous sandstone there are numerous intermediate stages. A body
of water, with a velocity too small to carry along pebbles of rock in
suspension or to roll them along the bed of the channel, is still able
to transport the finer fragments or grains of sand, but as a further
decrease in the velocity occurs, these are eventually deposited as beds
of coarse or fine sand. The stretches of sand on a gradually shelving
sea shore, or the deposits of the same material in a river’s delta,
have been formed by the gradual wearing away and disintegration of
various rocks, the detritus of which has been spread out in more or
less regular beds on the floor of a lake or sea. Such accumulations
of fine detrital material, if compacted or cemented together, become
typical SANDSTONES.

In tracing beds of sandstone across a tract of country, it is
frequently found that the character of the strata gradually alters; mud
or clay becomes associated with the sandy deposit, until finally the
sandstone is replaced by beds of dark coloured shale. Similarly the
sandy detritus on the ocean floor, or in an inland lake, when followed
further and further from the source from which the materials were
derived, passes by degrees into argillaceous sand, and finally into
sheets of dark clay or mud. The hardened beds of clay or fine grained
mud become transformed into SHALES. As a general rule, then, shales are
rocks which have been laid down in places further from the land, or at
a greater distance from the source of origin of the detrital material,
than sandstones or conglomerates. The conglomerates, or old shingle
beaches, usually occur in somewhat irregular patches, marking old
shore-lines or the head of a river delta. Coarse sandstones, or grits,
may occur in the form of regularly bedded strata stretching over a
wide area; and shales or clays may be followed through a considerable
extent of country. The finer material composing the clays and shales
has been held longer in suspension and deposited in deeper water in
widespread and fairly horizontal layers.

In some districts sandstones occur in which the individual grains
show a well marked rounding of the angles, and in which fossils
are extremely rare or entirely absent. The close resemblance of
such deposits to modern desert sands suggests a similar method of
formation; and there can be no doubt that in some instances there have
been preserved the wind-worn desert sands of former ages. Aeolian
or wind-formed accumulations, although by no means common, are of
sufficient importance to be mentioned as illustrating a certain type of
rock.

[Sidenote: CALCAREOUS ROCKS.]

The thick masses of limestone which form so prominent a feature in
parts of England and Ireland, have been formed in a manner different
from that to which sandstones and shales owe their origin. On the
floor of a clear sea, too far from land to receive any water-borne
sediment, there is usually in process of formation a mass of calcareous
material, which in a later age may rise above the surface of the water
as chalk or LIMESTONE. Those organisms living in the sea, which are
enclosed either wholly or in part by calcareous shells, are agents of
limestone-building; their shells constantly accumulating on the floor
of the sea give rise in course of time to a thick mass of sediment,
composed in great part of carbonate of lime. Some of the shells in
such a deposit may retain their original form, the calcareous body
may on the other hand be broken up into minute fragments which are
still recognisable with the help of a microscope, or the shells and
other hard parts may be dissolved or disintegrated beyond recognition,
leaving nothing in the calcareous sediment to indicate its method of
formation.

Not a few limestones consist in part of fossil corals, and owe their
origin to colonies of coral polyps which built up reefs or banks of
coral in the ancient seas.

In the white cliffs of Dover, Flamborough Head and other places, we
have a somewhat different form of calcareous rock, which in part
consists of millions of minute shells of Foraminifera, in part of
broken fragments of larger shells of extinct molluscs, and to some
extent of the remains of siliceous sponges. As a general rule,
limestones and chalk rocks are ancient sediments, formed in clear and
comparatively deep water, composed in the main of carbonate of lime,
in some cases with a certain amount of carbonate of magnesium, and
occasionally with a considerable admixture of silica.

In such rocks land-plants must necessarily be rare. There are, however,
limestones which wholly or in part owe their formation to masses of
calcareous algae, which grew in the form of submarine banks or on coral
reefs. Occasionally the remains of these algae are clearly preserved,
but frequently all signs of plant structure have been completely
obliterated. Again, there occur limestone rocks formed by chemical
means, and in a manner similar to that in which beds of travertine are
now being accumulated.

Granites, basalts, volcanic lavas, tuffs, and other igneous rocks
need not claim our attention, except in such cases as permit of plant
remains being found in association with these materials. Showers of
ashes blown from a volcano, may fall on the surface of a lake or sea
and become mixed with sand and mud of subaerial origin. Streams of lava
occasionally flow into water, or they may be poured from submarine
vents, and so spread out on the ocean bed with strata of sand or clay.

Passing from the nature and mode of origin of the sedimentary strata to
the manner of their arrangement in the Earth’s crust, we must endeavour
to sketch in the merest outline the methods of stratigraphical geology.
The surface of the Earth in some places stands out in the form of bare
masses of rock, roughly hewn or finely carved by Nature’s tools of
frost, rain or running water; in other places we have gently undulating
ground with beds of rock exposed to view here and there, but for the
most part covered with loose material such as gravel, sands, boulder
clay and surface soil.

[Sidenote: GEOLOGICAL SECTIONS.]

In the flat lands of the fen districts, the peat beds and low-lying
salt marshes form the surface features, and are the connecting links
between the rock-building now in progress and the deposits of an
earlier age. If we could remove all these surface accumulations of
sand, gravel, peat and surface soil, and take a bird’s eye view of
the bare surface of the rocky skeleton of the earth’s crust, we
should have spread before us the outlines of a geological map. In
some places fairly horizontal beds of rock stretching over a wide
extent of country, in another the upturned edges of almost vertical
strata form the surface features; or, again, irregular bosses of
crystalline igneous rock occur here and there as patches in the
midst of bedded sedimentary or volcanic strata. A map showing the
boundaries and distribution of the rocks as seen at the surface,
tells us comparatively little as to the relative positions of the
different rocks below ground, or of the relative ages of the several
strata. If we supplement this superficial view by an inspection of
the position of the strata as shown on the walls of a deep trench cut
across the country, we at once gain very important information as to
the relative position of the beds below the earth’s surface. The face
of a quarry, the side of a river bed or a railway cutting, afford
HORIZONTAL SECTIONS or PROFILES which show whether certain strata lie
above or below others, whether a series of rocks consists of parallel
and regularly stratified beds, or whether the succession of the strata
is interfered with by a greater or less divergence from a parallel
arrangement. If, for example, a section shows comparatively horizontal
strata lying across the worn down edges of a series of vertical
sedimentary rocks, we may fairly assume that some such changes as the
following have taken place in that particular area.

The underlying beds were originally laid down as more or less
horizontal deposits; these were gradually hardened and compacted,
then elevated above sea-level by a folding of the earth’s crust; the
crests of the folds were afterwards worn down by denudation, and the
eroded surface finally subsided below sea-level and formed the floor
on which newer deposits were built up. Such breaks in the continuity
of stratified deposits are known as UNCONFORMITIES; in the interval of
time which they represent great changes took place of which the records
are either entirely lost, or have to be sought elsewhere.

In certain more exceptional cases, it is possible to obtain what is
technically known as a VERTICAL SECTION; for example if a deep boring
is sunk through a series of rocks, and the core of the boring examined,
we have as it were a sample of the earth’s crust which may often teach
us valuable lessons which cannot be learnt from maps or horizontal
sections.

[Sidenote: INVERSION OF STRATA.]

It is obvious, that in a given series of beds, which are either
horizontal or more or less obliquely inclined, the underlying strata
were the first formed, and the upper beds were laid down afterwards.
If, however, we trusted solely to the order of superposition in
estimating relative age, our conclusions would sometimes be very far
from the truth. Recent geological investigations have brought to
light facts well nigh incredible as to the magnitude and extent of
rock-foldings. In regions of great earth-movements, the crust has been
broken along certain lines, and great masses of strata have been thrust
for miles along the tops of newer rocks. Thus it may be brought about
that the natural sequence of a set of beds has been entirely altered,
and older rocks have come to overlie sediments of a later geological
age. Facts such as these clearly illustrate the difficulties of correct
geological interpretation.

In the horizontal section (Fig. 2), from the summit of Büzistock on
the left to Saasterg on the right, we have a striking case of intense
rock-folding and dislocation[46]. Prof. Heim[47] of Geneva has given
numerous illustrations of the almost incredible positions assumed
in the Swiss Mountains by vast thicknesses of rocks, and in the
accompanying section taken from a recent work by Rothpletz we have a
compact example of the possibilities of earth-movements as an agent of
rock-folding. The section illustrates very clearly an exception to the
rule that the order of superposition of a set of beds indicates the
relative age of the strata. The horizontal line at the base is drawn at
a height of 1650 metres above sea-level, and the summit of Büzistock
reaches a height of 2340 m. The youngest rocks seen in the diagram are
the Eocene beds _e_, at the base and as small isolated patches on the
right-hand end of the section; the main mass of material composing the
higher ground has been bodily thrust over the Eocene rocks, and in this
process some of the beds, _b_ and _c_, have been folded repeatedly on
themselves. Similar instances of the overthrusting of a considerable
thickness of strata have been described in the North-west Highlands
of Scotland[48] and elsewhere in the British Isles. It is important
therefore to draw attention to cases of extreme folding, as such
phenomena are by no means exceptional in many parts of the world.

[Illustration: FIG. 2. Section from Büzistock to Saasterg. [After
  Rothpletz, (94) Pl. II. fig. 2.]

  _a_ = Sernifit or Verrucano (Permian).
  _b_ = Röthidolomit etc. (Permian).
  _c_ = Dogger (Jurassic).
  _d_ = Malm (Jurassic).
  _e_ = Eocene.]

The order of superposition of strata has afforded the key to our
knowledge of the succession of life in geologic time, and the
refinements of the stratigraphical correlation of sedimentary rocks
are based on the comparison of their fossil contents. By a careful
examination of the relics of fossil organisms obtained from rocks
of all ages and countries, it has been found possible to restore in
broken outline the past history of the Earth. By means, then, of
stratigraphical and palaeontological evidence, a classification of the
various rocks has been established, the lines of division being drawn
in such places as represent gaps in the fossil records, or striking and
widespread unconformities between different series of deposits.

It is only in a few regions that we find rocks which can reasonably be
regarded as the foundation stones of the Earth. As the globe gradually
cooled, and its molten mass became skinned over with a solid crust,
crystalline rocks must have been produced before the dawn of life, and
before water could remain in a liquid form on the rocky surface. As
soon as the temperature became sufficiently low, running water and rain
began the work of denudation and rock disintegration which has been
ceaselessly carried on ever since. In this continual breaking down and
building up of the Earth’s surface, it would be no wonder if but few
remnants were left of the first formed sediments of the earliest age.

The action of heat, pressure and chemical change accompanying
rock-foldings and crust-wrinklings, often so far alters sedimentary
deposits, that their original form is entirely lost, and sandstone,
shales and limestones become metamorphosed into crystalline quartzites,
slates and marbles.

The operation of metamorphism is therefore another serious difficulty
in the way of recognising the oldest rocks. The earliest animals and
plants which have been discovered are not such as we should expect
to find as examples of the first products of organic life. Below the
oldest known fossiliferous rocks, there must have been thousands of
feet of sedimentary material, which has either been altered beyond
recognition, or from some cause or other does not form part of our
present geological record.

As a general introduction to geological chronology, a short summary
may be given of the different formations or groups of strata, to which
certain names have been assigned to serve as convenient designations
for succeeding epochs in the world’s evolution. The following table
(Fig. 3, pp. 32, 33) represents the geological series in a convenient
form; the most characteristic rocks of each period are indicated by the
usual conventional shading, and the most important breaks or lacunae in
the records are shown by gaps and uneven lines. The relative thickness
of the rocks of each period is approximately shown; but the vertical
extent of the oldest or Archaean rocks as shown in Fig. 3 represents
what is without doubt but a fraction of their proportional thickness.
This table is taken, with certain alterations, from a paper by Prof.
T. McKenny Hughes in the Cambridge Philosophical Proceedings for 1879.
Speaking of the graphic method of showing the geological series, the
author of the paper says, “It is convenient to have a table of the
known strata, and although we cannot arrange all the rocks of the
world in parallel columns, and say that _ABC_ of one area are exactly
synchronous with _A′B′C′_ of another, still if we take any one country
and establish a grouping for it, we find so many horizons at which
equivalent formations can be identified in distant places, that we
generally make an approximation to HOMOTAXIS as Huxley called it. The
most convenient grouping is obviously to bracket together locally
continuous deposits, _i.e._ all the sediment which was formed from the
time when the land went down and accumulation began, to the time when
the sea bottom was raised and the work of destruction began. In the
accompanying table I have given the rocks of Great Britain classified
on this system, and bearing in mind that waste in one place must be
represented by deposit elsewhere, I have represented the periods of
degradation by intervals estimated where possible by the amount of
denudation known to have taken place between the periods of deposition
in the same district[49].”

[Illustration: TABLE OF STRATA.

                  RECENT              ╮
                  GLACIAL             ├ QUATERNARY
                  PLIOCENE            ╯

                  MIOCENE             ╮
                                      │
                  OLIGOCENE           ├ TERTIARY
                                      │
                  EOCENE              ╯

                  CRETACEOUS          ╮
                                      │
                  JURASSIC            │
                                      ├ MESOZOIC
                  TRIAS               │
                                      │
                  PERMIAN             ╯

                ╭ Coal-Measures       ╮
                │                     │
                │ Millstone Grit      │
  CARBONIFEROUS ┤                     │
                │ Yoredale Rocks      │
                │                     │
                ╰ Mountain Limestone  │
                                      │
                ╭  Devonian           │
                │                     │
                │ Upper Old Red       │
  DEVONIAN      ┤   Sandstone         │
                │                     │
                │ Lower Old Red       │
                ╰   Sandstone         │
                                      │
                ╭ Ludlow              │
                │                     │
  SILURIAN      ┤ Wenlock             ├ PALAEOZOIC
                │                     │
                ╰ May Hill            │
                                      │
                ╭ Upper Bala          │
                │                     │
                │ Lower Bala          │
  ORDOVICIAN    ┤                     │
                │ Llandeilo           │
                │                     │
                ╰ Arenig              │
                                      │
                ╭ Tremadoc            │
                │                     │
                │ Lingula Flags       │
  CAMBRIAN      ┤                     │
                │ Menevian            │
                │                     │
                ╰ Harlech             ╯

                  LAVAS,              ╮
                  VOLCANIC            │
                  ASHES,              │
                  GRANITOID           ├ ARCHAEAN
                  ROCKS AND           │
                  SCHISTS OF          │
                  ENORMOUS            │
                  THICKNESS           ╯

                    Fig 3.]

                            I. =Archaean.=

  “Men can do nothing without the make-believe of a beginning.”
                                                    GEORGE ELIOT.

There is perhaps no problem at once so difficult and so full of
interest to the student of the Earth’s history, as the interpretation
of the fragmentary records of the opening stages in geological and
organic evolution. In tracing the growth and development of the human
race, it becomes increasingly difficult to discover and decipher
written documents as we penetrate farther back towards the beginning
of the historical period; the records are usually incomplete and
fragmentary, or rendered illegible by the superposed writings of a
later date. So in the records of the rocks, as we pass beyond the
oldest strata in which clearly preserved fossils are met with, we come
to older rocks which afford either no data as to the period in which
they were formed, or like the palimpsest, with its original characters
almost obliterated by a late MS., the older portions of the Earth’s
crust have been used and re-used in the rock-building of later ages.
In the first place, it is exceedingly difficult to determine with any
certainty what rocks may be regarded as trustworthy fragments of a
primaeval land. Throughout the geological eras the Earth’s surface
has been subjected to foldings and wrinklings, volcanic activity has
been almost unceasing, and there is abundant evidence to show how
the original characters of both igneous and sedimentary rocks may be
entirely effaced by the operation of chemical and physical forces. It
was formerly held that coarsely crystalline rocks such as granite are
the oldest portions of the crust, but modern geology has conclusively
proved that many of the so-called fundamental masses of rock are merely
piles of ancient sediments which have been subjected to the repeated
operation of powerful physical and chemical forces, and have undergone
a complete rearrangement of their substance. As the result of more
detailed investigations, many regions formerly supposed to consist of
the foundation stones of the Earth’s crust, are now known to have been
centres of volcanic disturbance and widespread metamorphism, and to be
made up of post-archaean rocks.

[Sidenote: THE OLDEST ROCKS.]

The first formed rocks no doubt became at once the prey of denudation
and disintegration, and on their surface would be accumulated the
products of their own destruction: newer strata would entirely cover up
portions of the original land, to be in their turn succeeded by still
later deposits. There is reason to believe that in the remotest ages of
the Earth’s history, the forces of denudation and igneous activity were
more potent than in later times, and thus the oldest rocks could hardly
retain their original structure through the long ages of geologic time.
The earliest representatives of organic life were doubtless of such
a perishable nature that their remains could not be preserved in a
fossil state even under the most favourable conditions. Such organisms,
whether plants or animals, as possessed any resistant tissues or hard
skeletons might be preserved in the oldest rocks, but as these strata
became involved in earth-foldings or were penetrated by injections of
igneous eruptions, the relics of life would be entirely destroyed.
It is, in short, practically hopeless to look for any fragments of
the primitive crust except such as have undergone very considerable
metamorphism, and equally futile to search for any recognisable remains
of primitive life.

In many parts of the world vast thicknesses of rock occur below the
oldest known fossiliferous strata; these consist largely of laminated
crystalline masses composed of quartz, felspar, and other minerals,
having in fact the same composition as granite, but differing in the
regular arrangement of the constituent parts. To such rocks the terms
gneiss and schist have been applied. Rocks of this kind are by no means
always of Archaean age, but many of the earliest known rocks consist of
gneisses of various kinds, associated with altered lavas, metamorphosed
ashes, breccias and other products of volcanic activity; with these
there may be limestones, shales, sandstones, and other strata more or
less closely resembling sedimentary deposits. Such a succession of
gneissic rocks has been described as occupying a wide area in the basin
of the St Lawrence river, and to these enormously thick and widespread
masses a late Director of the Canadian Geological Survey applied
the term Laurentian. These Laurentian rocks, with similar strata in
Scandinavia, the north-west Highlands of Scotland, in certain parts of
such mountain ranges as the Alps, Pyrenees, Carpathians, Himalayas,
Andes, Atlas, &c., have been classed together as members of the oldest
geological period, and are usually referred to under the name of
Archaean, or less frequently Azoic rocks. In some of the uppermost
Archaean rocks there have been recently discovered a few undoubted
traces of fossil animals, but with this exception no fossils are known
throughout the great mass of Archaean strata. It is true that some
authorities regard the beds of graphite and other rocks as a proof of
the abundance of plant life, but this supposition is not supported by
any convincing evidence.

The term Azoic[50] applied by some writers to these oldest rocks
suggests the absence of life during the period in which they were
formed. Life there must have been, though we are unable to discover its
records. The period of time represented by the Archaean or Pre-Cambrian
rocks must be enormous, and it was in that earliest era that the first
links in the chain of life were forged.

                            II. =Cambrian.=

The term Cambrian was adopted by Sedgwick for a series of sedimentary
rocks in North Wales (_Cambria_). In that district, in South Wales,
the Longmynd Hills, the Malverns, in Scotland, and other regions
there occur more or less highly folded and contorted beds of pebbly
conglomerate, sandstones, shales and slates resting on the uneven
surface of an Archaean foundation.

It is in these Cambrian rocks that trustworthy records of organic life
are first met with. Among the most constant and characteristic fossils
of this period are the extinct and aberrant members of the crustacea,
the trilobites; these with some brachiopods, sponges, and other fossils
comprise the oldest fauna, of which the ancestral types have yet to
be discovered. During the last few decades the number of Cambrian
fossils has been considerably increased, and in certain regions of
North America and China there are found many thousand feet of strata
above the typical Archaean rocks and below the newer fossiliferous beds
of Cambrian age. It is reasonable to suppose that future research may
extend the present limits of fossil-bearing rocks below the horizon,
which is marked by the occurrence of the widely distributed and oldest
known trilobite, the genus _Olenellus_.

The vast thickness of Cambrian strata was for the most part laid down
on the floor of a comparatively deep sea; other members of the series
represent the shingle beaches and coast deposits accumulated on the
slopes of Archaean islands. There have been many conjectures as to the
distribution of land and sea during the deposition of these rocks; but
the data are too imperfect to enable us to restore with any degree
of confidence the physical geography of this Palaeozoic epoch, of
which the sediments stood out as islands of Cambrian land during many
succeeding ages.

                          III. =Ordovician.=

Since the days when Sedgwick and Murchison first worked out the
succession of Palaeozoic strata in North Wales, there has always
existed a considerable difference of opinion as to the best method of
subdividing the Cambrian-Silurian strata. Later research has shown
that the rocks included by Sedgwick in his Cambrian system, fall
naturally into two groups; for the upper of these Prof. Lapworth has
suggested the term Ordovician, from the name of the Ordovices, who
inhabited a part of northern Wales. At the base of the system we have
a series of volcanic and sedimentary rocks to which Sedgwick gave the
name Arenig; above these there occur the Llandeilo Flags, succeeded
by a considerable thickness of rocks known as the Bala series. The
rocks making up these Ordovician sediments consist for the most part
of slates, sandstones and limestones with volcanic ashes and lavas.
Much of the typical Welsh scenery owes its character to the folded and
weathered rocks laid down on the floor of the Ordovician sea, on which
from many centres of volcanic activity lava streams and showers of ash
were spread out between sheets of marine sediment. The Arenig Hills,
Snowdonia, and many other parts of North and South Wales, parts of
Shropshire, Scotland, Sweden, Russia, Bohemia, North America and other
regions consist of great thicknesses of Ordovician strata.

                            IV. =Silurian.=

Passing up a stage higher in the geologic series, we have a succession
of conglomerates, sandstones, shales, and limestones; in other words,
a series of beds which represent pebbly shore deposits, the sands
and muds of deeper water, and the accumulated débris of calcareous
skeletons of animals which lived in the clear water of the Silurian
sea. The term Silurian (Siluria was the country of Caractacus and the
old Britons known as Silures[51]) was first applied by Murchison in
1835 to a more comprehensive series of rocks than are now included
in the Silurian system. The rocks of this period occur in Wales,
Shropshire, parts of Scotland, Ireland, Scandinavia, Russia, the
United States and other countries. After the accumulation of the
thick Ordovician sediments, the sea-floor was upraised and in places
converted into ridges or islands of land, of which the detritus formed
part of the material of Silurian deposits. The limestones of the
Wenlock ridge have yielded an abundant fauna, consisting of corals,
crinoids, molluscs and other invertebrates. In this period we have the
first representatives of the Vertebrata, discovered in the rocks of
Ludlow. In fact, in the Silurian period, “all the great divisions of
the Animal Kingdom were already represented[52].”

                            V. =Devonian.=

By the continued elevation of the Silurian sea-floor, large portions
became dry land, and during the succeeding period most of the British
area formed part of a continental mass. Over the southern part of
England, there still lay an arm of the sea, and in this were laid
down the marine sediments which now form part of Devon, and from
which the name Devonian has been taken as a convenient designation
for the strata of this period. In parts of the northern land, in the
region now occupied by Scotland, there were large inland lakes, on
the floor of which vast thicknesses of shingle beds and coarse sands
(“Old Red Sandstone”) were slowly accumulated; and it has been shown
by Sir Archibald Geikie and others that during this epoch there were
considerable outpourings of volcanic material in the Scotch area.

Farther to the West and South-west there was another large lake in
which the so-called Kiltorkan beds of Ireland were deposited. In these
Irish sediments, and others of the same age in Belgium and elsewhere
a few forms of land plants have been discovered; but it is from the
Devonian rocks of North America that most of our knowledge of the flora
of this period has been obtained.

                         VI. =Carboniferous.=

From the point of view of palaeobotany, the shales, sandstones, and
seams of coal included in the Carboniferous system are of special
interest. It is from the relics of this Palaeozoic vegetation that the
most important botanical lessons have been learnt.

The following classification of Carboniferous rocks shows the order of
succession of the various beds, and the nature of the rocks which were
formed at this stage in the Earth’s history.

                                    ╭ Upper Coal-Measures.
                ╭ Coal-Measures[53] ┤ Transition Series.
                │                   │ Middle Coal-Measures.
                │                   ╰ Lower Coal-Measures.
                │ Millstone Grit.
  CARBONIFEROUS ┤                         ╭ Upper limestone shales
                │                         │     and Yoredale rocks.
                │ Carboniferous limestone ┤ Carboniferous or
                │     series              │     Mountain limestone.
                │                         ╰ Lower limestone shales.
                ╰ Basement conglomerate.

In the classification of Carboniferous rocks adopted in Geikie’s
text-book of Geology the following arrangement is followed for the
Carboniferous limestone series[54]:—

                      ╭ _Yoredale group_ of shales and grits passing
                      │   down into dark shales and limestones.
                      │ _Thick (Scaur or Main) limestone_ in the
                      │   south and centre of England and Ireland,
                      │   passing northwards into sandstones,
                      │   shales and coals with limestones.
  Carboniferous       ┤ _Lower limestone shale_ of the south and
    limestone series  │   centre of England. The Calciferous
                      │   sandstone group of Scotland (marine,
                      │   estuarine, and terrestrial organisms)
                      │   probably represents the Scaur limestone
                      │   and lower limestone shale, and graduates
                      │   downwards insensibly into the Upper
                      ╰   Old Red Sandstone.

The thick beds of mountain limestone, with their characteristic marine
fossil shells and corals play an important part in English scenery.
In Derbyshire, West Yorkshire, and other places, the limestone crags
and hills are made up of the raised floor of a comparatively deep
Carboniferous sea, which covered a considerable portion of the British
Isles at the beginning of this epoch.

[Sidenote: CARBONIFEROUS ROCKS.]

The accumulation of the calcareous skeletons of marine animals,
with masses of coral, veritable shell-banks of extinct oyster-like
lamellibranchs, built up during the lapse of a long period of time,
formed widespread deposits of calcareous sediments. These were
eventually succeeded by less pure calcareous deposits, the sea became
shallower, and land detritus found its way over an area formerly
occupied by the clear waters of an open sea. The shallowing process
was gradually continued, and the sea was by some means converted into
a more confined fresh-water or brackish area, in which were laid down
many hundred feet of coarse sandy sediments derived from the waste
of granitic highlands. Finally the conditions became less constant;
the continuous deposition of sandy detritus being interrupted by the
more or less complete filling up of the area of sedimentation, and the
formation of a land surface which supported a luxuriant vegetation,
of which the débris was subsequently converted into beds of coal. By
further subsidence the land was again submerged, and the forest-covered
area became overspread with sands and muds.

Such are the imperfect outlines of the general physical conditions
which are represented by the series of sedimentary strata included in
the Carboniferous system. At the close of this period, the Earth’s
surface in Western Europe was subjected to crust-foldings on a large
scale, along lines running approximately North and South and East and
West, the two sets of movements resulting in the formation of ridges
of Carboniferous rocks. The uppermost series of grits, sandstones and
coal-seams were in great part removed by denudation from the crests
of the elevated ridges, but remained in the intervening troughs or
basins where they were less exposed to denudation. It is the direct
consequence of this, that we have our Coal-Measures preserved in the
form of detached basins of upper Carboniferous beds.

A closer examination of the comparative thickness and succession of
Carboniferous rocks in different parts of Britain shows very clearly
that in the northern area of Scotland and in the North of England the
conditions were different from those which obtained further South.
Seeing how much palaeobotanical interest attaches to these rocks, it is
important to treat a little more fully of their geology.

In parts of Devon, Cornwall and West Somerset, the Devonian strata
are succeeded by a series of folded and contorted rocks which have
yielded a comparatively small number of Carboniferous fossils. To this
succession of limestones, shales and grits the term _Culm-Measures_ was
applied by Sedgwick and Murchison in 1837. The rocks of this series
occupy a trough between the Devonian rocks of North and South Devon.
While some authorities have correlated the Culm-Measures with the
Millstone Grit, others regard them as representing a portion of the
true Coal-Measures, as well as the Carboniferous and Lower Limestone
Shale[55]. It has recently been shown that among the lower Culm strata
there occur bands of ancient deep-sea sediments, consisting of beds
of chert containing siliceous casts of various species of Radiolaria.
There can be no doubt that the discovery of deep-sea fossils in this
particular development of the British Carboniferous system leads to
the conclusion that “while the massive deposits of the Carboniferous
limestone—formed of the skeletons of calcareous organisms—were in
process of growth in the seas to the North, there existed to the
South-west a deeper ocean in which siliceous organisms predominated and
formed these siliceous radiolarian rocks[56].”

The Upper Culm-Measures consist of conglomerates, grits, sandstones
and shales with some plant remains and other fossils, and constitute a
typical set of shallow water sediments. In Westphalia, the Harz region,
Thuringia, Silesia and Moravia there are rocks corresponding to the
Culm-Measures of Devon, and some of these have also afforded evidence
of deep water conditions.

[Sidenote: COAL-MEASURES.]

_S. W. England, S. Wales, Derbyshire and Yorkshire._ In these districts
the Carboniferous limestone reaches a considerable thickness; in the
Mendips it has a thickness of 3000 feet, and in the Pennine chain of
4000 feet. At the base of this limestone series there occurs in the
southern districts the so-called lower limestone shale, consisting of
clays, shales and sandy beds. Above the limestone we have the Millstone
grit and Coal-Measures; but in the Pennine district there is a series
of rocks consisting of impure limestones and shales, intercalated
between the Millstone grit and Carboniferous limestone; for this group
of rocks the term _Yoredale series_ has been proposed. In the Isle of
Man and Derbyshire sheets of lava are interbedded with the calcareous
sediments, affording clear proof of submarine volcanic eruptions.

_N. England and Scotland._ In the Carboniferous rocks of Northumberland
we have distinct indications of a shallower sea. The regular succession
of limestone strata in West Yorkshire and other districts, gives place
to a series of thinner beds of limestones, interstratified with shales
and impure calcareous rocks. We have come within the range of land
detritus which was spread out on the floor of a shallow sea. The lowest
portion of the Mountain limestone is here represented by about 200 feet
of shales and other rocks grouped together in the _Tuedian series_.
The Upper Carboniferous limestone and Yoredale rocks of Yorkshire are
represented by sandstones, carbonaceous limestones and some seams of
coal, included in the _Bernician series_. Further north, again, another
classification has been proposed for the still more aberrant succession
of rocks; the lowest being spoken of as the _Calciferous sandstone_,
and the upper as the _Carboniferous limestone_. The calciferous
sandstone may be compared with the lower limestone shale and part of
the Carboniferous limestone of England. The Carboniferous limestone of
Scotland probably represents the upper part of the limestone of England
and the Yoredale rocks of the Pennine and other areas.

Turning to the upper members of the Carboniferous system—in the
Coal-Measures, as they were called in 1817 by William Smith,—we have a
series of coal seams, sandstones, shales, and ironstones occurring for
the most part in basin-shaped areas. As a general rule, each seam of
coal, which varies in thickness from one inch to thirty feet, rests on
a characteristic unstratified argillaceous rock known as Underclay.

The accompanying diagram (Fig. 4) illustrates the frequent
intercalation of small bands of argillaceous and sandy rocks associated
with the seams of coal.

The usual classification adopted for the British Coal-Measures is that
of Upper, Middle, and Lower Coal-Measures; between the Upper and Middle
divisions there occur certain transition or passage beds which are
known as the Transition series. Continental writers, and more recently
Mr Kidston of Stirling, have attempted with considerable success to
correlate the Coal-producing strata by means of fossil plants[57].

  10 in.  Massive clay-shale with a few
           coal films in the lower part.

  10½ in. Shale full of thin streaks of
           coal.

  14 in.  Massive shale with a few streaks
           of coal and iron pyrites.

  5½ in.  Bastard coal; more coal than
           shale.

  6½ in.  Good coal, with masses of iron
           pyrites.

  1½ in.  Coal and seat-rock mixed.

  5 in.   Seat-rock.

    Fig. 4.

  Vertical section of the Bassey or Salts Coal seam, Rushton
  Colliery, Blackburn (Lower Coal-Measures). From a specimen 4 feet
  4 inches in height, presented by Mr P. W. Pickup to the Manchester
  Museum, Owens College.]

Finally, some reference must be made to the occurrence of Carboniferous
rocks underneath more recent strata. In a geological map, or bird’s-eye
view of a country, we see such rocks as appear at the surface; by
means of deep borings, however, we are occasionally enabled to follow
the course of older beds a considerable distance below the usually
accessible part of the Earth’s crust. In the neighbourhood of London,
Dover, and other places we have Tertiary and Mesozoic strata forming
the surface of the country, but below these comparatively recent
formations, the sinking of deep wells and other borings have proved
the existence of a ridge of Palaeozoic rocks stretching from the South
Wales Coal-field through the South-east of England to northern France,
Belgium and Westphalia. It is from rocks forming part of this old
ridge that characteristic Coal-Measure plants have been obtained from
the Dover boring. In Fig. 5 is shown an almost complete pinnule of
_Neuropteris Scheuchzeri_ Hoffm., a well-known fern, marking a definite
horizon of Upper Carboniferous rocks[58]. The small hairs on the
pinnules, shown in the figure as fine lines lying more or less parallel
to the midrib and across the lateral veins, are a characteristic
feature of this species.

[Illustration: FIG. 5.

  Imperfect pinnule of _Neuropteris Scheuchzeri_ Hoffm., showing the
  characteristic hairs as fine lines traversing the lateral veins.
  From a specimen obtained from the Dover boring and now in the
  British Museum. Nat. size.]

                            VII. =Permian.=

Reference has already been made to the earth-foldings which marked
the close of Carboniferous times; “the open Mediterranean sea of the
Carboniferous period in Europe was converted into a large inland sea,
like the Caspian of the present day, surrounded by a rocky and hilly
continent, on which grew trees and plants of various kinds[59].” In
parts of

Lancashire, Westmoreland, the Eden Valley, and in the East of England
from Sunderland to Nottingham, there occurs a succession of limestones,
sandstones, clays and other rocks with occasional beds of rock-salt
and gypsum, which represent the various forms of sediment and chemical
precipitates formed on the floor of Permian lakes. The poverty of the
fauna and flora of Permian strata points to conditions unfavourable to
life; and there can be little doubt that the characteristic red rocks
of St Bees Head, and the creamy limestones of the Durham coast are the
upraised sediments of an inland salt-water lake. The term Dyas was
proposed by Marcou for this series of strata as represented in Germany,
where the rocks are conveniently grouped in two series, the _Magnesian
limestone_ or _Zechstein_ and the red sandstones or _Rothliegendes_.
The older and better known name of Permian was instituted by Murchison
for the rocks of this age, from their extreme development in the old
kingdom of Permia in Russia. Unfortunately considerable confusion has
arisen from the employment of different names for rocks of the same
geological period; and the grouping of the beds varies in different
parts of the world. It is of interest to note, that in the Tyrol,
Carinthia, and other places there are found patches of old marine beds
which were originally laid down in an open sea, which extended over
the site of the Mediterranean, into Russia and Asia. In Bohemia, the
Harz district, Autun in Burgundy, and other regions, there are seams
of Permian coal interstratified with the marls and sands. From these
last named beds many fossil plants have been obtained, and important
palaeobotanical facts brought to light by the investigations of
continental workers. Volcanic eruptions, accompanied by lava streams
and showers of ash, have been recognised in the Permian rocks of
Scotland, and elsewhere.

In North America, Australia, and India the term Permo-Carboniferous is
often made use of in reference to the continuous and regular sequence
of beds which were formed towards the close of the Carboniferous and
into the succeeding Permian epoch. The enormous series of freshwater
Indian rocks, to which geologists have given the name of the GONDWANA
SYSTEM, includes the sediments of more than one geological period,
some of the older members being regarded as Permo-Carboniferous in
age. These Indian beds, with others in Australia, South Africa, and
South America, are of special interest on account of the characteristic
southern hemisphere plants which they have afforded, and from the
association with the fossiliferous strata of extensive boulder beds
pointing to widespread glacial conditions.

                            VIII. =Trias.=

As we ascend the geologic series, and pass up to the rocks overlying
the Permian deposits, there are found many indications of a marked
change in the records of animal and plant life. Many of the
characteristic Palaeozoic fossils are no longer represented, and
in their place we meet with fresh and in many cases more highly
differentiated organisms. The threefold division of the rocks of this
period which suggested the term Trias to those who first worked out the
succession of the strata, is typically illustrated over a wide area
in Germany, in which the lowest or _Bunter_ series is followed by the
calcareous _Muschelkalk_, and this again by the clays, rock-salt, and
sandstones of the _Keuper_ series. In the Cheshire plain and in the
low ground of the Midlands, we have a succession of red sandstones,
conglomerates, and layers of rock-salt which correspond to the Bunter
and Keuper beds of German geologists. These Triassic rocks were
obviously formed in salt-water lakes, in which from time to time long
continued evaporation gave rise to extensive deposit of rock-salt
and other minerals. From the fact that it is this type of Triassic
sediments which was first made known, it is often forgotten that the
British and German rocks are not the typical representatives of this
geological period. The ‘Alpine’ Trias of the Mediterranean region,
in Asia, North America, and other countries, has a totally different
facies, and includes limestones and dolomites of deep-sea origin. “The
widespread Alpine Trias is the pelagic facies of the formation; the
more restricted German Trias, on the other hand, is a shallow shore,
bay or inland sea formation[60].”

In the Keuper beds of southern Sweden there are found workable
seams of coal, and the beds of this district have yielded numerous
well-preserved examples of the Triassic flora. A more impure coal
occurs in the lower Keuper of Thuringia and S.-W. Germany, and to this
group of rocks the term _Lettenkohle_ is occasionally applied.

In the Rhaetic Alps of Lombardy, in the Tyrol, and in England, from
Yorkshire to Lyme Regis, Devonshire, Somersetshire, and other districts
there are certain strata at the top of the Triassic system known as
the _Rhaetic_ or _Penarth_ beds. The uppermost Rhaetic beds, often
described as the White Lias, afford evidence of a change from the salt
lakes of the Trias to the open sea of the succeeding Jurassic period.
Passing beyond this period of salt lakes and wind-swept barren tracts
of land, we enter on another phase of the earth’s history.

                            IX. =Jurassic.=

The Jura mountains of western Switzerland consist in great part of
folded and contorted rocks which were originally deposited on the
floor of a Jurassic sea. In England the Jurassic rocks are of special
interest, both for geological and historical reasons, as it is in them
that we find a rich fauna and flora of Mesozoic age, and it was the
classification of these beds by means of their fossil contents that
gained for William Smith the title of the Father of English Geology. A
glance at a geological map of England shows a band of Jurassic rocks
stretching across from the Yorkshire coast to Dorset. These are in a
large measure calcareous, argillaceous, and arenaceous sediments of an
open sea; but towards the upper limit of the series, both freshwater
and terrestrial beds are met with. Numerous fragments of old coral
reefs, sea-urchins, crinoids, and other marine fossils are especially
abundant; in the freshwater beds and old surface-soils, as well as in
the marine sandstones and shales, we have remnants of an exceedingly
rich and apparently tropical vegetation. This was an age of Reptiles
as well as an age of Cycads. An interesting feature of these widely
distributed Jurassic strata is the evidence they afford of distinct
climatal zones; there are clear indications, according to the late Dr
Neumayr, of a Mediterranean, a middle European, and a Boreal or Russian
province[61]. The subdivisions of the English Jurassic rocks are as
follows[62]:—

           ╭ ╭ Purbeck beds           ╮          ╮
           │ │ Portland beds          ├ _Upper_  │
           │ │ Kimeridge clay         ╯          │
           │ ┤                                   │
           │ │ Corallian beds         ╮          │
  JURASSIC ┤ │ Oxford clay, with      ├ _Middle_ ├ Oolite.
           │ ╰   Kellaways rock       ╯          │
           │                                     │
           │ ╭ Great Oolite series    ╮ _Lower_  │
           │ ╰ Inferior Oolite series ╯          ╯
           │
           ╰ Lias

In tracing the several groups across England, and into other parts of
Europe, their characters are naturally found to vary considerably; in
one area a series is made up of typical clear water or comparatively
deep sea sediments, and in another we have shallow water and shore
deposits of the same age. The Lias rocks have been further subdivided
into zones by means of the species of Ammonites which form so
characteristic a feature of the Jurassic fauna. In the lower Oolite
strata there are shelly limestones, clays, sandstones, and beds of
lignite and ironstone. Without discussing the other subdivisions of
the Jurassic period, we may note that in the uppermost members there
are preserved patches of old surface-soils exposed in the face of the
cliffs of the Dorset coast and of the Isle of Portland.

                           X. =Cretaceous.=

In the south of England, and in some other districts, it is difficult
to draw any definite line between the uppermost strata of the Jurassic
and the lowest of the Cretaceous period. The rocks of the so-called
_Wealden_ series of Kent, Surrey, Sussex, and the Isle of Wight, are
usually classed as Lower Cretaceous, but there is strong evidence
in favour of regarding them as sediments of the Jurassic period.
The Cretaceous rocks of England are generally speaking parallel to
the Jurassic strata, and occupy a stretch of country from the east
of Yorkshire and the Norfolk coast to Dorset in the south-west. The
Chalk downs and cliffs represent the most familiar type of Cretaceous
strata. In the white chalk with its numerous flints, we have part
of the elevated floor of a comparatively deep sea, which extended
in Cretaceous times over a large portion of the east and south-east
of England and other portions of the European continent. On the bed
of this sea, beyond the reach of any river-borne detritus, there
accumulated through long ages the calcareous and siliceous remains of
marine animals, to be afterwards converted into chalk and flints. At
the beginning of the period, however, other conditions obtained, and
there extended over the south-east of England, and parts of north and
north-west Germany and Belgium, a lake or estuary in which were built
up deposits of clay, sand and other material, forming the delta of
one or more large rivers. For these sediments the name _Wealden_ was
suggested in 1828. Eventually the gradual subsidence of this area led
to an incursion of the sea, and the delta became overflowed by the
waters of a large Cretaceous sea. At first the sea was shallow, and in
it were laid down coarse sands and other sediments known as the _Lower
Greensand_ rocks. By degrees, as the subsidence continued, the shallows
became deep water, and calcareous material slowly accumulated, to be
at last upraised as beds of white chalk. The distribution of fossils
in the Cretaceous rocks of north and south Europe distinctly points to
the existence of two fairly well-marked sets of organisms in the two
regions; no doubt the expression of climatal zones similar to those
recognised in Jurassic times. In North America, Cretaceous rocks are
spread over a wide area, also in North Africa, India, South Africa,
and other parts of the world. Within the Arctic Circle strata of this
age have become famous, chiefly on account of the rich flora described
from them by the Swiss palaeobotanist Heer. The fauna and flora of this
epoch are alike in their advanced state of development and in the great
variety of specific types; the highest class of plants is first met
with at the base of the Cretaceous system.

                            XI. =Tertiary.=

“At the close of the Chalk age a change took place both in the
distribution of land and water, and also in the development of organic
life, so great and universal, that it has scarcely been equalled at
any other period of the earth’s geological history[63].” The Tertiary
period seems to bring us suddenly to the threshold of our own times. In
England at least, the deposits of this age are of the nature of loose