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diff --git a/old/14279-0.txt b/old/14279-0.txt new file mode 100644 index 0000000..abb984d --- /dev/null +++ b/old/14279-0.txt @@ -0,0 +1,17706 @@ +The Project Gutenberg eBook of The Ancient Life History of the Earth, by Henry Alleyne Nicholson + +This eBook is for the use of anyone anywhere in the United States and +most other parts of the world at no cost and with almost no restrictions +whatsoever. You may copy it, give it away or re-use it under the terms +of the Project Gutenberg License included with this eBook or online at +www.gutenberg.org. If you are not located in the United States, you +will have to check the laws of the country where you are located before +using this eBook. + +Title: The Ancient Life History of the Earth + A Comprehensive Outline Of The Principles And Leading Facts Of Palæontological Science + +Author: Henry Alleyne Nicholson + +Release Date: December 6, 2004 [eBook #14279] +[Most recently updated: April 2, 2023] + +Language: English + +Produced by: Robert J. Hall + +*** START OF THE PROJECT GUTENBERG EBOOK THE ANCIENT LIFE-HISTORY OF THE EARTH *** + + + + +THE ANCIENT LIFE-HISTORY OF THE EARTH + +A COMPREHENSIVE OUTLINE OF THE PRINCIPLES AND LEADING FACTS OF +PALÆONTOLOGICAL SCIENCE + + +BY H. ALLEYNE NICHOLSON + +M.D., D.SC., M.A., PH. D. (GÖTT), F.R.S.E, F.L.S. + +PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF ST ANDREWS + + + + +PREFACE. + +The study of Palæontology, or the science which is concerned +with the living beings which flourished upon the globe during +past periods of its history, may be pursued by two parallel but +essentially distinct paths. By the one method of inquiry, we may +study the anatomical characters and structure of the innumerable +extinct forms of life which lie buried in the rocks simply as +so many organisms, with but a slight and secondary reference +to the _time_ at which they lived. By the other method, fossil +animals are regarded principally as so many landmarks in the +ancient records of the world, and are studied _historically_ +and as regards their relations to the chronological succession +of the strata in which they are entombed. In so doing, it is of +course impossible to wholly ignore their structural characters, +and their relationships with animals now living upon the earth; +but these points are held to occupy a subordinate place, and to +require nothing more than a comparatively general attention. + +In a former work, the Author has endeavoured to furnish a summary +of the more important facts of Palæontology regarded in its strictly +scientific aspect, as a mere department of the great science of +Biology. The present work, on the other hand, is an attempt to +treat Palæontology more especially from its historical side, and +in its more intimate relations with Geology. In accordance with +this object, the introductory portion of the work is devoted to a +consideration of the general principles of Palæontology, and the +bearings of this science upon various geological problems--such +as the mode of formation of the sedimentary rocks, the reactions +of living beings upon the crust of the earth, and the sequence +in time of the fossiliferous formations. The second portion of +the work deals exclusively with Historical Palæontology, each +formation being considered separately, as regards its lithological +nature and subdivisions, its relations to other formations, its +geographical distribution, its mode of origin, and its characteristic +life-forms. + +In the consideration of the characteristic fossils of each successive +period, a general account is given of their more important zoological +characters and their relations to living forms; but the technical +language of Zoology has been avoided, and the aid of illustrations +has been freely called into use. It may therefore be hoped that +the work may be found to be available for the purposes of both the +Geological and the Zoological student; since it is essentially an +outline of Historical Palæontology, and the student of either of +the above-mentioned sciences must perforce possess some knowledge +of the last. Whilst primarily intended for students, it may be +added that the method of treatment adopted has been so far +untechnical as not to render the work useless to the general +reader who may desire to acquire some knowledge of a subject of +such vast and universal interest. + +In carrying out the object which he has held before him, the +Author can hardly expect, from the nature of the materials with +which he has had to deal, that he has kept himself absolutely +clear of errors, both of omission and commission. The subject, +however, is one to which he has devoted the labour of many years, +both in studying the researches of others and in personal +investigations of his own; and he can only trust that such errors +as may exist will be found to belong chiefly to the former class, +and to be neither serious nor numerous. It need only be added +that the work is necessarily very limited in its scope, and that +the necessity of not assuming a thorough previous acquaintance +with Natural History in the reader has inexorably restricted its +range still further. The Author does not, therefore, profess to +have given more than a merely general outline of the subject; and +those who desire to obtain a more minute and detailed knowledge +of Palæontology, must have recourse to other and more elaborate +treatises. + +UNITED COLLEGE, ST ANDREWS. + +October 2, 1876. + + + + +CONTENTS. + + +PART I. + +PRINCIPLES OF PALÆONTOLOGY. + + +INTRODUCTION. + +The general objects or geological science--The older theories of +catastrophistic and intermittent action--The more modern doctrines +of continuous and uniform action--Bearing of these doctrines +respectively on the origin or the existing terrestrial +order--Elements or truth in Catastrophism--General truth of the +doctrine of Continuity--Geological time. + +CHAPTER I. + +Definition of Palæontology--Nature of Fossils--Different processes +of fossilisation. + +CHAPTER II. + +Aqueous and igneous rocks--General characters of the sedimentary +rocks--Mode or formation of the sedimentary rocks--Definition +of the term "formation"--Chief divisions of the aqueous +rocks--Mechanically-formed rocks, their characters and mode of +origin--Chemically and organically formed rocks--Calcareous +rocks--Chalk, its microscopic structure and mode of +formation--Limestone, varieties, structure, and origin--Phosphate +of lime--Concretions--Sulphate of lime--Silica and siliceous +deposits of various kinds--Greensands--Red clays--Carbon and +carbonaceous deposits. + +CHAPTER III. + +Chronological succession of the fossiliferous rocks--Tests or age +of strata--Value of Palæontological evidence in stratigraphical +Geology--General sequence of the great formations. + +CHAPTER IV. + +The breaks in the palæontological and geological record--Use of +the term "contemporaneous" as applied to groups of strata--General +sequence of strata and of life-forms interfered with by more or +less extensive gaps--Unconformability--Phenomena implied by +this--Causes of the imperfection of the palæontological record. + +CHAPTER V. + +Conclusions to be drawn from fossils--Age of rocks--Mode of origin +of any fossiliferous bed--Fluviatile, lacustrine, and marine +deposits--Conclusions as to climate--Proofs of elevation and +subsidence of portions of the earth's crust derived from fossils. + +CHAPTER VI. + +The biological relations of fossils--Extinction of +life-forms--Geological range of different species--Persistent types +of life--Modern origin of existing animals and plants--Reference +of fossil forms to the existing primary divisions of the animal +kingdom--Departure of the older types of life from those now in +existence--Resemblance of the fossils of a given formation to +those of the formation next above and next below--Introduction +of new life-forms. + + +PART II. + +HISTORICAL PALÆONTOLOGY. + + +CHAPTER VII. + +The Laurentian and Huronian periods--General nature, divisions, +and geographical distribution of the Laurentian deposits--Lower +and Upper Laurentian--Reasons for believing that the Laurentian +rocks are not azoic based upon their containing limestones, beds of +oxide of iron, and graphite--The characters, chemical composition, +and minute structure of _Eozoön Canadense_--Comparison of _Eozoön_ +with existing Foraminifera--_Archoeosphoerinoe_--Huronian +formation--Nature and distribution of Huronian deposits--Organic +remains of the Huronian--Literature. + +CHAPTER VIII. + +The Cambrian period--General succession of Cambrian deposits in +Wales--Lower Cambrian and Upper Cambrian--Cambrian deposits of +the continent of Europe and North American--Life of the Cambrian +period--Fucoids--Eophyton--Oldhamia--Sponges--Echinoderms--Annelides +--Crustaceans--Structure of Trilobites--Brachiopods--Pteropods, +Gasteropods, and Bivalves--Cephalopods--Literature. + +CHAPTER IX. + +The Lower Silurian period--The Silurian rocks generally--Limits +of Lower and Upper Silurian--General succession, subdivisions, +and characters of the Lower Silurian rocks of Wales--General +succession, subdivisions, and characters of the Lower Silurian +rocks of the North American continent--Life of the +period--Fucoids--Protozoa--Graptolites--Structure of +Graptolites--Corals--General structure of Corals--Crinoids-- +Cystideans--General characters of Cystideans--Annelides-- +Crustaceans--Polyzoa--Brachiopods--Bivalve and Univalve +Molluscs--Chambered Cephalopods--General characters of the +Cephalopoda--Conodonts. + +CHAPTER X. + +The Upper Silurian period--General succession of the Upper Silurian +deposits of Wales--Upper Silurian deposits of North America--Life +of the Upper Silurian--Plants--Protozoa--Graptolites--Corals-- +Crinoids--General structure of Crinoids--Star-fishes--Annelides-- +Crustaceans--Eurypterids--Polyzoa--Brachiopods--Structure of +Brachiopods--Bivalves and Univalves--Pteropods--Cephalopods-- +Fishes--Silurian literature. + +CHAPTER XI. + +The Devonian period--Relations between the Old Red Sandstone +and the marine Devonian deposits--The Old Red Sandstone of +Scotland--The Devonian strata of Devonshire--Sequence and +subdivisions of the Devonian deposits of North America--Life +of the period--Plants--Protozoa--Corals-Crinoids--Pentremites-- +Annelides--Crustaceans--Insects--Polyzoa--Brachiopods--Bivalves-- +Univalves--Pteropods--Cephalopods--Fishes--General divisions of +the Fishes--Palæontological evidence as to the independent +existence of the Devonian system as a distinct +formation--Literature. + +CHAPTER XII. + +The Carboniferous period--Relations of Carboniferous rocks to +Devonian--The Carboniferous Limestone or Sub-Carboniferous +series--The Millstone-grit and the Coal-measures--Life of the +period--Structure and mode of formation of Coal--Plants of the +Coal. + +CHAPTER XIII. + +Animal life of the Carboniferous period--Protozoa--Corals-- +Crinoids--Pentremites--Structure of Pentremites--Echinoids-- +Structure of Echinoidea--Annelides--Crustacea--Insects-- +Arachnids--Myriapods--Polyzoa--Brachiopods--Bivalves and +Univalves--Cephalopods--Fishes--Labyrinthodont Amphibians-- +Literature. + +CHAPTER XIV. + +The Permian period--General succession, characters, and mode +of formation of the Permian deposits--Life of the period-- +Plants--Protozoa--Corals--Echinoderms--Annelides--Crustaceans-- +Polyzoa--Brachiopods--Bivalves-Univalves--Pteropods-- +Cephalopods--Fishes--Amphibians--Reptiles--Literature. + +CHAPTER XV. + +The Triassic period--General characters and subdivisions of the +Trias of the Continent of Europe and Britain--Trias of North +America--Life of the period--Plants--Echinoderms--Crustaceans-- +Polyzoa--Brachiopods--Bivalves--Univalves--Cephalopods-- +Intermixture of Palæozoic with Mesozoic types of Molluscs-- +Fishes--Amphibians--Reptiles--Supposed footprints of Birds-- +Mammals--Literature. + +CHAPTER XVI. + +The Jurassic period--General sequence and subdivisions of the +Jurassic deposits in Britain--Jurassic rocks of North America--Life +of the period--Plants--Corals--Echinoderms--Crustaceans--Insects-- +Brachiopods--Bivalves--Univalves-Pteropods--Tetrabranchiate +Cephalopods--Dibranchiate Cephalopods--Fishes--Reptiles--Birds-- +Mammals--Literature. + +CHAPTER XVII. + +The Cretaceous period--General succession and subdivisions of +the Cretaceous rocks in Britain--Cretaceous rocks of North +America--Life of the period--Plants--Protozoa--Corals--Echinoderms-- +Crustaceans--Polyzoa--Brachiopods--Bivalves--Univalves-- +Tetrabranchiate and Dibranchiate Cephalopods--Fishes--Reptiles-- +Birds--Literature. + +CHAPTER XVIII. + +The Eocene period--Relations between the Kainozoic and Mesozoic +rocks in Europe and in North America--Classification of the Tertiary +deposits--The sequence and subdivisions of the Eocene rocks of +Britain and France--Eocene strata of the United States--Life of the +period--Plants--Foraminifera--Corals--Echinoderms--Mollusca--Fishes-- +Reptiles--Birds--Mammals. + +CHAPTER XIX. + +The Miocene period--Miocene strata of Britain--Of France--Of +Belgium--Of Austria--Of Switzerland--Of Germany--Of Greece--Of +India--Of North America--Of the Arctic regions--Life of the +period--Vegetation of the Miocene period--Foraminifera--Corals-- +Echinoderms--Articulates--Mollusca--Fishes-Amphibians--Reptiles-- +Mammals. + +CHAPTER XX. + +The Pliocene period--Pliocene deposits of Britain--Of Europe--Of +North America--Life of the period--Climate of the period as indicated +by the Invertebrate animals--The Pliocene Mammalia--Literature +relating to the Tertiary deposits and their fossils. + +CHAPTER XXI. + +The Post-Pliocene period--Division of the Quaternary deposits into +Post-Pliocene and Recent--Relations of the Post-Pliocene deposits +of the northern hemisphere to the "Glacial period"--Pre-Glacial +deposits--Glacial deposits--Arctic Mollusca in Glacial +beds--Post-Glacial deposits--Nature and mode of formation of +high-level and low-level gravels--Nature and mode of formation +of cavern-deposits--Kent's Cavern-Post--Pliocene deposits of +the southern hemisphere. + +CHAPTER XXII. + +Life of the Post-Pliocene period--Effect of the coming on and +departure of the Glacial period upon the animals inhabiting the +northern hemisphere--Birds of the Post-Pliocene--Mammalia of the +Post-Pliocene--Climate of the Post-Glacial period as deduced from +the Post-Glacial Mammals--Occurrence of the bones and implements +of Man in Post-Pliocene deposits in association with the remains +of extinct Mammalia--Literature relating to the Post-Pliocene +period. + +CHAPTER XXIII. + +The succession of life upon the globe--Gradual and successive +introduction of life-forms--What is meant by "lower" and "higher" +groups of animals and plants--Succession in time of the great +groups of animals in the main corresponding with their zoological +order--Identical phenomena in the vegetable kingdom--Persistent +types of life--High organisation of many early forms--Bearings +of Palæontology on the general doctrine of Evolution. + +APPENDIX.--Tabular view of the chief Divisions of the Animal Kingdom. + +GLOSSARY. + +INDEX. + + + +LIST OF ILLUSTRATIONS + + FIG. + 1. Cast of _Trigonia longa_. + 2. Microscopic section of the wood of a fossil Conifer. + 3. Microscopic section of the wood of the Larch. + 4. Section of Carboniferous strata, Kinghorn, Fife. + 5. Diagram illustrating the formation of stratified deposits. + 6. Microscopic section of a calcareous breccia. + 7. Microscopic section of White Chalk. + 8. Organisms in Atlantic Ooze. + 9. Crinoidal marble. + 10. Piece of Nummulitic limestone, Pyramids. + 11. Microscopic section of Foraminiferal + limestone--Carboniferous, America. + 12. Microscopic section of Lower Silurian limestone. + 13. Microscopic section of oolitic limestone, Jurassic. + 14. Microscopic section of oolitic limestone, Carboniferous. + 15. Organisms in Barbadoes earth. + 16. Organisms in Richmond earth. + 17. Ideal section of the crust of the earth. + 18. Unconformable junction of Chalk and Eocene rocks. + 19. Erect trunk of a _Sigillaria_. + 20. Diagrammatic section of the Laurentian rocks. + 21. Microscopic section of Laurentian limestone. + 22. Fragment of a mass of _Eozoön Canadense_. + 23. Diagram illustrating the structure of _Eozoön_. + 24. Microscopic section of _Eozoön Canadense_. + 25. _Nonionina_ and _Gromia_. + 26. Group of shells of living _Foraminifera_. + 27. Diagrammatic section of Cambrian strata. + 28. _Eophyton Linneanum_. + 29. _Oldhamia antiqua_. + 30. _Scolithus Canadensis_. + 31. Group of Cambrian Trilobites. + 32. Group of characteristic Cambrian fossils. + 33. Fragment of _Dictyonema sociale_. + 34. Generalised section of the Lower Silurian rocks + of Wales. + 35. Generalised section of the Lower Silurian rocks + of North America. + 36. _Licrophycus Ottawaensis_. + 37. _Astylospongia proemorsa_. + 38. _Stromatopora rugosa_. + 39. _Dichograptus octobrachiatus_. + 40. _Didymograptus divaricatus_. + 41. _Diplograptus pristis_. + 42. _Phyllograptus typus_. + 43. _Zaphrentis Stokesi_. + 44. _Strombodes pentagonus_. + 45. _Columnaria alveolata_. + 46. Group of Cystideans. + 47. Group of Lower Silurian Crustaceans. + 48. _Ptilodictya falciformis_. + 49. _Ptilodictya Schafferi_. + 50. Group of Lower Silurian Brachiopods. + 51. Group of Lower Silurian Brachiopods. + 52. _Murchisonia gracilis_. + 53. _Bellerophon argo_. + 54. _Maclurea crenulata_. + 55. _Orthoceras crebriseptum_. + 56. Restoration of _Orthoceras_. + 57. Generalised section of the Upper Silurian rocks. + 58. _Monograptus priodon_. + 59. _Halysites catenularia_ and _H. agglomerata_. + 60. Group of Upper Silurian Star-fishes. + 61. _Protaster Sedgwickii_. + 62. Group of Upper Silurian Crinoids. + 63. _Planolites vulgaris_. + 64. Group of Upper Silurian Trilobites. + 65. _Pterygotus Anglicus_. + 66. Group of Upper Silurian _Polyzoa_. + 67. _Spirifera hysterica_. + 68. Group of Upper Silurian Brachiopods. + 69. Group of Upper Silurian Brachiopods. + 70. _Pentamerus Knightii_. + 71. _Cardiola interrupta, C. fibrosa_, and _Pterinoea + subfalcata_. + 72. Group of Upper Silurian Univalves. + 73. _Tentaculites ornatus_. + 74. _Pteraspis Banksii_. + 75. _Onchus tenuistriatus_ and _Thelodus_. + 76. Generalised section of the Devonian rocks of North America. + 77. _Psilophyton princeps_. + 78. _Prototaxites Logani_. + 79. _Stromatopora tuberculata_. + 80. _Cystiphyllum vesiculosum_. + 81. _Zaphrentis cornicula_. + 82. _Heliophyllum exiguum_. + 83. _Crepidophyllum Archiaci_. + 84. _Favosites Gothlandica_. + 85. _Favosites hemisphoerica_. + 86. _Spirorbis omphalodes_ and _S. Arkonensis_. + 87. _Spirorbis laxus_ and _S. Spinulifera_. + 88. Group of Devonian Trilobites. + 89. Wing of _Platephemera antiqua_. + 90. _Clathropora intertexta_. + 91. _Ceriopora Hamiltonensis_. + 92. _Fenestella magnifica_. + 93. _Retepora Phillipsi_. + 94. _Fenestella cribrosa_. + 95. _Spirifera sculptilis_. + 96. _Spirifera mucronata_. + 97. _Atrypa reticularis_. + 98. _Strophomena rhomboidalis_. + 99. _Platyceras dumosum_. +100. _Conularia ornata_. +101. _Clymenia Sedgwickii_. +102. Group of Fishes from the Devonian rocks of North America. +103. _Cephalaspis Lyellii_. +104. _Pterichthys cornutus_. +105. _Polypterus_ and _Osteolepis_. +106. _Holoptychius nobilissimus_. +107. Generalised section of the Carboniferous rocks of the + North of England. +108. _Odontopteris Schlotheimii_. +109. _Calamites cannoeformis_. +110. _Lepidodendron Sternbergii_. +111. _Sigillaria Groeseri_. +112. _Stigmaria ficoides_. +113. _Trigonocarpum ovatum_. +114. Microscopic section of Foraminiferal + limestone--Carboniferous, North America. +115. _Fusulina cylindrica_. +116. Group of Carboniferous Corals. +117. _Platycrinus tricontadactylus_. +118. _Pentremites pyriformis_ and _P. conoideus_. +119. _Archoeocidaris ellipticus_. +120. _Spirorbis Carbonarius_. +121. _Prestwichia rotundata_. +122. Group of Carboniferous Crustaceans. +123. _Cyclophthalmus senior_. +124. _Xylobius Sigillarioe_. +125. _Haplophlebium Barnesi_. +126. Group of Carboniferous _Polyzoa_. +127. Group of Carboniferous _Brachiopoda_. +128. _Pupa vetusta_. +129. _Goniatites Fossoe_. +130. _Amblypterus macropterus_. +131. _Cochliodus contortus_. +132. _Anthracosaurus Russelli_. +133. Generalised section of the Permian rocks. +134. _Walchia piniformis_. +135. Group of Permian _Brachiopods_. +136. _Arca antiqua_. +137. _Platysomus gibbosus_. +138. _Protorosaurus Speneri_. +139. Generalised section of the Triassic rocks. +140. _Zamia spiralis_. +141. Triassic Conifers and Cycads. +142. _Encrinus liliiformis_. +143. _Aspidura loricata_. +144. Group of Triassic Bivalves. +145. _Ceratites nodosus_. +146. Tooth of _Ceratodus serratus_ and _C. Altus_. +147. _Ceratodus Fosteri_. +148. Footprints of _Cheirotherium_. +149. Section of tooth of _Labyrinthodont_. +150. Skull of _Mastodonsaurus_. +151. Skull of _Rhynchosaurus_. +152. _Belodon_, _Nothosaurus_, _Paloeosaurus_, &c. +153. _Placodus gigas_. +154. Skulls of _Dicynodon_ and _Oudenodon_. +155. Supposed footprint of Bird, from the Trias of Connecticut. +156. Lower jaw of _Dromatherium sylvestre_. +157. Molar tooth of _Microlestes antiquus_. +158. _Myrmecobius fasciatus_. +159. Generalised section of the Jurassic rocks. +160. _Mantellia megalophylla_. +161. _Thecosmilia annularis_. +162. _Pentacrinus fasciculosus_. +163. _Hemicidaris crenularis_. +164. _Eryon arctiformis_. +165. Group of Jurassic Brachiopods. +166. _Ostrea Marshii_. +167. _Gryphoea incurva_ +168. _Diceras arietina_. +169. _Nerinoea Goodhallii_. +170. _Ammonites Humphresianus_. +171. _Ammonites bifrons_. +172. _Beloteuthis subcostata_. +173. Belemnite restored; diagram of Belemnite; _Belemnites + canaliculata_. +174. _Tetragonolepis_. +175. _Acrodus nobilis_. +176. _Ichthyosaurus communis_. +177. _Plesiosaurus dolichodeirus_. +178. _Pterodactylus crassirostris_. +179. _Ramphorhynchus Bucklandi_, restored. +180. Skull of _Megalosaurus_. +181. _Archoeopteryx macrura_. +182. _Archoeopteryx, restored_. +183. Jaw of _Amphitherium Prevostii_. +184. Jaws of Oolitic Mammals. +185. Generalised section of the Cretaceous rocks. +186. Cretaceous Angiosperms. +187. _Rotalia Boueana_. +188. _Siphonia ficus_. +189. _Ventriculites simplex_. +190. _Synhelia Sharpeana_. +191. _Galerites albogalerus_. +192. _Discoidea cylindrica_. +193. _Escharina Oceani_. +194. _Terebratella Astieriana_. +195. _Crania Ignabergensis_. +196. _Ostrea Couloni_. +197. _Spondylus spinosus_. +198. _Inoceramus sulcatus_. +199. _Hippurites Toucasiana_. +200. _Voluta elongata_. +201. _Nautilus Danicus_. +202. _Ancyloceras Matheronianus_. +203. _Turrilites catenatus_ +204. Forms of Cretaceous _Ammonitidoe_. +205. _Belemnitella mucronata_. +206. Tooth of _Hybodus_. +207. Fin-spine of _Hybodus_. +208. _Beryx Lewesiensis_ and _Osmeroides Mantelli_. +209. Teeth of _Iguanodon_. +210. Skull of _Mosasaurus Camperi_. +211. _Chelone Benstedi_. +212. Jaws and vertebræ of _Odontornithes_. +213. Fruit of _Nipadites_. +214. _Nummulina loevigata_. +215. _Turbinolia sulcata_. +216. _Cardita planicosta_. +217. _Typhis tubifer_. +218. _Cyproea elegans_. +219. _Cerithium hexagonum_. +220. _Limnoea pyramidalis_. +221. _Physa columnaris_. +222. _Cyclostoma Arnoudii_. +223. _Rhombus minimus_. +224. _Otodus obliquus_. +225. _Myliobatis Edwardsii_. +226. Upper jaw of Alligator. +227. Skull of _Odontopteryx toliapicus_. +228. _Zeuglodon cetoides_. +229. _Paloeotherium magnum_, restored. +230. Feet of _Equidoe_. +231. _Anoplothelium commune_. +232. Skull of _Dinoceras mirabilis_. +233. _Vespertilio Parisiensis_. +234. Miocene Palms. +235. _Platanus aceroides_. +236. _Cinnamomum polymorphum_. +237. _Textularia Meyeriana_. +238. _Scutella subrotunda_. +239. _Hyalea Orbignyana_. +240. Tooth of _Oxyrhina_. +241. Tooth of _Carcharodon_. +242. _Andrias Scheuchzeri_. +243. Skull of _Brontotherium ingens_. +244, _Hippopotamus Sivalensis_. +245. Skull of _Sivatherium_. +246. Skull of _Deinotherium_. +247. Tooth of _Elephas planfrons_ and of _Mastodon + Sivalensis_. +248. Jaw of _Pliopithecus_. +249. _Rhinoceros Etruscus_ and _R. megarhinus_. +250. Molar tooth of _Mastodon Arvernensis_. +251. Molar tooth of _Etephas meridionalis_. +252. Molar tooth of _Elephas antiquus_. +253. Skull and tooth of _Machairodus cultridens_. +254. _Pecten Islandicus_. +255. Diagram of high-level and low-level gravels. +256. Diagrammatic section of Cave. +257. _Dinornis elephantopus_. +258. Skull of _Diprotodon_. +259. Skull of _Thylacoleo_. +260. Skeleton of _Megatherium_. +261. Skeleton of _Mylodon_. +262. _Glyptodon clavipes_. +263. Skull of _Rhinoceros tichorhinus_. +264. Skeleton of _Cervus megaceros_. +265. Skull of _Bos primigenius_. +266. Skeleton of Mammoth. +267. Molar tooth of Mammoth. +268. Skull of _Ursus speloeus_. +269. Skull of _Hyoena speloea_. +270. Lower jaw of _Trogontherium Cuvieri_. + + + +PART I. + +PRINCIPLES OF PALÆONTOLOGY. + + + + +INTRODUCTION. + +THE LAWS OF GEOLOGICAL ACTION. + +Under the general title of "Geology" are usually included at +least two distinct branches of inquiry, allied to one another in +the closest manner, and yet so distinct as to be largely capable +of separate study. _Geology_,[1] in its strict sense, is the +science which is concerned with the investigation of the materials +which compose the earth, the methods in which those materials +have been arranged, and the causes and modes of origin of these +arrangements. In this limited aspect, Geology is nothing more than +the Physical Geography of the past, just as Physical Geography +is the Geology of to-day; and though it has to call in the aid +of Physics, Astronomy, Mineralogy, Chemistry, and other allies +more remote, it is in itself a perfectly distinct and individual +study. One has, however, only to cross the threshold of Geology +to discover that the field and scope of the science cannot be +thus rigidly limited to purely physical problems. The study of +the physical development of the earth throughout past ages brings +us at once in contact with the forms of animal and vegetable +life which peopled its surface in bygone epochs, and it is found +impossible adequately to comprehend the former, unless we possess +some knowledge of the latter. However great its physical advances +may be, Geology remains imperfect till it is wedded with +Palæontology,[2] a study which essentially belongs to the vast +complex of the Biological Sciences, but at the same time has its +strictly geological side. Dealing, as it does, wholly with the +consideration of such living beings as do not belong exclusively +to the present order of things, Palæontology is, in reality, a +branch of Natural History, and may be regarded as substantially +the Zoology and Botany of the past. It is the ancient life-history +of the earth, as revealed to us by the labours of palæontologists, +with which we have mainly to do here; but before entering upon +this, there are some general questions, affecting Geology and +Palæontology alike, which may be very briefly discussed. + +[Footnote 1: Gr. _ge_, the earth; _logos_, a discourse.] + +[Footnote 2: Gr. _palaios_, ancient; _onta_, beings; _logos_, +discourse.] + +The working geologist, dealing in the main with purely physical +problems, has for his object to determine the material structure +of the earth, and to investigate, as far as may be, the long chain +of causes of which that structure is the ultimate result. No wider +or more extended field of inquiry could be found; but philosophical +geology is not content with this. At all the confines of his +science, the transcendental geologist finds himself confronted +with some of the most stupendous problems which have ever engaged +the restless intellect of humanity. The origin and primæval +constitution of the terrestrial globe, the laws of geologic action +through long ages of vicissitude and development, the origin of +life, the nature and source of the myriad complexities of living +beings, the advent of man, possibly even the future history of +the earth, are amongst the questions with which the geologist +has to grapple in his higher capacity. + +These are problems which have occupied the attention of philosophers +in every age of the world, and in periods long antecedent to +the existence of a science of geology. The mere existence of +cosmogonies in the religion of almost every nation, both ancient +and modern, is a sufficient proof of the eager desire of the +human mind to know something of the origin of the earth on which +we tread. Every human being who has gazed on the vast panorama +of the universe, though it may have been but with the eyes of +a child, has felt the longing to solve, however imperfectly, +"the riddle of the painful earth," and has, consciously or +unconsciously, elaborated some sort of a theory as to the why and +wherefore of what he sees. Apart from the profound and perhaps +inscrutable problems which lie at the bottom of human existence, +men have in all ages invented theories to explain the common +phenomena of the material universe; and most of these theories, +however varied in their details, turn out on examination to have a +common root, and to be based on the same elements. Modern geology +has its own theories on the same subject, and it will be well to +glance for a moment at the principles underlying the old and +the new views. + +It has been maintained, as a metaphysical hypothesis, that there +exists in the mind of man an inherent principle, in virtue of +which he believes and expects that what has been, will be; and +that the course of nature will be a continuous and uninterrupted +one. So far, however, from any such belief existing as a necessary +consequence of the constitution of the human mind, the real fact +seems to be that the contrary belief has been almost universally +prevalent. In all old religions, and in the philosophical systems +of almost all ancient nations, the order of the universe has +been regarded as distinctly unstable, mutable, and temporary. +A beginning and an end have always been assumed, and the course +of terrestrial events between these two indefinite points has +been regarded as liable to constant interruption by revolutions +and catastrophes of different kinds, in many cases emanating from +supernatural sources. Few of the more ancient theological creeds, +and still fewer of the ancient philosophies, attained body and +shape without containing, in some form or another, the belief +in the existence of periodical convulsions, and of alternating +cycles of destruction and repair. + +That geology, in its early infancy, should have become imbued +with the spirit of this belief, is no more than might have been +expected; and hence arose the at one time powerful and +generally-accepted doctrine of "Catastrophism." That the succession +of phenomena upon the globe, whereby the earth's crust had assumed +the configuration and composition which we find it to possess, +had been a discontinuous and broken succession, was the almost +inevitable conclusion of the older geologists. Everywhere in +their study of the rocks they met with apparently impassable +gaps, and breaches of continuity that could not be bridged over. +Everywhere they found themselves conducted abruptly from one system +of deposits to others totally different in mineral character or +in stratigraphical position. Everywhere they discovered that +well-marked and easily recognisable groups of animals and plants +were succeeded, without the intermediation of any obvious lapse +of time, by other assemblages of organic beings of a different +character. Everywhere they found evidence that the earth's crust +had undergone changes of such magnitude as to render it seemingly +irrational to suppose that they could have been produced by any +process now in existence. If we add to the above the prevalent +belief of the time as to the comparative brevity of the period +which had elapsed since the birth of the globe, we can readily +understand the general acceptance of some form of catastrophism +amongst the earlier geologists. + +As regards its general sense and substance, the doctrine of +catastrophism held that the history of the earth, since first +it emerged from the primitive chaos, had been one of periods +of repose, alternating with catastrophes and cataclysms of a +more or less violent character. The periods of tranquillity were +supposed to have been long and protracted; and during each of them +it was thought that one of the great geological "formations" was +deposited. In each of these periods, therefore, the condition of +the earth was supposed to be much the same as it is now--sediment +was quietly accumulated at the bottom of the sea, and animals and +plants flourished uninterruptedly in successive generations. +Each period of tranquillity, however, was believed to have been, +sooner or later, put an end to by a sudden and awful convulsion +of nature, ushering in a brief and paroxysmal period, in which +the great physical forces were unchained and permitted to spring +into a portentous activity. The forces of subterranean fire, +with their concomitant phenomena of earthquake and volcano, were +chiefly relied upon as the efficient causes of these periods of +spasm and revolution. Enormous elevations of portions of the +earth's crust were thus believed to be produced, accompanied by +corresponding and equally gigantic depressions of other portions. +In this way new ranges of mountains were produced, and previously +existing ranges levelled with the ground, seas were converted into +dry land, and continents buried beneath the ocean--catastrophe +following catastrophe, till the earth was rendered uninhabitable, +and its races of animals and plants were extinguished, never to +reappear in the same form. Finally, it was believed that this +feverish activity ultimately died out, and that the ancient peace +once more came to reign upon the earth. As the abnormal throes +and convulsions began to be relieved, the dry land and sea once +more resumed their relations of stability, the conditions of +life were once more established, and new races of animals and +plants sprang into existence, to last until the supervention +of another fever-fit. + +Such is the past history of the globe, as sketched for us, in +alternating scenes of fruitful peace and revolutionary destruction, +by the earlier geologists. As before said, we cannot wonder at the +former general acceptance of Catastrophistic doctrines. Even in +the light of our present widely-increased knowledge, the series +of geological monuments remains a broken and imperfect one; nor +can we ever hope to fill up completely the numerous gaps with +which the geological record is defaced. Catastrophism was the +natural method of accounting for these gaps, and, as we shall see, +it possesses a basis of truth. At present, however, catastrophism +may be said to be nearly extinct, and its place is taken by the +modern doctrine of "Continuity" or "Uniformity"--a doctrine with +which the name of Lyell must ever remain imperishably associated. + +The fundamental thesis of the doctrine of Uniformity is, that, +in spite of all apparent violations of continuity, the sequence +of geological phenomena has in reality been a regular and +uninterrupted one; and that the vast changes which can be shown +to have passed over the earth in former periods have been the +result of the slow and ceaseless working of the ordinary physical +forces--acting with no greater intensity than they do now, but +acting through enormously prolonged periods. The essential element +in the theory of Continuity is to be found in the allotment of +indefinite time for the accomplishment of the known series of +geological changes. It is obviously the case, namely, that there +are two possible explanations of all phenomena which lie so far +concealed in "the dark backward and abysm of time," that we can +have no direct knowledge of the manner in which they were produced. +We may, on the one hand, suppose them to be the result of some +very powerful cause, acting through a short period of time. That +is Catastrophism. Or, we may suppose them to be caused by a much +weaker force operating through a proportionately prolonged period. +This is the view of the Uniformitarians. It is a question of +_energy_ versus _time_ and it is _time_ which is the true element +of the case. An earthquake may remove a mountain in the course +of a few seconds; but the dropping of the gentle rain will do +the same, if we extend its operations over a millennium. And +this is true of all agencies which are now at work, or ever have +been at work, upon our planet. The Catastrophists, believing +that the globe is but, as it were, the birth of yesterday, were +driven of necessity to the conclusion that its history had been +checkered by the intermittent action of paroxysmal and almost +inconceivably potent forces. The Uniformitarians, on the other +hand, maintaining the "adequacy of existing causes," and denying +that the known physical forces ever acted in past time with greater +intensity than they do at present, are, equally of necessity, +driven to the conclusion that the world is truly in its "hoary +eld," and that its present state is really the result of the +tranquil and regulated action of known forces through unnumbered +and innumerable centuries. + +The most important point for us, in the present connection, is +the bearing of these opposing doctrines upon the question, as +to the origin of the existing terrestrial order. On any doctrine +of uniformity that order has been evolved slowly, and, according +to law, from a pre-existing order. Any doctrine of catastrophism, +on the other hand, carries with it, by implication, the belief +that the present order of things was brought about suddenly and +irrespective of any pre-existent order; and it is important to +hold clear ideas as to which of these beliefs is the true one. In +the first place, we may postulate that the world had a beginning, +and, equally, that the existing terrestrial order had a beginning. +However far back we may go, geology does not, and cannot, reach the +actual beginning of the world; and we are, therefore, left simply +to our own speculations on this point. With regard, however, to +the existing terrestrial order, a great deal can be discovered, +and to do so is one of the principal tasks of geological science. +The first steps in the production of that order lie buried in +the profound and unsearchable depths of a past so prolonged as +to present itself to our finite minds as almost in eternity. +The last steps are in the prophetic future, and can be but dimly +guessed at. Between the remote past and the distant future, we +have, however, a long period which is fairly open to inspection; +and in saying a "long" period, it is to be borne in mind that +this term is used in its _geological_ sense. Within this period, +enormously long as it is when measured by human standards, we +can trace with reasonable certainty the progressive march of +events, and can determine the laws of geological action, by which +the present order of things has been brought about. + +The natural belief on this subject doubtless is, that the world, +such as we now see it, possessed its present form and configuration +from the beginning. Nothing can be more natural than the belief +that the present continents and oceans have always been where +they are now; that we have always had the same mountains and +plains; that our rivers have always had their present courses, +and our lakes their present positions; that our climate has always +been the same; and that our animals and plants have always been +identical with those now familiar to us. Nothing could be more +natural than such a belief, and nothing could be further removed +from the actual truth. On the contrary, a very slight acquaintance +with geology shows us, in the words of Sir John Herschel, that +"the actual configuration of our continents and islands, the +coast-lines of our maps, the direction and elevation of our +mountain-chains, the courses of our rivers, and the soundings +of our oceans, are not things primordially arranged in the +construction of our globe, but results of successive and complex +actions on a former state of things; _that_, again, of similar +actions on another still more remote; and so on, till the original +and really permanent state is pushed altogether out of sight +and beyond the reach even of imagination; while on the other +hand, a similar, and, as far as we can see, interminable vista +is opened out for the future, by which the habitability of our +planet is secured amid the total abolition on it of the present +theatres of terrestrial life." + +Geology, then, teaches us that the physical features which now +distinguish the earth's surface have been produced as the ultimate +result of an almost endless succession of precedent changes. +Palæontology teaches us, though not yet in such assured accents, +the same lesson. Our present animals and plants have not been +produced, in their innumerable forms, each as we now know it, +as the sudden, collective, and simultaneous birth of a renovated +world. On the contrary, we have the clearest evidence that some +of our existing animals and plants made their appearance upon the +earth at a much earlier period than others. In the confederation +of animated nature some races can boast of an immemorial antiquity, +whilst others are comparative _parvenus_. We have also the clearest +evidence that the animals and plants which now inhabit the globe +have been preceded, over and over again, by other different +assemblages of animals and plants, which have flourished in +successive periods of the earth's history, have reached their +culmination, and then have given way to a fresh series of living +beings. We have, finally, the clearest evidence that these successive +groups of animals and plants (faunæ and floræ) are to a greater +or less extent directly connected with one another. Each group +is, to a greater or less extent, the lineal descendant of the +group which immediately preceded it in point of time, and is +more or less fully concerned with giving origin to the group +which immediately follows it. That this law of "evolution" has +prevailed to a great extent is quite certain; but it does not +meet all the exigencies of the case, and it is probable that +its action has been supplemented by some still unknown law of +a different character. + +We shall have to consider the question of geological "continuity" +again. In the meanwhile, it is sufficient to state that this +doctrine is now almost universally accepted as the basis of all +inquiries, both in the domain of geology and that of palæontology. +The advocates of continuity possess one immense advantage over +those who believe in violent and revolutionary convulsions, that +they call into play only agencies of which we have actual knowledge. +We _know_ that certain forces are now at work, producing certain +modifications in the present condition of the globe; and we _know_ +that these forces are capable of producing the vastest of the +changes which geology brings under our consideration, provided +we assign a time proportionately vast for their operation. On +the other hand, the advocates of catastrophism, to make good +their views, are compelled to invoke forces and actions, both +destructive and restorative, of which we have, and can have, no +direct knowledge. They endow the whirlwind and the earthquake, +the central fire and the rain from heaven, with powers as mighty +as ever imagined in fable, and they build up the fragments of a +repeatedly shattered world by the intervention of an intermittently +active creative power. + +It should not be forgotten, however, that from one point of view +there is a truth in catastrophism which is sometimes overlooked +by the advocates of continuity and uniformity. Catastrophism +has, as its essential feature, the proposition that the known +and existing forces of the earth at one time acted with much +greater intensity and violence than they do at present, and they +carry down the period of this excessive action to the commencement +of the present terrestrial order. The Uniformitarians, in effect, +deny this proposition, at any rate as regards any period of the +earth's history of which we have actual cognisance. If, however, +the "nebular hypothesis" of the origin of the universe be well +founded--as is generally admitted--then, beyond question, the +earth is a gradually cooling body, which has at one time been +very much hotter than it is at present. There has been a time, +therefore, in which the igneous forces of the earth, to which we +owe the phenomena of earthquakes and volcanoes, must have been +far more intensely active than we can conceive of from anything +that we can see at the present day. By the same hypothesis, the +sun is a cooling body, and must at one time have possessed a +much higher temperature than it has at present. But increased +heat of the sun would seriously alter the existing conditions +affecting the evaporation and precipitation of moisture on our +earth; and hence the aqueous forces may also have acted at one +time more powerfully than they do now. The fundamental principle +of catastrophism is, therefore, not wholly vicious; and we have +reason to think that there must have been periods--very remote, +it is true, and perhaps unrecorded in the history of the earth--in +which the known physical forces may have acted with an intensity +much greater than direct observation would lead us to imagine. +And this may be believed, altogether irrespective of those great +secular changes by which hot or cold epochs are produced, and +which can hardly be called "catastrophistic," as they are produced +gradually, and are liable to recur at definite intervals. + +Admitting, then, that there _is_ a truth at the bottom of the once +current doctrines of catastrophism, still it remains certain that +the history of the earth has been one of _law_ in all past time, +as it is now. Nor need we shrink back affrighted at the vastness +of the conception--the vaster for its very vagueness--that we +are thus compelled to form as to the duration of _geological +time_. As we grope our way backward through the dark labyrinth +of the ages, epoch succeeds to epoch, and period to period, each +looming more gigantic in its outlines and more shadowy in its +features, as it rises, dimly revealed, from the mist and vapour +of an older and ever-older past. It is useless to add century +to century or millennium to millennium. When we pass a certain +boundary-line, which, after all, is reached very soon, figures +cease to convey to our finite faculties any real notion of the +periods with which we have to deal. The astronomer can employ +material illustrations to give form and substance to our conceptions +of celestial space; but such a resource is unavailable to the +geologist. The few thousand years of which we have historical +evidence sink into absolute insignificance beside the unnumbered +æons which unroll themselves one by one as we penetrate the dim +recesses of the past, and decipher with feeble vision the ponderous +volumes in which the record of the earth is written. Vainly does +the strained intellect seek to overtake an ever-receding +commencement, and toil to gain some adequate grasp of an apparently +endless succession. A beginning there must have been, though we +can never hope to fix its point. Even speculation droops her +wings in the attenuated atmosphere of a past so remote, and the +light of imagination is quenched in the darkness of a history so +ancient. In _time_, as in _space_, the confines of the universe +must ever remain concealed from us, and of the end we know no +more than of the beginning. Inconceivable as is to us the lapse +of "geological time," it is no more than "a mere moment of the +past, a mere infinitesimal portion of eternity." Well may "the +human heart, that weeps and trembles," say, with Richter's pilgrim +through celestial space, "I will go no farther; for the spirit of +man acheth with this infinity. Insufferable is the glory of God. +Let me lie down in the grave, and hide me from the persecution +of the Infinite, for end, I see, there is none." + + + + +CHAPTER I. + +THE SCOPE AND MATERIALS OF PALÆONTOLOGY. + +The study of the rock-masses which constitute the crust of the +earth, if carried out in the methodical and scientific manner of +the geologist, at once brings us, as has been before remarked, in +contact with the remains or traces of living beings which formerly +dwelt upon the globe. Such remains are found, in greater or less +abundance, in the great majority of rocks; and they are not only of +great interest in themselves, but they have proved of the greatest +importance as throwing light upon various difficult problems in +geology, in natural history, in botany, and in philosophy. Their +study constitutes the science of palæontology; and though it is +possible to proceed to a certain length in geology and zoology +without much palæontological knowledge, it is hardly possible to +attain to a satisfactory general acquaintance with either of +these subjects without having mastered the leading facts of the +first. Similarly, it is not possible to study palæontology without +some acquaintance with both geology and natural history. + +Palæontology, then, is the science which treats of the living +beings, whether animal or vegetable, which have inhabited the earth +during past periods of its history. Its object is to elucidate, +as far as may be, the structure, mode of existence, and habits +of all such ancient forms of life; to determine their position +in the scale of organised beings; to lay down the geographical +limits within which they flourished; and to fix the period of +their advent and disappearance. It is the ancient life-history +of the earth; and were its record complete, it would furnish +us with a detailed knowledge of the form and relations of all +the animals and plants which have at any period flourished upon +the land-surfaces of the globe or inhabited its waters; it would +enable us to determine precisely their succession in time; and +it would place in our hands an unfailing key to the problems of +evolution. Unfortunately, from causes which will be subsequently +discussed, the palæontological record is extremely imperfect, +and our knowledge is interrupted by gaps, which not only bear +a large proportion to our solid information, but which in many +cases are of such a nature that we can never hope to fill them +up. + +Fossils.--The remains of animals or vegetables which we now find +entombed in the solid rock, and which constitute the working +material of the palæontologist, are termed "fossils,"[3] or +"petrifactions." In most cases, as can be readily understood, +fossils are the actual hard parts of animals and plants which +were in existence when the rock in which they are now found was +being deposited. Most fossils, therefore, are of the nature of +the shells of shell-fish, the skeletons of coral-zoophytes, the +bones of vertebrate animals, or the wood, bark, or leaves of +plants. All such bodies are more or less of a hard consistence +to begin with, and are capable of resisting decay for a longer +or shorter time--hence the frequency with which they occur in +the fossil condition. Strictly speaking, however, by the term +"fossil" must be understood "any body, _or the traces of the +existence of any body_, whether animal or vegetable, which has +been buried in the earth by natural causes" (Lyell). We shall +find, in fact, that many of the objects which we have to study +as "fossils" have never themselves actually formed parts of any +animal or vegetable, though they are due to the former existence +of such organisms, and indicate what was the nature of these. +Thus the footprints left by birds, or reptiles, or quadrupeds +upon sand or mud, are just as much proofs of the former existence +of these animals as would be bones, feathers, or scales, though +in themselves they are inorganic. Under the head of fossils, +therefore, come the footprints of air-breathing vertebrate animals; +the tracks, trails, and burrows of sea-worms, crustaceans, or +molluscs; the impressions left on the sand by stranded jelly-fishes; +the burrows in stone or wood of certain shell-fish; the "moulds" +or "casts" of shells, corals, and other organic remains; and +various other bodies of a more or less similar nature. + +[Footnote 3: Lat. _fossus_, dug up.] + +Fossilisation.-- The term "fossilisation" is applied to all those +processes through which the remains of organised beings may pass +in being converted into fossils. These processes are numerous +and varied; but there are three principal modes of fossilisation +which alone need be considered here. In the first instance, the +fossil is to all intents and purposes an actual portion of the +original organised being--such as a bone, a shell, or a piece +of wood. In some rare instances, as in the case of the body of +the Mammoth discovered embedded in ice at the mouth of the Lena +in Siberia, the fossil may be preserved almost precisely in its +original condition, and even with its soft parts uninjured. More +commonly, certain changes have taken place in the fossil, the +principal being the more or less total removal of the organic +matter originally present. Thus bones become light and porous +by the removal of their gelatine, so as to cleave to the tongue +on being applied to that organ; whilst shells become fragile, and +lose their primitive colours. In other cases, though practically +the real body it represents, all the cavities of the fossil, +down to its minutest recesses, may have become infiltrated with +mineral matter. It need hardly be added, that it is in the more +modern rocks that we find the fossils, as a rule, least changed +from their former condition; but the original structure is often +more or less completely retained in some of the fossils from +even the most ancient formations. + +In the second place, we very frequently meet with fossils in the +state of "casts" or moulds of the original organic body. What +occurs in this case will be readily understood if we imagine any +common bivalve shell, as an Oyster, or Mussel, or Cockle, embedded +in clay or mud. If the clay were sufficiently soft and fluid, the +first thing would be that it would gain access to the interior +of the shell, and would completely fill up the space between the +valves. The pressure, also, of the surrounding matter would insure +that the clay would everywhere adhere closely to the exterior of +the shell. If now we suppose the clay to be in any way hardened +so as to be converted into stone, and if we were to break up the +stone, we should obviously have the following state of parts. +The clay which filled the shell would form an accurate cast of +the _interior_ of the shell, and the clay outside would give us +an exact impression or cast of the _exterior_ of the shell (fig. +1). We should have, then, two casts, an interior and an exterior, +and the two would be very different to one another, since the +inside of a shell is very unlike the outside. In the case, in +fact, of many univalve shells, the interior cast or "mould" is +so unlike the exterior cast, or unlike the shell itself, that +it may be difficult to determine the true origin of the former. + +[Illustration: Fig. 1.--_Trigonia longa_, showing casts to of +the exterior and interior of the shell.--Cretaceous (Neocomian).] + +It only remains to add that there is sometimes a further +complication. If the rock be very porous and permeable by water, +it may happen that the original shell is entirely dissolved away, +leaving the interior cast loose, like the kernel of a nut, within +the case formed by the exterior cast. Or it may happen that +subsequent to the attainment of this state of things, the space +thus left vacant between the interior and exterior cast--the space, +that is, formerly occupied by the shell itself--may be filled up +by some foreign mineral deposited there by the infiltration of +water. In this last case the splitting open of the rock would +reveal an interior cast, an exterior cast, and finally a body +which would have the exact form of the original shell, but which +would be really a much later formation, and which would not exhibit +under the microscope the minute structure of shell. + +[Illustration: Fig. 2.--Microscopic section of the silicified +wood of a Conifer (_Sequoia_) cut in the long direction of the +fibres. Post-tertiary? Colorado. (Original.)] + +[Illustration: Footnote: Fig. 3.--Microscopic section of the wood +of the common Larch (_Abies larix_), cut in the long direction of +the fibres. In both the fresh and the fossil wood (fig. 2) are +seen the discs characteristic of coniferous wood. (Original.)] + +In the third class of cases we have fossils which present with +the greatest accuracy the external form, and even sometimes the +internal minute structure, of the original organic body, but +which, nevertheless, are not themselves truly organic, but have +been formed by a "replacement" of the particles of the primitive +organism by some mineral substance. The most elegant example +of this is afforded by fossil wood which has been "silicified" +or converted into flint (_silex_). In such cases we have fossil +wood which presents the rings of growth and fibrous structure of +recent wood, and which under the microscope exhibits the minutest +vessels which characterise ligneous tissue, together with the even +more minute markings of the vessels (fig. 2). The whole, however, +instead of being composed of the original carbonaceous matter of +the wood, is now converted into flint. The only explanation that +can be given of this by no means rare phenomenon, is that the +wood must have undergone a slow process of decay in water charged +with silica or flint in solution. As each successive particle of +wood was removed by decay, its place was taken by a particle of +flint deposited from the surrounding water, till ultimately the +entire wood was silicified. The process, therefore, resembles +what would take place if we were to pull down a house built of +brick by successive bricks, replacing each brick as removed by +a piece of stone of precisely the same size and form. The result +of this would be that the house would retain its primitive size, +shape, and outline, but it would finally have been converted +from a house of brick into a house of stone. Many other fossils +besides wood--such as shells, corals, sponges, &c.--are often +found silicified; and this may be regarded as the commonest form +of fossilisation by replacement. In other cases, however, though +the principle of the process is the same, the replacing substance +may be iron pyrites, oxide of iron, sulphur, malachite, magnesite, +talc, &c.; but it is rarely that the replacement with these minerals +is so perfect as to preserve the more delicate details of internal +structure. + + + + +CHAPTER II. + +THE FOSSILIFEROUS ROCKS. + +Fossils are found in rocks, though not universally or promiscuously; +and it is therefore necessary that the palæontologist should +possess some acquaintance with, at any rate, those rocks which +yield organic remains, and which are therefore said to be +"_fossiliferous_." In geological language, all the materials +which enter into the composition of the solid crust of the earth, +be their texture what it may--from the most impalpable mud to +the hardest granite--are termed "rocks;" and for our present +purpose we may divide these into two great groups. In the first +division are the _Igneous Rocks_--such as the lavas and ashes of +volcanoes--which are formed within the body of the earth itself, +and which owe their structure and origin to the action of heat. +The Igneous Rocks are formed primarily below the surface of the +earth, which they only reach as the result of volcanic action; +they are generally destitute of distinct "stratification," or +arrangement in successive layers; and they do not contain fossils, +except in the comparatively rare instances where volcanic ashes +have enveloped animals or plants which were living in the sea +or on the land in the immediate vicinity of the volcanic focus. +The second great division of rocks is that of the _Fossiliferous, +Aqueous_, or _Sedimentary_ Rocks. These are formed at the surface +of the earth, and, as implied by one of their names, are invariably +deposited in water. They are produced by vital or chemical action, +or are formed from the "sediment" produced by the disintegration +and reconstruction of previously existing rocks, without previous +solution; they mostly contain fossils; and they are arranged +in distinct layers or "strata." The so-called "aerial" rocks +which, like beds of blown sand, have been formed by the action +of the atmosphere, may also contain fossils; but they are not +of such importance as to require special notice here. + +For all practical purposes, we may consider that the Aqueous +Rocks are the natural cemetery of the animals and plants of bygone +ages; and it is therefore essential that the palæontological +student should be acquainted with some of the principal facts as +to their physical characters, their minute structure and mode of +origin, their chief varieties, and their historical succession. + +The Sedimentary or Fossiliferous Rocks form the greater portion of +that part of the earth's crust which is open to our examination, and +are distinguished by the fact that they are regularly "stratified" or +arranged in distinct and definite layers or "strata." These layers +may consist of a single material, as in a block of sandstone, or +they may consist of different materials. When examined on a large +scale, they are always found to consist of alternations of layers +of different mineral composition. We may examine any given area, +and find in it nothing but one kind of rock--sandstone, perhaps, +or limestone. In all cases, however, if we extend our examination +sufficiently far, we shall ultimately come upon different rocks; +and, as a general rule, the thickness of any particular set of +beds is comparatively small, so that different kinds of rock +alternate with one another in comparatively small spaces. + +[Illustration: Fig. 4.--Sketch of Carboniferous strata at Kinghorn, +in Fife, showing stratified beds (limestone and shales) surmounted +by an unstratified mass of trap. (Original.)] + +As regards the origin of the Sedimentary Rocks, they are for +the most part "derivative" rocks, being derived from the wear +and tear of pre-existent rocks. Sometimes, however, they owe +their origin to chemical or vital action, when they would more +properly be spoken of simply as Aqueous Rocks. As to their mode +of deposition, we are enabled to infer that the materials which +compose them have formerly been spread out by the action of water, +from what we see going on every day at the mouths of our great +rivers, and on a smaller scale wherever there is running water. +Every stream, where it runs into a lake or into the sea, carries +with it a burden of mud, sand, and rounded pebbles, derived from +the waste of the rocks which form its bed and banks. When these +materials cease to be impelled by the force of the moving water, +they sink to the bottom, the heaviest pebbles, of course, sinking +first, the smaller pebbles and sand next, and the finest mud +last. Ultimately, therefore, as might have been inferred upon +theoretical grounds, and as is proved by practical experience, +every lake becomes a receptacle for a series of stratified rocks +produced by the streams flowing into it. These deposits may vary +in different parts of the lake, according as one stream brought +down one kind of material and another stream contributed another +material; but in all cases the materials will bear ample evidence +that they were produced, sorted, and deposited by running water. +The finer beds of clay or sand will all be arranged in thicker or +thinner layers or laminæ; and if there are any beds of pebbles +these will all be rounded or smooth, just like the water-worn +pebbles of any brook-course. In all probability, also, we should +find in some of the beds the remains of fresh-water shells or +plants or other organisms which inhabited the lake at the time +these beds were being deposited. + +In the same way large rivers--such as the Ganges or +Mississippi--deposit all the materials which they bring down +at their mouths, forming in this way their "deltas." Whenever +such a delta is cut through, either by man or by some channel of +the river altering its course, we find that it is composed of a +succession of horizontal layers or strata of sand or mud, varying +in mineral composition, in structure, or in grain, according to +the nature of the materials brought down by the river at different +periods. Such deltas, also, will contain the remains of animals +which inhabit the river, with fragments of the plants which grew +on its banks, or bones of the animals which lived in its basin. + +Nor is this action confined, of course, to large rivers only, +though naturally most conspicuous in the greatest bodies of water. +On the contrary, all streams, of whatever size, are engaged in +the work of wearing down the dry land, and of transporting the +materials thus derived from higher to lower levels, never resting +in this work till they reach the sea. + +[Illustration: Fig. 5.--Diagram to illustrate the formation of +sedimentary deposits at the point where a river debouches into +the sea.] + +Lastly, the sea itself--irrespective of the materials delivered +into it by rivers--is constantly preparing fresh stratified deposits +by its own action. Upon every coast-line the sea is constantly +eating back into the land and reducing its component rocks to +form the shingle and sand which we see upon every shore. The +materials thus produced are not, however, lost, but are ultimately +deposited elsewhere in the form of new stratified accumulations, +in which are buried the remains of animals inhabiting the sea +at the time. + +Whenever, then, we find anywhere in the interior of the land +any series of beds having these characters--composed, that is, +of distinct layers, the particles of which, both large and small, +show distinct traces of the wearing action of water--whenever and +wherever we find such rocks, we are justified in assuming that +they have been deposited by water in the manner above mentioned. +Either they were laid down in some former lake by the combined +action of the streams which flowed into it; or they were deposited +at the mouth of some ancient river, forming its delta; or they +were laid down at the bottom of the ocean. In the first two cases, +any fossils which the beds might contain would be the remains +of fresh-water or terrestrial organisms. In the last case, the +majority, at any rate, of the fossils would be the remains of +marine animals. + +The term "formation" is employed by geologists to express "any +group of rocks which have some character in common, whether of +origin, age, or composition" (Lyell); so that we may speak of +stratified and unstratified formations, aqueous or igneous +formations, fresh-water or marine formations, and so on. + + +CHIEF DIVISIONS OF THE AQUEOUS ROCKS. + +The Aqueous Rocks may be divided into two great sections, the +Mechanically-formed and the Chemically-formed, including under +the last head all rocks which owe their origin to vital action, +as well as those produced by ordinary chemical agencies. + +[Illustration: Fig. 6.--Microscopic section of a calcareous breccia +in the Lower Silurian (Coniston Limestone) of Shap Wells, +Westmoreland. The fragments are all of small size, and consist of +angular pieces of transparent quartz, volcanic ashes, and limestone +embedded in a matrix of crystalline limestone. (Original.)] + +A. MECHANICALLY-FORMED ROCKS.--These are all those Aqueous Rocks +of which we can obtain proofs that their particles have been +mechanically transported to their present situation. Thus, if +we examine a piece of _conglomerate_ or puddingstone, we find +it to be composed of a number of rounded pebbles embedded in an +enveloping matrix or paste, which is usually of a sandy nature, +but may be composed of carbonate of lime (when the rock is said to +be a "calcareous conglomerate"). The pebbles in all conglomerates +are worn and rounded by the action of water in motion, and thus +show that they have been subjected to much mechanical attrition, +whilst they have been mechanically transported for a greater +or less distance from the rock of which they originally formed +part. The analogue of the old conglomerates at the present day +is to be found in the great beds of shingle and gravel which +are formed by the action of the sea on every coast-line, and +which are composed of water-worn and well-rounded pebbles of +different sizes. A _breccia_ is a mechanically-formed rock, very +similar to a conglomerate, and consisting of larger or smaller +fragments of rock embedded in a common matrix. The fragments, +however, are in this case all more or less angular, and are not +worn or rounded. The fragments in breccias may be of large size, +or they may be comparatively small (fig. 6); and the matrix may +be composed of sand (arenaceous) or of carbonate of lime +(calcareous). In the case of an ordinary sandstone, again, we +have a rock which may be regarded as simply a very fine-grained +conglomerate or breccia, being composed of small grains of sand +(silica), sometimes rounded, sometimes more or less angular, +cemented together by some such substance as oxide of iron, silicate +of iron, or carbonate of lime. A sandstone, therefore, like a +conglomerate is a mechanically-formed rock, its component grams +being equally the result of mechanical attrition and having equally +been transported from a distance; and the same is true of the +ordinary sand of the sea-shore, which is nothing more than an +unconsolidated sandstone. Other so-called sands and sandstones, +though equally mechanical in their origin, are truly calcareous in +their nature, and are more or less entirely composed of carbonate +of lime. Of this kind are the shell-sand so common on our coasts, +and the coral-sand which is so largely formed in the neighbourhood +of coral-reefs. In these cases the rock is composed of fragments +of the skeletons of shellfish, and numerous other marine animals, +together, in many instances, with the remains of certain sea-weeds +(_Corallines_, _Nullipores_, &c,) which are endowed with the +power of secreting carbonate of lime from the sea-water. Lastly, +in certain rocks still finer in their texture than sandstones, +such as the various mud-rocks and shales, we can still recognise +a mechanical source and origin. If slices of any of these rocks +sufficiently thin to be transparent are examined under the +microscope, it will be found that they are composed of minute +grains of different sizes, which are all more or less worn and +rounded, and which clearly show, therefore, that they have been +subjected to mechanical attrition. + +All the above-mentioned rocks, then, are _mechanically-formed_ +rocks; and they are often spoken of as "Derivative Rocks," in +consequence of the fact that their particles can be shown to +have been mechanically _derived_ from other pre-existent rocks. +It follows from this that every bed of any mechanically-formed +rock is the measure and equivalent of a corresponding amount of +destruction of some older rock. It is not necessary to enter +here into a minute account of the subdivisions of these rocks, but +it may be mentioned that they may be divided into two principal +groups, according to their chemical composition. In the one group +we have the so-called _Arenaceous_ (Lat. _arena_, sand) or +_Siliceous_ Rocks, which are essentially composed of larger or +smaller grains of flint or silica. In this group are comprised +ordinary sand, the varieties of sandstone and grit, and most +conglomerates and breccias. We shall, however, afterwards see +that some siliceous rocks are of organic origin. In the second +group are the so-called _Argillaceous_ (Lat. _argilla_, clay) +Rocks, which contain a larger or smaller amount of clay or hydrated +silicate of alumina in their composition. Under this head come +clays, shales, marls, marl-slate, clay-slates, and most flags +and flagstones. + +B. CHEMICALLY-FORMED ROCKS.--In this section are comprised all +those Aqueous or Sedimentary Rocks which have been formed by +chemical agencies. As many of these chemical agencies, however, +are exerted through the medium of living beings, whether animals +or plants, we get into this section a number of what may be called +"_organically-formed rocks_." These are of the greatest possible +importance to the palæontologist, as being to a greater or less +extent composed of the actual remains of animals or vegetables, +and it will therefore be necessary to consider their character +and structure in some detail. + +By far the most important of the chemically-formed rocks are +the so-called _Calcareous Rocks_ (Lat. _calx_, lime), comprising +all those which contain a large proportion of carbonate of lime, +or are wholly composed of this substance. Carbonate of lime is +soluble in water holding a certain amount of carbonic acid gas +in solution; and it is, therefore, found in larger or smaller +quantity dissolved in all natural waters, both fresh and salt, +since these waters are always to some extent charged with the +above-mentioned solvent gas. A great number of aquatic animals, +however, together with some aquatic plants, are endowed with +the power of separating the lime thus held in solution in the +water, and of reducing it again to its solid condition. In this +way shell-fish, crustaceans, sea-urchins, corals, and an immense +number of other animals, are enabled to construct their skeletons; +whilst some plants form hard structures within their tissues +in a precisely similar manner. We do meet with some calcareous +deposits, such as the "stalactites" and "stalagmites" of caves, +the "calcareous tufa" and "travertine" of some hot springs, and +the spongy calcareous deposits of so-called "petrifying springs," +which are purely chemical in their origin, and owe nothing to the +operation of living beings. Such deposits are formed simply by +the precipitation of carbonate of lime from water, in consequence +of the evaporation from the water of the carbonic acid gas which +formerly held the lime in solution; but, though sometimes forming +masses of considerable thickness and of geological importance, +they do not concern us here. Almost all the limestones which +occur in the series of the stratified rocks are, primarily at any +rate, of _organic_ origin, and have been, directly or indirectly, +produced by the action of certain lime-making animals or plants, +or both combined. The presumption as to all the calcareous rocks, +which cannot be clearly shown to have been otherwise produced, +is that they are thus organically formed; and in many cases this +presumption can be readily reduced to a certainty. There are +many varieties of the calcareous rocks, but the following are +those which are of the greatest importance:-- + +_Chalk_ is a calcareous rock of a generally soft and pulverulent +texture, and with an earthy fracture. It varies in its purity, +being sometimes almost wholly composed of carbonate of lime, +and at other times more or less intermixed with foreign matter. +Though usually soft and readily reducible to powder, chalk is +occasionally, as in the north of Ireland, tolerably hard and +compact; but it never assumes the crystalline aspect and stony +density of limestone, except it be in immediate contact with +some mass of igneous rock. By means of the microscope, the true +nature and mode of formation of chalk can be determined with +the greatest ease. In the case of the harder varieties, the +examination can be conducted by means of slices ground down to +a thinness sufficient to render them transparent; but in the +softer kinds the rock must be disintegrated under water, and the +_débris_ examined microscopically. When investigated by either +of these methods, chalk is found to be a genuine organic rock, +being composed of the shells or hard parts of innumerable marine +animals of different kinds, some entire, some fragmentary, cemented +together by a matrix of very finely granular carbonate of lime. +Foremost amongst the animal remains which so largely compose +chalk are the shells of the minute creatures which will be +subsequently spoken of under the name of _Foraminifera_ (fig. +7), and which, in spite of their microscopic dimensions, play a +more important part in the process of lime-making than perhaps +any other of the larger inhabitants of the ocean. + +[Illustration: Fig. 7.--Section of Gravesend Chalk, examined +by transmitted light and highly magnified. Besides the entire +shells of _Globigerina_, _Rotalia_, and _Textularia_, numerous +detached chambers of _Globigerina_ are seen. (Original.)] + +As chalk is found in beds of hundreds of feet in thickness, +and of great purity, there was long felt much difficulty +in satisfactorily accounting for its mode of formation and origin. +By the researches of Carpenter, Wyville Thomson, +Huxley, Wallich, and others, it has, however, been shown +that there is now forming, in the profound depths of our +great oceans, a deposit which is in all essential respects +identical with chalk, and which is +generally known as the "Atlantic ooze," from its having been +first discovered in that sea. This ooze is found at great +depths (5000 to over 15,000 feet) in both the Atlantic and +Pacific, covering enormously large areas of the sea-bottom, +and it presents itself as a whitish-brown, sticky, impalpable mud, +very like greyish chalk when dried. Chemical examination +shows that the ooze is composed almost wholly of carbonate of +lime, and microscopical examination proves it to be of organic +origin, and to be made up of the remains of living beings. +The principal forms of these belong to the _Foraminifera_, and +the commonest of these are the irregularly-chambered shells of +_Globigerina_, absolutely indistinguishable from the +_Globigerinoe_ which are so largely present in the chalk (fig. 8). +Along with these occur fragments of the skeletons of other larger +creatures, and a certain proportion of the flinty cases of minute +animal and vegetable organisms (_Polycystina_ and _Diatoms_). +Though many of the minute animals, the hard parts of which form +the ooze, undoubtedly live at or near the surface of the sea, +others, probably, really live near the bottom; and the ooze +itself forms a congenial home for numerous sponges, sea-lilies, +and other marine animals which flourish at great +depths in the sea. There is thus established an intimate +and most interesting parallelism between the chalk and +the ooze of modern oceans. Both are formed essentially in +the same way, and the latter only requires consolidation to +become actually converted into chalk. Both are fundamentally +organic deposits, apparently requiring a great depth of water +for their accumulation, and mainly composed of the remains of +_Foraminifera_, together with the entire or broken skeletons +of other marine animals of greater dimensions. It is to be +remembered, however, that the ooze, though strictly +representative of the chalk, cannot be said in any proper sense +to be actually _identical_ with the formation so called by +geologists. A great lapse of time separates the two, and though +composed of the remains of representative classes or groups of +animals, it is only in the case of the lowly-organised +_Globigerinoe_, and of some other organisms of little higher +grade, that we find absolutely the same kinds or species of +animals in both. + +[Illustration: Fig. 8.--Organisms in the Atlantic Ooze, chiefly +_Foraminifera_ (_Globigerina_ and _Textularia_), with _Polycystina_ +and sponge-spicules; highly magnified. (Original.)] + +[Illustration: Fig. 9.--Slab of Crinoidal marble, from the +Carboniferous limestone of Dent, in Yorkshire, of the natural +size. The polished surface intersects the columns of the Crinoids +at different angles, and thus gives rise to varying appearances. +(Original.)] + +_Limestone_, like chalk, is composed of carbonate of lime, sometimes +almost pure, but more commonly with a greater or less intermixture +of some foreign material, such as alumina or silica. The varieties +of limestone are almost innumerable, but the great majority can +be clearly proved to agree with chalk in being essentially of +organic origin, and in being more or less largely composed of the +remains of living beings. In many instances the organic remains +which compose limestone are so large as to be readily visible to +the naked eye, and the rock is at once seen to be nothing more +than an agglomeration of the skeletons, generally fragmentary, of +certain marine animals, cemented together by a matrix of carbonate +of lime. This is the case, for example, with the so-called "Crinoidal +Limestones" and "Encrinital Marbles" with which the geologist +is so familiar, especially as occurring in great beds amongst +the older formations of the earth's crust. These are seen, on +weathered or broken surfaces, or still better in polished slabs +(fig. 9), to be composed more or less exclusively of the broken +stems and detached plates of sea-lilies (_Crinoids_). Similarly, +other limestones are composed almost entirely of the skeletons of +corals; and such old coralline limestones can readily be paralleled +by formations which we can find in actual course of production +at the present day. We only need to transport ourselves to the +islands of the Pacific, to the West Indies, or to the Indian +Ocean, to find great masses of lime formed similarly by living +corals, and well known to everyone under the name of "coral-reefs." +Such reefs are often of vast extent, both superficially and in +vertical thickness, and they fully equal in this respect any of +the coralline limestones of bygone ages. Again, we find other +limestones--such as the celebrated "Nummulitic Limestone" (fig. 10), +which sometimes attains a thickness of some thousands of feet--which +are almost entirely made up of the shells of _Foraminifera_. In +the case of the "Nummulitic Limestone," just mentioned, these +shells are of large size, varying from the size of a split pea +up to that of a florin. There are, however, as we shall see, +many other limestones, which are likewise largely made up of +_Foraminifera_, but in which the shells are very much more minute, +and would hardly be seen at all without the microscope. + +[Illustration: Fig. 10.--Piece of Nummulitic Limestone from the +Great Pyramid. Of the natural size. (Original.)] + +We may, in fact, consider that the great agents in the production +of limestones in past ages have been animals belonging to the +_Crinoids_, the _Corals_, and the _Foraminifera_. At the present +day, the Crinoids have been nearly extinguished, and the few known +survivors seem to have retired to great depths in the ocean; but +the two latter still actively carry on the work of lime-making, +the former being very largely helped in their operations by certain +lime-producing marine plants (_Nullipores_ and _Corallines_). We +have to remember, however, that though the limestones, both ancient +and modern, that we have just spoken of, are truly organic, they +are not necessarily formed out of the remains of animals which +actually lived on the precise spot where we now find the limestone +itself. We may find a crinoidal limestone, which we can show to +have been actually formed by the successive growth of generations +of sea-lilies _in place_; but we shall find many others in which +the rock is made up of innumerable fragments of the skeletons +of these creatures, which have been clearly worn and rubbed by +the sea-waves, and which have been mechanically transported to +their present site. In the same way, a limestone may be shown +to have been an actual coral-reef, by the fact that we find in +it great masses of coral, growing in their natural position, +and exhibiting plain proofs that they were simply quietly buried +by the calcareous sediment as they grew; but other limestones +may contain only numerous rolled and water-worn fragments of +corals. This is precisely paralleled by what we can observe in +our existing coral-reefs. Parts of the modern coral-islands and +coral-reefs are really made up of corals, dead or alive, which +actually grew on the spot where we now find them; but other parts +are composed of a limestone-rock ("coral-rock"), or of a loose +sand ("coral-sand"), which is organic in the sense that it is +composed of lime formed by living beings, but which, in truth, +is composed of fragments of the skeletons of these living beings, +mechanically transported and heaped together by the sea. To take +another example nearer home, we may find great accumulations of +calcareous matter formed _in place_, by the growth of shell-fish, +such as oysters or mussels; but we can also find equally great +accumulations on many of our shores in the form of "shell-sand," +which is equally composed of the shells of molluscs, but which is +formed by the trituration of these shells by the mechanical power +of the sea-waves. We thus see that though all these limestones are +primarily organic, they not uncommonly become "mechanically-formed" +rocks in a secondary sense, the materials of which they are composed +being formed by living beings, but having been mechanically +transported to the place where we now find them. + +[Illustration: Fig. 11.--Section of Carboniferous Limestone from +Spergen Hill, Indiana, U.S., showing numerous large-sized +_Foraminifera_ (_Endothyra_) and a few oolitic grains; magnified. +(Original.)] + +[Illustration: Fig 12.--Section of Coniston Limestone (Lower +Silurian) from Keisler, Westmoreland; magnified. The matrix is +very coarsely crystalline, and the included organic remains are +chiefly stems of Crinoids. (Original.)] + +Many limestones, as we have seen, are composed of large and +conspicuous organic remains, such as strike the eye at once. +Many others, however, which at first sight appear compact, more +or less crystalline, and nearly devoid of traces of life, are +found, when properly examined, to be also composed of the remains +of various organisms. All the commoner limestones, in fact, from +the Lower Silurian period onwards, can be easily proved to be +thus _organic_ rocks, if we investigate weathered or polished +surfaces with a lens, or, still better, if we cut thin slices +of the rock and grind these down till they are transparent. When +thus examined, the rock is usually found to be composed of +innumerable entire or fragmentary fossils, cemented together +by a granular or crystalline matrix of carbonate of lime (figs. +11 and 12). When the matrix is granular, the rock is precisely +similar to chalk, except that it is harder and less earthy in +texture, whilst the fossils are only occasionally referable to +the _Foraminifera_. In other cases, the matrix is more or less +crystalline, and when this crystallisation has been carried to +a great extent, the original organic nature of the rock may be +greatly or completely obscured thereby. Thus, in limestones which +have been greatly altered or "metamorphosed" by the combined +action of heat and pressure, all traces of organic remains become +annihilated, and the rock becomes completely crystalline throughout. +This, for example, is the case with the ordinary white "statuary +marble," slices of which exhibit under the microscope nothing but +an aggregate of beautifully transparent crystals of carbonate +of lime, without the smallest traces of fossils. There are also +other cases, where the limestone is not necessarily highly +crystalline, and where no metamorphic action in the strict sense +has taken place, in which, nevertheless, the microscope fails +to reveal any evidence that the rock is organic. Such cases are +somewhat obscure, and doubtless depend on different causes in +different instances; but they do not affect the important +generalisation that limestones are fundamentally the product +of the operation of living beings. This fact remains certain; +and when we consider the vast superficial extent occupied by +calcareous deposits, and the enormous collective thickness of +these, the mind cannot fail to be impressed with the immensity of +the period demanded for the formation of these by the agency of +such humble and often microscopic creatures as Corals, Sea-lilies, +Foraminifers, and Shell-fish. + +Amongst the numerous varieties of limestone, a few are of such +interest as to deserve a brief notice. _Magnesian limestone_ +or _dolomite_, differs from ordinary limestone in containing +a certain proportion of carbonate of magnesia along with the +carbonate of lime. The typical dolomites contain a large proportion +of carbonate of magnesia, and are highly crystalline. The ordinary +magnesian limestones (such as those of Durham in the Permian +series, and the Guelph Limestones of North America in the Silurian +series) are generally of a yellowish, buff, or brown colour, +with a crystalline or pearly aspect, effervescing with acid much +less freely than ordinary limestone, exhibiting numerous cavities +from which fossils have been dissolved out, and often assuming +the most varied and singular forms in consequence of what is +called "concretionary action." Examination with the microscope +shows that these limestones are composed of an aggregate of minute +but perfectly distinct crystals, but that minute organisms of +different kinds, or fragments of larger fossils, are often present +as well. Other magnesian limestones, again, exhibit no striking +external peculiarities by which the presence of magnesia would be +readily recognised, and though the base of the rock is crystalline, +they are replete with the remains of organised beings. Thus many +of the magnesian limestones of the Carboniferous series of the +North of England are very like ordinary limestone to look at, +though effervescing less freely with acids, and the microscope +proves them to be charged with the remains of _Foraminifera_ +and other minute organisms. + +_Marbles_ are of various kinds, all limestones which are sufficiently +hard and compact to take a high polish going by this name. Statuary +marble, and most of the celebrated foreign marbles, are "metamorphic" +rocks, of a highly crystalline nature, and having all traces +of their primitive organic structure obliterated. Many other +marbles, however, differ from ordinary limestone simply in the +matter of density. Thus, many marbles (such as Derbyshire marble) +are simply "crinoidal limestones" (fig. 9); whilst various other +British marbles exhibit innumerable organic remains under the +microscope. Black marbles owe their colour to the presence of +very minute particles of carbonaceous matter, in some cases at +any rate; and they may either be metamorphic, or they may be +charged with minute fossils such as _Foraminifera_ (_e.g._, the +black limestones of Ireland, and the black marble of Dent, in +Yorkshire). + +[Illustration: Fig. 13.--Slice of oolitic limestone from the +Jurassic series (Coral Rag) of Weymouth; magnified. (Original.)] + +"_Oolitic_" _limestones_, or "_oolites_," as they are often called, +are of interest both to the palæontologist and geologist. The +peculiar structure to which they owe their name is that the rock +is more or less entirely composed of spheroidal or oval grains, +which vary in size from the head of a small pin or less up to +the size of a pea, and which may be in almost immediate contact +with one another, or may be cemented together by a more or less +abundant calcareous matrix. When the grains are pretty nearly +spherical and are in tolerably close contact, the rock looks very +like the roe of a fish, and the name of "oolite" or "egg-stone" +is in allusion to this. When the grains are of the size of peas +or upwards, the rock is often called a "pisolite" (Lat. _pisum_, +a pea). Limestones having this peculiar structure are especially +abundant in the Jurassic formation, which is often called the +"Oolitic series" for this reason; but essentially similar limestones +occur not uncommonly in the Silurian, Devonian, and Carboniferous +formations, and, indeed, in almost all rock-groups in which +limestones are largely developed. Whatever may be the age of +the formation in which they occur, and whatever may be the size +of their component "eggs," the structure of oolitic limestones +is fundamentally the same. All the ordinary oolitic limestones, +namely, consist of little spherical or ovoid "concretions," as +they are termed, cemented together by a larger or smaller amount +of crystalline carbonate of lime, together, in many instances, +with numerous organic remains of different kinds (fig. 13). When +examined in polished slabs, or in thin sections prepared for the +microscope, each of these little concretions is seen to consist +of numerous concentric coats of carbonate of lime, which sometimes +simply surround an imaginary centre, but which, more commonly, +have been successively deposited round some foreign body, such as +a little crystal of quartz, a cluster of sand-grains, or a minute +shell. In other cases, as in some of the beds of the Carboniferous +limestone in the North of England, where the limestone is highly +"arenaceous," there is a modification of the oolitic structure. +Microscopic sections of these sandy limestones (fig. 14) show +numerous generally angular or oval grains of silica or flint, +each of which is commonly surrounded by a thin coating of carbonate +of lime, or sometimes by several such coats, the whole being +cemented together along with the shells of _Foraminifera_ and +other minute fossils by a matrix of crystalline calcite. As compared +with typical oolites, the concretions in these limestones are +usually much more irregular in shape, often lengthened out and +almost cylindrical, at other times angular, the central nucleus +being of large size, and the surrounding envelope of lime being +very thin, and often exhibiting no concentric structure. In both +these and the ordinary oolites, the structure is fundamentally +the same. Both have been formed in a sea, probably of no great +depth, the waters of which were charged with carbonate of lime +in solution, whilst the bottom was formed of sand intermixed with +minute shells and fragments of the skeletons of larger marine +animals. The excess of lime in the sea-water was precipitated +round the sand-grams, or round the smaller shells, as so many +nuclei, and this precipitation must often have taken place time +after time, so as to give rise to the concentric structure so +characteristic of oolitic concretions. Finally, the oolitic grains +thus produced were cemented together by a further precipitation +of crystalline carbonate of lime from the waters of the ocean. + +[Illustration: Fig. 14.--Slice of arenaceous and oolitic limestone +from the Carboniferous series of Shap, Westmoreland; magnified. +The section also exhibit _Foraminifera_ and other minute fossils. +(Original.)] + +_Phosphate of Lime_ is another lime-salt, which is of interest to +the palæontologist. It does not occur largely in the stratified +series, but it is found in considerable beds [4] in the Laurentian +formation, and less abundantly in some later rock-groups, whilst +it occurs abundantly in the form of nodules in parts of the +Cretaceous (Upper Greensand) and Tertiary deposits. Phosphate +of lime forms the larger proportion of the earthy matters of the +bones of Vertebrate animals, and also occurs in less amount in the +skeletons of certain of the Invertebrates (_e.g._, _Crustacea_). It +is, indeed, perhaps more distinctively than carbonate of lime, an +organic compound; and though the formation of many known deposits +of phosphate of lime cannot be positively shown to be connected +with the previous operation of living beings, there is room for +doubt whether this salt is not in reality always primarily a +product of vital action. The phosphatic nodules of the Upper +Greensand are erroneously called "coprolites," from the belief +originally entertained that they were the droppings or fossilised +excrements of extinct animals; and though this is not the case, +there can be little doubt but that the phosphate of lime which +they contain is in this instance of organic origin.[5] It appears, +in fact, that decaying animal matter has a singular power of +determining the precipitation around it of mineral salts dissolved +in water. Thus, when any animal bodies are undergoing decay at the +bottom of the sea, they have a tendency to cause the precipitation +from the surrounding water of any mineral matters which may be +dissolved in it; and the organic body thus becomes a centre round +which the mineral matters in question are deposited in the form +of a "concretion" or "nodule." The phosphatic nodules in question +were formed in a sea in which phosphate of lime, derived from the +destruction of animal skeletons, was held largely in solution; +and a precipitation of it took place round any body, such as a +decaying animal substance, which happened to be lying on the +sea-bottom, and which offered itself as a favourable nucleus. In +the same way we may explain the formation of the calcareous nodules, +known as "septaria" or "cement stones," which occur so commonly in +the London Clay and Kimmeridge Clay, and in which the principal +ingredient is carbonate of lime. A similar origin is to be ascribed +to the nodules of clay iron-stone (impure carbonate of iron) which +occur so abundantly in the shales of the Carboniferous series and +in other argillaceous deposits; and a parallel modern example +is to be found in the nodules of manganese, which were found +by Sir Wyville Thomson, in the Challenger, to be so numerously +scattered over the floor of the Pacific at great depths. In +accordance with this mode of origin, it is exceedingly common +to find in the centre of all these nodules, both old and new, +some organic body, such as a bone, a shell, or a tooth, which +acted as the original nucleus of precipitation, and was thus +preserved in a shroud of mineral matter. Many nodules, it is +true, show no such nucleus; but it has been affirmed that all of +them can be shown, by appropriate microscopical investigation, +to have been formed round an original organic body to begin with +(Hawkins Johnson). + +[Footnote 4: Apart from the occurrence or phosphate of lime in +actual beds in the stratified rocks, as in the Laurentian and +Silurian series, this salt may also occur disseminated through +the rock, when it can only be detected by chemical analysis. It +is interesting to note that Dr Hicks has recently proved the +occurrence of phosphate of lime in this disseminated form in +rocks as old as the Cambrian, and that in quantity quite equal to +what is generally found to be present in the later fossiliferous +rocks. This affords a chemical proof that animal life flourished +abundantly in the Cambrian seas.] + +[Footnote 5: It has been maintained, indeed, that the phosphatic +nodules so largely worked for agricultural purposes, are in +themselves actual organic bodies or true fossils. In a few cases +this admits of demonstration, as it can be shown that the nodule +is simply an organism (such as a sponge) infiltrated with phosphate +of lime (Sollas); but there are many other cases in which no actual +structure has yet been shown to exist, and as to the true origin +of which it would be hazardous to offer a positive opinion.] + +The last lime-salt which need be mentioned is _gypsum_, or _sulphate +of lime_. This substance, apart from other modes of occurrence, is +not uncommonly found interstratified with the ordinary sedimentary +rocks, in the form of more or less irregular beds; and in these +cases it has a palæontological importance, as occasionally yielding +well-preserved fossils. Whilst its exact mode of origin is uncertain, +it cannot be regarded as in itself an organic rock, though clearly +the product of chemical action. To look at, it is usually a whitish +or yellowish-white rock, as coarsely crystalline as loaf-sugar, +or more so; and the microscope shows it to be composed entirely +of crystals of sulphate of lime. + +We have seen that the _calcareous_ or lime-containing rocks are +the most important of the group of organic deposits; whilst the +_siliceous_ or flint-containing rocks may be regarded as the +most important, most typical, and most generally distributed +of the mechanically-formed rocks. We have, however, now briefly +to consider certain deposits which are more or less completely +formed of flint; but which, nevertheless, are essentially organic +in their origin. + +Flint or silex, hard and intractable as it is, is nevertheless +capable of solution in water to a certain extent, and even of +assuming, under certain circumstances, a gelatinous or viscous +condition. Hence, some hot-springs are impregnated with silica +to a considerable extent; it is present in small quantity in +sea-water; and there is reason to believe that a minute proportion +must very generally be present in all bodies of fresh water as +well. It is from this silica dissolved in the water that many +animals and some plants are enabled to construct for themselves +flinty skeletons; and we find that these animals and plants are and +have been sufficiently numerous to give rise to very considerable +deposits of siliceous matter by the mere accumulation of their +skeletons. Amongst the animals which require special mention in +this connection are the microscopic organisms which are known to +the naturalist as _Polycystina_. These little creatures are of the +lowest possible grade of organisation, very closely related to the +animals which we have previously spoken of as _Foraminifera_, but +differing in the fact that they secrete a shell or skeleton composed +of flint instead of lime. The _Polycystina_ occur abundantly in +our present seas; and their shells are present in some numbers +in the ooze which is found at great depths in the Atlantic and +Pacific oceans, being easily recognised by their exquisite shape, +their glassy transparency, the general presence of longer or +shorter spines, and the sieve-like perforations in the walls. +Both in Barbadoes and in the Nicobar islands occur geological +formations which are composed of the flinty skeletons of these +microscopic animals; the deposit in the former locality attaining +a great thickness, and having been long known to workers with +the microscope under the name of "Barbadoes earth" (fig. 15). + +[Illustration: Fig. 15.--Shells of _Polycystina_ from "Barbadoes +earth;" greatly magnified. (Original.)] + +[Illustration: Fig. 16.--Cases of Diatoms in the Richmond "Infusorial +earth;" highly magnified. (Original.)] + +In addition to flint-producing animals, we have also the great +group of fresh-water and marine microscopic plants known as +_Diatoms_, which likewise secrete a siliceous skeleton, often of +great beauty. The skeletons of Diatoms are found abundantly at the +present day in lake-deposits, guano, the silt of estuaries, and in +the mud which covers many parts of the sea-bottom; they have been +detected in strata of great age; and in spite of their microscopic +dimensions, they have not uncommonly accumulated to form deposits +of great thickness, and of considerable superficial extent. Thus +the celebrated deposit of "tripoli" ("Polir-schiefer") of Bohemia, +largely worked as polishing-powder, is composed wholly, or almost +wholly, of the flinty cases of Diatoms, of which it is calculated +that no less than forty-one thousand millions go to make up a +single cubic inch of the stone. Another celebrated deposit is +the so-called "Infusorial earth" of Richmond in Virginia, where +there is a stratum in places thirty feet thick, composed almost +entirely of the microscopic shells of Diatoms. + +Nodules or layers of _flint_, or the impure variety of flint +known as _chert_, are found in limestones of almost all ages +from the Silurian upwards; but they are especially abundant in +the chalk. When these flints are examined in thin and transparent +slices under the microscope, or in polished sections, they are +found to contain an abundance of minute organic bodies--such as +_Foraminifera_, sponge-spicules, &c.--embedded in a siliceous +basis. In many instances the flint contains larger organisms--such +as a Sponge or a Sea-urchin. As the flint has completely surrounded +and infiltrated the fossils which it contains, it is obvious +that it must have been deposited from sea-water in a gelatinous +condition, and subsequently have hardened. That silica is capable +of assuming this viscous and soluble condition is known; and +the formation of flint may therefore be regarded as due to the +separation of silica from the sea-water and its deposition round +some organic body in a state of chemical change or decay, just as +nodules of phosphate of lime or carbonate of iron are produced. +The existence of numerous organic bodies in flint has long been +known; but it should be added that a recent observer (Mr Hawkins +Johnson) asserts that the existence of an organic structure can +be demonstrated by suitable methods of treatment, even in the +actual matrix or basis of the flint.[6] + +[Footnote 6: It has been asserted that the flints of the chalk +are merely fossil sponges. No explanation of the origin of flint, +however, can be satisfactory, unless it embraces the origin of +chert in almost all great limestones from the Silurian upwards, +as well as the common phenomenon of the silicification of organic +bodies (such as corals and shells) which are known with certainty +to have been originally calcareous.] + +In addition to deposits formed of flint itself, there are other +siliceous deposits formed by certain _silicates_, and also of +organic origin. It has been shown, namely--by observations carried +out in our present seas--that the shells of _Foraminifera_ are +liable to become completely infiltrated by silicates (such as +"glauconite," or silicate of iron and potash). Should the actual +calcareous shell become dissolved away subsequent to this +infiltration--as is also liable to occur--then, in place of the +shells of the _Foraminifera_, we get a corresponding number of +green sandy grains of glauconite, each grain being the _cast_ +of a single shell. It has thus been shown that the green sand +found covering the sea-bottom in certain localities (as found by +the Challenger expedition along the line of the Agulhas current) +is really organic, and is composed of casts of the shells of +_Foraminifera_. Long before these observations had been made, +it had been shown by Professor Ehrenberg that the green sands of +various geological formations are composed mainly of the internal +casts of the shells of _Foraminifera_, and we have thus another +and a very interesting example how rock-deposits of considerable +extent and of geological importance can be built up by the operation +of the minutest living beings. + +As regards _argillaceous_ deposits, containing _alumina_ or _clay_ +as their essential ingredient, it cannot be said that any of +these have been actually shown to be of organic origin. A recent +observation by Sir Wyville Thomson would, however, render it not +improbable that some of the great argillaceous accumulations of +past geological periods may be really organic. This distinguished +observer, during the cruise of the Challenger, showed that the +calcareous ooze which has been already spoken of as covering +large areas of the floor of the Atlantic and Pacific at great +depths, and which consists almost wholly of the shells of +_Foraminifera_, gave place at still greater depths to a red ooze +consisting of impalpable clayey mud, coloured by oxide of iron, +and devoid of traces of organic bodies. As the existence of this +widely-diffused red ooze, in mid-ocean, and at such great depths, +cannot be explained on the supposition that it is a sediment +brought down into the sea by rivers, Sir Wyville Thomson came to +the conclusion that it was probably formed by the action of the +sea-water upon the shells of _Foraminifera_. These shells, though +mainly consisting of lime, also contain a certain proportion of +alumina, the former being soluble in the carbonic acid dissolved +in the sea-water, whilst the latter is insoluble. There would +further appear to be grounds for believing that the solvent power +of the sea-water over lime is considerably increased at great +depths. If, therefore, we suppose the shells of _Foraminifera_ +to be in course of deposition over the floor of the Pacific, at +certain depths they would remain unchanged, and would accumulate +to form a calcareous ooze; but at greater depths they would be +acted upon by the water, their lime would be dissolved out, their +form would disappear, and we should simply have left the small +amount of alumina which they previously contained. In process +of time this alumina would accumulate to form a bed of clay; and +as this clay had been directly derived from the decomposition +of the shells of animals, it would be fairly entitled to be +considered an organic deposit. Though not finally established, +the hypothesis of Sir Wyville Thomson on this subject is of the +greatest interest to the palæontologist, as possibly serving to +explain the occurrence, especially in the older formations, of +great deposits of argillaceous matter which are entirely destitute +of traces of life. + +It only remains, in this connection, to shortly consider the +rock-deposits in which _carbon_ is found to be present in greater +or less quantity. In the great majority of cases where rocks +are found to contain carbon or carbonaceous matter, it can be +stated with certainty that this substance is of organic origin, +though it is not necessarily derived from vegetables. Carbon +derived from the decomposition of animal bodies is not uncommon; +though it never occurs in such quantity from this source as it +may do when it is derived from plants. Thus, many limestones are +more or less highly bituminous; the celebrated siliceous flags +or so-called "bituminous schists" of Caithness are impregnated +with oily matter apparently derived from the decomposition of the +numerous fishes embedded in them; Silurian shales containing +Graptolites, but destitute of plants, are not uncommonly +"anthracitic," and contain a small percentage of carbon derived +from the decay of these zoophytes; whilst the petroleum so largely +worked in North America has not improbably an animal origin. +That the fatty compounds present in animal bodies should more or +less extensively impregnate fossiliferous rock-masses, is only +what might be expected; but the great bulk of the carbon which +exists stored up in the earth's crust is derived from plants; +and the form in which it principally presents itself is that of +coal. We shall have to speak again, and at greater length, of +coal, and it is sufficient to say here that all the true coals, +anthracites, and lignites, are of organic origin, and consist +principally of the remains of plants in a more or less altered +condition. The bituminous shales which are found so commonly +associated with beds of coal also derive their carbon primarily +from plants; and the same is certainly, or probably, the case +with similar shales which are known to occur in formations younger +than the Carboniferous. Lastly, carbon may occur as a conspicuous +constituent of rock-masses in the form of _graphite_ or _black-lead_. +In this form, it occurs in the shape of detached scales, of veins +or strings, or sometimes of regular layers;[7] and there can be +little doubt that in many instances it has an organic origin, +though this is not capable of direct proof. When present, at any +rate, in quantity, and in the form of layers associated with +stratified rocks, as is often the case in the Laurentian formation, +there can be little hesitation in regarding it as of vegetable +origin, and as an altered coal. + +[Footnote 7: In the Huronian formation at Steel River, on the +north shore of Lake Superior, there exists a bed of carbonaceous +matter which is regularly interstratified with the surrounding +rocks, and has a thickness of from 30 to 40 feet. This bed is +shown by chemical analysis to contain about 50 per cent of carbon, +partly in the form of graphite, partly in the form of anthracite; +and there can be little doubt but that it is really a stratum +of "metamorphic" coal.] + + + + +CHAPTER III. + +CHRONOLOGICAL SUCCESSION OF THE FOSSILIFEROUS ROCKS. + +The physical geologist, who deals with rocks simply as rocks, +and who does not necessarily trouble himself about what fossils +they may contain, finds that the stratified deposits which form +so large a portion of the visible part of the earth's crust are +not promiscuously heaped together, but that they have a certain +definite arrangement. In each country that he examines, he finds +that certain groups of strata lie above certain other groups; +and in comparing different countries with one another, he finds +that, in the main, the same groups of rocks are always found in the +same relative position to each other. It is possible, therefore, +for the physical geologist to arrange the known stratified rocks +into a successive series of groups, or "formations," having a +certain definite order. The establishment of this physical order +amongst the rocks introduces, however, at once the element of +_time_, and the physical succession of the strata can be converted +directly into a historical or _chronological_ succession. This +is obvious, when we reflect that any bed or set of beds of +sedimentary origin is clearly and necessarily younger than all +the strata upon which it rests, and older than all those by which +it is surmounted. + +It is possible, then, by an appeal to the rocks alone, to determine +in each country the general physical succession of the strata, +and this "stratigraphical" arrangement, when once determined, +gives us the _relative_ ages of the successive groups. The task, +however, of the physical geologist in this matter is immensely +lightened when he calls in palæontology to his aid, and studies +the evidence of the fossils embedded in the rocks. Not only is +it thus much easier to determine the order of succession of the +strata in any given region, but it becomes now for the first time +possible to compare, with certainty and precision, the order of +succession in one region with that which exists in other regions +far distant. The value of fossils as tests of the relative ages +of the sedimentary rocks depends on the fact that they are not +indefinitely or promiscuously scattered through the crust of the +earth,--as it is conceivable that they might be. On the contrary, +the first and most firmly established law of Palæontology is, that +_particular kinds of fossils are confined to particular rocks_, +and _particular groups of fossils are confined to particular +groups of rocks_. Fossils, then, are distinctive of the rocks in +which they are found--much more distinctive, in fact, than the +mere mineral character of the rock can be, for _that_ commonly +changes as a formation is traced from one region to another, +whilst the fossils remain unaltered. It would therefore be quite +possible for the palæontologist, by an appeal to the fossils +alone, to arrange the series of sedimentary deposits into a pile +of strata having a certain definite order. Not only would this +be possible, but it would be found--if sufficient knowledge had +been brought to bear on both sides--that the palæontological +arrangement of the strata would coincide in its details with the +stratigraphical or physical arrangement. + +Happily for science, there is no such division between the +palæontologist and the physical geologist as here supposed; but +by the combined researches of the two, it has been found possible +to divide the entire series of stratified deposits into a number +of definite _rock-groups_ or _formations_, which have a recognised +order of succession, and each of which is characterised by possessing +an assemblage of organic remains which do not occur in association +in any other formation. Such an _assemblage of fossils_, +characteristic of any given formation, represents the _life_ of +the particular _period_ in which the formation was deposited. +In this way the past history of the earth becomes divided into a +series of successive _life-periods_, each of which corresponds +with the deposition of a particular _formation_ or group of strata. + +Whilst particular _assemblages_ of organic forms characterise +particular _groups_ of rocks, it may be further said that, in +a general way, each subdivision of each formation has its own +peculiar fossils, by which it may be recognised by a skilled +worker in Palæontology. Whenever, for instance, we meet with +examples of the fossils which are known as _Graptolites_, we may +be sure that we are dealing with _Silurian_ rocks (leaving out +of sight one or two forms doubtfully referred to this family). +We may, however, go much farther than this with perfect safety. If +the Graptolites belong to certain genera, we may be quite certain +that we are dealing with _Lower_ Silurian rocks. Furthermore, if +certain special forms are present, we may be even able to say to +what exact subdivision of the Lower Silurian series they belong. + +As regards particular fossils, however, or even particular classes +of fossils, conclusions of this nature require to be accompanied +by a tacit but well-understood reservation. So far as our present +observation goes, none of the undoubted Graptolites have ever been +discovered in rocks later than those known upon other grounds +to be Silurian; but it is possible that they might at any time be +detected in younger deposits. Similarly, the species and genera +which we now regard as characteristic of the Lower Silurian, may +at some future time be found to have survived into the Upper +Silurian period. We should not forget, therefore, in determining +the age of strata by palæontological evidence, that we are always +reasoning upon generalisations which are the result of experience +alone, and which are liable to be vitiated by further and additional +discoveries. + +When the palæontological evidence as to the age of any given +set of strata is corroborated by the physical evidence, our +conclusions may be regarded as almost certain; but there are +certain limitations and fallacies in the palæontological method +of inquiry which deserve a passing mention. In the first place, +fossils are not always present in the stratified rocks; many +aqueous rocks are unfossiliferous, through a thickness of hundreds +or even thousands of feet of little-altered sediments; and even +amongst beds which do contain fossils, we often meet with strata +of many feet or yards in thickness which are wholly destitute +of any traces of fossils. There are, therefore, to begin with, +many cases in which there is no palæontological evidence extant +or available as to the age of a given group of strata. In the +second place, palæontological observers in different parts of +the world are liable to give different names to the same fossil, +and in all parts of the world they are occasionally liable to +group together different fossils under the same title. Both these +sources of fallacy require to be guarded against in reasoning as +to the age of strata from their fossil remains. Thirdly, the mere +fact of fossils being found in beds which are known by physical +evidence to be of different ages, has commonly led palæontologists +to describe them as different species. Thus, the same fossil, +occurring in successive groups of strata, and with the merely +trivial and varietal differences due to the gradual change in its +environment, has been repeatedly described as a distinct species, +with a distinct name, in every bed in which it was found. We know, +however, that many fossils range vertically through many groups +of strata, and there are some which even pass through several +formations. The mere fact of a difference of physical position +ought never to be taken into account at all in considering and +determining the true affinities of a fossil. Fourthly, the results +of experience, instead of being an assistance, are sometimes +liable to operate as a source of error. When once, namely, a +generalisation has been established that certain fossils occur +in strata of a certain age, palæontologists are apt to infer +that _all_ beds containing similar fossils must be of the same +age. There is a presumption, of course, that this inference would +be correct; but it is not a conclusion resting upon absolute +necessity, and there might be physical evidence to disprove it. +Fifthly, the physical geologist may lead the palæontologist astray +by asserting that the physical evidence as to the age and position +of a given group of beds is clear and unequivocal, when such +evidence may be, in reality, very slight and doubtful. In this +way, the observer may be readily led into wrong conclusions as +to the nature of the organic remains--often obscure and +fragmentary--which it is his business to examine, or he may be +led erroneously to think that previous generalisations as to +the age of certain kinds of fossils are premature and incorrect. +Lastly, there are cases in which, owing to the limited exposure +of the beds, to their being merely of local development, or to +other causes, the physical evidence as to the age of a given +group of strata may be entirely uncertain and unreliable, and +in which, therefore, the observer has to rely wholly upon the +fossils which he may meet with. + +In spite of the above limitations and fallacies, there can be +no doubt as to the enormous value of palæontology in enabling us +to work out the historical succession of the sedimentary rocks. +It may even be said that in any case where there should appear +to be a clear and decisive discordance between the physical and +the palæontological evidence as to the age of a given series +of beds, it is the former that is to be distrusted rather than +the latter. The records of geological science contain not a few +cases in which apparently clear physical evidence of superposition +has been demonstrated to have been wrongly interpreted; but the +evidence of palæontology, when in any way sufficient, has rarely +been upset by subsequent investigations. Should we find strata +containing plants of the Coal-measures apparently resting upon +other strata with Ammonites and Belemnites, we may be sure that +the physical evidence is delusive; and though the above is an +extreme case, the presumption in all such instances is rather that +the physical succession has been misunderstood or misconstrued, +than that there has been a subversion of the recognised succession +of life-forms. + +We have seen, then, that as the collective result of observations +made upon the superposition of rocks in different localities, +from their mineral characters, and from their included fossils, +geologists have been able to divide the entire stratified series into +a number of different divisions or formations, each characterised +by a _general_ uniformity of mineral composition, and by a special +and peculiar _assemblage_ of organic forms. Each of these primary +groups is in turn divided into a series of smaller divisions, +characterised and distinguished in the same way. It is not pretended +for a moment that all these primary rock-groups can anywhere be seen +surmounting one another regularly.[8] There is no region upon the +earth where all the stratified formations can be seen together; +and, even when most of them occur in the same country, they can +nowhere be seen all succeeding each other in their regular and +uninterrupted succession. The reason of this is obvious. There +are many places--to take a single example--where one may see the +the Silurian rocks, the Devonian, and the Carboniferous rocks +succeeding one another regularly, and in their proper order. This +is because the particular region where this occurs was always +submerged beneath the sea while these formations were being +deposited. There are, however, many more localities in which +one would find the Carboniferous rocks resting unconformably upon +the Silurians without the intervention of any strata which could +be referred to the Devonian period. This might arise from one of +two causes: 1. The Silurians might have been elevated above the +sea immediately after their deposition, so as to form dry land +during the whole of the Devonian period, in which case, of course, +no strata of the latter age could possibly be deposited in that +area. 2. The Devonian might have been deposited upon the Silurian, +and then the whole might have been elevated above the sea, and +subjected to an amount of denudation sufficient to remove the +Devonian strata entirely. In this case, when the land was again +submerged, the Carboniferous rocks, or any younger formation, +might be deposited directly upon Silurian strata. From one or +other of these causes, then, or from subsequent disturbances +and denudations, it happens that we can rarely find many of the +primary formations following one another consecutively and in +their regular order. + +[Footnote 8: As we have every reason to believe that dry land +and sea have existed, at any rate from the commencement of the +Laurentian period to the present day, it is quite obvious that +no one of the great formations can ever, under any circumstances, +have extended over the entire globe. In other words, no one of +the formations can ever have had a greater geographical extent +than that of the seas of the period in which the formation was +deposited. Nor is there any reason for thinking that the proportion +of dry land to ocean has ever been materially different to what +it is at present, however greatly the areas of sea and land may +have changed as regards their place. It follows from the above, +that there is no sufficient basis for the view that the crust of +the earth is composed of a succession of concentric layers, like +the coats of an onion, each layer representing one formation.] + +In no case, however, do we ever find the Devonian resting upon +the Carboniferous, or the Silurian rocks reposing on the Devonian. +We have therefore, by a comparison of many different areas, an +established order of succession of the stratified formations, as +shown in the subjoined ideal section of the crust of the earth +(fig. 17). + +The main subdivisions of the stratified rocks are known by the +following names:-- + + 1. Laurentian. + 2. Cambrian (with Huronian ?). + 3. Silurian. + 4. Devonian or Old Red Sandstone. + 5. Carboniferous. + 6. Permian \_ New Red Sandstone. + 7. Triassic / + 8. Jurassic or Oolitic. + 9. Cretaceous. + 10. Eocene. + 11. Miocene. + 12. Pliocene. + 13. Post-tertiary. + +[Illustration: Fig. 17. IDEAL SECTION OF THE CRUST OF THE EARTH.] + +Of these primary rock divisions, the Laurentian, Cambrian, Silurian, +Devonian, Carboniferous, and Permian are collectively grouped +together under the name of the Primary or _Paloeozoic_ rocks (Gr. +_palaios_, ancient; _zoe_, life). Not only do they constitute the +oldest stratified accumulations, but from the extreme divergence +between their animals and plants and those now in existence, they may +appropriately be considered as belonging to an "Old-Life" period of +the world's history. The Triassic, Jurassic, and Cretaceous systems +are grouped together as the _Secondary_ or _Mesozoic_ formations +(Gr. _mesos_, intermediate; _zoe_, life); the organic remains of +this "Middle-Life" period being, on the whole, intermediate in +their characters between those of the palæozoic epoch and those +of more modern strata. Lastly, the Eocene, Miocene, and Pliocene +formations are grouped together as the _Tertiary_ or _Kainozoic_ +rocks (Gr. _kainos_, new; _zoe_, life); because they constitute +a "New-Life" period, in which the organic remains approximate in +character to those now existing upon the globe. The so-called +_Post-Tertiary_ deposits are placed with the Kainozoic, or may +be considered as forming a separate _Quaternary_ system. + + + + +CHAPTER IV. + +THE BREAKS IN THE GEOLOGICAL AND PALÆONTOLOGICAL RECORD. + +The term "contemporaneous" is usually applied by geologists to +groups of strata in different regions which contain the same +fossils, or an assemblage of fossils in which many identical +forms are present. That is to say, beds which contain identical, +or nearly identical, fossils, however widely separated they may +be from one another in point of actual distance, are ordinarily +believed to have been deposited during the same period of the +earth's history. This belief, indeed, constitutes the keystone +of the entire system of determining the age of strata by their +fossil contents; and if we take the word "contemporaneous" in a +general and strictly geological sense, this belief can be accepted +as proved beyond denial. We must, however, guard ourselves against +too literal an interpretation of the word "contemporaneous," +and we must bear in mind the enormously-prolonged periods of +time with which the geologist has to deal. When we say that two +groups of strata in different regions are "contemporaneous," we +simply mean that they were formed during the same geological +period, and perhaps at different stages of that period, and we +do not mean to imply that they were formed at precisely the same +instant of time. + +A moment's consideration will show us that it is only in the former +sense that we can properly speak of strata being "contemporaneous;" +and that, in point of fact, beds containing the same fossils, if +occurring in widely distant areas, can hardly be "contemporaneous" +in any literal sense; but that the very identity of their fossils +is proof that they were deposited one after the other. If we find +strata containing identical fossils within the limits of a single +geographical region--say in Europe--then there is a reasonable +probability that these beds are strictly contemporaneous, in the +sense that they were deposited at the same time. There is a +reasonable probability of this, because there is no improbability +involved in the idea of an ocean occupying the whole area of +Europe, and peopled throughout by many of the same species of +marine animals. At the present day, for example, many identical +species of animals are found living on the western coasts of +Britain and the eastern coasts of North America, and beds now +in course of deposition off the shores of Ireland and the seaboard +of the state of New York would necessarily contain many of the +same fossils. Such beds would be both literally and geologically +contemporaneous; but the case is different if the distance between +the areas where the strata occur be greatly increased. We find, +for example, beds containing identical fossils (the Quebec or +Skiddaw beds) in Sweden, in the north of England, in Canada, +and in Australia. Now, if all these beds were contemporaneous, +in the literal sense of the term, we should have to suppose that +the ocean at one time extended uninterruptedly between all these +points, and was peopled throughout the vast area thus indicated +by many of the same animals. Nothing, however, that we see at +the present day would justify us in imagining an ocean of such +enormous extent, and at the same time so uniform in its depth, +temperature, and other conditions of marine life, as to allow the +same animals to flourish in it from end to end; and the example +chosen is only one of a long and ever-recurring series. It is +therefore much more reasonable to explain this, and all similar +cases, as owing to the _migration_ of the fauna, in whole or in +part, from one marine area to another. Thus, we may suppose an +ocean to cover what is now the European area, and to be peopled +by certain species of animals. Beds of sediment--clay, sands, +and limestones--will be deposited over the sea-bottom, and will +entomb the remains of the animals as fossils. After this has +lasted for a certain length of time, the European area may undergo +elevation, or may become otherwise unsuitable for the perpetuation +of its fauna; the result of which would be that some or all of the +marine animals of the area would migrate to some more suitable +region. Sediments would then be accumulated in the new area to +which they had betaken themselves, and they would then appear, +for the second time, as fossils in a set of beds widely separated +from Europe. The second set of beds would, however, obviously +not be strictly or literally contemporaneous with the first, but +would be separated from them by the period of time required for +the migration of the animals from the one area into the other. +It is only in a wide and comprehensive sense that such strata +can be said to be contemporaneous. + +It is impossible to enter further into this subject here; but it +may be taken as certain that beds in widely remote geographical +areas can only come to contain the same fossils by reason of a +migration having taken place of the animals of the one area to +the other. That such migrations can and do take place is quite +certain, and this is a much more reasonable explanation of the +observed facts than the hypothesis that in former periods the +conditions of life were much more uniform than they are at present, +and that, consequently, the same organisms were able to range over +the entire globe at the same time. It need only be added, that +taking the evidence of the present as explaining the phenomena +of the past--the only safe method of reasoning in geological +matters--we have abundant proof that deposits which _are_ actually +contemporaneous, in the strict sense of the term, _do not contain +the same fossils, if far removed from one another in point of +distance_. Thus, deposits of various kinds are now in process of +formation in our existing seas, as, for example, in the Arctic +Ocean, the Atlantic, and the Pacific, and many of these deposits +are known to us by actual examination and observation with the +sounding-lead and dredge. But it is hardly necessary to add that +the animal remains contained in these deposits--the fossils of some +future period--instead of being identical, are widely different +from one another in their characters. + +We have seen, then, that the entire stratified series is capable of +subdivision into a number of definite rock-groups or "formations," +each possessing a peculiar and characteristic assemblage of fossils, +representing the "life" of the "period" in which the formation +was deposited. We have still to inquire shortly how it came to +pass that two successive formations _should_ thus be broadly +distinguished by their life-forms, and why they should not rather +possess at any rate a majority of identical fossils. It was +originally supposed that this could be explained by the hypothesis +that the close of each formation was accompanied by a general +destruction of all the living beings of the period, and that +the commencement of each new formation was signalised by the +creation of a number of brand-new organisms, destined to figure +as the characteristic fossils of the same. This theory, however, +ignores the fact that each formation--as to which we have any +sufficient evidence--contains a few, at least, of the life-forms +which existed in the preceding period; and it invokes forces +and processes of which we know nothing, and for the supposed +action of which we cannot account. The problem is an undeniably +difficult one, and it will not be possible here to give more than +a mere outline of the modern views upon the subject. Without +entering into the at present inscrutable question as to the manner +in which new life-forms are introduced upon the earth, it may be +stated that almost all modern geologists hold that the living +beings of any given formation are in the main modified forms of +others which have preceded them. It is not believed that any +general or universal destruction of life took place at the +termination of each geological period, or that a general introduction +of new forms took place at the commencement of a new period. +It is, on the contrary, believed that the animals and plants +of any given period are for the most part (or exclusively) the +lineal but modified descendants of the animals and plants of +the immediately preceding period, and that some of them, at any +rate, are continued into the next succeeding period, either +unchanged, or so far altered as to appear as new species. To +discuss these views in detail would lead us altogether too far, +but there is one very obvious consideration which may advantageously +receive some attention. It is obvious, namely, that the great +discordance which is found to subsist between the animal life of +any given formation and that of the next succeeding formation, +and which no one denies, would be a fatal blow to the views just +alluded to, unless admitting of some satisfactory explanation. +Nor is this discordance one purely of life-forms, for there is +often a physical break in the successions of strata as well. +Let us therefore briefly consider how far these interruptions +and breaks in the geological and palæontological record can be +accounted for, and still allow us to believe in some theory of +continuity as opposed to the doctrine of intermittent and occasional +action. + +In the first place, it is perfectly clear that if we admit the +conception above mentioned of a continuity of life from the +Laurentian period to the present day, we could never _prove_ our +view to be correct, unless we could produce in evidence fossil +examples of _all_ the kinds of animals and plants that have lived +and died during that period. In order to do this, we should require, +to begin with, to have access to an absolutely unbroken and perfect +succession of all the deposits which have ever been laid down +since the beginning. If, however, we ask the physical geologist +if he is in possession of any such uninterrupted series, he will +at once answer in the negative. So far from the geological series +being a perfect one, it is interrupted by numerous gaps of unknown +length, many of which we can never expect to fill up. Nor are +the proofs of this far to seek. Apart from the facts that we +have hitherto examined only a limited portion of the dry land, +that nearly two-thirds of the entire area of the globe is +inaccessible to geological investigation in consequence of its +being covered by the sea, that many deposits can be shown to +have been more or less completely destroyed subsequent to their +deposition, and that there may be many areas in which living +beings exist where no rock is in process of formation, we have +the broad fact that rock-deposition only goes on to any extent +in water, and that the earth must have always consisted partly of +dry land and partly of water--at any rate, so far as any period +of which we have geological knowledge is concerned. There _must_, +therefore, always have existed, at some part or another of the +earth's surface, areas where no deposition of rock was going on, +and the proof of this is to be found in the well-known phenomenon +of "_unconformability_." Whenever, namely, deposition of sediment +is continuously going on within the limits of a single ocean, the +beds which are laid down succeed one another in uninterrupted +and regular sequence. Such beds are said to be "conformable," and +there are many rock-groups known where one may pass through fifteen +or twenty thousand feet of strata without a break--indicating +that the beds had been deposited in an area which remained +continuously covered by the sea. On the other hand, we commonly +find that there is no such regular succession when we pass from +one great formation to another, but that, on the contrary, the +younger formation rests "unconformably," as it is called, either +upon the formation immediately preceding it in point of time, +or upon some still older one. The essential physical feature of +this unconformability is that the beds of the younger formation +rest upon a worn and eroded surface formed by the beds of the +older series (fig. 18); and a moment's consideration will show +us what this indicates. It indicates, beyond the possibility of +misconception, that there was an interval between the deposition +of the older series and that of the newer series of strata; and +that during this interval the older beds were raised above the +sea-level, so as to form dry land, and were subsequently depressed +again beneath the waters, to receive upon their worn and wasted +upper surface the sediments of the later group. During the interval +thus indicated, the deposition of rock must of necessity have +been proceeding more or less actively in other areas. Every +unconformity, therefore, indicates that at the spot where it +occurs, a more or less extensive series of beds must be actually +missing; and though we may sometimes be able to point to these +missing strata in other areas, there yet remains a number of +unconformities for which we cannot at present supply the deficiency +even in a partial manner. + +[Illustration: Fig. 18.--Section showing strata of Tertiary age +(a) resting upon a worn and eroded surface of White Chalk (b), +the stratification of which is marked by lines of flint.] + +It follows from the above that the series of stratified deposits +is to a greater or less extent irremediably imperfect; and in +this imperfection we have one great cause why we can never obtain +a perfect series of all the animals and plants that have lived +upon the globe. Wherever one of these great physical gaps occurs, +we find, as we might expect, a corresponding break in the series +of life-forms. In other words, whenever we find two formations +to be unconformable, we shall always find at the same time that +there is a great difference in their fossils, and that many of +the fossils of the older formation do not survive into the newer, +whilst many of those in the newer are not known to occur in the +older. The cause of this is, obviously, that the lapse of time, +indicated by the unconformability, has been sufficiently great +to allow of the dying out or modification of many of the older +forms of life, and the introduction of new ones by immigration. + +Apart, however, altogether, from these great physical breaks +and their corresponding breaks in life, there are other reasons +why we can never become more than partially acquainted with the +former denizens of the globe. Foremost amongst these is the fact +that an enormous number of animals possess no hard parts of the +nature of a skeleton, and are therefore incapable, under any +ordinary circumstances, of leaving behind them any traces of +their existence. It is true that there are cases in which animals +in themselves completely soft-bodied are nevertheless able to leave +marks by which their former presence can be detected: Thus every +geologist is familiar with the winding and twisting "trails" formed +on the surface of the strata by sea-worms; and the impressions +left by the stranded carcases of Jelly-fishes on the fine-grained +lithographic slates of Solenhofen supply us with an example of how +a creature which is little more than "organised sea-water" may +still make an abiding mark upon the sands of time. As a general +rule, however, animals which have no skeletons are incapable of +being preserved as fossils, and hence there must always have +been a vast number of different kinds of marine animals of which +we have absolutely no record whatever. Again, almost all the +fossiliferous rocks have been laid down in water; and it is a +necessary result of this that the great majority of fossils are +the remains of aquatic animals. The remains of air-breathing +animals, whether of the inhabitants of the land or of the air +itself, are comparatively rare as fossils, and the record of +the past existence of these is much more imperfect than is the +case with animals living in water. Moreover, the fossiliferous +deposits are not only almost exclusively aqueous formations, but +the great majority are marine, and only a comparatively small +number have been formed by lakes and rivers. It follows from the +foregoing that the palæontological record is fullest and most +complete so far as sea-animals are concerned, though even here we +find enormous gaps, owing to the absence of hard structures in +many great groups; of animals inhabiting fresh waters our knowledge +is rendered still further incomplete by the small proportion +that fluviatile and lacustrine deposits bear to marine; whilst +we have only a fragmentary acquaintance with the air-breathing +animals which inhabited the earth during past ages. + +Lastly, the imperfection of the palæontological record, due to +the causes above enumerated, is greatly aggravated, especially +as regards the earlier portion of the earth's history, by the +fact that many rocks which contained fossils when deposited have +since been rendered barren of organic remains. The principal cause +of this common phenomenon is what is known as "metamorphism"--that +is, the subjection of the rock to a sufficient amount of heat to +cause a rearrangement of its particles. When at all of a pronounced +character, the result of metamorphic action is invariably the +obliteration of any fossils which might have been originally +present in the rock. Metamorphism may affect rocks of any age, +though naturally more prevalent in the older rocks, and to this +cause must be set down an irreparable loss of much fossil evidence. +The most striking example which is to be found of this is the +great Laurentian series, which comprises some 30,000 feet of +highly-metamorphosed sediments, but which, with one not wholly +undisputed exception, has as yet yielded no remains of living +beings, though there is strong evidence of the former existence +in it of fossils. + +Upon the whole, then, we cannot doubt that the earth's crust, so +far as yet deciphered by us, presents us with but a very imperfect +record of the past. Whether the known and admitted imperfections +of the geological and palæontological records are sufficiently +serious to account satisfactorily for the deficiency of direct +evidence recognisable in some modern hypotheses, may be a matter +of individual opinion. There can, however, be little doubt that +they are sufficiently extensive to throw the balance of evidence +decisively in favour of some theory of _continuity_, as opposed +to any theory of intermittent and occasional action. The apparent +breaks which divide the great series of the stratified rocks +into a number of isolated formations, are not marks of mighty +and general convulsions of nature, but are simply indications +of the imperfection of our knowledge. Never, in all probability, +shall we be able to point to a complete series of deposits, or a +complete succession of life linking one great geological period +to another. Nevertheless, we may well feel sure that such deposits +and such an unbroken succession must have existed at one time. +We are compelled to believe that nowhere in the long series of +the fossiliferous rocks has there been a total break, but that +there must have been a complete continuity of life, and a more +or less complete continuity of sedimentation, from the Laurentian +period to the present day. One generation hands on the lamp of +life to the next, and each system of rocks is the direct offspring +of those which preceded it in time. Though there has not been +continuity in any given area, still the geological chain could +never have been snapped at one point, and taken up again at a +totally different one. Thus we arrive at the conviction that +_continuity_ is the fundamental law of geology, as it is of the +other sciences, and that the lines of demarcation between the +great formations are but gaps in our own knowledge. + + + + +CHAPTER V. + +CONCLUSIONS TO BE DRAWN FROM FOSSILS. + +We have already seen that geologists have been led by the study +of fossils to the all-important generalisation that the vast +series of the Fossiliferous or Sedimentary Rocks may be divided +into a number of definite groups or "formations," each of which is +characterised by its organic remains. It may simply be repeated here +that these formations are not properly and strictly characterised +by the occurrence in them of any one particular fossil. It may be +that a formation contains some particular fossil or fossils not +occurring out of that formation, and that in this way an observer +may identify a given group with tolerable certainty. It very often +happens, indeed, that some particular stratum, or sub-group of a +series, contains peculiar fossils, by which its existence may +be determined in various localities. As before remarked, however, +the great formations are characterised properly by the association +of certain fossils, by the predominance of certain families or +orders, or by an _assemblage_ of fossil remains representing +the "life" of the period in which the formation was deposited. + +Fossils, then, enable us to determine the _age_ of the deposits +in which they occur. Fossils further enable us to come to very +important conclusions as to the mode in which the fossiliferous +bed was deposited, and thus as to the condition of the particular +district or region occupied by the fossiliferous bed at the time +of the formation of the latter. If, in the first place, the bed +contain the remains of animals such as now inhabit rivers, we +know that it is "fluviatile" in its origin, and that it must at +one time have either formed an actual riverbed, or been deposited +by the overflowing of an ancient stream. Secondly, if the bed +contain the remains of shellfish, minute crustaceans, or fish, +such as now inhabit lakes, we know that it is "lacustrine," and +was deposited beneath the waters of a former lake. Thirdly, if +the bed contain the remains of animals such as now people the +ocean, we know that it is "marine" in its origin, and that it +is a fragment of an old sea-bottom. + +We can, however, often determine the conditions under which a bed +was deposited with greater accuracy than this. If, for example, the +fossils are of kinds resembling the marine animals now inhabiting +shallow waters, if they are accompanied by the detached relics +of terrestrial organisms, or if they are partially rolled and +broken, we may conclude that the fossiliferous deposit was laid +down in a shallow sea, in the immediate vicinity of a coast-line, +or as an actual shore-deposit. If, again, the remains are those +of animals such as now live in the deeper parts of the ocean, +and there is a very sparing intermixture of extraneous fossils +(such as the bones of birds or quadrupeds, or the remains of +plants), we may presume that the deposit is one of deep water. +In other cases, we may find, scattered through the rock, and +still in their natural position, the valves of shells such as +we know at the present day as living buried in the sand or mud +of the sea-shore or of estuaries. In other cases, the bed may +obviously have been an ancient coral-reef, or an accumulation of +social shells, like Oysters. Lastly, if we find the deposit to +contain the remains of marine shells, but that these are dwarfed +of their fair proportions and distorted in figure, we may conclude +that it was laid down in a brackish sea, such as the Baltic, in +which the proper saltness was wanting, owing to its receiving +an excessive supply of fresh water. + +In the preceding, we have been dealing simply with the remains +of aquatic animals, and we have seen that certain conclusions +can be accurately reached by an examination of these. As regards +the determination of the conditions of deposition from the remains +of aerial and terrestrial animals, or from plants, there is not +such an absolute certainty. The remains of land-animals would, +of course, occur in "sub-aerial" deposits--that is, in beds, +like blown sand, accumulated upon the land. Most of the remains +of land-animals, however, are found in deposits which have been +laid down in water, and they owe their present position to the +fact that their former owners were drowned in rivers or lakes, +or carried out to sea by streams. Birds, Flying Reptiles, and +Flying Mammals might also similarly find their way into aqueous +deposits; but it is to be remembered that many birds and mammals +habitually spend a great part of their time in the water, and +that these might therefore be naturally expected to present +themselves as fossils in Sedimentary Rocks. Plants, again, even +when undoubtedly such as must have grown on land, do not prove +that the bed in which they occur was formed on land. Many of the +remains of plants known to us are extraneous to the bed in which +they are now found, having reached their present site by falling +into lakes or rivers, or being carried out to sea by floods or +gales of wind. There are, however, many cases in which plants +have undoubtedly grown on the very spot where we now find them. +Thus it is now generally admitted that the great coal-fields +of the Carboniferous age are the result of the growth _in situ_ +of the plants which compose coal, and that these grew on vast +marshy or partially submerged tracts of level alluvial land. We +have, however, distinct evidence of old land-surfaces, both in +the Coal-measures and in other cases (as, for instance, in the +well-known "dirt-bed" of the Purbeck series). When, for example, +we find the erect stumps of trees standing at right angles to +the surrounding strata, we know that the surface through which +these send their roots was at one time the surface of the dry +land, or, in other words, was an ancient soil (fig. 19). + +[Illustration: Fig. 19.--Erect Tree containing Reptilian remains. +Coal-measures, Nova Scotia. (After Dawson.) + +In many cases fossils enable us to come to important conclusions +as to the climate of the period in which they lived but only a +few instances of this can be here adduced. As fossils in the +majority of instances are the remains of marine animals, it is +mostly the temperature of the sea which can alone be determined +in this way; and it is important to remember that, owing to the +existence of heated currents, the marine climate of a given area +does not necessarily imply a correspondingly warm climate in +the neighbouring land. Land-climates can only be determined by +the remains of land-animals or land-plants, and these are +comparatively rare as fossils. It is also important to remember +that all conclusions on this head are really based upon the present +distribution of animal and vegetable life on the globe, and are +therefore liable to be vitiated by the following considerations:-- + +a. Most fossils are extinct, and it is not certain that the +habits and requirements of any extinct animal were exactly similar +to those of its nearest living relative. + +b. When we get very far back in time, we meet with groups of +organisms so unlike anything we know at the present day as to +render all conjectures as to climate founded upon their supposed +habits more or less uncertain and unsafe. + +c. In the case of marine animals, we are as yet very far from +knowing the exact limits of distribution of many species within +our present seas; so that conclusions drawn from living forms +as to extinct species are apt to prove incorrect. For instance, +it has recently been shown that many shells formerly believed to +be confined to the Arctic Seas have, by reason of the extension +of Polar currents, a wide range to the south; and this has thrown +doubt upon the conclusions drawn from fossil shells as to the +Arctic conditions under which certain beds were supposed to have +been deposited. + +d. The distribution of animals at the present day is certainly +dependent upon other conditions beside climate alone; and the causes +which now limit the range of given animals are certainly such as +belong to the existing order of things. But the establishment of +the present order of things does not date back in many cases to +the introduction of the present species of animals. Even in the +case, therefore, of existing species of animals, it can often +be shown that the past distribution of the species was different +formerly to what it is now, not necessarily because the climate +has changed, but because of the alteration of other conditions +essential to the life of the species or conducing to its extension. + +Still, we are in many cases able to draw completely reliable +conclusions as to the climate of a given geological period, by +an examination of the fossils belonging to that period. Among +the more striking examples of how the past climate of a region +may be deduced from the study of the organic remains contained in +its rocks, the following may be mentioned: It has been shown that +in Eocene times, or at the commencement of the Tertiary period, +the climate of what is now Western Europe was of a tropical or +sub-tropical character. Thus the Eocene beds are found to contain +the remains of shells such as now inhabit tropical seas, as, for +example, Cowries and Volutes; and with these are the fruits of +palms, and the remains of other tropical plants. It has been +shown, again, that in Miocene times, or about the middle of the +Tertiary period, Central Europe was peopled with a luxuriant +flora resembling that of the warmer parts of the United States, +and leading to the conclusion that the mean annual temperature +must have been at least 30° hotter than it is at present. It has +been shown that, at the same time, Greenland, now buried beneath +a vast ice-shroud, was warm enough to support a large number of +trees, shrubs, and other plants, such as inhabit temperate regions +of the globe. Lastly, it has been shown upon physical as well as +palæontological evidence, that the greater part of the North +Temperate Zone, at a comparatively recent geological period, has +been visited with all the rigours of an Arctic climate, resembling +that of Greenland at the present day. This is indicated by the +occurrence of Arctic shells in the superficial deposits of this +period, whilst the Musk-ox and the Reindeer roamed far south of +their present limits. + +Lastly, it was from the study of fossils that geologists learnt +originally to comprehend a fact which may be regarded as of cardinal +importance in all modern geological theories and +speculations--namely, that the crust of the earth is liable to +local elevations and subsidences. For long after the remains of +shells and other marine animals were for the first time observed +in the solid rocks forming the dry land, and at great heights +above the sea-level, attempts were made to explain this almost +unintelligible phenomenon upon the hypothesis that the fossils +in question were not really the objects they represented, but +were in truth mere _lusus naturoe_, due to some "plastic virtue +latent in the earth." The common-sense of scientific men, however, +soon rejected this idea, and it was agreed by universal consent +that these bodies really were remains of animals which formerly +lived in the sea. When once this was admitted, the further steps +were comparatively easy, and at the present day no geological +doctrine stands on a firmer basis than that which teaches us +that our present continents and islands, fixed and immovable as +they appear, have been repeatedly sunk beneath the ocean. + + + + +CHAPTER VI. + +THE BIOLOGICAL RELATIONS OF FOSSILS. + +Not only have fossils, as we have seen, a most important bearing +upon the sciences of Geology and Physical Geography, but they +have relations of the most complicated and weighty character with +the numerous problems connected with the study of living beings, +or in other words, with the science of Biology. To such an extent +is this the case, that no adequate comprehension of Zoology and +Botany, in their modern form, is so much as possible without +some acquaintance with the types of animals and plants which have +passed away. There are also numerous speculative questions in +the domain of vital science, which, if soluble at all, can only +hope to find their key in researches carried out on extinct +organisms. To discuss fully the biological relations of fossils +would, therefore, afford matter for a separate treatise; and all +that can be done here is to indicate very cursorily the principal +points to which the attention of the palæontological student +ought to be directed. + +In the first place, the great majority of fossil animals and +plants are "extinct"--that is to say, they belong to species +which are no longer in existence at the present day. So far, +however, from there being any truth in the old view that there +were periodic destructions of all the living beings in existence +upon the earth, followed by a corresponding number of new creations +of animals and plants, the actual facts of the case show that +the extinction of old forms and the introduction of new forms +have been processes constantly going on throughout the whole +of geological time. Every species seems to come into being at +a certain definite point of time, and to finally disappear at +another definite point; though there are few instances indeed, +if there are any, in which our present knowledge would permit +us safely to fix with precision the times of entrance and exit. +There are, moreover, marked differences in the actual time during +which different species remained in existence, and therefore +corresponding differences in their "vertical range," or, in other +words, in the actual amount and thickness of strata through which +they present themselves as fossils. Some species are found to +range through two or even three formations, and a few have an +even more extended life. More commonly the species which begin +in the commencement of a great formation die out at or before its +close, whilst those which are introduced for the first time near +the middle or end of the formation may either become extinct, or +may pass on into the next succeeding formation. As a general rule, +it is the animals which have the lowest and simplest organisation +that have the longest range in time, and the additional possession +of microscopic or minute dimensions seems also to favour longevity. +Thus some of the _Foraminifera_ appear to have survived, with +little or no perceptible alteration, from the Silurian period +to the present day; whereas large and highly-organised animals, +though long-lived as _individuals_, rarely seem to live long +_specifically_, and have, therefore, usually a restricted vertical +range. Exceptions to this, however, are occasionally to be found +in some "persistent types," which extend through a succession +of geological periods with very little modification. Thus the +existing Lampshells of the genus _Lingula_ are little changed +from the _Linguloe_ which swarmed in the Lower Silurian seas; and +the existing Pearly Nautilus is the last descendant of a clan +nearly as ancient. On the other hand, some forms are singularly +restricted in their limits, and seem to have enjoyed a comparatively +brief lease of life. An example of this is to be found in many of +the _Ammonites_--close allies of the Nautilus--which are often +confined strictly to certain zones of strata, in some cases of +very insignificant thickness. + +Of the _causes_ of extinction amongst fossil animals and plants, +we know little or nothing. All we can say is, that the attributes +which constitute a _species_ do not seem to be intrinsically +endowed with permanence, any more than the attributes which +constitute an _individual_, though the former may endure whilst +many successive generations of the latter have disappeared. Each +species appears to have its own life-period, its commencement, +its culmination, and its gradual decay; and the life-periods +of different species may be of very different duration. + +From what has been said above, it may be gathered that our existing +species of animals and plants are, for the most part, quite of modern +origin, using the term "modern" in its geological acceptation. +Measured by human standards, the majority of existing animals +(which are capable of being preserved as fossils) are known to +have a high antiquity; and some of them can boast of a pedigree +which even the geologist may regard with respect. Not a few of +our shellfish are known to have commenced their existence at +some point of the Tertiary period; one Lampshell (_Terebratulina +caput-serpentis_) is believed to have survived since the Chalk; and +some of the _Foraminifera_ date, at any rate, from the Carboniferous +period. We learn from this the additional fact that our existing +animals and plants do not constitute an assemblage of organic +forms which were introduced into the world collectively and +simultaneously, but that they commenced their existence at very +different periods, some being extremely old, whilst others may be +regarded as comparatively recent animals. And this introduction of +the existing fauna and flora was a slow and _gradual_ process, as +shown admirably by the study of the fossil shells of the Tertiary +period. Thus, in the earlier Tertiary period, we find about 95 +per cent of the known fossil shells to be species that are no +longer in existence, the remaining 5 per cent being forms which are +known to live in our present seas. In the middle of the Tertiary +period we find many more recent and still existing species of +shells, and the extinct types are much fewer in number; and this +gradual introduction of forms now living goes on steadily, till, +at the close of the Tertiary period, the proportions with which +we started may be reversed, as many as 90 or 95 per cent of the +fossil shells being forms still alive, while not more than 5 per +cent may have disappeared. + +All known animals at the present day may be divided into some +five or six primary divisions, which are known technically as +"_sub-kingdoms_." Each of these sub-kingdoms [9] may be regarded +as representing a certain type or plan of structure, and all +the animals comprised in each are merely modified forms of this +common type. Not only are all known living animals thus reducible +to some five or six fundamental plans of structure, but amongst +the vast series of fossil forms no one has yet been found--however +unlike any existing animal--to possess peculiarities which would +entitle it to be placed in a new sub-kingdom. All fossil animals, +therefore, are capable of being referred to one or other of the +primary divisions of the animal kingdom. Many fossil groups have +no closely-related group now in existence; but in no case do +we meet with any grand structural type which has not survived +to the present day. + +[Footnote 9: In the Appendix a brief definition is given of the +sub-kingdoms, and the chief divisions of each are enumerated.] + +The old types of life differ in many respects from those now +upon the earth; and the further back we pass in time, the more +marked does this divergence become. Thus, if we were to compare +the animals which lived in the Silurian seas with those inhabiting +our present oceans, we should in most instances find differences +so great as almost to place us in another world. This divergence +is the most marked in the Palæozoic forms of life, less so in +those of the Mesozoic period, and less still in the Tertiary +period. Each successive formation has therefore presented us +with animals becoming gradually more and more like those now in +existence; and though there is an immense and striking difference +between the Silurian animals and those of to-day, this difference +is greatly reduced if we compare the Silurian fauna with the +Devonian; _that_ again with the Carboniferous; and so on till +we reach the present. + +It follows from the above that the animals of any given formation +are more like those of the next formation below, and of the next +formation above, than they are to any others; and this fact of +itself is an almost inexplicable one, unless we believe that +the animals of any given formation are, in part at any rate, the +lineal descendants of the animals of the preceding formation, +and the progenitors, also in part at least, of the animals of the +succeeding formation. In fact, the palæontologist is so commonly +confronted with the phenomenon of closely-allied forms of animal +life succeeding one another in point of time, that he is compelled +to believe that such forms have been developed from some common +ancestral type by some process of "_evolution_." On the other +hand, there are many phenomena, such as the apparently sudden +introduction of new forms throughout all past time, and the common +occurrence of wholly isolated types, which cannot be explained +in this way. Whilst it seems certain, therefore, that many of +the phenomena of the succession of animal life in past periods +can only be explained by some law of evolution, it seems at the +same time certain that there has always been some other deeper +and higher law at work, on the nature of which it would be futile +to speculate at present. + +Not only do we find that the animals of each successive formation +become gradually more and more like those now existing upon the +globe, as we pass from the older rocks into the newer, but we also +find that there has been a gradual progression and development +in the _types_ of animal life which characterise the geological +ages. If we take the earliest-known and oldest examples of any +given group of animals, it can sometimes be shown that these +primitive forms, though in themselves highly organised, possessed +certain characters such as are now only seen in the _young_ of +their existing representatives. In technical language, the early +forms of life in some instances possess "_embryonic_" characters, +though this does not prevent them often attaining a size much +more gigantic than their nearest living relatives. Moreover, the +ancient forms of life are often what is called "comprehensive +types"--that is to say, they possess characters in combination +such as we nowadays only find separately developed in different, +groups of animals. Now, this permanent retention of embryonic +characters and this "comprehensiveness" of structural type are +signs of what a zoologist considers to be a comparatively low +grade of organisation; and the prevalence of these features in +the earlier forms of animals is a very striking phenomenon, though +they are none the less perfectly organised so far as their own +type is concerned. As we pass upwards in the geological scale, +we find that these features gradually disappear, higher and ever +higher forms are introduced, and "specialisation" of type takes +the place of the former comprehensiveness. We shall have occasion +to notice many of the facts on which these views are based at +a later period, and in connection with actual examples. In the +meanwhile, it is sufficient to state, as a widely-accepted +generalisation of palæontology, that there has been in the past +a general progression of organic types, and that the appearance +of the lower forms of life has in the main preceded that of the +higher forms in point of time. + + + + +PART II + +HISTORICAL PALÆONTOLOGY + + + +CHAPTER VII. + +THE LAURENTIAN AND HURONIAN PERIODS. + +The _Laurentian Rocks_ constitute the base of the entire stratified +series, and are, therefore, the oldest sediments of which we have +as yet any knowledge. They are more largely and more typically +developed in North America, and especially in Canada, than in +any known part of the world, and they derive their title from +the range of hills which the old French geographers named the +"Laurentides." These hills are composed of Laurentian Rocks, and +form the watershed between the valley of the St Lawrence river +on the one hand, and the great plains which stretch northwards +to Hudson Bay on the other hand. The main area of these ancient +deposits forms a great belt of rugged and undulating country, +which extends from Labrador westwards to Lake Superior, and then +bends northwards towards the Arctic Sea. Throughout this extensive +area the Laurentian Rocks for the most part present themselves +in the form of low, rounded, ice-worn hills, which, if generally +wanting in actual sublimity, have a certain geological grandeur +from the fact that they "have endured the battles and the storms +of time longer than any other mountains" (Dawson). In some places, +however, the Laurentian Rocks produce scenery of the most magnificent +character, as in the great gorge cut through them by the river +Saguenay, where they rise at times into vertical precipices 1500 +feet in height. In the famous group of the Adirondack mountains, +also, in the state of New York, they form elevations no less than +6000 feet above the level of the sea. As a general rule, the +character of the Laurentian region is that of a rugged, rocky, +rolling country, often densely timbered, but rarely well fitted +for agriculture, and chiefly attractive to the hunter and the +miner. + +As regards its mineral characters, the Laurentian series is composed +throughout of metamorphic and highly crystalline rocks, which +are in a high degree crumpled, folded, and faulted. By the late +Sir William Logan the entire series was divided into two great +groups, the _Lower Laurentian_ and the _Upper Laurentian_, of +which the latter rests unconformably upon the truncated edges +of the former, and is in turn unconformably overlaid by strata +of Huronian and Cambrian age (fig. 20). + +[Illustration: Fig. 20.--Diagrammatic section of the Laurentian +Rocks in Lower Canada. a Lower Laurentian; b Upper Laurentian, +resting unconformably upon the lower series; c Cambrian strata +(Potsdam Sandstone), resting unconformably on the Upper Laurentian.] + +The _Lower Laurentian_ series attains the enormous thickness of +over 20,000 feet, and is composed mainly of great beds of gneiss, +altered sandstones (quartzites), mica-schist, hornblende-schist, +magnetic iron-ore, and hæmatite, together with masses of limestone. +The limestones are especially interesting, and have an extraordinary +development--three principal beds being known, of which one is +not less than 1500 feet thick; the collective thickness of the +whole being about 3500 feet. + +The _Upper Laurentian_ series, as before said, reposes unconformably +upon the Lower Laurentian, and attains a thickness of at least +10,000 feet. Like the preceding, it is wholly metamorphic, and +is composed partly of masses of gneiss and quartzite; but it +is especially distinguished by the possession of great beds of +felspathic rock, consisting principally of "Labrador felspar." + +Though typically developed in the great Canadian area already +spoken of, the Laurentian Rocks occur in other localities, both +in America and in the Old World. In Britain, the so-called +"fundamental gneiss" of the Hebrides and of Sutherlandshire is +probably of Lower Laurentian age, and the "hypersthene rocks" +of the Isle of Skye may, with great probability, be regarded +as referable to the Upper Laurentian. In other localities in +Great Britain (as in St David's, South Wales; the Malvern Hills; +and the North of Ireland) occur ancient metamorphic deposits +which also are probably referable to the Laurentian series. The +so-called "primitive gneiss" of Norway appears to belong to the +Laurentian, and the ancient metamorphic rocks of Bohemia and +Bavaria may be regarded as being approximately of the same age. + +[Illustration: Fig. 21.--Section of Lower Laurentian Limestone +from Hull, Ottawa; enlarged five diameters. The rock is very +highly crystalline, and contains mica and other minerals. The +irregular black masses in it are graphite. (Original.)] + +By some geological writers the ancient and highly metamorphosed +sediments of the Laurentian and the succeeding Huronian series +have been spoken of as the "Azoic rocks" (Gr. _a_, without; _zoe_, +life); but even if we were wholly destitute of any evidence of +life during these periods, this name would be objectionable upon +theoretical grounds. If a general name be needed, that of "Eozoic" +(Gr. _eos_, dawn; _zoe_, life), proposed by Principal Dawson, is the +most appropriate. Owing to their metamorphic condition, geologists +long despaired of ever detecting any traces of life in the vast pile +of strata which constitute the Laurentian System. Even before any +direct traces were discovered, it was, however, pointed out that +there were good reasons for believing that the Laurentian seas had +been tenanted by an abundance of living beings. These reasons are +briefly as follows:--(1) Firstly, the Laurentian series consists, +beyond question, of marine sediments which originally differed +in no essential respect from those which were subsequently laid +down in the Cambrian or Silurian periods. (2) In all formations +later than the Laurentian, any limestones which are present can +be shown, with few exceptions, to be _organic_ rocks, and to be +more or less largely made up of the comminuted debris of marine +or fresh-water animals. The Laurentian limestones, in consequence +of the metamorphism to which they have been subjected, are so +highly crystalline (fig. 21) that the microscope fails to detect +any organic structure in the rock, and no fossils beyond those +which will be spoken of immediately have as yet been discovered in +them. We know, however, of numerous cases in which limestones, +of later age, and undoubtedly organic to begin with, have been +rendered so intensely crystalline by metamorphic action that +all traces of organic structure have been obliterated. We have +therefore, by analogy, the strongest possible ground for believing +that the vast beds of Laurentian limestone have been originally +organic in their origin, and primitively composed, in the main, +of the calcareous skeletons of marine animals. It would, in fact, +be a matter of great difficulty to account for the formation +of these great calcareous masses on any other hypothesis. (3) +The occurrence of phosphate of lime in the Laurentian Rocks in +great abundance, and sometimes in the form of irregular beds, +may very possibly be connected with the former existence in the +strata of the remains of marine animals of whose skeleton this +mineral is a constituent. (4) The Laurentian Rocks contain a +vast amount of carbon in the form of black-lead or _graphite_. +This mineral is especially abundant in the limestones, occurring +in regular beds, in veins or strings, or disseminated through +the body of the limestone in the shape of crystals, scales, or +irregular masses. The amount of graphite in some parts of the +Lower Laurentian is so great that it has been calculated as equal +to the quantity of carbon present in an equal thickness of the +Coal-measures. The general source of solid carbon in the crust +of the earth is, however, plant-life; and it seems impossible to +account for the Laurentian graphite, except upon the supposition +that it is metamorphosed vegetable matter. (5) Lastly, the great +beds of iron-ore (peroxide and magnetic oxide) which occur in the +Laurentian series interstratified with the other rocks, point +with great probability to the action of vegetable life; since +similar deposits in later formations can commonly be shown to +have been formed by the deoxidising power of vegetable matter +in a state of decay. + +In the words of Principal Dawson, "anyone of these reasons might, +in itself, be held insufficient to prove so great and, at first +sight, unlikely a conclusion as that of the existence of abundant +animal and vegetable life in the Laurentian; but the concurrence +of the whole in a series of deposits unquestionably marine, forms +a chain of evidence so powerful that it might command belief +even if no fragment of any organic or living form or structure +had ever been recognised in these ancient rocks." Of late years, +however, there have been discovered in the Laurentian Rocks certain +bodies which are believed to be truly the remains of animals, +and of which by far the most important is the structure known +under the now celebrated name of _Eozoön_. If truly organic, a +very special and exceptional interest attaches itself to _Eozoön_, +as being the most ancient fossil animal of which we have any +knowledge; but there are some who regard it really a peculiar +form of mineral structure, and a severe, protracted, and still +unfinished controversy has been carried on as to its nature. Into +this controversy it is wholly unnecessary to enter here; and it +will be sufficient to briefly explain the structure of _Eozoön_, +as elucidated by the elaborate and masterly investigations of +Carpenter and Dawson, from the standpoint that it is a genuine +organism--the balance of evidence up to this moment inclining +decisively to this view. + +[Illustration: Fig. 22.--Fragment of _Eozoön_, of the natural +size, showing alternate laminæ of loganite and dolomite. (After +Dawson.)] + +The structure known as _Eozoön_ is found in various localities +in the Lower Laurentian limestones of Canada, in the form of +isolated masses or spreading layers, which are composed of thin +alternating laminæ, arranged more or less concentrically (fig. +22). The laminæ of these masses are usually of different colours +and composition; one series being white, and composed of carbonate +of lime--whilst the laminæ of the second series alternate with +the preceding, are green in colour, and are found by chemical +analysis to consist of some silicate, generally serpentine or the +closely-related "loganite." In some instances, however, all the +laminæ are calcareous, the concentric arrangement still remaining +visible in consequence of the fact that the laminæ are composed +alternately of lighter and darker coloured limestone. + +When first discovered, the masses of _Eozoön_ were supposed to +be of a mineral nature; but their striking general resemblance +to the undoubted fossils which will be subsequently spoken of +under the name of _Stromatopora_ was recognised by Sir William +Logan, and specimens were submitted for minute examination, first +to Principal Dawson, and subsequently to Dr W. B. Carpenter. +After a careful microscopic examination, these two distinguished +observers came to the conclusion that _Eozoön_ was truly organic, +and in this opinion they were afterwards corroborated by other +high authorities (Mr W. K. Parker, Professor Rupert Jones, Mr H. +B. Brady, Professor Gümbel, &c.) Stated briefly, the structure +of _Eozoön_, as exhibited by the microscope, is as follows:-- + +[Illustration: Fig. 23.--Diagram of a portion of _Eozoön_ cut +vertically. A, B, C, Three tiers of chambers communicating with +one another by slightly constricted apertures: _a a_, The true +shell-wall, perforated by numerous delicate tubes; _b b_. The +main calcareous skeleton ("intermediate skeleton"); c, Passage +of communication ("stolon-passage") from one tier of chambers +to another; d, Ramifying tubes in the calcareous skeleton. +(After Carpenter.)] + +The concentrically-laminated mass of _Eozoön_ is composed of +numerous calcareous layers, representing the original skeleton +of the organism (fig. 23, b). These calcareous layers serve to +separate and define a series of chambers arranged in successive +tiers, one above the other (fig. 23, A, B, C); and they are +perforated not only by passages (fig. 23, c), which serve to +place successive tiers of chambers in communication, but also by +a system of delicate branching canals (fig. 23, d). Moreover, +the central and principal portion of each calcareous layer, with +the ramified canal-system just spoken of, is bounded both above +and below by a thin lamina which has a structure of its own, and +which may be regarded as the proper shell-wall (fig. 23, a a). +This proper wall forms the actual lining of the chambers, as well +as the outer surface of the whole mass; and it is perforated with +numerous fine vertical tubes (fig. 24, a a), opening into the +chambers and on to the surface by corresponding fine pores. From +the resemblance of this tubulated layer to similar structures +in the shell of the Nummulite, it is often spoken of as the +"Nummuline layer." The chambers are sometimes piled up one above +the other in an irregular manner; but they are more commonly +arranged in regular tiers, the separate chambers being marked +off from one another by projections of the wall in the form of +partitions, which are so far imperfect as to allow of a free +communication between contiguous chambers. In the original condition +of the organism, all these chambers, of course, must have been +filled with living-matter; but they are found in the present +state of the fossil to be generally filled with some silicate, +such as serpentine, which not only fills the actual chambers, +but has also penetrated the minute tubes of the proper wall and +the branching canals of the intermediate skeleton. In some cases +the chambers are simply filled with crystalline carbonate of +lime. When the originally porous fossil has been permeated by +a silicate, it is possible to dissolve away the whole of the +calcareous skeleton by means of acids, leaving an accurate and +beautiful cast of the chambers and the tubes connected with them +in the insoluble silicate. + +[Illustration: Fig. 24.--Portion of one of the calcareous layers +of _Eozoön_, magnified 100 diameters. a a, The proper wall +("Nummuline layer") of one of the chambers, showing the fine +vertical tubuli with which it is penetrated, and which are slightly +bent along the line a' a'. c c, The intermediate skeleton, +with numerous branched canals. The oblique lines are the cleavage +planes of the carbonate of lime, extending across both the +intermediate skeleton and the proper wall. (After Carpenter.)] + +The above are the actual appearances presented by _Eozoön_ when +examined microscopically, and it remains to see how far they +enable us to decide upon its true position in the animal kingdom. +Those who wish to study this interesting subject in detail must +consult the admirable memoirs by Dr W. B. Carpenter and Principal +Dawson: it will be enough here to indicate the results which +have been arrived at. The only animals at the present day which +possess a continuous calcareous skeleton, perforated by pores +and penetrated by canals, are certain organisms belonging to +the group of the _Foraminifera_. We have had occasion before +to speak of these animals, and as they are not conspicuous or +commonly-known forms of life, it may be well to say a few words +as to the structure of the living representatives of the group. +The _Foraminifera_ are all inhabitants of the sea, and are mostly +of small or even microscopic dimensions. Their bodies are composed +of an apparently structureless animal substance of an albuminous +nature ("sarcode"), of a gelatinous consistence, transparent, and +exhibiting numerous minute granules or rounded particles. The +body-substance cannot be said in itself to possess any definite +form, except in so far as it may be bounded by a shell; but it +has the power, wherever it may be exposed, of emitting long +thread-like filaments ("pseudopodia"), which interlace with one +another to form a network (fig. 25, b). These filaments can be +thrown out at will, and to considerable distances, and can be +again retracted into the soft mass of the general body-substance, +and they are the agents by which the animal obtains its food. +The soft bodies of the _Foraminifera_ are protected by a shell, +which is usually calcareous, but may be composed of sand-grains +cemented together; and it may consist of a single chamber (fig. +26, a), or of many chambers arranged in different ways (fig. +26, _b-f_). Sometimes the shell has but one large opening into +it--the mouth; and then it is from this aperture that the animal +protrudes the delicate net of filaments with which it seeks its +food. In other cases the entire shell is perforated with minute +pores (fig. 26, e), through which the soft body-substance gains +the exterior, covering the whole shell with a gelatinous film +of animal matter, from which filaments can be emitted at any +point. When the shell consists of many chambers, all of these are +placed in direct communication with one another, and the actual +substance of the shell is often traversed by minute canals filled +with living matter (e.g., in _Calcarina_ and _Nummulina_). The +shell, therefore, may be regarded, in such cases, as a more or +less completely porous calcareous structure, filled to its minutest +internal recesses with the substance of the living animal, and +covered externally with a layer of the same substance, giving +off a network of interlacing filaments. + +[Illustration: Fig. 25.--The animal of _Nonionina_, one of the +_Foraminifera_, after the shell has been removed by a weak acid; +b, _Gromia_, a single-chambered Foraminifer (after Schultze), +showing the shell surrounded by a network of filaments derived +from the body substance.] + +[Illustration: Fig 26.--Shells of living _Foraminifera_. a, +_Orbulina universa_, in its perfect condition, showing the tubular +spines which radiate from the surface of the shell; b, _Globigerina +bulloides_, in its ordinary condition, the thin hollow spines +which are attached to the shell when perfect having been broken +off; c, Textularia variabilis; d, Peneroplis planatus; e, Rotalia +concamerata; f, _Cristellaria subarcuatula._ [Fig. a is after +Wyville Thomson; the others are after Williamson. All the figures +are greatly enlarged.]] + +Such, in brief, is the structure of the living _Foraminifera_; +and it is believed that in _Eozoön_ we have an extinct example of +the same group, not only of special interest from its immemorial +antiquity, but hardly less striking from its gigantic dimensions. +In its original condition, the entire chamber-system of _Eozoön_ +is believed to have been filled with soft structureless living +matter, which passed from chamber to chamber through the wide +apertures connecting these cavities, and from tier to tier by +means of the tubuli in the shell-wall and the branching canals +in the intermediate skeleton. Through the perforated shell-wall +covering the outer surface the soft body-substance flowed out, +forming a gelatinous investment, from every point of which radiated +an interlacing net of delicate filaments, providing nourishment +for the entire colony. In its present state, as before said, +all the cavities originally occupied by the body-substance have +been filled with some mineral substance, generally with one of +the silicates of magnesia; and it has been asserted that this +fact militates strongly against the organic nature of _Eozoön_, +if not absolutely disproving it. As a matter of fact, however--as +previously noticed--it is by no means very uncommon at the present +day to find the shells of living species of _Foraminifera_ in which +all the cavities primitively occupied by the body-substance, down +to the minutest pores and canals, have been similarly injected +by some analogous silicate, such as glauconite. + +Those, then, whose opinions on such a subject deservedly carry the +greatest weight, are decisively of opinion that we are presented +in the _Eozoön_ of the Laurentian Rocks of Canada with an ancient, +colossal, and in some respects abnormal type of the _Foraminifera_. +In the words of Dr Carpenter, it is not pretended that "the doctrine +of the Foraminiferal nature of _Eozoön_ can be _proved_ in the +demonstrative sense;" but it may be affirmed "that the _convergence +of a number of separate and independent probabilities_, all accordant +with that hypothesis, while a separate explanation must be invented +for each of them on any other hypothesis, gives it that _high +probability_ on which we rest in the ordinary affairs of life, in +the verdicts of juries, and in the interpretation of geological +phenomena generally." + +It only remains to be added, that whilst _Eozoön_ is by far the +most important organic body hitherto found in the Laurentian, and +has been here treated at proportionate length, other traces of life +have been detected, which may subsequently prove of great interest +and importance. Thus, Principal Dawson has recently described +under the name of _Archoeosphoerinoe_ certain singular rounded +bodies which he has discovered in the Laurentian limestones, and +which he believes to be casts of the shells of _Foraminifera_ +possibly somewhat allied to the existing _Globigerinoe_. The same +eminent palæontologist has also described undoubted worm-burrows +from rocks probably of Laurentian age. Further and more extended +researches, we may reasonably hope, will probably bring to light +other actual remains of organisms in these ancient deposits. + + +THE HURONIAN PERIOD. + +The so-called _Huronian Rocks_, like the Laurentian, have their +typical development in Canada, and derive their name from the +fact that they occupy an extensive area on the borders of Lake +Huron. They are wholly metamorphic, and consist principally of +altered sandstones or quartzites, siliceous, felspathic, or talcose +slates, conglomerates, and limestones. They are largely developed +on the north shore of Lake Superior, and give rise to a broken +and hilly country, very like that occupied by the Laurentians, +with an abundance of timber, but rarely with sufficient soil +of good quality for agricultural purposes. They are, however, +largely intersected by mineral veins, containing silver, gold, +and other metals, and they will ultimately doubtless yield a rich +harvest to the miner. The Huronian Rocks have been identified, +with greater or less certainty, in other parts of North America, +and also in the Old World. + +The total thickness of the Huronian Rocks in Canada is estimated +as being not less than 18,000 feet, but there is considerable +doubt as to their precise geological position. In their typical +area they rest unconformably on the edges of strata of _Lower_ +Laurentian age; but they have never been seen in direct contact +with the _Upper_ Laurentian, and their exact relations to this +series are therefore doubtful. It is thus open to question whether +the Huronian Rocks constitute a distinct formation, to be +intercalated in point of time between the Laurentian and the +Cambrian groups; or whether, rather, they should not be considered +as the metamorphosed representatives of the Lower Cambrian Rocks +of other regions. + +As regards the fossils of the Huronian Rocks, little can be said. +Some of the specimens of _Eozoön Canadense_ which have been +discovered in Canada are thought to come from rocks which are +probably of Huronian age. In Bavaria, Dr Gümbel has described a +species of _Eozoön_ under the name of _Eozoön Bavaricum_, from +certain metamorphic limestones which he refers to the Huronian +formation. Lastly, the late Mr Billings described, from rocks +in Newfoundland apparently referable to the Huronian, certain +problematical limpet-shaped fossils, to which he gave the name +of _Aspidella_. + + +LITERATURE. + +Amongst the works and memoirs which the student may consult with +regard to the Laurentian and Huronian deposits may be mentioned +the following:[10]-- + +(1) 'Report of Progress of the Geological Survey of Canada from its + Commencement to 1863,' pp. 38-49, and pp. 50-66. +(2) 'Manual of Geology.' Dana. 2d Ed. 1875. +(3) 'The Dawn of Life.' J. W, Dawson. 1876. +(4) "On the Occurrence of Organic Remains in the Laurentian Rocks + of Canada." Sir W. E. Logan. 'Quart. Journ. Geol. Soc.,' + xxi. 45-50.' +(5) "On the Structure of Certain Organic Remains in the Laurentian + Limestones of Canada." J. W. Dawson. 'Quart. Journ. Geol. + Soc.,' xxi. 51-59. +(6) "Additional Note on the Structure and Affinities of Eozoön + Canadense." W. B, Carpenter. 'Quart. Journ. Geol. Soc.,' xxi. + 59-66. +(7) "Supplemental Notes on the Structure and Affinities of Eozoön' + Canadense," W. B. Carpenter, 'Quart. Journ. Geol. Soc.,' + xxii. 219-228. +(8) "On the So-Called Eozoönal Rocks." King & Rowney. 'Quart. + Journ. Geol. Soc.,' xxii. 185-218. +(9) 'Chemical and Geological Essays.' Sterry Hunt. + +The above list only includes some of the more important memoirs +which may be consulted as to the geological and chemical features +of the Laurentian and Huronian Rocks, and as to the true nature +of _Eozoön_. Those who are desirous of studying the later phases +of the controversy with regard to _Eozoön_ must consult the papers +of Carpenter, Carter, Dawson, King & Rowney, Hahn, and others, in +the 'Quart. Journ. of the Geological Society,' the 'Proceedings +of the Royal Irish Academy,' the 'Annals of Natural History,' +the 'Geological Magazine,' &c. Dr Carpenter's 'Introduction to +the Study of the Foraminifera' should also be consulted. + +[Footnote 10: In this and in all subsequently following +bibliographical lists, not only is the selection of works and +memoirs quoted necessarily extremely limited; but only such have, +as a general rule, been chosen for mention as are easily accessible +to students who are in the position of being able to refer to a good +library. Exceptions, however, are occasionally made to this rule, +in favour of memoirs or works of special historical interest. It +is also unnecessary to add that it has not been thought requisite +to insert in these lists the well-known handbooks of geological +and palæontological science; except in such instances as where +they contain special information on special points.] + + + + +CHAPTER VIII. + +THE CAMBRIAN PERIOD. + +The traces of life in the Laurentian period, as we have seen, +are but scanty; but the _Cambrian Rocks_--so called from their +occurrence in North Wales and its borders ("Cambria ")--have +yielded numerous remains of animals and some dubious plants. +The Cambrian deposits have thus a special interest as being the +oldest rocks in which occur any number of well-preserved and +unquestionable organisms. We have here the remains of the first +_fauna_, or assemblage of animals, of which we have at present +knowledge. As regards their geographical distribution, the Cambrian +Rocks have been recognised in many parts of the world, but there +is some question as to the precise limits of the formation, and +we may consider that their most typical area is in South Wales, +where they have been carefully worked out, chiefly by Dr Henry +Hicks. In this region, in the neighbourhood of the promontory +of St David's, the Cambrian Rocks are largely developed, resting +upon an ancient ridge of Pre-Cambrian (Laurentian?) strata, and +overlaid by the lowest beds of the Lower Silurian. The subjoined +sketch-section (fig. 27) exhibits in a general manner the succession +of strata in this locality. + +From this section it will be seen that the Cambrian Rocks in +Wales are divided in the first place into a lower and an upper +group. The _Lower Cambrian_ is constituted at the base by a great +series of grits, sandstones, conglomerates, and slates, which +are known as the "Longmynd group," from their vast development +in the Longmynd Hills in Shropshire, and which attain in North +Wales a thickness of 8000 feet or more. The Longmynd beds are +succeeded by the so-called "Menevian group," a series of sandstones, +flags, and grits, about 600 feet in thickness, and containing +a considerable number of fossils. The _Upper Cambrian_ series +consists in its lower portion of nearly 5000 feet of strata, +principally shaly and slaty, which are known as the "Lingula +Flags," from the great abundance in them of a shell referable +to the genus _Lingula_. These are followed by 1000 feet of dark +shales and flaggy sandstones, which are known as the "Tremadoc +slates," from their occurrence near Tremadoc in North Wales; +and these in turn are surmounted, apparently quite conformably, +by the basement beds of the Lower Silurian. + +[Illustration: Fig 27. GENERALIZED SECTION OF THE CAMBRIAN ROCKS +IN WALES.] + +The above may be regarded as giving a typical series of the Cambrian +Rocks in a typical locality; but strata of Cambrian age are known in +many other regions, of which it is only possible here to allude to +a few of the most important. In Scandinavia occurs a well-developed +series of Cambrian deposits, representing both the lower and +upper parts of the formation. In Bohemia, the Upper Cambrian, in +particular, is largely developed, and constitutes the so-called +"Primordial zone" of Barrande. Lastly, in North America, whilst the +Lower Cambrian is only imperfectly developed, or is represented by +the Huronian, the Upper Cambrian formation has a wide extension, +containing fossils similar in character to the analogous strata +in Europe, and known as the "Potsdam Sandstone." The subjoined +table shows the chief areas where Cambrian Rocks are developed, +and their general equivalency: + +TABULAR VIEW OF THE CAMBRIAN FORMATION. + + _Britain._ | _Europe._ | _America._ + | | + /a. Tremadoc Slates. | a. Primordial zone | a. Potsdam + | | of Bohemia. | Sandstone. + | b. Lingula Flags. | b. Paradoxides | b. Acadian + Upper < | Schists, Olenus | group of New +Cambrian. | | Schists, and | Brunswick. + | | Dictyonema schists | + \ | of Sweden. | + | | + /a. Longmynd Beds. | a. Fucoidal | Huronian + | | Sandstone of Sweden | Formation? + | b. Llanberis Slates.| b. _Eophyton_ | + | | Sandstone of Sweden.| + Lower < c. Harlech Grits. | | +Cambrian. | d. _Oldhamia_ | | + | Slates of Ireland.| | + | e. Conglomerates and| | + | and Sandstones of | | + | Sutherlandshire? | | + \f. Menevian Beds. | | + +Like all the older Palæozoic deposits, the Cambrian Rocks, though +by no means necessarily what would be called actually "metamorphic," +have been highly cleaved, and otherwise altered from their original +condition. Owing partly to their indurated state, and partly to +their great antiquity, they are usually found in the heart of +mountainous districts, which have undergone great disturbance, +and have been subjected to an enormous amount of denudation. In +some cases, as in the Longmynd Hills in Shropshire, they form +low rounded elevations, largely covered by pasture, and with few +or no elements of sublimity. In other cases, however, they rise +into bold and rugged mountains, girded by precipitous cliffs. +Industrially, the Cambrian Rocks are of interest, if only for +the reason that the celebrated Welsh slates of Llanberis are +derived from highly-cleaved beds of this age. Taken as a whole, +the Cambrian formation is essentially composed of arenaceous +and muddy sediments, the latter being sometimes red, but more +commonly nearly black in colour. It has often been supposed that +the Cambrians are a deep-sea deposit, and that we may thus account +for the few fossils contained in them; but the paucity of fossils +is to a large extent imaginary, and some of the Lower Cambrian +beds of the Longmynd Hills would appear to have been laid down +in shallow water; as they exhibit rain-prints, sun-cracks, and +ripple-marks--incontrovertible evidence of their having been a +shore-deposit. The occurrence, of innumerable worm-tracks and +burrows in many Cambrian strata is also a proof of shallow-water +conditions; and the general absence of limestones, coupled with +the coarse mechanical nature of many of the sediments of the +Lower Cambrian, maybe taken as pointing in the same direction. + +The _life_ of the Cambrian, though not so rich as in the succeeding +Silurian period, nevertheless consists of representatives of +most of the great classes of invertebrate animals. The coarse +sandy deposits of the formation, which abound more particularly +towards its lower part, naturally are to a large extent barren +of fossils; but the muddy sediments, when not too highly cleaved, +and especially towards the summit of the group, are replete with +organic remains. This is also the case, in many localities at any +rate, with the finer beds of the Potsdam Sandstone in America. +Limestones are known to occur in only a few areas (chiefly in +America), and this may account for the apparent total absence +of corals. It is, however, interesting to note that, with this +exception, almost all the other leading groups of Invertebrates +are known to have come into existence during the Cambrian period. + +Fig. 28.--Fragment of _Eophyton Linneanum_, a supposed land-plant. +Lower Cambrian, Sweden, of the natural size. + +Of the land-surfaces of the Cambrian period we know nothing; +and there is, therefore, nothing surprising in the fact that +our acquaintance with the Cambrian vegetation is confined to +some marine plants or sea-weeds, often of a very obscure and +problematical nature. The "Fucoidal Sandstone" of Sweden, and the +"Potsdam Sandstone" of North America, have both yielded numerous +remains which have been regarded as markings left by sea-weeds or +"Fucoids;" but these are highly enigmatical in their characters, +and would, in many instances, seem to be rather referable to the +tracks and burrows of marine worms. The first-mentioned of these +formations has also yielded the curious, furrowed and striated +stems which have been described as a kind of land-plant under +the name of _Eopkyton_ (fig. 28). It cannot be said, however, +that the vegetable origin of these singular bodies has been +satisfactorily proved. Lastly, there are found in certain green +and purple beds of Lower Cambrian age at Bray Head, Wicklow, +Ireland, some very remarkable fossils, which are well known under +the name of _Oldhamia_, but the true nature of which is very +doubtful. The commonest form of _Oldhamia_ (fig. 29) consists of +a thread-like stem or axis, from which spring at regular intervals +bundles of short filamentous branches in a fan-like manner. In +the locality where it occurs, the fronds of _Oldhamia_ are very +abundant, and are spread over the surfaces of the strata in tangled +layers. That it is organic is certain, and that it is a calcareous +sea-weed is probable; but it may possibly belong to the sea-mosses +(_Polyzoa_), or to the sea-firs (_Sertularians_). + +Amongst the lower forms of animal life (_Protozoa_), we find the +Sponges represented by the curious bodies, composed of netted +fibres, to which the name of _Protospongia_ has been given (fig. +32, a); and the comparatively gigantic, conical, or cylindrical +fossils termed _Archoeocyathus_ by Mr Billings are certainly +referable either to the _Foraminifera_ or to the Sponges. The +almost total absence of limestones in the formation may be regarded +as a sufficient explanation of the fact that the _Foraminifera_ +are not more largely and unequivocally represented; though the +existence of greensands in the Cambrian beds of Wisconsin and +Tennessee may be taken as an indication that this class of animals +was by no means wholly wanting. The same fact may explain the +total absence of corals, so far as at present known. + +[Illustration: Fig. 29.--A portion of _Oldhamia antiqua_, Lower +Cambrian, Wicklow, Ireland, of the natural size. (After Salter.)] + +The group of the _Echinodermata_ (Sea-lilies, Sea-urchins, and +their allies) is represented by a few forms, which are principally +of interest as being the earliest-known examples of the class. +It is also worthy of note that these precursors of a group which +subsequently attains such geological importance, are referable to +no less than three distinct _orders_--the Crinoids or Sea-lilies, +represented by a species of _Dendrocrinus_; the Cystideans by +_Protocystites_; and the Star-fishes by _Palasterina_ and some +other forms. Only the last of these groups, however, appears +to occur in the Lower Cambrian. + +[Illustration: Fig. 30.--Annelide-burrows (_Scolithus linearus_) +from the Potsdam Sandstone of Canada, of the natural size. (After +Billings.)] + +The Ringed-worms (_Annelida_), if rightly credited with all the +remains usually referred to them, appear to have swarmed in the +Cambrian seas. Being soft-bodied, we do not find the actual worms +themselves in the fossil condition, but we have, nevertheless, +abundant traces of their existence. In some cases we find vertical +burrows of greater or less depth, often expanded towards their +apertures, in which the worm must have actually lived (fig. 30), +as various species do at the present day. In these cases, the +tube must have been rendered more or less permanent by receiving +a coating of mucus, or perhaps a genuine membranous secretion, +from the body of the animal; and it may be found quite empty, +or occupied by a cast of sand or mud. Of this nature are the +burrows which have been described under the names of _Scolithus_ +and _Scolecoderma_, and probably the _Histioderma_ of the Lower +Cambrian of Ireland. In other cases, as in _Arenicolites_ (fig. +32, b), the worm seems to have inhabited a double burrow, shaped +like the letter U, and having two openings placed close together +on the surface of the stratum. Thousands of these twin-burrows +occur in some of the strata of the Longmynd, and it is supposed +that the worm used one opening to the burrow as an aperture of +entrance, and the other as one of exit. In other cases, again, +we find simply the meandering trails caused by the worm dragging +its body over the surface of the mud. Markings of this kind are +commoner in the Silurian Rocks, and it is generally more or less +doubtful whether they may not have been caused by other marine +animals, such as shellfish, whilst some of them have certainly +nothing whatever to do with the worms. Lastly, the Cambrian beds +often show twining cylindrical bodies, commonly more or less +matted together, and not confined to the surfaces of the strata, +but passing through them. These have often been regarded as the +remains of sea-weeds, but it is more probable that they represent +casts of the underground burrows of worms of similar habits to +the common lob-worm (_Arenicola_) of the present day. + +The _Articulate_ animals are numerously represented in the Cambrian +deposits, but exclusively by the class of _Crustaceans_. Some +of these are little double-shelled creatures, resembling our +living water-fleas (_Ostracoda_). A few are larger forms, and +belong to the same group as the existing brine-shrimps and +fairy-shrimps (_Phyllopoda_). One of the most characteristic of +these is the _Hymenocaris vermicauda_ of the Lingula Flags (fig. +32, d). By far the larger number of the Cambrian _Crustacea_ +belong, however, to the remarkable and wholly extinct group of +the _Trilobites_. These extraordinary animals must have literally +swarmed in the seas of the later portion of this and the whole of +the succeeding period; and they survived in greatly diminished +numbers till the earlier portion of the Carboniferous period. +They died out, however, wholly before the close of the Palæozoic +epoch, and we have no Crustaceans at the present day which can be +considered as their direct representatives. They have, however, +relationships of a more or less intimate character with the existing +groups of the Phyllopods, the King-crabs (_Limulus_), and the +Isopods ("Slaters," Wood-lice, &c.) Indeed, one member of the +last-mentioned order, namely, the _Serolis_ of the coasts of +Patagonia, has been regarded as the nearest living ally of the +Trilobites. Be this as it may, the Trilobites possessed a skeleton +which, though capable of undergoing almost endless variations, +was wonderfully constant in its pattern of structure, and we +may briefly describe here the chief features of this. + +[Illustration: Fig. 31.--Cambrian Trilobites: a, _Paradoxides +Bohemicus_, reduced in size; b, _Ellipsocephalus Hoffi_; c, _Sao +hirsuta_; d, _Conocorypke Sultzeri_ (all the above, together with +fig. g, are from the Upper Cambrian or "Primordial Zone" of +Bohemia); e, Head-shield of _Dikellocephalus Celticus_, from the +Lingula Flags of Wales; f, Head-shield of _Conocoryphe Matthewi_, +from the Upper Cambrian (Acadian Group) of New Brunswick; g, +_Agnostus rex_, Bohemia; h, Tail-shield of _Dikellocephalus +Minnesotensis_, from the Upper Cambrian (Potsdam Sandstone) of +Minnesota. (After Barrande, Dawson, Salter, and Dale Owen.)] + +The upper surface of the body of a Trilobite was defended by a +strong shell or "crust," partly horny and partly calcareous in +its composition. This shell (fig. 31) generally exhibits a very +distinct "trilobation" or division into three longitudinal lobes, +one central and two lateral. It also exhibits a more important and +more fundamental division into three transverse portions, which +are so loosely connected with one another as very commonly to be +found separate. The first and most anterior of these divisions +is a shield or buckler which covers the head; the second or middle +portion is composed of movable rings covering the trunk ("thorax +"); and the third is a shield which covers the tailor "abdomen." The +head-shield (fig. 31, e) is generally more or less semicircular +in shape; and its central portion, covering the stomach of the +animal, is usually strongly elevated, and generally marked by +lateral furrows. A little on each side of the head are placed +the eyes, which are generally crescentic in shape, and resemble +the eyes of insects and many existing Crustaceans in being +"compound," or made up of numerous simple eyes aggregated together. +So excellent is the state of preservation of many specimens of +Trilobites, that the numerous individual lenses of the eyes have +been uninjured, and as many as four hundred have been counted +in each eye of some forms. The eyes may be supported upon +prominences, but they are never carried on movable stalks (as +they are in the existing lobsters and crabs); and in some of the +Cambrian Trilobites, such as the little _Agnosti_ (fig. 31 g), +the animal was blind. The lateral portions of the head-shield +are usually separated from the central portion by a peculiar +line of division (the so-called "facial suture") on each side; +but this is also wanting in some of the Cambrian species. The +backward angles of the head-shield, also, are often prolonged +into spines, which sometimes reach a great length. Following +the head-shield behind, we have a portion of the body which is +composed of movable segments or "body-rings," and which is +technically called the "thorax," Ordinarily, this region is strongly +trilobed, and each ring consists of a central convex portion, +and of two flatter side-lobes. The number of body-rings in the +thorax is very variable (from two to twenty-six), but is fixed +for the adult forms of each group of the Trilobites. The young +forms have much fewer rings than the full-grown ones; and it +is curious to find that the Cambrian Trilobites very commonly +have either a great many rings (as in _Paradoxides_, fig. 31, +a), or else very few (as in _Agnostus_, fig. 31, g). In some +instances, the body-rings do not seem to have been so constructed +as to allow of much movement, but in other cases this region of +the body is so flexible that the animal possessed the power of +rolling itself up completely, like a hedgehog; and many individuals +have been permanently preserved as fossils in this defensive +condition. Finally, the body of the Trilobite was completed by +a tail-shield (technically termed the "pygidium"), which varies +much in size and form, and is composed of a greater or less number +of rings, similar to those which form the thorax, but immovably +amalgamated with one another (fig. 31, h). + +The under surface of the body in the Trilobites appears to have +been more or less entirely destitute of hard structures, with the +exception of a well-developed upper lip, in the form of a plate +attached to the inferior side of the head-shield in front. There +is no reason to doubt that the animal possessed legs; but these +structures seem to have resembled those of many living Crustaceans +in being quite soft and membranous. This, at any rate, seems to +have been generally the case; though structures which have been +regarded as legs have been detected on the under surface of one +of the larger species of Trilobites. There is also, at present, +no direct evidence that the Trilobites possessed the two pairs +of jointed feelers ("antennæ") which are so characteristic of +recent Crustaceans. + +The Trilobites vary much in size, and the Cambrian formation +presents examples of both the largest and the smallest members +of the order. Some of the young forms may be little bigger than +a millet-seed, and some adult examples of the smaller species +(such as _Agnostus_) may be only a few lines in length; whilst +such giants of the order as _Paradoxides_ and _Asaphus_ may reach +a length of from one to two feet. Judging from what we actually +know as to the structure of the Trilobites, and also from analogous +recent forms, it would seem that these ancient Crustaceans were +mud-haunting creatures, denizens of shallow seas, and affecting +the soft silt of the bottom rather than the clear water above. +Whenever muddy sediments are found in the Cambrian and Silurian +formations, there we are tolerably sure to find Trilobites, though +they are by no means absolutely wanting in limestones. They appear +to have crawled out upon the sea-bottom, or burrowed in the yielding +mud, with the soft under surface directed downwards; and it is +probable that they really derived their nutriment from the organic +matter contained in the ooze amongst which they lived. The vital +organs seem to have occupied the central lobe of the skeleton, +by which they were protected; and a series of delicate leaf-like +paddles, which probably served as respiratory organs, would appear +to have been carried on the under surface of the thorax. That +they had their enemies may be regarded as certain; but we have +no evidence that they were furnished with any offensive weapons, +or, indeed, with any means of defence beyond their hard crust, +and the power, possessed by so many of them, of rolling themselves +into a ball. An additional proof of the fact that they for the +most part crawled along the sea-bottom is found in the occurrence +of tracks and markings of various kinds, which can hardly be +ascribed to any other creatures with any show of probability. +That this is the true nature of some of the markings in question +cannot be doubted at all; and in other cases no explanation so +probable has yet been suggested. If, however, the tracks which have +been described from the Potsdam Sandstone of North America under +the name of _Protichnites_ are really due to the peregrinations +of some Trilobite, they must have been produced by one of the +largest examples of the order. + +As already said, the Cambrian Rocks are very rich in the remains +of Trilobites. In the lowest beds of the series (Longmynd Rocks), +representatives of some half-dozen genera have now been detected, +including the dwarf _Agnostus_ and the giant _Paradoxides_. In +the higher beds, the number both of genera and species is largely +increased; and from the great comparative abundance of individuals, +the Trilobites have every right to be considered as the most +characteristic fossils of the Cambrian period,--the more so as +the Cambrian species belong to peculiar types, which, for the +most part, died out before the commencement of the Silurian epoch. + +All the remaining Cambrian fossils which demand any notice here +are members of one or other division of the great class of the +_Mollusca_, or "Shell-fish" properly so called. In the Lower +Cambrian Rocks the Lamp-shells (_Brachiopoda_) are the principal +or sole representatives of the class, and appear chiefly in three +interesting and important types--namely, _Lingulella, Discina,_ +and _Obolella_. Of these the last (fig. 32, i) is highly +characteristic of these ancient deposits; whilst _Discina_ is +one of those remarkable persistent types which, commencing at +this early period, has continued to be represented by varying +forms through all the intervening geological formations up to the +present day. _Lingulella_ (fig. 32, c), again, is closely allied +to the existing "Goose-bill" Lamp-shell (_Lingula anatina_), and +thus presents us with another example of an extremely long-lived +type. The _Lingulelloe_ and their successors; the _Linguloe_, are +singular in possessing a shell which is of a horny texture, and +contains but a small proportion of calcareous matter. In the Upper +Cambrian Rocks, the _Lingulelloe_ become much more abundant, the +broad satchel-shaped species known as _L. Davisii_ (fig. 32, +e) being so abundant that one of the great divisions of the +Cambrian is termed the "Lingula Flags." Here, also, we meet for +the first time with examples of the genus Orthis (fig. 32, f, +k, l) a characteristic Palæozoic type of the Brachiopods, which +is destined to undergo a vast extension in later ages. + +[Illustration: Fig 32.--Cambrian Fossils: a, _Protospongia +fenestrata_, Menevian Group; b, _Arenicolites didymus_, Longmynd +Group; c, _Lingulella ferruginea_, Longmynd and Menevian, enlarged; +d, _Hymenocaris vermicauda_, Lingula Flags; e, _Lingulella Davisii_, +Lingula Flags; f, _Orthis lenticularis_, Lingula Flags; g, _Theca +Davidii_, Tremadoc Slates; h, _Modiolopsis Solvensis_, Tremadoc +Slates; i, _Obolela sagittalis_, interior of valve, Menevian; +j, Exterior of the same; k, _Orthis Hicksii_, Menevian; l, +Cast of the same; m, _Olenus micrurus_, Lingula Flags. (Alter +Salter, Hicks, and Davidson.)] + +Of the higher groups of the _Mollusca_ the record is as yet but +scanty. In the Lower Cambrian, we have but the thin, fragile, +dagger-shaped shells of the free-swimming oceanic Molluscs or +"Winged-snails" (_Pteropoda_), of which the most characteristic +is the genus _Theca_ (fig. 32, g). In the Upper Cambrian, in +addition to these, we have a few Univalves (_Gasteropoda_), and, +thanks to the researches of Dr Hicks, quite a small assemblage +of Bivalves (_Lamellibranchiata_), though these are mostly of no +great dimensions (fig. 32, h). Of the chambered _Cephalopoda_ +(Cuttle-fishes and their allies), we have but few traces; and these +wholly confined to the higher beds of the formation. We meet, +however, with examples of the wonderful genus _Orthoceras_, with +its straight, partitioned shell, which we shall find in an immense +variety of forms in the Silurian rocks. Lastly, it is worthy of +note that the lowest of all the groups of the _Mollusca_--namely, +that of the Sea-mats, Sea-mosses, and Lace-corals (_Polyzoa_)--is +only doubtfully known to have any representatives in the Cambrian, +though undergoing a large and varied development in the Silurian +deposits. + +[Illustration: Fig. 33.--Fragment of _Dictyonema sociale_, +considerably enlarged, showing the horny branches, with their +connecting cross-bars, and with a row of cells on each side. +(Original.)] + +An exception, however, may with much probability be made to this +statement in favour of the singular genus _Dictyonema_ (fig. +33), which is highly characteristic of the highest Cambrian beds +(Tremadoc Slates). This curious fossil occurs in the form of +fan-like or funnel-shaped expansions, composed of slightly-diverging +horny branches, which are united in a net-like manner by numerous +delicate cross-bars, and exhibit a row of little cups or cells, +in which the animals were contained, on each side. _Dictyonema_ +has generally been referred to the _Graptolites_; but it has a +much greater affinity with the plant-like Sea-firs (_Sertularians_) +or the Sea-mosses (_Polyzoa_), and the balance of evidence is +perhaps in favour of placing it with the latter. + + +LITERATURE. + +The following are the more important and accessible works and +memoirs which may be consulted in studying the stratigraphical +and palæontological relations of the Cambrian Rocks:-- + + (1) 'Siluria.' Sir Roderick Murchison. 5th ed., pp. 21-46. + (2) 'Synopsis of the Classification of the British Palæozoic Rocks.' + Sedgwick. Introduction to the 3d Fasciculus of the 'Descriptions + of British Palæozoic Fossils in the Woodwardian Museum,' + by F. M'Coy, pp. i-xcviii, 1855. + (3) 'Catalogue of the Cambrian and Silurian Fossils in the Geological + Museum of the University of Cambridge.' Salter. With a Preface + by Prof. Sedgwick. 1873. + (4) 'Thesaurus Siluricus.' Bigsby. 1868. + (5) "History of the Names Cambrian and Silurian." Sterry + Hunt.--'Geological Magazine.' 1873. + (6) 'Système Silurien du Centre de la Bohême.' Barrande. Vol. I. + (7) 'Report of Progress of the Geological Survey of Canada, from its + Commencement to 1863,' pp. 87-109. + (8) 'Acadian Geology.' Dawson. Pp. 641-657. + (9) "Guide to the Geology of New York," Lincklaen; and "Contributions + to the Palæontology of New York," James Hall.--'Fourteenth + Report on the State Cabinet.' 1861. +(10) 'Palæozoic Fossils of Canada.' Billings. 1865. +(11) 'Manual of Geology.' Dana. Pp. 166-182. 2d ed. 1875. +(12) "Geology of North Wales," Ramsay; with Appendix on the + Fossils, Salter.--'Memoirs of the Geological Survey of Great + Britain,' vol. iii. 1866. +(13) "On the Ancient Rocks of the St David's Promontory, South Wales, + and their Fossil Contents." Harkness and Hicks.--' Quart. + Journ. Geol. Soc.,' xxvii. 384-402. 1871. +(14) "On the Tremadoc Rocks in the Neighbourhood of St David's, + South Wales, and their Fossil Contents." Hicks.--'Quart. + Journ. Geol. Soc.,' xxix. 39-52. 1873. + +In the above list, allusion has necessarily been omitted to numerous +works and memoirs on the Cambrian deposits of Sweden and Norway, +Central Europe, Russia, Spain, and various parts of North America, +as well as to a number of important papers on the British Cambrian +strata by various well-known observers. Amongst these latter +may be mentioned memoirs by Prof. Phillips, and Messrs Salter, +Hicks, Belt, Plant, Homfray, Ash, Holl, &c. + + + + +CHAPTER IX. + +THE LOWER SILURIAN PERIOD. + +The great system of deposits to which Sir Roderick Murchison +applied the name of "Silurian Rocks" reposes directly upon the +highest Cambrian beds, apparently without any marked unconformity, +though with a considerable change in the nature of the fossils. The +name "Silurian" was originally proposed by the eminent geologist +just alluded to for a great series of strata lying below the Old +Red Sandstone, and occupying districts in Wales and its borders +which were at one time inhabited by the "Silures," a tribe of +ancient Britons. Deposits of a corresponding age are now known +to be largely developed in other parts of England, in Scotland, +and in Ireland, in North America, in Australia, in India, in +Bohemia, Saxony, Bavaria, Russia, Sweden and Norway, Spain, and +in various other regions of less note. In some regions, as in +the neighbourhood of St Petersburg, the Silurian strata are found +not only to have preserved their original horizontality, but +also to have retained almost unaltered their primitive soft and +incoherent nature. In other regions, as in Scandinavia and many +parts of North America, similar strata, now consolidated into +shales, sandstones, and limestones, may be found resting with +a very slight inclination on still older sediments. In a great +many regions, however, the Silurian deposits are found to have +undergone more or less folding, crumpling, and dislocation, +accompanied by induration and "cleavage" of the finer and softer +sediments; whilst in some regions, as in the Highlands of Scotland, +actual "metamorphism" has taken place. In consequence of the +above, Silurian districts usually present the bold, rugged, and +picturesque outlines which are characteristic of the older +"Primitive" rocks of the earth's crust in general. In many instances, +we find Silurian strata rising into mountain-chains of great +grandeur and sublimity, exhibiting the utmost diversity of which +rock-scenery is capable, and delighting the artist with endless +changes of valley, lake, and cliff. Such districts are little +suitable for agriculture, though this is often compensated for +by the valuable mineral products contained in the rocks. On the +other hand, when the rocks are tolerably soft and uniform in +their nature, or when few disturbances of the crust of the earth +have taken place, we may find Silurian areas to be covered with +an abundant pasturage or to be heavily timbered. + +Under the head of "Silurian Rocks," Sir Roderick Murchison included +all the strata between the summit of the "Longmynd." beds and the +Old Red Sandstone, and he divided these into the two great groups +of the _Lower_ Silurian and _Upper_ Silurian. It is, however, now +generally admitted that a considerable portion of the basement +beds of Murchison's Silurian series must be transferred---if only +upon palæontological grounds--to the Upper Cambrian, as has here +been done; and much controversy has been carried on as to the proper +nomenclature of the Upper Silurian and of the remaining portion +of Murchison's Lower Silurian. Thus, some would confine the name +"Silurian" exclusively to the Upper Silurian, and would apply the +name of "Cambro-Silurian" to the Lower Silurian, or would include +all beds of the latter age in the "Cambrian" series of Sedgwick. +It is not necessary to enter into the merits of these conflicting +views. For our present purpose, it is sufficient to recognise +that there exist two great groups of rocks between the highest +Cambrian beds, as here defined, and the base of the Devonian or +Old Red Sandstone. These two great groups are so closely allied +to one another, both physically and palæontologically, that many +authorities have established a third or intermediate group (the +"Middle Silurian"), by which a passage is made from one into +the other. This method of procedure involves disadvantages which +appear to outweigh its advantages; and the two groups in question +are not only generally capable of very distinct stratigraphical +separation, but at the same time exhibit, together with the alliances +above spoken of, so many and such important palæontological +differences, that it is best to consider them separately. We +shall therefore follow this course in the present instance; and +pending the final solution of the controversy as to Cambrian and +Silurian nomenclature, we shall distinguish these two groups +of strata as the "Lower Silurian" and the "Upper Silurian." + +The _Lower Silurian Rocks_ are known already to be developed +in various regions; and though their _general_ succession in +these areas is approximately the same, each area exhibits +peculiarities of its own, whilst the subdivisions of each are +known by special names. All, therefore, that can be attempted +here, is to select two typical areas--such as Wales and North +America and to briefly consider the grouping and divisions of +the Lower Silurian in each. + +In Wales, the line between the Cambrian and Lower Silurian is +somewhat ill-defined, and is certainly not marked by any strong +unconformity. There are, however; grounds for accepting the line +proposed, for palæontological reasons, by Dr Hicks, in accordance +with which the Tremadoc Slates ("Lower Tremadoc" of Salter) become +the highest of the Cambrian deposits of Britain. If we take this +view, the Lower Silurian rocks of Wales and adjoining districts +are found to have the following _general_ succession from below +upwards (fig. 34):-- + +1. The _Arenig Group_.--This group derives its name from the +Arenig mountains, where it is extensively developed. It consists +of about 4000 feet of slates, shales, and flags, and is divisible +into a lower, middle, and upper division, of which the former +is often regarded as Cambrian under the name of "Upper Tremadoc +Slates." + +2. The _Llandeilo Group_.--The thickness of this group varies +from about 4000 to as much as 10,000 feet; but in this latter +case a great amount of the thickness is made up of volcanic ashes +and interbedded traps. The sedimentary beds of this group are +principally slates and flags, the latter occasionally with calcareous +bands; and the whole series can be divided into a lower, middle, +and upper Llandeilo division, of which the last is the most +important. The name of "Llandeilo" is derived from the town of +the same name in Wales, where strata of this age were described +by Murchison. + +3. The _Caradoc_ or _Bala Group_.--The alternative names of this +group are also of local origin, and are derived, the one from +Caer Caradoc in Shropshire, the other from Bala in Wales, strata +of this age occurring in both localities. The series is divided +into a lower and upper group, the latter chiefly composed of +shales and flags, and the former of sandstones and shales, together +with the important and interesting calcareous band known as the +"Bala Limestone." The thickness of the entire series varies from +4000 to as much as 12,000 feet, according as it contains more +or less of interstratified igneous rocks. + +4. The _Llandovery Group_ (Lower Llandovery of Murchison).--This +series, as developed near the town of Llandovery, in +Caermarthenshire, consists of less than 1000 feet of conglomerates, +sandstones, and shales. It is probable, however, that the little +calcareous band known as the "Hirnant Limestone," together with +certain pale-coloured slates which lie above the Bala Limestone, +though usually referred to the Caradoc series, should in reality +be regarded as belonging to the Llandovery group. + +The general succession of the Lower Silurian strata of Wales +and its borders, attaining a maximum thickness (along with +contemporaneous igneous matter) of nearly 30,000 feet, is +diagramatically represented in the annexed sketch-section (fig. +34):-- + +[Illustration: Fig 34. GENERALIZED SECTION OF THE LOWER SILURIAN +ROCKS OF WALES.] + +In North America, both in the United States and in Canada, the +Silurian rocks are very largely developed, and may be regarded +as constituting an exceedingly full and typical series of the +deposits of this period. The chief groups of the Silurian rocks +of North America are as follows, beginning, as before, with the +lowest strata, and proceeding upwards (fig. 35):-- + +1. _Quebec Group_.--This group is typically developed in the +vicinity of Quebec, where it consists of about 5000 feet of strata, +chiefly variously-coloured shales, together with some sandstones +and a few calcareous bands. It contains a number of peculiar +Graptolites, by which it can be identified without question with +the Arenig group of Wales and the corresponding Skiddaw Slates +of the North of England. It is also to be noted that numerous +Trilobites of a distinct Cambrian _facies_ have been obtained in +the limestones of the Quebec group, near Quebec. These fossils, +however, have been exclusively obtained from the limestones of +the group; and as these limestones are principally calcareous +breccias or conglomerates, there is room for believing that these +primordial fossils are really derived, in part at any rate, from +fragments of an upper Cambrian limestone. In the State of New +York, the Graptolitic shales of Quebec are wanting; and the base +of the Silurian is constituted by the so-called "Calciferous +Sand-rock" and "Chazy Limestone."[11] The first of these is +essentially and typically calcareous, and the second is a genuine +limestone. + +[Footnote 11: The precise relations of the Quebec shales with +Graptolites (Levis Formation) to the Calciferous and Chazy beds +are still obscure, though there seems little doubt but that the +Quebec Shales are superior to the Calciferous Sand-rock.] + +2. The _Trenton Group_.--This is an essentially calcareous group, +the various limestones of which it is composed being known as +the "Bird's-eye," "Black River," and "Trenton" Limestones, of +which the last is the thickest and most important. The thickness +of this group is variable, and the bands of limestone in it are +often separated by beds of shale. + +3. The _Cincinnati Group_ (Hudson River Formation[12]).--This +group consists essentially of a lower series of shales, often +black in colour and highly charged with bituminous matter (the +"Utica Slates "), and of an upper series of shales, sandstones, and +limestones (the "Cincinnati" rocks proper). The exact parallelism +of the Trenton and Cincinnati groups with the subdivisions of the +Welsh Silurian series can hardly be stated positively. Probably +no precise equivalency exists; but there can be no doubt but that +the Trenton and Cincinnati groups correspond, as a whole, with the +Llandeilo and Caradoc groups of Britain. The subjoined diagrammatic +section (fig. 35) gives a general idea of the succession of the +Lower Silurian rocks of North America:-- + +[Illustration: Fig 35. GENERALIZED SECTION OF THE LOWER SILURIAN +ROCKS OF NORTH AMERICA.] + +[Illustration: Fig. 36.--_Licrophycus Ottawaensis_ a "Fucoid," +from the Trenton Limestone (Lower Silurian) of Canada. (After +Billings.)] + +[Footnote 12: There is some difficulty about the precise nomenclature +of this group. It was originally called the "Hudson River Formation;" +but this name is inappropriate, as rocks of this age hardly touch +anywhere the actual Hudson River itself, the rocks so called +formerly being now known to be of more ancient date. There is +also some want of propriety in the name of "Cincinnati Group," +since the rocks which are known under this name in the vicinity of +Cincinnati itself are the representatives of the Trenton Limestone, +Utica Slates, and the old Hudson River group, inseparably united +in what used to be called the "Blue Limestone Series."]. + +Of the _life_ of the Lower Silurian period we have record in +a vast number of fossils, showing that the seas of this period +were abundantly furnished with living denizens. We have, however, +in the meanwhile, no knowledge of the land-surfaces of the period. +We have therefore no means of speculating as to the nature of +the terrestrial animals of this ancient age, nor is anything +known with certainty of any land-plants which may have existed. +The only relics of vegetation upon which a positive opinion can +be expressed belong to the obscure group of the "Fucoids," and +are supposed to be the remains of sea-weeds. Some of the fossils +usually placed under this head are probably not of a vegetable +nature at all, but others (fig. 36) appear to be unquestionable +plants. The true affinities of these, however, are extremely +dubious. All that can be said is, that remains which appear to +be certainly vegetable, and which are most probably due to marine +plants, have been recognised nearly at the base of the Lower +Silurian (Arenig), and that they are found throughout the series +whenever suitable conditions recur. + +The Protozoans appear to have flourished extensively in the Lower +Silurian seas, though to a large extent under forms which are +still little understood. We have here for the first time the +appearance of Foraminifera of the ordinary type--one of the most +interesting observations in this collection being that made by +Ehrenberg, who showed that the Lower Silurian sandstones of the +neighbourhood of St Petersburg contained casts in glauconite of +Foraminiferous shells, some of which are referable to the existing +genera _Rotalia_ and _Texularia_. True _Sponges_, belonging to +that section of the group in which the skeleton is calcareous, +are also not unknown, one of the most characteristic genera being +_Astylospongia_ (fig. 37). In this genus are included more or +less globular, often lobed sponges, which are believed not to +have been attached to foreign bodies. In the form here figured +there is a funnel-shaped cavity at the summit; and the entire +mass of the sponge is perforated, as in living examples, by a +system of canals which convey the sea-water to all parts of the +organism. The canals by which the sea-water gains entrance open +on the exterior of the sphere, and those by which it again escapes +from the sponge open into the cup-shaped depression at the summit. + +[Illustration: Fig. 37.--_Astylospongia proemorsa_, cut vertically +so as to exhibit the canal-system in the interior. Lower Silurian, +Tennessee. (After Ferdinand Roemer.)] + +The most abundant, and at the same time the least understood, +of Lower Silurian Protozoans belong, however, to the genera +_Stromatopora_ and _Receptaculites_, the structure of which can +merely be alluded to here. The specimens of _Stromatopora_ (fig. +38) occur as hemispherical, pear-shaped, globular, or irregular +masses, often of very considerable size, and sometimes demonstrably +attached to foreign bodies. In their structure these masses consist +of numerous thin calcareous laminæ, usually arranged concentrically, +and separated by narrow interspaces. These interspaces are generally +crossed by numerous vertical calcareous pillars, giving the vertical +section of the fossil a lattice-like appearance. There are also +usually minute pores in the concentric laminæ, by which the +successive interspaces are placed in communication; and sometimes +the surface presents large rounded openings, which appear to +correspond with the water-canals of the Sponges. Upon the whole, +though presenting some curious affinities to the calcareous Sponges, +_Stromatopora_ is perhaps more properly regarded as a gigantic +_Foraminifer_. If this view be correct, it is of special interest +as being probably the nearest ally of _Eozoön_, the general +appearance of the two being strikingly similar, though their +minute structure is not at all the same. Lastly, in the fossils +known as _Receptaculites_ and _Ischadites_ we are also presented +with certain singular Lower Silurian Protozoans, which may with +great probability be regarded as gigantic _Foraminifera_. Their +structure is very complex; but fragments are easily recognised +by the fact that the exterior is covered with numerous rhomboidal +calcareous plates, closely fitting together, and arranged in +peculiar intersecting curves, presenting very much the appearance +of the engine-turned case of a watch. + +[Illustration: Fig. 38.--A small and perfect specimen of +_Stromatopora rugosa_, of the natural size, from the Trenton +Limestone of Canada. (After Billings.)] + +Passing next to the sub-kingdom of _Coelenterate_ animals (Zoophytes, +Corals, &c.), we find that this great group, almost or wholly +absent in the Cambrian, is represented in Lower Silurian deposits +by a great number of forms belonging on the one hand to the true +Corals, and en the other hand to the singular family of the +_Graptolites_. If we except certain plant-like fossils which +probably belong rather to the Sertularians or the Polyzoans (e.g., +_Dictyonema, Dendrograptus_, &c.), the family of the _Graptolites_ +may be regarded as exclusively Silurian in its distribution. Not +only is this the case, but it attained its maximum development +almost upon its first appearance, in the Arenig Rocks; and whilst +represented by a great variety of types in the Lower Silurian; +it only exists in the Upper Silurian in a much diminished form. +The _Graptolites_ (Gr. _grapho_, I write; _lithos_, stone) were +so named by Linnæus, from the resemblance of some of them to +written or pencilled marks upon the stone, though the great +naturalist himself did not believe them to be true fossils at +all. They occur as linear or leaf-like bodies, sometimes simple, +sometimes compound and branched; and no doubt whatever can be +entertained as to their being the skeletons of composite organisms, +or colonies of semi-independent animals united together by a common +fleshy trunk, similar to what is observed in the colonies of the +existing Sea-firs (Sertularians). This fleshy trunk or common +stem of the colony was protected by a delicate horny sheath, and +it gave origin to the little flower-like "polypites," which +constituted the active element of the whole assemblage. These +semi-independent beings were, in turn, protected each by a little +horny cup or cell, directly connected with the common sheath +below, and terminating above in an opening through which the +polypite could protrude its tentacled head or could again withdraw +itself for safety. The entire skeleton, again, was usually, if +not universally, supported by a delicate horny rod or "axis," +which appears to have been hollow, and which often protrudes to +a greater or less extent beyond one or both of the extremities +of the actual colony. + +The above gives the elementary constitution of any _Graptolite_, +but there are considerable differences as to the manner in which +these elements are arranged and combined. In some forms the common +stem of the colony gives origin to but a single row of cells +on one side. If the common stem is a simple, straight, or +slightly-curved linear body, then we have the simplest form of +Graptolite known (the genus _Monograptus_); and it is worthy of +note that these simple types do not come into existence till +comparatively late (Llandeilo), and last nearly to the very close +of the Upper Silurian. In other cases, whilst there is still but +a single row of cells, the colony may consist of two of these +simple stems springing from a common point, as in the so-called +"twin Graptolites" (_Didymograptus_, fig. 40). This type is entirely +confined to the earlier portion of the Lower Silurian period +(Arenig and Llandeilo). In other cases, again, there may be four +of such stems springing from a central point (_Tetragraptus_). +Lastly, there are numerous complex forms (such as _Dichograptus, +Loganograptus_, &c.) in which there are eight or more of these +simple branches, all arising from a common centre (fig. 39), +which is sometimes furnished with a singular horny disc. These +complicated branching forms, as well as the _Tetragrapti_, are +characteristic of the horizon of the Arenig group. Similar forms, +often specifically identical, are found at this horizon in Wales, +in the great series of the Skiddaw Slates of the north of England, +in the Quebec group in Canada, in equivalent beds in Sweden, and +in certain gold-bearing slates of the same age in Victoria in +Australia. + +[Illustration: Fig. 39.--_Dichograptus octobrachiatus_, a branched, +"unicellular" Graptolite from the Skiddaw and Quebec Groups (Arenig). +(After Hall.)] + +In another great group of Graptolites (including the genera +_Diplograptus, Dicranograptus, Climacograptus_, &c.) the common +stem of the colony gives origin, over part or the whole or its +length, to _two_ rows of cells, one on each side (fig. 41). These +"double-celled" Graptolites are highly characteristic of the Lower +Silurian deposits; and, with an exception more apparent than real +in Bohemia, they are exclusively confined to strata of Lower +Silurian age, and are not known to occur in the Upper Silurian. +Lastly, there is a group of Graptolites (_Phyllograptus_, fig. +42) in which the colony is leaf-like in form, and is composed +of _four_ rows of cells springing in a cross-like manner from +the common stem. These forms are highly characteristic of the +Arenig group. + +[Illustration: Fig. 40.--Central portion of the colony of +_Didymegraptus divaricatus_, Upper Llandeilo, Dumfresshire. +(Original.)] + +[Illustration: Fig. 41.--Examples of _Diplograptus pristis_, +showing variations in the appendages at the base. Upper Llandeilo, +Dumfriesshire. (Original.)] + +[Illustration: Fig. 42.--Group of individuals of _Phyllograptus +typus_, from the Quebec group of Canada. (After Hall.) One of +the four rows of cells is hidden on the under surface.] + +The Graptolites are usually found in dark-coloured, often black +shales, which sometimes contain so much carbon as to become +"anthracitic." They may be simply carbonaceous; but they are +more commonly converted into iron-pyrites, when they glitter +with the brilliant lustre of silver as they lie scattered on the +surface of the rock, fully deserving in their metallic tracery +the name of "written stones." They constitute one of the most +important groups of Silurian fossils, and are of the greatest +value in determining the precise stratigraphical position of +the beds in which they occur. They present, however, special +difficulties in their study; and it is still a moot point as +to their precise position in the zoological scale. The balance +of evidence is in favour of regarding them as an ancient and +peculiar group of the Sea-firs (Hydroid Zoophytes), but some +regard them as belonging rather to the Sea-mosses (_Polyzoa_). +Under any circumstances, they cannot be directly compared either +with the ordinary Sea-firs or the ordinary Sea-mosses; for these +two groups consist of fixed organisms, whereas the Graptolites +were certainly free-floating creatures, living at large in the +open sea. The only Hydroid Zoophytes or Polyzoans which have +a similar free mode of existence, have either no skeleton at +all, or have hard structures quite unlike the horny sheaths of +the Graptolites. + +The second great group of Coelenterate animals (_Actinozoa_) +is represented in the Lower Silurian rocks by numerous Corals. +These, for obvious reasons, are much more abundant in regions +where the Lower Silurian series is largely calcareous (as in +North America) than in districts like Wales, where limestones +are very feebly developed. The Lower Silurian Corals, though +the first of their class, and presenting certain peculiarities, +may be regarded as essentially similar in nature to existing +Corals. These, as is well known, are the calcareous skeletons of +animals--the so-called "Coral-Zoophytes"--closely allied to the +common Sea-anemones in structure and habit. A _simple_ coral (fig. +43) consists of a calcareous cup embedded in the soft tissues of +the flower-like polype, and having at its summit a more or less +deep depression (the "calice") in which the digestive organs +are contained. The space within the coral is divided into +compartments by numerous vertical calcareous plates (the "septa"), +which spring from the inside of the wall of the cup, and of which +some generally reach the centre. _Compound_ corals, again (fig. +44), consist of a greater or less number of structures similar +in structure to the above, but united together in different ways +into a common mass. _Simple_ corals, therefore, are the skeletons +of _single_ and independent polypes; whilst _compound_ corals +are the skeletons of assemblages or colonies of similar polypes, +living united with one another another as an organic community. + +[Illustration: Fig. 43.--_Zaphrentis Stokesi_, a simple "cup-coral," +Upper Silurian, Canada. (After Billings.)] + +[Illustration: Fig. 44.--Upper surface of a mass of _Strombodes +pentagonus_. Upper Silurian, Canada. (After Billings.)] + +In the general details of their structure, the Lower Silurian +Corals do not differ from the ordinary Corals of the present +day. The latter, however, have the vertical calcareous plates +of the coral ("septa") arranged in multiples of six or five; +whereas the former have these structures arranged in multiples +of four, and often showing a cross-like disposition. For this +reason, the common Lower Silurian Corals are separated to form +a distinct group under the name of _Rugose_ Corals or _Rugosa_. +They are further distinguished by the fact that the cavity of +the coral ("visceral chamber") is usually subdivided by more +or less numerous horizontal calcareous plates or partitions, +which divide the coral into so many tiers or storeys, and which +are known as the "tabulæ" (fig. 45). + +[Illustration: Fig. 45.--_Columnaria alveolata_, a Rugose compound +coral, with imperfect septa, but having the corallites partitioned +off into storeys by "tabulæ." Lower Silurian, Canada. (After +Billings.)] + +In addition to the Rugose Corals, the Lower Silurian rocks contain +a number of curious compound corals, the tubes of which have +either no septa at all or merely rudimentary ones, but which +have the transverse partitions or "tabulæ" very highly developed. +These are known as the _Tabulate Corals_; and recent researches +on some of their existing allies (such as _Heliopora_) have shown +that they are really allied to the modern Sea-pens, Organ-pipe +Corals, and Red Coral, rather than to the typical stony Corals. +Amongst the characteristic Rugose Corals of the Lower Silurian +may be mentioned species belonging to the genera _Columnaria, +Favistella, Streptelasma_, and _Zaphrentis_; whilst amongst the +"Tabulate" Corals, the principal forms belong to the genera +_Choetetes, Halysites_ (the Chain-coral), _Constellaria_, and +_Heliolites_. These groups of the Corals, however, attain a greater +development at a later period, and they will be noticed more +particularly hereafter. + +[Illustration: Fig. 46.--Group of Cystideans. A, _Caryocrinus +ornatus_,[13] Upper Silurian, America; B, _Pleurocystites squamosus_, +showing two short "arms," Lower Silurian, Canada; C, _Pseudocrinus +bifasciatus_, Upper Silurian, England; D, _Lepadocrinus Gebhartii_, +Upper Silurian, America. (After Hall, Billings, and Salter.)] + +[Footnote 13: The genus _Caryocrinus_ is sometimes regarded as +properly belonging to the _Crinoids_, but there seem to be good +reasons for rather considering it as an abnormal form of +_Cystidean_.] + +Passing onto higher animals, we find that the class of the +_Echinodermata_ is represented by examples of the Star-fishes +(_Asteroidea_), the Sea-lilies (_Crinoidea_), and the peculiar +extinct group of the Cystideans (_Cystoidea_), with one or two of +the Brittle-stars (_Ophiuroidea_)--the Sea-urchins (_Echinoidea_) +being still wanting. The Crinoids, though in some places extremely +numerous, have not the varied development that they possess in +the Upper Silurian, in connection with which their structure will +be more fully spoken of. In the meanwhile, it is sufficient to +note that many of the calcareous deposits of the Lower Silurian +are strictly entitled to the name of "Crinoidal limestones," +being composed in great part of the detached joints, and plates, +and broken stems, of these beautiful but fragile organisms (see +fig. 12). Allied to the Crinoids are the singular creatures which +are known as _Cystideans_ (fig. 46). These are generally composed +of a globular or ovate body (the "calyx"), supported upon a short +stalk (the "column"), by which the organism was usually attached +to some foreign body. The body was enclosed by closely-fitting +calcareous plates, accurately jointed together; and the stem was +made up of numerous distinct pieces or joints, flexibly united +to each other by membrane. The chief distinction which strikes +one in comparing the Cystideans with the Crinoids is, that the +latter are always furnished, as will be subsequently seen, with +a beautiful crown of branched and feathery appendages, springing +from the summit of the calyx, and which are composed of innumerable +calcareous plates or joints, and are known as the "arms." In the +Cystideans, on the other hand, there are either no "arms" at all, +or merely short, unbranched, rudimentary arms. The Cystideans are +principally, and indeed nearly exclusively, Silurian fossils; +and though occurring in the Upper Silurian in no small numbers, +they are pre-eminently characteristic of the Llandeilo-Caradoc +period of Lower Silurian time. They commenced their existence, +so far as known, in the Upper Cambrian; and though examples are +not absolutely unknown in later periods, they are pre-eminently +characteristic of the earlier portion of the Palæozoic epoch. + +[Illustration: Fig. 47.--Lower Silurian Crustaceans. a, _Asaphus +tyrannus_, Upper Llandeilo; b. _Ogygia Buchii_, Upper Llandeilo; +c, _Trinucleus concentricus_, Caradoc; d, _Caryocaris Wrightii_, +Arenig (Skiddaw Slates); e, _Beyrichia complicata_, natural size and +enlarged, Upper Llandeilo and Caradoc; f, _Primitia strangulata_, +Caradoc: g. Head-shield of _Calymene Blumenbachii_, var. +_brevicapitata_, Caradoc; h, Head-shield of _Triarthrus Becki_ +(Utica Slates), United States: i, Shield of _Leperditia +Canadensis_, var. _Josephiana_, of the natural size, Trenton +Limestone, Canada; j, The same, viewed from the front. (After +Salter, M'Coy, Rupert Jones, and Dana.)] + +The Ringed Worms (_Annelides_) are abundantly represented in the +Lower Silurian, but principally by tracks and burrows similar +in essential respects to those which occur so commonly in the +Cambrian formation, and calling for no special comment. Much more +important are the _Articulate_ animals, represented as heretofore, +wholly by the remains of the aquatic group of the _Crustaceans_. +Amongst these are numerous little bivalved forms--such as species +of _Primitia_ (fig. 47, f), _Beyrichia_ (fig. 47, e), and +_Leperditia_ (fig. 47, i and j). Most of these are very small, +varying from the size of a pin's head up to that of a hemp seed; +but they are sometimes as large as a small bean (fig. 47, i), +and they are commonly found in myriads together in the rock. As +before said, they belong to the same great group as the living +Water-fleas (_Ostracoda_). Besides these, we find the pod-shaped +head-shields of the shrimp-like Phyllopods--such as _Caryocaris_ +(fig. 47, d) and _Ceratiocaris_. More important, however, than +any of these are the _Trilobites_, which may be considered as +attaining their maximum development in the Lower Silurian. The +huge _Paradoxides_ of the Cambrian have now disappeared, and with +them almost all the principal and characteristic "primordial" +genera, save _Olenus_ and _Agnostus_. In their place we have a +great number of new forms--some of them, like the great _Asaphus +tyrannus_ of the Upper Llandeilo (fig. 47, a), attaining a +length of a foot or more, and thus hardly yielding in the matter +of size to their ancient rivals. Almost every subdivision of the +Lower Silurian series has its own special and characteristic +species of Trilobites; and the study of these is therefore of +great importance to the geologist. A few widely-dispersed and +characteristic species have been here figured (fig. 47); and +the following may be considered as the principal Lower Silurian +genera--_Asaphus, Ogygia, Cheirurus, Ampyx, Caiymene, Trinucleus, +Lichas, Illoenus, Æglina, Harpes, Remopleurides, Phacops, Acidaspis_, +and _Homalonotus_, a few of them passing upwards under new forms +into the Upper Silurian. + +Coming next to the _Mollusca_, we find the group of the Sea-mosses +and Sea-mats (_Polyzoa_) represented now by quite a number of forms. +Amongst these are examples of the true Lace-corals (_Retepora_ +and _Fenestella_), with their netted fan-like or funnel-shaped +fronds; and along with these are numerous delicate encrusting +forms, which grew parasitically attached to shells and corals +(_Hippothoa, Alecto_, &c.); but perhaps the most characteristic +forms belong to the genus _Ptilodictya_ (figs. 48 and 49). In +this group the frond is flattened, with thin striated edges, +sometimes sword-like or scimitar-shaped, but often more or less +branched; and it consists of two layers of cells, separated by +a delicate membrane, and opening upon opposite sides. Each of +these little chambers or "cells" was originally tenanted by a +minute animal, and the whole thus constituted a compound organism +or colony. + +[Illustration: Fig. 48.--_Ptilodictya falciformis_. a, Small +specimen of the natural size; b, Cross-section, showing the +shape of the frond; c, Portion of the surface, enlarged. Trenton +Limestone and Cincinnati Group, America. (Original.)] + +[Illustration: Fig. 49.--A, _Ptilodictya acuta_; B, _Ptilodictya +Schafferi_. a, Fragment, of the natural size; b, Portion, +enlarged to show the cells. Cincinnati Group of Ohio and Canada. +(Original.)] + +[Illustration: Fig. 50.--Lower Silurian Brachiopods. a and +a', _Orthis biforata_, Llandeilo-Caradoc, Britain and America: +b, _Orthis flabellulum_, Caradoc, Britain: c, _Orthis subquadrata_, +Cincinnati Group, America; c', Interior of the dorsal valve of +the same: d, _Strophomena deltoidea_, Llandeilo-Caradoc, Britain +and America. (After Meek, Hall, and Salter.)] + +The Lamp-shells or _Brachiopods_ are so numerous, and present +such varied types, both in this and the succeeding period of +the Upper Silurian, that the name of "Age of Brachiopods" has +with justice been applied to the Silurian period as a whole. It +would be impossible here to enter into details as to the many +different forms of Brachiopods which present themselves in the +Lower Silurian deposits; but we may select the three genera _Orthis, +Strophomena_, and _Leptoena_ for illustration, as being specially +characteristic of this period, though not exclusively confined to it. +The numerous shells which belong to the extensive and cosmopolitan +genus _Orthis_ (fig. 50, a, b, c, and fig. 51, c and d), +are usually more or less transversely-oblong or subquadrate, the +two valves (as more or less in all the Brachiopods) of unequal +sizes, generally more or less convex, and marked with radiating +ribs or lines. The valves of the shell are united to one another +by teeth and sockets, and there is a straight hinge-line. The beaks +are also separated by a distinct space ("hinge-area"), formed in +part by each valve, which is perforated by a triangular opening, +through which, in the living condition, passed a muscular cord +attaching the shell to some foreign object. The genus _Strophomena_ +(fig. 50, d, and 51, a and b) is very like _Orthis_ in +general character; but the shell is usually much flatter, one +or other valve often being concave, the hinge-line is longer, +and the aperture for the emission of the stalk of attachment is +partially closed by a calcareous plate. In _Leptoena_, again +(fig. 51, e), the shell is like _Strophomena_ in many respects, +but generally comparatively longer, often completely semicircular, +and having one valve convex and the other valve concave. Amongst +other genera of Brachiopods which are largely represented in the +Lower Silurian rocks may be mentioned _Lingula, Crania, Discina, +Trematis, Siphonotreta, Acrotreta, Rhynchonella_, and _Athyris_; +but none of these can claim the importance to which the three +previously-mentioned groups are entitled. + +[Illustration: Fig. 51.--Lower Silurian Brachiopods, a, _Strophomena +alternata_, Cincinnati Group, America; b, _Strophomena filitexta, +Trenton and Cincinnati Groups, America; c, _Orthis testudinaria_, +Caradoc, Europe, and America; d, d', _Orthis plicateila_, Cincinnati +Group, America; e, e', e'', _Leptoena sericea_, Llandeilo and +Caradoc, Europe and America. (After Meek, Hall, and the Author.)] + +The remaining Lower Silurian groups of _Mollusca_ can be but +briefly glanced at here. The Bivalves (_Lamellibranchiata_) find +numerous representatives, belonging to such genera as _Modiolopsis, +Ctenodonta, Orthonota, Paloearca, Lyrodesma, Ambonychia_, and +_Cleidophorus_. The Univalves (_Gasteropoda_) are also very numerous, +the two most important genera being _Murchisonia_ (fig. 52) and +_Pleurotomaria_. In both these groups the outer lip of the shell +is notched; but the shell in the former is elongated and turreted, +whilst in the latter it is depressed. The curious oceanic Univalves +known as the _Heteropods_ are also very abundant, the principal +forms belonging to _Bellerophon_ and _Maclurea_. In the former +(fig. 53) there is a symmetrical convoluted shell, like that of +the Pearly Nautilus in shape, but without any internal partitions, +and having the aperture often expanded and notched behind. The +species of _Maclurea_ (fig. 54) are found both in North America +and in Scotland, and are exclusively confined to the Lower Silurian +period, so far as known. They have the shell coiled into a flat +spiral, the mouth being furnished with a very curious, thick, +and solid lid or "operculum." The Lower Silurian _Pteropods_, +or "Winged snails," are numerous, and belong principally to the +genera _Theca, Conularia_, and _Tentaculites_, the last-mentioned +of these often being extremely abundant in certain strata. + +[Illustration: Fig. 52.--_Murchisonia gracilis_, Trenton Limestone, +America. (After Billings.)] + +[Illustration: Fig. 53.--Different views of _Bellerophon Argo_, +Trenton Limestone, Canada. (After Billings.)] + +[Illustration: Fig. 54.--Different views of _Maclurea crenulata_, +Quebec Group, Newfoundland. (After Billings.)] + +[Illustration: Fig. 55.--Fragment of _Orthoceras crebriseptum_, +Cincinnati Group, North America, of the natural size. The lower +figure section showing the air-chambers, and the form and position +of the siphuncle. (After Billings.)] + +[Illustration: Fig. 56.--[14] Restoration of Orthoceras, the shell +being supposed to be divided vertically, and only its upper part +being shown. a, Arms; f, Muscular tube ("funnel") by which +water is expelled from the mantle-chamber; c, Air-chambers; +s, Siphuncle.] + +[Footnote 14: This illustration is taken from a rough sketch +made by the author many years ago, but he is unable to say from +what original source it was copied.] + +Lastly, the Lower Silurian Rocks have yielded a vast number of +chambered shells, referable to animals which belong to the same +great division as the Cuttle-fishes (the _Cephalopoda_), and +of which the Pearly Nautilus is the only living representative +at the present day. In this group of _Cephalopods_ the animal +possesses a well-developed external shell, which is divided into +chambers by shelly partitions ("septa"). The animal lives in +the last-formed and largest chamber of the shell, to which it +is organically connected by muscular attachments. The head is +furnished with long muscular processes or "arms," and can be +protruded from the mouth of the shell at will, or again withdrawn +within it. We learn, also, from the Pearly Nautilus, that these +animals must have possessed two pairs of breathing organs or +"gills;" hence all these forms are grouped together under the +name of the "Tetrabranchiate" Cephalopods (Gr. _tetra_, four; +_bragchia_, gill). On the other hand, the ordinary Cuttle-fishes +and Calamaries either possess an internal skeleton, or if they +have an external shell, it is not chambered; their "arms" are +furnished with powerful organs of adhesion in the form of suckers; +and they possess only a single pair of gills. For this last reason +they are termed the "Dibranchiate" Cephalopods (Gr. _dis_, twice; +_bragchia_, gill). No trace of the true Cuttle-fishes has yet +been found in Lower Silurian deposits; but the Tetrabranchiate +group is represented by a great number of forms, sometimes of +great size. The principal Lower Silurian genus is the well-known +and widely-distributed _Orthoceras_ (fig. 55). The shell in this +genus agrees with that of the existing _Pearly Nautilus_, in +consisting of numerous chambers separated by shelly partitions +(or septa), the latter being perforated by a tube which runs the +whole length of the shell after the last chamber, and is known +as the "siphuncle" (fig. 56, s). The last chamber formed is the +largest, and in it the animal lives. The chambers behind this +are apparently filled with some gas secreted by the animal itself; +and these are supposed to act as a kind of float, enabling the +creature to move with ease under the weight of its shell. The +various air-chambers, though the siphuncle passes through them, +have no direct connection with one another; and it is believed +that the animal has the power of slightly altering its specific +gravity, and thus of rising or sinking in the water by driving +additional fluid into the siphuncle or partially emptying it. +The _Orthoceras_ further agrees with the Pearly Nautilus in the +fact that the partitions or septa separating the different +air-chambers are simple and smooth, concave in front and convex +behind, and devoid of the elaborate lobation which they exhibit +in the Ammonites; whilst the siphuncle pierces the septa either +in the centre or near it. In the Nautilus, however, the shell is +coiled into a flat spiral; whereas in _Orthoceras_ the shell is +a straight, longer or shorter cone, tapering behind, and gradually +expanding towards its mouth in front. The chief objections to +the belief that the animal of the _Orthoceras_ was essentially +like that of the Pearly Nautilus are--the comparatively small +size of the body-chamber, the often contracted aperture of the +mouth, and the enormous size of some specimens of the shell. +Thus, some _Orthocerata_ have been discovered measuring ten or +twelve feet in length, with a diameter of a foot at the larger +extremity. These colossal dimensions certainly make it difficult +to imagine that the comparatively small body-chamber could have +held an animal large enough to move a load so ponderous as its +own shell. To some, this difficulty has appeared so great that +they prefer to believe that the _Orthoceras_ did not live in +its shell at all, but that its shell was an internal skeleton +similar to what we shall find to exist in many of the true +Cuttle-fishes. There is something to be said in favour of this +view, but it would compel us to believe in the existence in Lower +Silurian times of Cuttle-fishes fully equal in size to the giant +"Kraken" of fable. It need only be added in this connection that +the Lower Silurian rocks have yielded the remains of many other +Tetrabranchiate Cephalopods besides _Orthoceras_. Some of these +belong to _Cyrtoceras_, which only differs from _Orthoceras_ in +the bow-shaped form of the shell; others belong to _Phragmoceras_, +_Lituites_, &c.; and, lastly; we have true _Nautili_, with their +spiral shells, closely resembling the existing Pearly Nautilus. + +Whilst all the sub-kingdoms of the Invertebrate animals are +represented in the Lower Silurian rocks, no traces of Vertebrate +animals have ever been discovered in these ancient deposits, +unless the so-called "Conodonts" found by Pander in vast numbers +in strata of this age [15] in Russia should prove to be really +of this nature. These problematical bodies are of microscopic +size, and have the form of minute, conical, tooth-shaped spines, +with sharp edges, and hollow at the base. Their original discoverer +regarded them as the horny teeth of fishes allied to the Lampreys; +but Owen came to the conclusion that they probably belonged to +Invertebrates. The recent investigation of a vast number of similar +but slightly larger bodies, of very various forms, in the +Carboniferous rocks of Ohio, has led Professor Newberry to the +conclusion that these singular fossils really are, as Pander +thought, the teeth of Cyclostomatous fishes. The whole of this +difficult question has thus been reopened, and we may yet have +to record the first advent of Vertebrate animals in the Lower +Silurian. + +[Footnote 15: According to Pander, the "Conodonts" are found not +only in the Lower Silurian beds, but also in the "Ungulite Grit" +(Upper Cambrian), as well as in the Devonian and Carboniferous +deposits of Russia. Should the Conodonts prove to be truly the +remains of fishes, we should thus have to transfer the first +appearance of vertebrates to, at any rate, as early a period as +the Upper Cambrian.] + + + + +CHAPTER X. + +THE UPPER SILURIAN PERIOD. + +Having now treated of the Lower Silurian period at considerable +length, it will not be necessary to discuss the succeeding group +of the _Upper Silurian_ in the same detail--the more so, as with a +general change of _species_ the Upper Silurian animals belong for +the most part to the same great types as those which distinguish +the Lower Silurian. As compared, also, as regards the total bulk of +strata concerned, the thickness of the Upper Silurian is generally +very much below that of the Lower Silurian, indicating that they +represent a proportionately shorter period of time. In considering +the general succession of the Upper Silurian beds, we shall, +as before, select Wales and America as being two regions where +these deposits are typically developed. + +In Wales and its borders the general succession of the Upper +Silurian rocks may be taken to be as follows, in ascending order +(fig. 57):-- + +(1) The base of the Upper Silurian series is constituted by a +series of arenaceous beds, to which the name of "May Hill Sandstone" +was applied by Sedgwick. These are succeeded by a series of +greenish-grey or pale-grey slates ("Tarannon Shales"), sometimes +of great thickness; and these two groups of beds together form +what may be termed the "_May Hill Group_" (Upper Llandovery of +Murchison). Though not very extensively developed in Britain, this +zone is one very well marked by its fossils; and it corresponds +with the "Clinton Group" of North America, in which similar fossils +occur. In South Wales this group is clearly unconformable to the +highest member of the subjacent Lower Silurian (the Llandovery +group); and there is reason to believe that a similar, though +less conspicuous, physical break occurs very generally between +the base of the Upper and the summit of the Lower Silurian. + +(2) The _Wenlock Group_ succeeds the May Hill group, and constitutes +the middle member of the Upper Silurian. At its base it may have +an irregular limestone ("Woolhope Limestone"), and its summit may +be formed by a similar but thicker calcareous deposit ("Wenlock +Limestone"); but the bulk of the group is made up of the argillaceous +and shaly strata known as the "Wenlock Shale." In North Wales +the Wenlock group is, represented by a great accumulation of +flaggy and gritty strata (the "Denbighshire Flags and Grits"), +and similar beds (the "Coniston Flags" and "Coniston Grits") +take the same place in the north of England. + +(3) The _Ludlow Group_ is the highest member of the Upper Silurian, +and consists typically of a lower arenaceous and shaly series (the +"Lower Ludlow Rock") a middle calcareous member (the "Aymestry +Limestone"), and an upper shaly and sandy series (the "Upper +Ludlow Rock" and "Downton Sandstone"). At the summit, or close +to the summit, of the Upper Ludlow, is a singular stratum only a +few inches thick (varying from an inch to a foot), which contains +numerous remains of crustaceans and fishes, and is well known +under the name of the "bone-bed." Finally, the Upper Ludlow rock +graduates invariably into a series of red sandy deposits, which, +when of a flaggy character, are known locally as the "Tile-stones." +These beds are probably to be regarded as the highest member +of the Upper Silurian; but they are sometimes looked upon as +passage-beds into the Old Red Sandstone, or as the base of this +formation. It is, in fact, apparently impossible to draw any +actual line of demarcation between the Upper Silurian and the +overlying deposits of the Devonian or Old Red Sandstone series. +Both in Britain and in America the Lower Devonian beds repose +with perfect conformity upon the highest Silurian beds, and the +two formations appear to pass into one another by a gradual and +imperceptible transition. + +The Upper Silurian strata of Britain vary from perhaps 3000 or +4000 feet in thickness up to 8000 or 10,000 feet. In North America +the corresponding series, though also variable, is generally of +much smaller thickness, and may be under 1000 feet. The general +succession of the Upper Silurian deposits of North America is +as follows:-- + +(1) _Medina Sandstone_.--This constitutes the base of the Upper +Silurian, and consists of sandy strata, singularly devoid of life, +and passing below in some localities into a conglomerate ("Oneida +Conglomerate"), which is stated to contain pebbles derived from +the older beds, and which would thus indicate an unconformity +between the Upper and Lower Silurian. + +(2) _Clinton Group_.--Above the Medina sandstone are beds of +sandstone and shale, sometimes with calcareous bands, which +constitute what is known as the "Clinton Group." The Medina and +Clinton groups are undoubtedly the equivalent of the "May Hill +Group" of Britain, as shown by the identity of their fossils. + +[Illustration: Fig. 57. GENERALIZED SECTION OF THE UPPER SILURIAN +STRATA OF WALES AND SHROPSHIRE.] + +(3) _Niagara Group_.--This group consists typically of a series of +argillaceous beds ("Niagara Shale") capped by limestones ("Niagara +Limestone"); and the name of the group is derived from the fact +that it is over limestones of this age that the Niagara river +is precipitated to form the great Falls. In places the Niagara +group is wholly calcareous, and it is continued upwards into a +series of marls and sandstones, with beds of salt and masses +of gypsum (the "Salina Group"), or into a series of magnesian +limestones ("Guelph Limestones"). The Niagara group, as a whole, +corresponds unequivocally with the Wenlock group of Britain. + +(4) _Lower Helderberg Group_.--The Upper Silurian period in North +America was terminated by the deposition of a series of calcareous +beds, which derive the name of "Lower Helderberg" from the Helderberg +mountains, south of Albany, and which are divided into several zones, +capable of recognition by their fossils, and known by local names +(Tentaculite Limestone, Water-lime, Lower Pentamerus Limestone, +Delthyris Shaly Limestone, and Upper Pentamerus Limestone). As +a whole, this series may be regarded as the equivalent of the +Ludlow group of Britain, though it is difficult to establish any +precise parallelism. The summit of the Lower Heiderberg group +is constituted by a coarse-grained sandstone (the "Oriskany +Sandstone"), replete with organic remains, which have to a large +extent a Silurian _facies_. Opinions differ as to whether this +sandstone is to be regarded as the highest bed of the Upper Silurian +or the base of the Devonian. We thus see that in America, as +in Britain, no other line than an artificial one can be drawn +between the Upper Silurian and the overlying Devonian. + +As regards the _life_ of the Upper Silurian period, we have, +as before, a number of so-called "Fucoids," the true vegetable +nature of which is in many instances beyond doubt. In addition +to these, however, we meet for the first time, in deposits of +this age, with the remains of genuine land-plants, though our +knowledge of these is still too scanty to enable us to construct +any detailed picture of the terrestrial vegetation of the period. +Some of these remains indicate the existence of the remarkable genus +_Lepidodendron_--a genus which played a part of great importance +in the forests of the Devonian and Carboniferous periods, and +which may be regarded as a gigantic and extinct type of the +Club-mosses (_Lycopodiaceoe_). Near the summit of the Ludlow +formation in Britain there have also been found beds charged +with numerous small globular bodies, which Dr Hooker has shown +to be the seed-vessels or "sporangia" of Club-mosses. Principal +Dawson further states that he has seen in the same formation +fragments of wood with the structure of the singular Devonian +Conifer known as _Prototaxites_. Lastly, the same distinguished +observer has described from the Upper Silurian of North America +the remains of the singular land-plants belonging to the genus +_Psilophyton_, which will be referred to at greater length hereafter. + +The marine life of the Upper Silurian is in the main constituted +by types of animals similar to those characterising the Lower +Silurian, though for the most part belonging to different species. +The _Protozoans_ are represented principally by _Stromatopora_ and +_Ischadites_, along with a number of undoubted sponges (such as +_Amphispongia, Astroeospongia, Astylospongia_, and _Paloeomanon_). + +Amongst the _Coelenterates_, we find the old group of _Graptolites_ +now verging on extinction. Individuals still remain numerous, +but the variety of generic and specific types has now become +greatly reduced. All the branching and complex forms of the Arenig, +the twin-Graptolites and _Dicranograpti_ of the Llandeilo, and +the double-celled _Diplograpti_ and _Climacograpti_ of the Bala +group, have now disappeared. In their place we have the singular +_Retiolites_, with its curiously-reticulated skeleton; and several +species of the single-celled genus _Monograptus_, of which a +characteristic species (_M. Priodon_) is here figured. If we +remove from this group the plant-like _Dictyonemoe_, which are +still present, and which survive into the Devonian, no known +species of _Graptolite_ has hitherto been detected in strata +higher in geological position than the Ludlow. This, therefore, +presents us with the first instance we have as yet met with of +the total disappearance and extinction of a great and important +series of organic forms. + +[Illustration: Fig. 58.--A, _Monograptus priodon_, slightly enlarged. +B, Fragment of the same viewed from behind. C, Fragment of the +same viewed in front, showing the mouths of the cellules. D, +Cross-section of the same. From the Wenlock Group (Coniston Flags +of the North of England). (Original.)] + +The _Corals_ are very numerously represented in the Upper Silurian +rocks some of the limestones (such as the Wenlock Limestone) +being often largely composed of the skeletons of these animals. +Almost all the known forms of this period belong to the two great +divisions of the Rugose and Tabulate corals, the former being +represented by species of _Zaphrentis, Omphyma, Cystiphyllum, +Strombodes, Acervularia, Cyathophyllum_, &c.; whilst the latter +belong principally to the genera _Favosites, Choetetes, Halysites, +Syringopora, Heliolites_, and _Plasmopora_. Amongst the _Rugosa_, the +first appearance of the great and important genus _Cyathophyllum_, +so characteristic of the Palæozoic period, is to be noted; and +amongst the _Tabulata_ we have similarly the first appearance, +in force at any rate, of the widely-spread genus _Favosites_--the +"Honeycomb-corals." The "Chain-corals" (_Halysites_), figured +below (fig. 59), are also very common examples of the Tabulate +corals during this period, though they occur likewise in the +Lower Silurian. + +[Illustration: Fig. 59.--a, _Halysites catenularia_, small variety, +of the natural size; b, Fragment of a large variety of the same, +of the natural size; c, Fragment of limestone with the tubes +of _Halysites agglomerata_, of the natural size; d, Vertical +section of two tubes of the same, showing the tabulæ, enlarged. +Niagara Limestone (Wenlock), Canada. (Original.)] + +[Illustration: Fig. 60.--Upper Silurian Star-fishes. 1, _Palasterina +primoeva_, Lower Ludlow; 2, _Paloeaster Ruthveni_, Lower Ludlow; +3, _Paloeocoma Colvini_, Lower Ludlow. (After Salter.)] + +[Illustration: Fig. 61.--A, _Protaster Sedgwickii_, showing the +disc and bases of the arms; B, Portion of an arm, greatly enlarged. +Lower Ludlow. (After Salter.)] + +Amongst the _Echinodermata_, all those orders which have hard parts +capable of ready preservation are more or less largely represented. +We have no trace of the Holothurians or Sea-cucumbers; but this +is not surprising, as the record of the past is throughout almost +silent as to the former existence of these soft-bodied creatures, +the scattered plates and spicules in their skin offering a very +uncertain chance of preservation in the fossil condition. The +Sea-urchins (_Echinoids_) are said to be represented by examples +of the old genus _Paloechinus_. The Star-fishes (_Asteroids_) and +the Brittle-stars (_Ophiuroids_) are, comparatively speaking, +largely represented; the former by species of _Palasterina_ (fig. +60), _Paloeaster_ (fig. 60), _Paloeocoma_ (fig. 60), _Petraster, +Glyptaster_, and _Lepidaster_--and the latter by species of +_Protaster_ (fig. 61), _Paloeodiscus, Acroura_, and _Eucladia_. +The singular _Cystideans_, or "Globe Crinoids," with their globular +or ovate, tesselated bodies (fig. 46, A, C, D,), are also not +uncommon in the Upper Silurian; and if they do not become finally +extinct here, they certainly survive the close of this period by +but a very brief time. By far the most important, however, of +the Upper Silurian Echinodenns, are the Sea-lilies or _Crinoids_. +The limestones of this period are often largely composed of the +fragmentary columns and detached plates of these creatures, and +some of them (such as the Wenlock Limestone of Dudley) have yielded +perhaps the most exquisitely-preserved examples of this group +with which we are as yet acquainted. However varied in their +forms, these beautiful organisms consist of a globular, ovate, +or pear-shaped body (the "calyx"), supported upon a longer or +shorter jointed stem (or "column"). The body is covered externally +with an armour of closely-fitting calcareous plates (fig. 62), +and its upper surface is protected by similar but smaller plates +more loosely connected by a leathery integument. From the upper +surface of the body, round its margin, springs a series of longer +or shorter flexible processes, composed of innumerable calcareous +joints or pieces, movably united with one another. The arms are +typically five in number; but they generally subdivide at least +once, sometimes twice, and they are furnished with similar but +more slender lateral branches or "pinnules," thus giving rise +to a crown of delicate feathery plumes. The "column" is the stem +by which the animal is attached permanently to the bottom of the +sea; and it is composed of numerous separate plates, so jointed +together that whilst the amount of movement between any two pieces +must be very limited, the entire column acquires more or less +flexibility, allowing the organism as a whole to wave backwards and +forwards on its stalk. Into the exquisite _minutioe_ of structure +by which the innumerable parts entering into the composition +of a single Crinoid are adapted for their proper purposes in +the economy of the animal, it is impossible to enter here. No +period, as before said, has yielded examples of greater beauty +than the Upper Silurian, the principal genera represented being +_Cyathocrinus, Platycrinus, Marsupiocrinus, Taxocrinus, +Eucalyptocrinus, Ichthyocrinus, Mariacrinus, Periechocrinus, +Glyptocrinus, Crotalocrinus_, and _Edriocrinus_. + +[Illustration: Fig 62.--Upper Silurian Crinoids. a, Calyx and +arms of _Eucalyptocrinus polydactylus_, Wenlock Limestone; b, +_Ichthyocrinus loevis_, Niagara Limestone, America; c, _Taxocrinus +tuberculatus_, Wenlock Limestone. (After M'Coy and Hall.)] + +[Illustration: Fig. 63.--_Planolites vulgaris_, the filled-up +burrows of a marine worm. Upper Silurian (Clinton Group), Canada. +(Original.)] + +The tracks and burrows of _Annelides_ are as abundant in the +Upper Silurian strata as in older deposits, and have just as +commonly been regarded as plants. The most abundant forms are the +cylindrical, twisted bodies (Planolites), which are so frequently +found on the surfaces of sandy beds, and which have been described +as the stems of sea-weeds. These fossils (fig. 63), however, +can be nothing more, in most cases, than the filled-up burrows +of marine worms resembling the living Lob-worms. There are also +various remains which belong to the group of the tube-inhabiting +Annelides (_Tubicola_). Of this nature are the tubes of _Serpulites_ +and _Cornultites_, and the little spiral discs of _Spirorbis +Lewisii_. + +[Illustration: Fig. 64.--Upper Silurian Trilobites. a, _Cheirurus +bimucronatus_, Wenlock and Caradoc; b, _Phacops longicaudatus_, +Wenlock, Britain, and America; c, _Phacops Downingioe_, Wenlock +and Ludlow; d, _Harpes ungula_, Upper Silurian, Bohemia. (After +Salter and Barrande.)] + +Amongst the _Articulates_, we still meet only with the remains of +_Crustaceans_. Besides the little bivalved _Ostracoda_--which here +are occasionally found of the size of beans--and various _Phyllopods_ +of different kinds, we have an abundance of _Trilobites_. These +last-mentioned ancient types, however, are now beginning to show +signs of decadence; and though still individually numerous, there +is a great diminution in the number of generic types. Many of +the old genera, which flourished so abundantly in Lower Silurian +seas, have now died out; and the group is represented chiefly +by species of _Cheirurus, Encrinurus, Harpes, Proetus, Lichas, +Acidaspis, Illoenus, Calymene, Homalonotus_, and _Phacops_--the +last of these, one of the highest and most beautiful of the groups +of Trilobites, attaining here its maximum of development. In the +annexed illustration (fig. 64) some of the characteristic Upper +Silurian Trilobites are represented--all, however, belonging +to genera which have their commencement in the Lower Silurian +period. In addition to the above, the Ludlow rocks of Britain +and the Lower Helderberg beds of North America have yielded the +remains of certain singular Crustaceans belonging to the extinct +order of the _Eurypterida_. Some of these wonderful forms are +not remarkable for their size; but others, such as _Pterygotus +Anglicus_ (fig. 65), attain a length of six feet or more, and +may fairly be considered as the giants of their class. The +Eurypterids are most nearly allied to the existing King-crabs +(_Limuli_), and have the anterior end of the body covered with +a great head-shield, carrying two pairs of eyes, the one simple +and the other compound. The feelers are converted into pincers, +whilst the last pair of limbs have their bases covered with spiny +teeth so as to act as jaws, and are flattened and widened out +towards their extremities so as to officiate as swimming-paddles. +The hinder extremity of the body is composed of thirteen rings, +which have no legs attached to them; and the last segment of +the tail is either a flattened plate or a narrow, sword-shaped +spine. Fragments of the skeleton are easily recognised by the +peculiar scale-like markings with which the surface is adorned, +and which look not at all unlike the scales of a fish. The most +famous locality for these great Crustaceans is Lesmahagow, in +Lanarkshire, where many different species have been found. The +true King-crabs (_Limuli_) of existing seas also appear to have +been represented by at least one form (_Neolimulus_) in the Upper +Silurian. + +[Illustration: Fig. 65.--_Pterygotus Anglicus_, viewed from the +under side, reduced in size, and restored. c c, The feelers +(antennæ), terminating in nipping-claws; o o, Eyes; m m, +Three pairs of jointed limbs, with pointed extremities; n n, +Swimming-paddles, the bases of which are spiny and act as jaws. +Upper Silurian, Lanarkshire. (After Henry Woodward.)] + +Coming to the _Mollusca_, we note the occurrence of the same +great groups as in the Lower Silurian. Amongst the Sea-mosses +(_Polyzoa_), we have the ancient Lace-corals (_Fenestella_ and +_Retepora_), with the nearly-allied _Glauconome_, and species +of _Ptilodictya_ (fig. 66); whilst many forms often referred +here may probably have to be transferred to the Corals, just as +some so-called Corals will ultimately be removed to the present +group. + +[Illustration: Fig. 66.--Upper Silurian Polyzoa. 1, Fan-shaped +frond of _Rhinopora verrucosa_; 1a, Portion of the surface of +the same, enlarged; 2 and 2a, _Phoenopora ensiformis_, of the +natural size and enlarged; 3 and 3a, _Helopora fragilis_, of +the natural size and enlarged; 4 and 4a, _Ptilodictya raripora_, +of the natural size and enlarged. The specimens are all from the +Clinton Formation (May Hill Group) of Canada. (Original.)] + +[Illustration: Fig. 67.--_Spirifera hysterica_. The right-hand +figure shows the interior of the dorsal valve with the calcareous +spires for the support of the arms.] + +[Illustration: Fig. 68.--Upper Silurian Brachiopods. a a', +_Leptocoelia plano-convexa_, Clinton Group, America; b b', +_Rhynchonella neglecta_, Clinton Group, America; c, _Rhynchonella +cuneata_, Niagara Group, America, and Wenlock Group, Britain; +d d', _Orthis elelgantula_, Llandeilo to Ludlow, America and +Europe; e e', _Atrypa hemispherica_, Clinton Group, America, and +Llandovery and May Hill Groups, Britain; f f', _Atrypa congesta_, +Clinton Group, America; g g', _Orthis Davidsoni_, Clinton Group, +America. (After Hall, Billings, and the Author.)] + +The Brachiopods continued to flourish during the Upper Silurian +Period in immense numbers and under a greatly increased variety +of forms. The three prominent Lower Silurian genera _Orthis, +Strophomena_, and _Leptoena_ are still well represented, though +they have lost their former preeminence. Amongst the numerous +types which have now come upon the scene for the first time, +or which have now a special development, are _Spirifera_ and +_Pentamerus_. In the first of these (fig. 69. b, c), one of +the valves of the shell (the dorsal) is furnished in its interior +with a pair of great calcareous spires, which served for the +support of the long and fringed fleshy processes or "arms" which +were attached to the sides of the mouth.[16] In the genus +_Pentamerus_ (fig. 70) the shell is curiously subdivided in its +interior by calcareous plates. The _Pentameri_ commenced their +existence at the very close of the Lower Silurian (Llandovery), +and survived to the close of the Upper Silurian; but they are +specially characteristic of the May Hill and Wenlock groups, +both in Britain and in other regions. One species, _Pentamerus +galeatus_, is common to Sweden, Britain, and America. Amongst +the remaining Upper Silurian Brachiopods are the extraordinary +_Trimerellids_; the old and at the same time modern _Linguloe, +Discinoe_, and _Cranioe_; together with many species of _Atrypa_ +(fig. 68, e), _Leptocoelia_ (fig. 68, a), _Rhynchonella_ +(fig. 68, b, c), _Meristella_ (fig. 69, a, e, f), _Athyris, +Retzia, Chonetes_, &c. + +[Footnote 16: In all the Lamp-shells the mouth is provided with +two long fleshy organs, which carry delicate filaments on their +sides, and which are usually coiled into a spiral. These organs +are known as the "arms," and it is from their presence that the +name of "_Brachiopoda_" is derived (Gr. _brachion_, arm; _podes_, +feet). In some cases the arms are merely coiled away within the +shell, without any support; but in other cases they are carried +upon a more or less elaborate shelly loop, often spoken of as the +"carriage-spring apparatus." In the _Spirifers_, and in other ancient +genera, this apparatus is coiled up into a complicated spiral (fig. +67). It is these "arms," with or without the supporting loops or +spires, which serve as one of the special characters distinguishing +the _Brachiopods_ from the true Bivalves (_Lamellibranchiata_).] + +[Illustration: Fig. 69.-a a', Meristella intermedia_, Niagara +Group, America; b, _Spirifera Niagarensis_, Niagara Group, America; +c c', _Spirifera crispa_, May Hill to Ludlow, Britain, and Niagara +Group, America; d, _Strophomena (Streptorhynchus) subplana_, +Niagara Group, America; e, _Meristella naviformis_, Niagara Group, +America; f, _Meristella cylindrica_, Niagara Group, America. +(After Hall, Billings, and the Author.)] + +[Illustration: Fig. 70.--_Pentamerus Knightii_. Wenlock and Ludlow. +The right-hand figure shows the internal partitions of the shell.] + +[Illustration: Fig. 71.--Upper Silurian Bivalves. A, _Cardiola +interrupta_, Wenlock and Ludlow; B, _Pterinea subfalcata_, Wenlock; +C, _Cardiola fibrosa_, Ludlow. (After Salter and M'Coy.)] + +[Illustration: Fig. 72.--Upper Silurian Gasteropods. a, _Platyceras +ventricosum_, Lower Helderberg, America; b, _Euomphalus discors_, +Wenlock, Britain; c, _Holopella obsoleta_ Ludlow, Britain; d, +_Platyschisma helicites_, Upper Ludlow, Britain; e, _Holopella +gracilior_, Wenlock, Britain; f, _Platyceras multisinuatum_, Lower +Helderberg, America; g, _Holopea subconica_, Lower Helderberg, +America; h, h', _Platyostoma Niagarense_, Niagara Group, America. +(After Hall, M'Coy, and Salter.)] + +[Illustration: Fig 73.--_Tentaculites ornatus_. Upper Silurian +of Europe and North America.] + +The higher groups of the _Mollusca_ are also largely represented +in the Upper Silurian. Apart from some singular types, such as +the huge and thick-shelled _Megalomi_ of the American Wenlock +formation, the Bivalves (_Lamellibranchiata_) present little of +special interest; for though sufficiently numerous, they are rarely +well preserved, and their true affinities are often uncertain. +Amongst the most characteristic genera of this period may be +mentioned _Cardiola_ (fig. 71, A and C) and _Pterinea_ (fig. 71, +B), though the latter survives to a much later date. The Univalves +(_Gasteropoda_) are very numerous, and a few characteristic forms +are here figured (fig. 72). Of these, no genus is perhaps more +characteristic than _Euomphalus_ (fig. 72, b), with its flat +discoidal shell, coiled up into an oblique spiral, and deeply +hollowed out on one side; but examples of this group are both +of older and of more modern date. Another very extensive genus, +especially in America, is Platyceras (fig. 72, a and f), +with its thin fragile shell--often hardly coiled up at all--its +minute spire, and its widely-expanded, often sinuated mouth. The +British _Acroculioe_ should probably be placed here, and the +group has with reason been regarded as allied to the Violet-snails +(_Ianthina_) of the open Atlantic. The species of _Platyostoma_ +(fig. 72, h) also belong to the same family; and the entire +group is continued throughout the Devonian into the Carboniferous. +Amongst other well-known Upper Silurian Gasteropods are species +of the genera _Holopea_ (fig. 72, g), _Holopella_ (fig. 72. +e), _Platyschisma_ (fig. 72, d), _Cyclonema, Pleurotomaria, +Murchisonia, Trochonema_, &c. The oceanic Univalves (_Heteropods_) +are represented mainly by species of _Bellerophon_; and the Winged +Snails, or _Pteropods_, can still boast of the gigantic _Thecoe_ +and _Conularioe_, which characterise yet older deposits. The +commonest genus of _Pteropoda_, however, is _Tentaculites_ (fig. +73), which clearly belongs here, though it has commonly been +regarded as the tube of an Annelide. The shell in this group +is a conical tube, usually adorned with prominent transverse +rings, and often with finer transverse or longitudinal striæ as +well; and many beds of the Upper Silurian exhibit myriads of +such tubes scattered promiscuously over their surfaces. + +The last and highest group of the _Mollusca_--that of the +_Cephalopoda_--is still represented only by _Tetrabranchiate_ +forms; but the abundance and variety of these is almost beyond +belief. Many hundreds of different species are known, chiefly +belonging to the straight _Orthoceratites_, but the slightly-curved +_Cyrtoceras_ is only little less common. There are also numerous +forms of the genera _Phragmoceras, Ascoceras, Gyroteras, Lituites_, +and _Nautilus_. Here, also, are the first-known species of the +genus _Goniatites_--a group which attains considerable importance +in later deposits, and which is to be regarded as the precursor +of the _Ammonites_ of the Secondary period. + +[Illustration: Fig. 74.--Head-shield of _Pteraspis Banksii_, Ludlow +rocks. (After Murchison.)] + +[Illustration: Fig. 75.--A, Spine of _Onchus tenuistriatus_; +B, Shagreen-scales of _Thelodus_. Both from the "bone-bed" of +the Upper Ludlow rocks. (After Murchison.)] + +Finally, we find ourselves for the first time called upon to +consider the remains of undoubted vertebrate animals, in the +form of _Fishes_. The oldest of these remains, so far as yet +known, are found in the Lower Ludlow rocks, and they consist of +the bony head-shields or bucklers of certain singular armoured +fishes belonging to the group of the _Ganoids_, represented at +the present day by the Sturgeons, the Gar-pikes of North America, +and a few other less familiar forms. The principal Upper Silurian +genus of these is _Pteraspis_, and the annexed illustration (fig. +74) will give some idea of the extraordinary form of the shield +covering the head in these ancient fishes. The remarkable stratum +near the top of the Ludlow formation known as the "bone-bed" has +also yielded the remains of shark-like fishes. Some of these, +for which the name of _Onchus_ has been proposed, are in the form +of compressed, slightly-curved spines (fig. 75, A), which would +appear to be of the nature of the strong defensive spines implanted +in front of certain of the fins in many living fishes. Besides +these, have been found fragments of prickly skin or shagreen +(_Sphagodus_), along with minute cushion-shaped bodies (_Thelodus_, +fig. 75, B), which are doubtless the bony scales of some fish +resembling the modern Dog-fishes. As the above mentioned remains +belong to two distinct, and at the same time highly-organised, +groups of the fishes, it is hardly likely that we are really +presented here with the first examples of this great class. On +the contrary, whether the so-called "Conodonts" should prove +to be the teeth of fishes or not, we are justified in expecting +that unequivocal remains of this group of animals will still be +found in the Lower Silurian. It is interesting, also, to note +that the first appearance of fishes--the lowest class of vertebrate +animals--so far as known to us at present, does not take place +until after all the great sub-kingdoms of invertebrates have +been long in existence; and there is no reason for thinking that +future discoveries will materially affect the _relative_ order +of succession thus indicated. + + +LITERATURE. + +From the vast and daily-increasing mass of Silurian literature, it +is impossible to do more than select a small number of works which +have a classical and historical interest to the English-speaking +geologist, or which embody researches on special groups of Silurian +animals--anything like an enumeration of all the works and papers +on this subject being wholly out of the question. Apart, therefore, +from numerous and in many cases extremely important memoirs, +by various well-known observers, both at home and abroad, the +following are some of the more weighty works to which the student +may refer in investigating the physical characters and succession +of the Silurian strata and their fossil contents:-- + + (1) 'Siluria.' Sir Roderick Murchison. + (2) 'Geology of Russia in Europe.' Murchison (with M. de Verneuil + and Count von Keyserling). + (3) 'Bassin Silurien de Bohême Centrale.' Barrande. + (4) 'Introduction to the Catalogue of British Palæozoic Fossils in + the Woodwardian Museum of Cambridge.' Sedgwick. + (5) 'Die Urwelt Russlands.' Eichwald. + (6) 'Report on the Geology of Londonderry, Tyrone,' &c. Portlock. + (7) "Geology of North Wales"--'Mem. Geol. Survey of Great Britain,' + vol. iii. Ramsay. + (8) 'Geology of Canada,' 1863. Sir W. E. Logan; and the 'Reports of + Progress of the Geological Survey' since 1863. + (9) 'Memoirs of the Geological Survey of Great Britain,' +(10) 'Reports of the Geological Surveys of the States of New York, + Illinois, Ohio, Iowa, Michigan, Vermont, Wisconsin, Minnesota,' + &c. By Emmons, Hall, Worthen, Meek, Newberry, Orton, Winchell, + Dale Owen, &c. +(11) 'Thesaurus Siluricus.' Bigsby. +(12) 'British Palæozoic Fossils.' M'Coy. +(13) 'Synopsis of the Silurian Fossils of Ireland,' M'Coy. +(14) "Appendix to the Geology of North Wales"--'Mem. Geol. Survey,' + vol. iii. Salter. +(15) 'Catalogue of the Cambrian and Silurian Fossils in the + Woodwardian Museum of Cambridge.' Salter. +(16) 'Characteristic British Fossils.' Baily. +(17) 'Catalogue of British Fossils.' Morris. +(18) 'Palæozoic Fossils of Canada.' Billings. +(19) 'Decades of the Geological Survey of Canada.' Billings, + Salter, Rupert Jones. +(20) 'Decades of the Geological Survey of Great Britain.' Salter, + Edward, Forbes. +(21) 'Palæontology of New York,' vols. i.-iii. Hall. +(22) 'Palæontology of Illinois.' Meek and Worthen. +(23) 'Palæontology of Ohio.' Meek, Hall, Whitfield, Nicholson. +(24) 'Silurian Fauna of West Tennessee' (Silurische Fauna des + Westlichen Tennessee). Ferdinand Roemer. +(25) 'Reports on the State Cabinet of New York.' Hall. +(26) 'Lethæa Geognostica.' Bronn. +(27) 'Index Palæontologicus.' Bronn. +(28) 'Lethæa Rossica.' Eichwald. +(29) 'Lethæa Suecica.' Hisinger. +(30) 'Palæontologica Suecica.' Angelin. +(31) 'Petrefacta Germaniæ.' Goldfuss. +(32) 'Versteinerungen der Grauwacken-Formation in Sachsen.' Geinitz. +(33) 'Organisation of Trilobites' (Ray Society). Burmeister. +(34) 'Monograph of the British Trilobites' (Palæontographical + Society). Salter. +(35) 'Monograph of the British Merostomata' (Palæontographical Society). + Henry Woodward. +(36) 'Monograph of British Brachiopoda' (Palæontographical Society). + Thomas Davidson. +(37) 'Graptolites of the Quebec Group.' James Hall. +(38) 'Monograph of the British Graptolitidæ.' Nicholson. +(39) 'Monographs on the Trilobites. Pteropods, Cephalopods, + Graptolites,' &c. Extracted from the 'Système Silurien du Centre + de la Bohême.' Barrande. +(40) 'Polypiers Fossiles des Terrains Paleozoiques,' and 'Monograph + of the British Corals' (Palæontographical Society). Milne + Edwards and Jules Haime. + + + + +CHAPTER XI. + +THE DEVONIAN AND OLD RED SANDSTONE PERIOD. + +Between the summit of the Ludlow formation and the strata which +are universally admitted to belong to the Carboniferous series +is a great system of deposits, to which the name of "Old Red +Sandstone" was originally applied, to distinguish them from certain +arenaceous strata which lie above the coal ("New Red Sandstone"). +The Old Red Sandstone, properly so called, was originally described +and investigated as occurring in Scotland and in South Wales and +its borders; and similar strata occur in the south of Ireland. +Subsequently it was discovered that sediments of a different mineral +nature, and containing different organic remains, intervened +between the Silurian and the Carboniferous rocks on the continent +of Europe, and strata with similar palæontological characters to +these were found occupying a considerable area in Devonshire. +The name of "Devonian" was applied to these deposits; and this +title, by common usage, has come to be regarded as synonymous +with the name of "Old Red Sandstone." Lastly, a magnificent series +of deposits, containing marine fossils, and undoubtedly equivalent +to the true "Devonian" of Devonshire, Rhenish Prussia, Belgium, +and France, is found to intervene in North America between the +summit of the Silurian and the base of the Carboniferous rocks. + +Much difficulty has been felt in correlating the true "Devonian +Rocks" with the typical "Old Red Sandstone"--this difficulty arising +from the fact that though both formations are fossiliferous, the +peculiar fossils of each have only been rarely and partially found +associated together. The characteristic crustaceans and many of the +characteristic fishes of the Old Red are wanting in the Devonian; +whilst the corals and marine shells of the latter do not occur in +the former. It is impossible here to enter into any discussion +as to the merits of the controversy to which this difficulty +has given origin. No one, however, can doubt the importance and +reality of the Devonian series as an independent system of rocks +to be intercalated in point of time between the Silurian and +the Carboniferous. The want of agreement, both lithologically +and palæontologically, between the Devonian and the Old Red, +can be explained by supposing that these two formations, though +wholly or in great part _contemporaneous_, and therefore strict +equivalents, represent deposits in two different geographical +areas, laid down under different conditions. On this view, the +typical Devonian rocks of Europe, Britain, and North America are +the deep-sea deposits of the Devonian period, or, at any rate, are +genuine marine sediments formed far from land. On the other hand, +the "Old Red Sandstone" of Britain and the corresponding "Gaspé +Group" of Eastern Canada represent the shallow-water shore-deposits +of the same period. In fact, the former of these last-mentioned +deposits contains no fossils which can be asserted positively +to be _marine_ (unless the Eurypterids be considered so); and +it is even conceivable that it represents the sediments of an +inland sea. Accepting this explanation in the meanwhile, we may +very briefly consider the general succession of the deposits of +this period in Scotland, in Devonshire, and in North America. + +In Scotland the "Old Red" forms a great series of arenaceous and +conglomeratic strata, attaining a thickness of many thousands of +feet, and divisible into three groups. Of these, the _Lower Old +Red Sandstone_ reposes with perfect conformity upon the highest +beds of the Upper Silurian, the two formations being almost +inseparably united by an intermediate series of "passage-beds." +In mineral nature this group consists principally of massive +conglomerates, sandstones, shales, and concretionary limestones; +and its fossils consist chiefly of large crustaceans belonging to +the family of the _Eurypterids_, fishes, and plants. The _Middle +Old Red Sandstone_ consists of flagstones, bituminous shales, +and conglomerates, sometimes with irregular calcareous bands; +and its fossils are principally fishes and plants. It may be +wholly wanting, when the _Upper Old Red_ seems to repose +unconformably upon the lower division of the series. The _Upper +Old Red Sandstone_ consists of conglomerates and grits, along +with a great series of red and yellow sandstones--the fossils, +as before, being fishes and remains of plants. The Upper Old +Red graduates upwards conformably into the Carboniferous series. + +The Devonian rocks of Devonshire are likewise divisible into a +lower, middle, and upper division. The _Lower Devonian_ or _Lynton +Group_ consists of red and purple sandstones, with marine fossils, +corresponding to the "Spirifer Sandstein" of Germany, and to the +arenaceous deposits (Schoharie and Cauda-Galli Grits) at the base +of the American Devonian. The _Middle Devonian_ or _Ilfracombe +Group_ consists of sandstones and flags, with calcareous slates +and crystalline limestones, containing many corals. It corresponds +with the great "Eifel Limestone" of the Continent, and, in a +general way, with the Corniferous Limestone and Hamilton group +of North America. The _Upper Devonian_ or _Pilton Group_, lastly, +consists of sandstones and calcareous shales which correspond with +the "Clymenia Limestone" and "Cypridina Shales" of the Continent, +and with the Chemung and Portage groups of North America. It +seems quite possible, also, that the so-called "Carboniferous +Slates" of Ireland correspond with this group, and that the former +would be more properly regarded as forming the summit of the +Devonian than the base of the Carboniferous. + +In no country in the world, probably, is there a finer or more +complete exposition of the strata intervening between the Silurian +and Carboniferous deposits than in the United States. The following +are the main subdivisions of the Devonian rocks in the State of +New York, where the series may be regarded as being typically +developed (fig. 67):-- + +(1) _Cauda-Galli Grit_ and _Schoharie Grit_.--Considering the +"Oriskany Sandstone" as the summit of the Upper Silurian, the +base of the Devonian is constituted by the arenaceous deposits +known by the above names, which rest quite conformably upon the +Silurian, and which represent the Lower Devonian of Devonshire. The +_Cauda-Galli Grit_ is so called from the abundance of a peculiar +spiral fossil (_Spirophyton cauda-Galli_), which is of common +occurrence in the Carboniferous rocks of Britain, and is supposed +to be the remains of a sea-weed. + +(2) The _Corniferous_ or _Upper Helderberg Limestone_.--A series +of limestones usually charged with considerable quantities of +siliceous matter in the shape of hornstone or chert (Lat. _cornu_, +horn). The thickness of this group rarely exceeds 300 feet; but +it is replete with fossils, more especially with the remains +of corals. The Corniferous Limestone is the equivalent of the +coral-bearing limestones of the Middle Devonian of Devonshire +and the great "Eifel Limestone" of Germany. + +(3) The _Hamilton Group_--consisting of shales at the base +("Marcellus shales"); flags, shales, and impure limestones ("Hamilton +beds") in the middle; and again a series of shales ("Genesee +Slates") at the top. The thickness of this group varies from +200 to 1200 feet, and it is richly charged with marine fossils. + +(4) The _Portage Group_.--A great series of shales, flags, and +shaly sandstones, with few fossils. + +(5) The _Chemung Group_.--Another great series of sandstones and +shales, but with many fossils. The Portage and Chemung groups +may be regarded as corresponding with the Upper Devonian of +Devonshire. The Chemung beds are succeeded by a great series +of red sandstones and shales--the "Catskill Group"--which pass +conformably upwards into the Carboniferous, and which may perhaps +be regarded as the equivalent of the great sandstones of the +Upper Old Red in Scotland. + +Throughout the entire series of Devonian deposits in North America +no unconformability or physical break of any kind has hitherto been +detected; nor is there any marked interruption to the current of +life, though each subdivision of the series has its own fossils. +No completely natural line can thus be indicated, dividing the +Devonian in this region from the Silurian on the one hand, and +the Carboniferous on the other hand. At the same time, there is +the most ample evidence, both stratigraphical and palæontological, +as to the complete independence of the American Devonian series +as a distinct life-system between the older Silurian and the +later Carboniferous. The subjoined section (fig. 76) shows +diagrammatically the general succession of the Devonian rocks +of North America. + +[Illustration: Fig. 76. GENERALIZED SECTION OF THE DEVONIAN ROCKS +OF NORTH AMERICA.] + +[Illustration: Fig. 77.--Restoration of _Psilophyton princeps_. +Devonian, Canada. (After Dawson.)] + +As regards the _life_ of the Devonian period, we are now acquainted +with a large and abundant terrestrial _flora_--this being the +first time that we have met with a land vegetation capable of +reconstruction in any fulness. By the researches of Goeppert, +Unger, Dawson, Carruthers, and other botanists, a knowledge has +been acquired of a large number of Devonian plants, only a few +of which can be noticed here. As might have been anticipated, +the greater number of the vegetable remains of this period have +been obtained from such shallow-water deposits as the Old Red +Sandstone proper and the Gaspè series of North America, and few +traces of plant-life occur in the strictly marine sediments. +Apart from numerous remains, mostly of a problematical nature, +referred to the comprehensive group of the Sea-weeds, a large +number of Ferns have now been recognised, some being, of the +ordinary plant-like type (_Pecopteris, Neuropteris, Alethopteris, +Sphenopteris_, &c.), whilst others belong to the gigantic group +of the "Tree-ferns" (_Psaronius, Caulopteris_, &c.) Besides these +there is an abundant development of the singular extinct types of +the _Lepidodendroids_, the _Sigillarioids_, and the _Calamites_, +all of which attained their maximum in the Carboniferous. Of +these, the _Lepidodendra_ may be regarded as gigantic, tree-like +Club-mosses (_Lycopodiaceoe_); the _Calamites_ are equally gigantic +Horse-tails (_Equisetaceoe_); and the _Sigillarioids_, equally huge +in size, in some respects hold a position intermediate between +the Club-mosses and the Pines (Conifers). The Devonian rocks have +also yielded traces of many other plants (such as _Annularia, +Asterophyllites, Cardiocarpon_, &c.), which acquire a greater +pre-dominance in the Carboniferous period, and which will be +spoken of in discussing the structure of the plants of the +Coal-measures. Upon the whole, the one plant which may be considered +as specially characteristic of the Devonian (though not confined +to this series) is the _Psilophyton_ (fig. 77) of Dr Dawson. +These singular plants have slender branching stems, with sparse +needle-shaped leaves, the young stems being at first coiled up, +crosier-fashion, like the young fronds of ferns, whilst the old +branches carry numerous spore-cases. The stems and branches seem +to have attained a height of two or three feet; and they sprang +from prostrate "root-stocks" or creeping stems. Upon the whole, +Principal Dawson is disposed to regard _Psilophyton_ as a +"generalised type" of plants intermediate between the Ferns and +the Club-mosses. Lastly, the Devonian deposits have yielded the +remains of the first actual _trees_ with which we are as yet +acquainted. About the nature of some of these (_Ormoxylon_ and +_Dadoxylon_) no doubt can be entertained, since their trunks +not only show the concentric rings of growth characteristic of +exogenous trees in general, but their woody tissue exhibits under +the microscope the "discs" which are characteristic of the wood of +the Pines and Firs (see fig. 2). The singular genus _Prototaxites_, +however, which occurs in an older portion of the Devonian series +than the above, is not in an absolutely unchallenged position. +By Principal Dawson it is regarded as the trunk of an ancient +_Conifer_--the most ancient known; but Mr Carruthers regards it +as more probably the stem of a gigantic sea-weed. The trunks +of _Prototaxites_ (fig. 78, A) vary from one to three feet in +diameter, and exhibit concentric rings of growth; but its woody +fibres have not hitherto been clearly demonstrated to possess discs. +Before leaving the Devonian vegetation, it may be mentioned that +the hornstone or chert so abundant in the Corniferous limestone +of North America has been shown to contain the remains of various +microscopic plants (_Diatoms_ and _Desmids_). We find also in +the same siliceous material the singular spherical bodies, with +radiating spines, which occur so abundantly in the chalk flints, +and which are termed _Xanthidia_. These may be regarded as probably +the spore-cases of the minute plants known as _Desmidioe_. + +[Illustration: Fig. 78.--A, Trunk of _Prototaxites Logani_, eighteen +inches in diameter, as seen in the cliff near L'Anse Brehaut, +Gaspé; B, Two wood-cells showing spiral fibres and obscure pores, +highly magnified. Lower Devonian, Canada. (After Dawson)] + +The Devonian _Protozoans_ have still to be fully investigated. +True Sponges (such as _Astrtoeospongia, Sphoerospongia_, &c.) +are not unknown; but by far the commonest representatives of +this sub-kingdom in the Devonian strata are _Stromatopora_ and +its allies. These singular organisms (fig. 79) are not only very +abundant in some of the Devonian limestones--both in the Old World +and the New--but they often attain very large dimensions. However +much they may differ in minor details, the general structure of +these bodies is that of numerous, concentrically-arranged, thin, +calcareous laminæ, separated by narrow interspaces, which in turn +are crossed by numerous delicate vertical pillars, giving the whole +mass a cellular structure, and dividing it into innumerable minute +quadrangular compartments. Many of the Devonian _Stromatoporoe_ +also exhibit on their surface the rounded openings of canals, +which can hardly have served any other purpose than that of +permitting the sea-water to gain ready access to every part of +the organism. + +[Illustration: Fig. 79.--a, Part of the under surface of +_Stromatopora tuberculata_, showing the wrinkled basement membrane +and the openings of water-canals, of the natural size; b, Portion +of the upper surface of the same, enlarged; c, Vertical section of +a fragment, magnified to show the internal structure. Corniferous +Limestone, Canada. (Original.)] + +[Illustration: Fig. 80.--_Cystiphyllum vesiculosum_, showing a +succession of cups produces by budding from the original coral. +Of the natural size. Devonian, America and Europe. (Original.)] + +[Illustration: Fig. 81--_Zaphrentis cornicula_, of the natural +size. Devonian, America. (Original.)] + +[Illustration: Fig. 82--_Heliophyllum exiguum_, viewed from in +front and behind. Of the natural size. Devonian, Canada. (Original.)] + +[Illustration: Fig. 83.--Portion of a mass of _Crepidophyllum +Archiaci_, of the natural size. Hamilton Formation, Canada. (After +Billings.)] + +No true _Graptolites_ have ever been detected in strata of Devonian +age; and the whole of this group has become extinguished--unless we +refer here the still surviving _Dictyonemoe_. The _Coelenterates_, +however, are represented by a vast number of _Corals_, of beautiful +forms and very varied types. The marbles of Devonshire, the Devonian +limestones of the Eifel and of France, and the calcareous strata +of the Corniferous and Hamilton groups of America, are often +replete with the skeletons of these organisms--so much so as to +sometimes entitle the rock to be considered as representing an +ancient coral-reef. In some instances the Corals have preserved +their primitive calcareous composition; and if they are embedded +in soft shales, they may weather out of the rock in almost all +their original perfection. In other cases, as in the marbles +of Devonshire, the matrix is so compact and crystalline that +the included corals can only be satisfactorily studied by means +of polished sections. In other cases, again, the corals have +been more or less completely converted into flint, as in the +Corniferous limestone of North America. When this is the case, +they often come, by the action of the weather, to stand out from +the enclosing rock in the boldest relief, exhibiting to the observer +the most minute details of their organization. As before, the +principal representatives of the Corals are still referable to +the groups of the _Rugosa_ and _Tabulata_. Amongst the Rugose +group we find a vast number of simple "cup-corals," generally +known by the quarrymen as "horns," from their shape. Of the many +forms of these, the species of _Cyathophyllum, Heliophyllum_ +(fig. 82), _Zaphrentis_ (fig. 81), and _Cystiphyllum_ (fig. 80), +are perhaps those most abundantly represented--none of these +genera, however, except _Heliophyllum_, being peculiar to the +Devonian period. There are also numerous compound Rugose corals, +such as species of _Eridophyllum, Diphyphyllum, Syringopora, +Phillipsastroea_, and some of the forms of _Cyathophyllum_ and +_Crepidophyllum_ (fig. 83). Some of these compound corals attain +a very large size, and form of themselves regular beds, which +have an analogy, at any rate, with existing coral-reefs, though +there are grounds for believing that these ancient types differed +from the modern reef-builders in being inhabitants of deep water. +The "Tabulate Corals" are hardly less abundant in the Devonian +rocks than the _Rugosa_; and being invariably compound, they +hardly yield to the latter in the dimensions of the aggregations +which they sometimes form. + +[Illustration: Fig. 84.--Portion of a mass of _Favosites +Gothlandica_, of the natural size. Upper Silurian and Devonian +of Europe and America. (Original.) Billings.] + +[Illustration: Fig. 85.--Fragment of _Favosites hemispherica_, +of the natural size. Upper Silurian and Devonian of America. +(After Billings.)] + +The commonest, and at the same time the largest, of these are +the "honeycomb corals," forming the genus _Favosites_ (figs. +84, 85), which derive both their vernacular and their technical +names from their great likeness to masses of petrified honeycomb. +The most abundant species are _Favosites Gothlandica_ and _F. +Hemispherica_, both here figured, which form masses sometimes +not less than two or three feet in diameter. Whilst _Favosites_ +has acquired a popular name by its honey-combed appearance, the +resemblance of _Michelinia_ to a fossilised wasp's nest with the +comb exposed is hardly less striking, and has earned for it a +similar recognition from the non-scientific public. In addition +to these, there are numerous branching or plant-like Tabulate +Corals, often of the most graceful form, which are distinctive +of the Devonian in all parts of the world. + +The _Echinoderms_ of the Devonian period call for little special +notice. Many of the Devonian limestones are "crinoidal;" and +the _Crinoids_ are the most abundant and widely-distributed +representatives of their class in the deposits of this period. + +The _Cystideans_, with doubtful exceptions, have not been recognised +in the Devonian; and their place is taken by the allied group of +the "Pentremites," which will be further spoken of as occurring +in the Carboniferous rocks. On the other hand, the Star-fishes, +Brittle-stars, and Sea-urchins are all continued by types more +or less closely allied to those of the preceding Upper Silurian. + +Of the remains of Ringed-worms (_Annelides_), the most numerous +and the most interesting are the calcareous envelopes of some +small tube-inhabiting species. No one who has visited the seaside +can have failed to notice the little spiral tubes of the existing +_Spirorbis_ growing attached to shells, or covering the fronds +of the commoner Sea weeds (especially _Fucus serratus_). These +tubes are inhabited by a small Annelide, and structures of a +similar character occur not uncommonly from the Upper Silurian +upwards. In the Devonian rocks, _Spirorbis_ is an extremely common +fossil, growing in hundreds attached to the outer surface of +corals and shells, and appearing in many specific forms (figs. +86 and 87); but almost all the known examples are of small size, +and are liable to escape a cursory examination. + +[Illustration: Fig. 87.--a, _Spirobois omphalodes_, natural size +and enlarged. Devonian, Europe and America; b, _Spirorbis +Arkonensis_, of the natural size and enlarged; c, The same, +with the tube twisted in the reverse direction. Devonian, America. +(Onginal.)] + +[Illustration: Fig. 88. a b, _Spirorbis laxus_, enlarged, Upper +Silurian, America; c, _Spirorbis spinulifera_, of the natural +size and enlarged, Devonian, Canada. (After Hall and the Author.)] + +[Illustration: Fig. 88.--Devonian Trilobites; a, _Phacops latifrons_, +Devonian of Britain, the Continent of Europe, and South America; +b, _Homalonotus armatus_, Europe; c, _Phacops (Trimerocephalus) +loevis_, Europe; d, Head-shield of _Phacops (Portlockia) +granulatus_, Europe. (After Salter and Burmeister.)] + +The _Crustaceans_ of the Devonian are principally _Eurypterids_ +and _Trilobites_. Some of the former attain gigantic dimensions, +and the quarrymen in the Scotch Old Red give them the name of +"seraphim" from their singular scale-like ornamentation. The +_Trilobites_, though still sufficiently abundant in some localites, +have undergone a yet further diminution since the close of the +Upper Silurian. In both America and Europe quite a number of +generic types have survived from the Silurian, but few or no +new ones make their appearance during this period in either the +Old World or the New. The _species_, however, are distinct; and +the principal forms belong to the genera _Phacops_ (fig. 88, a, +c, d), _Homalonotus_ (fig. 88, b), _Proetus_, and _Bronteus_. +The species figured above under the name of _Phacops latifrons_ +(fig. 88, a), has an almost world-wide distribution, being found +in the Devonian of Britain, Belgium, France, Germany, Russia, +Spain, and South America; whilst its place is taken in North +America by the closely-allied _Phacops rana_. In addition to the +_Trilobites_, the Devonian deposits have yielded the remains of a +number of the minute _Ostracoda_, such as _Entomis_ ("_Cypridina_"), +_Leperditia_, &c., which sometimes occur in vast numbers, as +in the so-called "_Cypridina_ Slates" of the German Devonian. +There are also a few forms of _Phyllopods_ (_Estheria_). Taken +as a whole, the Crustacean fauna of the Devonian period presents +many alliances with that of the Upper Silurian, but has only +slight relationships with that of the Lower Carboniferous. + +Besides _Crustaceans_, we meet here for the first time with the +remains of _air-breathing Articulates_, in the shape of _Insects_. +So far, these have only been obtained from the Devonian rocks of +North America, and they indicate the existence of at least four +generic types, all more or less allied to the existing May-flies +(_Ephemeridoe_). One of these interesting primitive insects, namely, +_Platephemera antiqua_ (fig. 89), appears to have measured five +inches in expanse of wing; and another (_Xelloneura antiquorum_) has +attached to its wing the remains of a "stridulating-organ" similar +to that possessed by the modern Grasshoppers--the instrument, as +Principal Dawson remarks, of "the first music of living things +that Geology as yet reveals to us." + +[Illustration: Fig. 89.--Wing of _Platephemera antiqua_ Devonian, +America. (After Dawson.)] + +Amongst the _Mollusca_, the Devonian rocks have yielded a great +number of the remains of Sea-mosses (_Polyzoa_). Some of these +belong to the ancient type _Ptilodictya_, which seems to disappear +here, or to the allied _Clathropora_ (fig. 90), with its fenestrated +and reticulated fronds. We meet also with the graceful and delicate +stems of _Ceriopora_ (fig. 91). + +[Illustration: Fig. 90.--Fragment of _Clathropora intertexta_, +of the natural size and enlarged. Devonian, Canada. (Original.)] + +[Illustration: Fig. 91.--Fragment of _Ceriopora Hamiltonensis_, +of the natural size and enlarged. Devonian, Canada. (Original.)] + +[Illustration: Fig. 92.--Fragment of _Fenestella magnifica_, of +the natural size and enlarged. Devonian, Canada. (Original.)] + +[Illustration: Fig. 93.--Fragment of _Retepora Phillipsi_, of +the natural size and enlarged. Devonian, Canada. (Original.)] + +[Illustration: Fig. 94.--Fragment of _Fenestella cribrosa_, of +the natural size and enlarged. Dovonian, Canada. (Original.)] + +The majority of the Devonian _Polyzoa_ belong, however, to the +great and important Palæozoic group of the Lace-corals (_Fenestella_, +figs. 92 and 94, _Retepora_, fig. 93, _Polypora_, and their allies). +In all these forms there is a horny skeleton, of a fan-like or +funnel-shaped form, which grew attached by its base to some foreign +body. The frond consists of slightly-diverging or nearly parallel +branches, which are either united by delicate cross-bars, or which +bend alternately from side to side, and become directly united +with one another at short intervals--in either case giving origin +to numerous oval or oblong perforations, which communicate to the +whole plant-like colony a characteristic netted and lace-like +appearance. On one of its surfaces--sometimes the internal, sometimes +the external--the frond carries a number of minute chambers or +"cells," which are generally borne in rows on the branches, and +of which each originally contained a minute animal. + +[Illustration: Fig. 95.--_Spirifera sculptilis_. Devonian, Canada. +(After Billings.)] + +[Illustration: Fig. 96.--_Spirifera mucronata_. Devonian, America. +(After Billings.)] + +[Illustration: Fig. 97.--_Atrypa reticularis_. Upper Silurian +and Devonian of Europe and America. (After Billings.)] + +The _Brachiopods_ still continue to be represented in great force +through all the Devonian deposits, though not occurring in the +true Old Red Sandstone. Besides such old types as _Orthis, +Strophomena, Lingula, Athyris_, and _Rhynchonella_, we find some +entirely new ones; whilst various types which only commenced their +existence in the Upper Silurian, now undergo a great expansion +and development. This last is especially the case with the two +families of the _Spiriferidoe_ and the _Produclidoe_. The +_Spirifers_, in particular, are especially characteristic of +the Devonian, both in the Old and New Worlds--some of the most +typical forms, such as _Spirifera mucronata_ (fig. 96), having +the shell "winged," or with the lateral angles prolonged to such +an extent as to have earned for them the popular name of +"fossil-butterflies." The closely-allied _Spirifera disjunda_ +occurs in Britain, France, Spain, Belgium, Germany, Russia, and +China. The family of the _Productidoe_ commenced to exist in the +Upper Silurian, in the genus _Chonetes_, and we shall hereafter +find it culminating in the Carboniferous in many forms of the great +genus _Producta_[17] itself. In the Devonian period, there is an +intermediate state of things, the genus _Chonetes_ being continued +in new and varied types, and the Carboniferous _Produdoe_ being +represented by many forms of the allied group _Productella_. +Amongst other well-known Devonian Brachiopods may be mentioned +the two long-lived and persistent types _Atrypa reticularis_ +(fig. 97) and _Strophomena rhomboidalis_ (fig. 98). The former +of these commences in the Upper Silurian, but is more abundantly +developed in the Devonian, having a geographical range that is +nothing less than world-wide; whilst the latter commences in the +Lower Silurian, and, with an almost equally cosmopolitan range, +survives into the Carboniferous period. + +[Footnote 17: The name of this genus is often written _Productus_, +just as _Spirifera_ is often given in the masculine gender as +_Spirifer_ (the name originally given to it). The masculine +termination to these names is, however, grammatically incorrect, +as the feminine noun _cochlea_ (shell) is in these cases +_understood_.] + +[Illustration: Fig. 98.--_Strophomena rhomboidalis_. Lower Silurian, +Upper Silurian, and Devonian of Europe and America.] + +[Illustration: Fig. 99.--Different views of _Platyceras dumosum_, +of the natural size. Devonian, Canada. (Original.)] + +The Bivalves (_Lamellibranchiata_) of the Devonian call for no +special comment, the genera _Pterinea_ and _Megalodon_ being, +perhaps, the most noticeable. The Univalves (_Gasteropods_), also, +need not be discussed in detail, though many interesting forms +of this group are known. The type most abundantly represented, +especially in America, is _Platyceras_ (fig. 99), comprising thin, +wide-mouthed shells, probably most nearly allied to the existing +"Bonnet-limpets," and sometimes attaining very considerable +dimensions. We may also note the continuance of the genus +_Euomphalus_, with its discoidal spiral shell. Amongst the +_Heteropods_, the survival of _Bellerophon_ is to be recorded; +and in the "Winged-snails," or _Pteropods_, we find new forms +of the old genera _Tentaculites_ and _Conularia_ (fig. 100). +The latter, with its fragile, conical, and often beautifully +ornamented shell, is especially noticeable. + +[Illustration: Fig. 100.--_Conularia ornata, of the natural size. +Devonian, Europe.] + +[Illustration: Fig. 101.--_Clymenia Sedgwickii_. Devonian, Europe.] + +The remains of _Cephalopoda_ are far from uncommon in the Devonian +deposits, all the known forms being still Tetrabranchiate. Besides +the ancient types _Orthoceras_ and _Cyrtoceras_, we have now +a predominance of the spirally-coiled chambered shells of +_Goniatites_ and _Clymenia_. In the former of these the shell is +shaped like that of the _Nautilus_; but the partitions between the +chambers ("septa") are more or less lobed, folded, or angulated, +and the "siphuncle" runs along the _back_ or convex side of the +shell--these being characters which approximate _Goniatites_ to +the true Ammonites of the later rocks. In _Clymenia_, on the +other hand, whilst the shell (fig. 101) is coiled into a flat +spiral, and the partitions or septa are simple or only slightly +lobed, there is still this difference, as compared with the +_Nautilus_, that the tube of the siphuncle is placed on the _inner_ +or concave side of the shell. The species of _Clymenia_ are +exclusively Devonian in their range; and some of the limestones +of this period in Germany are so richly charged with fossils of +this genus as to have received the name of "Clymenien-kalk." + +The sub-kingdom of the _Vertebrates_ is still represented by +_Fishes_ only; but these are so abundant, and belong to such +varied types, that the Devonian period has been appropriately +called the "Age of Fishes." Amongst the existing fishes there are +three great groups which are of special geological importance, +as being more or less extensively represented in past time. These +groups are: (1) The _Bony Fishes_ (_Teleostei_), comprising most +existing fishes, in which the skeleton is more or less completely +converted into bone; the tail is symmetrically lobed or divided +into equal moieties; and the scales are usually thin, horny, +flexible plates, which overlap one another to a greater or less +extent. (2) The _Ganoid Fishes_ (_Ganoidei_), comprising the modern +Gar-pikes, Sturgeons, &c., in which the skeleton usually more or +less completely retains its primitive soft and cartilaginous +condition; the tail is generally markedly unsymmetrical, being +divided into two unequal lobes; and the scales (when present) +have the form of plates of bone, usually covered by a layer of +shining enamel. These scales may overlap; or they may be rhomboidal +plates, placed edge to edge in oblique rows; or they have the form +of large-sized bony plates, which are commonly united in the region +of the head to form a regular buckler. (3) The _Placoid Fishes_, +or _Elasmobranchii_, comprising the Sharks, Rays, and _Chimoeroe_ +of the present day, in which the skeleton is cartilaginous; the +tail is unsymmetrically lobed; and the scales have the form of +detached bony plates of variable size, scattered in the integument. + +It is to the two last of these groups that the Devonian fishes +belong, and they are more specially referable to the _Ganoids_. +The order of the Ganoid fishes at the present day comprises but +some seven or eight genera, the species of which principally or +exclusively inhabit fresh waters, and all of which are confined +to the northern hemisphere. As compared, therefore, with the Bony +fishes, which constitute the great majority of existing forms, +the Ganoids form but an extremely small and limited group. It was +far otherwise, however, in Devonian times. At this period, the +bony fishes are not known to have come into existence at all, and +the Ganoids held almost undisputed possession of the waters. To +what extent the Devonian Ganoids were confined to fresh waters +remains yet to be proved; and that many of them lived in the sea +is certain. It was formerly supposed that the Old Red Sandstone +of Scotland and Ireland, with its abundant fish-remains, might +perhaps be a fresh-water deposit, since the habitat of its fishes +is uncertain, and it contains no indubitable marine fossils. It +has been now shown, however, that the marine Devonian strata +of Devonshire and the continent of Europe contain some of the +most characteristic of the Old Red Sandstone fishes of Scotland; +whilst the undoubted marine deposit of the Corniferous limestone +of North America contains numerous shark-like and Ganoid fishes, +including such a characteristic Old Red genus as _Coccosleus_. +There can be little doubt, therefore, but that the majority of +the Devonian fishes were truly marine in their habits, though +it is probable that many of them lived in shallow water, in the +immediate neighbourhood of the shore, or in estuaries. + +[Illustration: Fig. 102.--Fishes of the Devonian rocks of America. +a, Diagram of the jaws and teeth of _Dinichthys Hertzeri_, +viewed from the front, and greatly reduced; b, Diagram of the +skull of _Macropetalichthys Sullivanti_, reduced in size; c, +A portion of the enamelled surface of the skull of the same, +magnified; d, One of the scales of _Onychodus sigmoides_, of +the natural size; e, One of the front teeth of the lower jaw of +the same, of the natural size: f, Fin-spine of _Machoeracanthus +major_, a shark-like fish, reduced in size. (After Newberry.)] + +[Illustration: Fig. 103.--_Cephalaspis Lyellii_. Old Red Sandstone, +Scotland. (After Page.)] + +[Illustration: Fig. 104.--_Pterichthys cornutus_. Old Red Sandstone, +Scotland. (After Agassiz.)] + +The Devonian Galloids belong to a number of groups; and it is +only possible to notice a few of the most important forms here. +The modern group of the Sturgeons is represented, more or less +remotely, by a few Devonian fishes--such as _Asterosteus_; and +the great _Macropetalichthys_ of the Corniferous limestone of +North America is believed by Newberry to belong to this group. In +this fish (fig. 102, b) the skull was of large size, its outer +surface being covered with a tuberculated enamel; and, as in the +existing Sturgeons, the mouth seems to have been wholly destitute +of teeth. Somewhat allied, also, to the Sturgeons, is a singular +group of armoured fishes, which is highly characteristic of the +Devonian of Britain and Europe, and less so of that of America. +In these curious forms the head and front extremity of the body +were protected by a buckler composed of large enamelled plates, +more or less firmly united to one another; whilst the hinder end +of the body was naked, or was protected with small scales. Some +forms of this group--such as _Pteraspis_ and _Coccosteus_--date +from the Upper Silurian; but they attain their maximum in the +Devonian, and none of them are known to pass upwards into the +overlying Carboniferous rocks. Amongst the most characteristic +forms of this group may be mentioned _Cephalaspis_ (fig. 103) and +_Pterichthys_ (fig. 104). In the former of these the head-shield is +of a crescentic shape, having its hinder angles produced backwards +into long "horns," giving it the shape of a "saddler's knife." +No teeth have been discovered; but the body was covered with +small ganoid scales, and there was an unsymmetrical tail-fin. +In _Pterichthys_--which, like the preceding, was first brought +to light by the labours of Hugh Miller--the whole of the head +and the front part of the body were defended by a buckler of +firmly-united enamelled plates, whilst the rest of the body was +covered with small scales. The form of the "pectoral fins" was +quite unique--these having the shape of two long, curved spines, +somewhat like wings, covered by finely-tuberculated ganoid plates. +All the preceding forms of this group are of small size; but +few fishes, living or extinct, could rival the proportions of +the great _Dinichthys_, referred to this family by Newberry. +In this huge fish (fig. 102, a) the head alone is over three +feet in length, and the body is supposed to have been twenty-five +or thirty feet long. The head was protected by a massive cuirass +of bony plates firmly articulated together, but the hinder end +of the body seems to have been simply enveloped in a leathery +skin. The teeth are of the most formidable description, consisting +in both jaws of serrated dental plates behind, and in front of +enormous conical tusks (fig. 102, a). Though immensely larger, +the teeth of _Dinichthys_ present a curious resemblance to those +of the existing Mud-fishes (_Lepidosiren_). + +In another great group of Devonian Ganoids, we meet with fishes +more or less closely allied to the living _Polypteri_ (fig. 105) +of the Nile and Senegal. In this group (fig. 106) the pectoral +fins consist of a central scaly lobe carrying the fin-rays on +both sides, the scales being sometimes rounded and overlapping +(fig. 106), or more commonly rhomboidal and placed edge to edge +(fig. 105, A). Numerous forms of these "Fringe-finned" Ganoids +occur in the Devonian strata, such as _Holoptychius, Glyotoloemus, +Osteolepis, Phaneropleuron_, &c. To this group is also to be +ascribed the huge _Onychodus_ (fig. 102, d and e), with its +large, rounded, overlapping scales, an inch in diameter, and its +powerful pointed teeth. It is to be remembered, however, that +some of these "Fringe-finned" Ganoids are probably referable +to the small but singular group of the "Mud-fishes" (_Dipnoi_), +represented at the present day by the singular _Lepidosiren_ +of South America and Africa, and the _Ceratodus_ of the rivers +of Queensland. + +[Illustration: Fig. 105.--A, _Polypterus_, a recent Ganoid +fish; B, _Osteolepis_, a Devonian Ganoid; a a, Pectoral fins, +showing the fin-rays arranged round a central lobe.] + +[Illusration: Fig. 106.--_Holoptychius nobilissimus_, restored. +Old Red Sandstone, Scotland. A, Scale of the same.] + +Leaving the Ganoid fishes, it still remains to be noticed that +the Devonian deposits have yielded the remains of a number of +fishes more or less closely allied to the existing Sharks, Rays, +and _Chimoeroe_ (the _Elasmobranchii_). The majority of the forms +here alluded to are allied not to the true Sharks and Dog-fishes, +but to the more peaceable "Port Jackson Sharks," with their blunt +teeth, adapted for crushing the shells of Molluscs. The collective +name of "Cestracionts" is applied to these; and we have evidence of +their past existence in the Devonian seas both by their teeth, and +by the defensive spines which were implanted in front of a greater +or less number of the fins. These are bony spines, often variously +grooved, serrated, or ornamented, with hollow bases, implanted +in the integument, and capable of being erected or depressed +at will. Many of these "fin-spines" have been preserved to us +in the fossil condition, and the Devonian rocks have yielded +examples belonging to many genera. As some of the true Sharks +and Dog-fishes, some of the Ganoids, and even some Bony Fishes, +possess similar defences, it is often a matter of some uncertainty +to what group a given spine is to be referred. One of these spines, +belonging to the genus _Machoeracanthus_, from the Devonian rocks +of America, has been figured in a previous illustration (fig. +102, f). + +In conclusion, a very few words may be said as to the validity of +the Devonian series as an independent system of rocks, preserving +in its successive strata the record of an independent system +of life. Some high authorities have been inclined to the view +that the Devonian formation has in nature no actual existence, +but that it is made up partly of beds which should be referred +to the summit of the Upper Silurian, and partly of beds which +properly belong to the base of the Carboniferous. This view seems +to have been arrived at in consequence of a too exclusive study +of the Devonian series of the British Isles, where the physical +succession is not wholly clear, and where there is a striking +discrepancy between the organic remains of those two members +of the series which are known as the "Old Red Sandstone" and +the "Devonian" rocks proper. This discrepancy, however, is not +complete; and, as we have seen, can be readily explained on the +supposition that the one group of rocks presents us with the +shallow water and littoral deposits of the period, while in the +other we are introduced to the deep-sea accumulations of the +same period. Nor can the problem at issue be solved by an appeal +to the phenomena of the British area alone, be the testimony of +these what it may. As a matter of fact, there is at present no +sufficient ground for believing that there is any irreconcilable +discordance between the succession of rocks and of life in Britain +during the period which elapsed between the deposition of the +Upper Ludlow and the formation of the Carboniferous Limestone, +and the order of the same phenomena during the same period in +other regions. Some of the Devonian types of life, as is the +case with all great formations, have descended unchanged from +older types; others pass upwards unchanged to the succeeding +period: but the fauna and flora of the Devonian period are, as +a whole, quite distinct from those of the preceding Silurian or +the succeeding Carboniferous; and they correspond to an equally +distinct rock-system, which in point of time holds an intermediate +position between the two great groups just mentioned. As before +remarked, this conclusion may be regarded as sufficiently proved +even by the phenomena of the British area; but it maybe said to +be rendered a certainty by the study of the Devonian deposits of +the continent of Europe--or, still more, by the investigation of +the vast, for the most part uninterrupted and continuous series +of sediments which commenced to be laid down in North America +at the beginning of the Upper Silurian, and did not cease till, +at any rate, the close of the Carboniferous. + + +LITERATURE. + +The following list comprises the more important works and memoirs +to which the student of Devonian rocks and fossils may refer:-- + + (1) 'Siluria.' Sir Roderick Murchison. + (2) 'Geology of Russia in Europe.' Murchison (together with De + Verneuil and Count von Keyserling). + (3) "Classification of the Older Rocks of Devon and Cornwall"--'Proc. + Geol. Soc.,' vol. iii., 1839. Sedgwick and Murchison. + (4) "On the Physical Structure of Devonshire;" and on the + "Classification of the Older Stratified Rocks of Devonshire + and Cornwall"--'Trans. Geol. Soc.,' vol. v., 1840. Sedgwick + and Murchison. + (5) "On the Distribution and Classification of the Older or Palæozoic + Rocks of North Germany and Belgium"--'Geol. Trans.,' 2d ser., + vol. vi., 1842. Sedgwick and Murchison. + (6) 'Report on the Geology of Cornwall, Devon, and West Somerset.' + De la Beche. + (7) 'Memoirs of the Geological Survey of Ireland and Scotland.' + Jukes and Geikie. + (8) "On the Carboniferous Slate (or Devonian Rocks) and the Old + Red Sandstone of South Ireland and North Devon"--'Quart. + Journ. Geol. Soc.,' vol. xxii. Jukes. + (9) "On the Physical Structure of West Somerset and North Devon;" + and on the "Palæontological Value of Devonian Fossils"--'Quart. + Journ. Geol. Soc.,' vol. iii. Etheridge. +(10) "On the Connection of the Lower, Middle, and Upper Old Red + Sandstone of Scotland"--'Trans. Edin. Geol. Soc.,' vol. i. + part ii. Powrie. +(11) 'The Old Red Sandstone,' 'The Testimony of the Rocks,' and + 'Footprints of the Creator.' Hugh Miller. +(12) "Report on the 4th Geological District"--'Geology of New York,' + vol. iv. James Hall. +(13) 'Geology of Canada,' 1863. Sir W. E. Logan. +(14) 'Acadian Geology.' Dawson. +(15) 'Manual of Geology.' Dana. +(16) 'Geological Survey of Ohio,' vol. i. +(17) 'Geological Survey of Illinois,' vol. i. +(18) 'Palæozoic Fossils of Cornwall, Devon, and West Somerset.' + Phillips. +(19) 'Recherches sur les Poissons Fossiles.' Agassiz. +(20) 'Poissous de l'Old Red.' Agassiz. +(21) "On the Classification of Devonian Fishes"--' Mem. Geol. Survey + of Great Britain,' Decade X. Huxley. +(22) 'Monograph of the Fishes of the Old Red Sandstone of Britain' + (Palæontographical Society). Powrie and Lankester. +(23) 'Fishes of the Devonian System, Palæontology of Ohio.' Newberry. +(24) 'Monograph of British Trilobites' (Palæontographical Society); + Salter. +(25) 'Monograph of British Merostomata' (Palæontographical Society). + Henry Woodward. +(26) 'Monograph of British Brachiopoda' (Palæontographical Society). + Davidson. +(27) 'Monograph of British Fossil Corals' (Palæontographical Society). + Milne-Edwards and Haime. +(28) 'Polypiers Foss. des Terrains Paléozoiques.' Milne-Edwards + and Jules Haime. +(29) "Devonian Fossils of Canada West"--'Canadian Journal,' new ser., + vols. iv.-vi. Billings. +(30) 'Palæontology of New York,' vol. iv. James Hall. +(31) 'Thirteenth, Fifteenth, and Twenty-third Annual Reports on the + State Cabinet.' James Hall. +(32) 'Palæozoic Fossils of Canada,' vol. ii. Billings. +(33) 'Reports on the Palæontology of the Province of Ontario for 1874 + and 1875.' Nicholson. +(34) "The Fossil Plants of the Devonian and Upper Silurian Formations + of Canada"--'Geol. Survey of Canada.' Dawson. +(35) 'Petrefacta Germaniæ.' Goldfuss. +(36) 'Versteinerungen der Grauwacken-formation.' &c. Geinitz. +(37) 'Beitrag zur Palæontologie des Thüringer-Waldes.' Richter and + Unger. +(38) 'Ueber die Placodermen der Devonischen System.' Pander. +(39) 'Die Gattungen der Fossilen Pflanzen.' Goeppert. +(40) 'Genera et Species Plantarum Fossilium.' Unger. + + + + +CHAPTER XII. + +THE CARBONIFEROUS PERIOD. + +Overlying the Devonian formation is the great and important series +of the _Carboniferous Rocks_, so called because workable beds +of coal are more commonly and more largely developed in this +formation than in any other. Workable coal-seams, however, occur +in various other formations (Jurassic, Cretaceous, Tertiary), so +that coal is not an exclusively Carboniferous product; whilst +even in the Coal-measures themselves the coal bears but a very +small proportion to the total thickness of strata, occurring +only in comparatively thin beds intercalated in a great series +of sandstones, shales, and other genuine aqueous sediments. + +Stratigraphically, the Carboniferous rocks usually repose conformably +upon the highest Devonian beds, so that the line of demarcation +between the Carboniferous and Devonian formations is principally +a palæontological one, founded on the observed differences in +the fossils of the two groups. On the other hand, the close of +the Carboniferous period seems to have been generally, though +not universally, signalised by movements of the crust of the +earth, so that the succeeding Permian beds often lie unconformably +upon the Carboniferous sediments. + +Strata of Carboniferous age have been discovered in almost every +large land-area which has been sufficiently investigated; but +they are especially largely developed in Britain, in various +parts of the continent of Europe, and in North America. Their +general composition, however, is, comparatively speaking, so +uniform, that it will suffice to take a comprehensive view of +the formation without considering any one area in detail, though +in each region the subdivisions of the formation are known by +distinctive local names. Taking such a comprehensive view, it is +found that the Carboniferous series is generally divisible into a +_Lower_ and essentially calcareous group (the "Sub-Carboniferous" or +"Carboniferous Limestone"); a _Middle_ and principally arenaceous +group (the "Millstone Grit"); and an Upper group, of alternating +shales and sandstones, with workable seams of coal (the +"Coal-measures"). + +I. The _Carboniferous, Sub-Carboniferous_, or _Mountain Limestone +Series_ constitutes the general base of the Carboniferous system. +As typically developed in Britain, the Carboniferous Limestone +is essentially a calcareous formation, sometimes consisting of a +mass of nearly pure limestone from 1000 to 2000 feet in thickness, +or at other times of successive great beds of limestone with +subordinate sandstones and shales. In the north of England the +base of the series consists of pebbly conglomerates and coarse +sandstones; and in Scotland generally, the group is composed +of massive sandstones with a comparatively feeble development +of the calcareous element. In Ireland, again, the base of the +Carboniferous Limestone is usually considered to be formed by +a locally-developed group of grits and shales (the "Coomhola +Grits" and "Carboniferous Slate"), which attain the thickness +of about 5000 feet, and contain an intermixture of Devonian with +Carboniferous types of fossils. Seeing that the Devonian formation +is generally conformable to the Carboniferous, we need feel no +surprise at this intermixture of forms; nor does it appear to be +of great moment whether these strata be referred to the former +or to the latter series. Perhaps the most satisfactory course +is to regard the Coomhola Grits and Carboniferous Slates as +"passage-beds" between the Devonian and Carboniferous; but any +view that may be taken as to the position of these beds, really +leaves unaffected the integrity of the Devonian series as a distinct +life-system, which, on the whole, is more closely allied to the +Silurian than to the Carboniferous. In North America, lastly, +the Sub-Carboniferous series is never purely calcareous, though +in the interior of the continent it becomes mainly so. In other +regions, however, it consists principally of shales and sandstones, +with subordinate beds of limestone, and sometimes with this beds +of coal or deposits of clay-ironstone. + +II. _The Millstone Grit_.--The highest beds of the Carboniferous +Limestone series are succeeded, generally with perfect conformity, +by a series of arenaceous beds, usually known as the _Millstone +Grit_. As typically developed in Britain, this group consists of +hard quartzose sandstones, often so large-grained and coarse in +texture as to properly constitute fine conglomerates. In other +cases there are regular conglomerates, sometimes with shales, +limestones, and thin beds of coal--the thickness of the whole +series, when well developed, varying from 1000 to 5000 feet. In +North America, the Millstone Grit rarely reaches 1000 feet in +thickness; and, like its British equivalent, consists of coarse +sandstones and grits, sometimes with regular conglomerates. Whilst +the Carboniferous Limestone was undoubtedly deposited in a tranquil +ocean of considerable depth, the coarse mechanical sediments +of the Millstone Grit indicate the progressive shallowing of +the Carboniferous seas, and the consequent supervention of +shore-conditions. + +III. _The Coal-measures_.--The Coal-measures properly so called +rest conformably upon the Millstone Grit, and usually consist of +a vast series of sandstones, shales, grits, and coals, sometimes +with beds of limestone, attaining in some regions a total thickness +of from 7000 to nearly 14,000 feet. Beds of workable coal are +by no means unknown in some areas in the inferior group of the +Sub-Carboniferous; but the general statement is true, that coal is +mostly obtained from the true Coal-measures--the largest known, and +at present most productive coal-fields of the world being in Great +Britain, North America, and Belgium. Wherever they are found, with +limited exceptions, the Coal-measures present a singular _general_ +uniformity of mineral composition. They consist, namely, of an +indefinite alternation of beds of sandstone, shale, and coal, +sometimes with bands of clay-ironstone or beds of limestone, +repeated in no constant order, but sometimes attaining the enormous +aggregate thickness of 14,000 feet, or little short of 3 miles. +The beds of coal differ in number and thickness in different +areas, but they seldom or never exceed one-fiftieth part of the +total bulk of the formation in thickness. The characters of the +coal itself, and the way in which the coal-beds were deposited, +will be briefly alluded to in speaking of the vegetable life +of the period. In Britain, and in the Old World generally, the +Coal-measures are composed partly of genuine terrestrial +deposits--such as the coal--and partly of sediments accumulated +in the fresh or brackish waters of vast lagoons, estuaries, and +marshes. The fossils of the Coal-measures in these regions are +therefore necessarily the remains either of terrestrial plants +and animals, or of such forms of life as inhabit fresh or brackish +waters, the occurrence of strata with marine fossils being quite +a local and occasional phenomenon. In various parts of North +America, on the other hand, the Coal-measures, in addition to +sandstones, shales, coal-seams, and bands of clay-ironstone, +commonly include beds of limestone, charged with marine remains, +and indicating marine conditions. The subjoined section (fig. 107) +gives, in a generalised form, the succession of the Carboniferous +strata in such a British area as the north of England, where +the series is developed in a typical form. + +As regards the _life_ of the Carboniferous period, we naturally +find, as has been previously noticed, great differences in different +parts of the entire series, corresponding to the different mode of +origin of the beds. Speaking generally, the Lower Carboniferous +(or the Sub-Carboniferous) is characterised by the remains of +marine animals; whilst the Upper Carboniferous (or Coal-measures) +is characterised by the remains of plants and terrestrial animals. +In all those cases, however, in which marine beds are found in +the series of the Coal-measures, as is common in America, then +we find that the fossils agree in their general characters with +those of the older marine deposits of the period. + +[Illustration: Fig. 107. GENERALIZED SECTION OF THE CARBONIFEROUS +STRATA OF THE NORTH OF ENGLAND.] + +Owing to the fact that coal is simply compressed and otherwise +altered vegetable matter, and that it is of the highest economic +value to man, the Coal-measures have been more thoroughly explored +than any other group of strata of equivalent thickness in the +entire geological series. Hence we have already a very extensive +acquaintance with the _plants_ of the Carboniferous period; and +our knowledge on this subject is daily undergoing increase. It +is not to be supposed, however, that the remains of plants are +found solely in Coal-measures; for though most abundant towards +the summit, they are found in less numbers in all parts of the +series. Wherever found, they belong to the same great types of +vegetation; but, before reviewing these, a few words must be +said as to the origin and mode of formation of _coal_. + +The coal-beds, as before mentioned, occur interstratified with +shales, sandstones, and sometimes limestones; and there may, +within the limits of a single coal-field, be as many as 80 or +100 of such beds, placed one above the other at different levels, +and varying in thickness from a few inches up to 20 or 30 feet. +As a general rule, each bed of coal rests upon a bed of shale or +clay, which is termed the "under-clay," and in which are found +numerous roots of plants; whilst the strata immediately on the +top of the coal may be shaly or sandy, but in either case are +generally charged with the leaves and stems of plants, and often +have upright trunks passing vertically through them. When we +add to this that the coal itself is, chemically, nearly wholly +composed of carbon, and that its microscopic structure shows it +to be composed almost entirely of fragments of stems, leaves, +bark, seeds, and vegetable _débris_ derived from _land-plants_, +we are readily enabled to understand how the coal was formed. +The "_under-clay_" immediately beneath the coal-bed represents +an old land-surface--sometimes, perhaps, the bottom of a swamp +or marsh, covered with a luxuriant vegetation; the _coal bed_ +itself represents the slow accumulation, through long periods, +of the leaves, seeds, fruits, stems, and fallen trunks of this +vegetation, now hardened and compressed into a fraction of its +original bulk by the pressure of the superincumbent rocks; and +the strata of sand or shale above the coal-bed--the so-called +"roof" of the coal--represent sediments quietly deposited as the +land, after a long period of repose, commenced to sink beneath +the sea. On this view, the rank and long-continued vegetation +which gave rise to each coal-bed was ultimately terminated by +a slow depression of the surface on which the plants grew. The +land-surface then became covered by the water, and aqueous sediments +were accumulated to a greater or less thickness upon the dense +mass of decaying vegetation below, enveloping any trunks of trees +which might still be in an erect position, and preserving between +their layers the leaves and branches of plants brought down from +the neighbouring land by streams, or blown into the wafer by the +wind. Finally, there set in a slow movement of elevation,--the +old land again reappeared above the water; a new and equally +luxuriant vegetation flourished upon the new land-surface; and +another coal-bed was accumulated, to be preserved ultimately in +a similar fashion. Some few beds of coal may have been formed by +drifted vegetable matter brought down into the ocean by rivers, and +deposited directly on the bottom of the sea; but in the majority +of cases the coal is undeniably the result of the slow growth and +decay of plants _in situ_: and as the plants of the coal are +not _marine_ plants, it is necessary to adopt some such theory +as the above to account for the formation of coal-seams. By this +theory, as is obvious, we are compelled to suppose that the vast +alluvial and marshy flats upon which the coal-plants grew were +liable to constantly-recurring oscillations of level, the successive +land-surfaces represented by the successive coal-beds of any +coal-field being thus successively buried beneath accumulations +of mud or sand. We have no need, however, to suppose that these +oscillations affected large areas at the same time; and geology +teaches us that local elevations and depressions of the land +have been matters of constant occurrence throughout the whole +of past time. + +All the varieties of coal (bituminous coal, anthracite; cannel-coal, +&c.) show a more or less distinct "lamination"--that is to say, +they are more or less obviously composed of successive thin layers, +differing slightly in colour and texture. All the varieties of coal, +also, consist chemically of _carbon_, with varying proportions of +certain gaseous constituents and a small amount of incombustible +mineral or "ash." By cutting thin and transparent slices of coal, +we are further enabled, by means of the microscope, to ascertain +precisely not only that the carbon of the coal is derived from +vegetables, but also, in many cases, what kinds of plants, and what +parts of these, enter into the formation of coal. When examined +in this way, all coals are found to consist more or less entirely +of vegetable matter; but there is considerable difference in +different coals as to the exact nature of this. By Professor +Huxley it has been shown that many of the English coals consist +largely of accumulations of rounded discoidal sacs or bags, which +are unquestionably the seed-vessels or "spore-cases" of certain +of the commoner coal-plants (such as the _Lepidodendra_). The +best bituminous coals seem to be most largely composed of these +spore-cases; whilst inferior kinds possess a progressively increasing +amount of the dull carbonaceous substance which is known as "mineral +charcoal," and which is undoubtedly composed of "the stems and +leaves of plants reduced to little more than their carbon." On +the other hand, Principal Dawson finds that the American coals +only occasionally exhibit spore-cases to any extent, but consist +principally of the cells, vessels, and fibres of the bark, +integumentary coverings, and woody portions of the Carboniferous +plants. + +The number of plants already known to have existed during the +Carboniferous period is so great, that nothing more can be done +here than to notice briefly the typical and characteristic _groups_ +of these--such as the Ferns, the Calamites, the Lepidodendroids, +the Sigillarioids, and the Conifers. + +[Illustration: Fig. 108.--_Odontopteris Schlotheimii_. Carboniferous, +Europe and North America.] + +[Illustration: Fig. 109.--_Calamites cannoeformis_. Carboniferous +Rocks, Europe and North America.] + +In accordance with M. Brongniart's generalisation, that the Palæozoic +period is, botanically speaking, the "Age of Acrogens," we find +the Carboniferous plants to be still mainly referable to the +Flowerless or "Cryptogamous" division of the vegetable kingdom. +The flowering or "Phanerogamous" plants, which form the bulk +of our existing vegetation, are hardly known, with certainty, +to have existed at all in the Carboniferous era, except as +represented by trees related to the existing Pines and Firs, +and possibly by the Cycads or "false palms."[18] Amongst the +"Cryptogams," there is no more striking or beautiful group of +Carboniferous plants than the _Ferns_. Remains of these are found +all through the Carboniferous, but in exceptional numbers in +the Coal-measures, and include both herbaceous forms like the +majority of existing species, and arborescent forms resembling +the living Tree-ferns of New Zealand. Amongst the latter, together +with some new types, are examples of the genera _Psaronius_ and +_Caulopteris_, both of which date from the Devonian. The simply +herbaceous ferns are extremely numerous, and belong to such +widely-distributed and largely-represented genera as _Neuropteris, +Odontopteris_ (fig. 108), _Alethopteris, Pecopteris, Sphenopteris, +Hymenophyllites_, &c. + +[Footnote 18: Whilst the vegetation of the Coal-period was mainly +a terrestrial one, aquatic plants are not unknown. Sea-weeds +(such as the _Spirophyton cauda-Galli_) are common in some of +the marine strata; whilst coal, according to the researches of +the Abbé Castracane, is asserted commonly to contain the siliceous +envelopes of Diatoms.] + +The fossils known as _Calamites_ (fig. 109) are very common in +the Carboniferous deposits, and have given occasion to an abundance +of research and speculation. They present themselves as prostrate +and flattened striated stems, or as similar uncompressed stems +growing in an erect position, and sometimes attaining a length +of twenty feet or more. Externally, the stems are longitudinally +ribbed, with transverse joints at regular intervals, these joints +giving origin to a whorl or branchlets, which mayor may not give +origin to similar whorls of smaller branchlets still. The stems, +further, were hollow, with transverse partitions at the joints, +and having neither true wood nor bark, but only a thin external +fibrous shell. There can be little doubt but that the _Calamites_ +are properly regarded as colossal representatives of the little +Horse-tails (_Equisetaceoe_) of the present day. They agree with +these not only in the general details of their organisation, but +also in the fact that the fruit was a species of cone, bearing +"spore-cases" under scales. According to Principal Dawson, the +_Calamites_ "grew in dense brakes on the sandy and muddy flats, +subject to inundation, or perhaps even in water; and they had +the power of budding out from the base of the stem, so as to +form clumps of plants, and also of securing their foothold by +numerous cord-like roots proceeding from various heights on the +lower part of the stem." + +[Illustration: Fig. 110.--_Lepidodendron Sternbergii_, Carboniferous, +Europe. The central figure represents a portion of the trunk with +its branches, much reduced in size. The right-hand figure is +a portion of a branch with the leaves partially attached to it; +and the left-hand figure represents the end of a branch bearing +a cone of fructification.] + +The _Lepidodendroids_, represented mainly by the genus +_Lepidodendron_ itself (fig. 110), were large tree-like plants, +which attain their maximum in the Carboniferous period, but which +appear to commence in the Upper Silurian, are well represented in +the Devonian, and survive in a diminished form into the Permian. +The trunks of the larger species of _Lepidodendron_ at times +reach a length of fifty feet and upwards, giving off branches in +a regular bifurcating manner. The bark is marked with numerous +rhombic or oval scars, arranged in quincunx order, and indicating +the points where the long, needle-shaped leaves were formerly +attached. The fruit consisted of cones or spikes, carried at the +ends of the branches, and consisting of a central axis surrounded +by overlapping scales, each of which supports a "spore-case" +or seed-vessel. These cones have commonly been described under +the name of _Lepidostrobi_. In the structure of the trunk there +is nothing comparable to what is found in existing trees, there +being a thick bark surrounding a zone principally composed of +"scalariform" vessels, this in turn enclosing a large central +pith. In their general appearance the _Lepidodendra_ bring to mind +the existing Araucarian Pines; but they are true "Cryptogams," +and are to be regarded as a gigantic extinct type of the modern +Club-mosses (_Lycopodiaceoe_). They are amongst the commonest +and most characteristic of the Carboniferous plants; and the +majority of the "spore-cases" so commonly found in the coal appear +to have been derived from the cones of Lepidodendroids. + +The so-called _Sigillanoids_, represented mainly by _Sigillaria_ +itself (fig. 111), were no less abundant and characteristic of +the Carboniferous forests than the _Lepidodendra_. They commence +their existence, so far as known, in the Devonian period, but +they attain their maximum in the Carboniferous; and--unlike the +Lepidodendroids--they are not known to occur in the Permian period. +They are comparatively gigantic in size, often attaining a height +of from thirty to fifty feet or more; but though abundant and +well preserved, great divergence of opinion prevails as to their +true affinities. The _name_ of Sigillarioids (Lat. _sigilla_, +little seals or images) is derived from the fact that the bark +is marked with seal-like impressions or leaf-scars (fig. 111). + +[Illustration: Fig. 111.--Fragment of the external surface of +_Sigillaria Groeseri_, showing the ribs and leaf-scars. The left-hand +figure represents a small portion enlarged. Carboniferous, Europe.] + +Externally, the trunks of _Sigillaria_ present strong longitudinal +ridges, with vertical alternating rows of oval leaf-scars indicating +the points where the leaves were originally attached. The trunk +was furnished with a large central pith, a thick outer bark, +and an intermediate woody zone,--composed, according to Dawson, +partly of the disc-bearing fibres so characteristic of Conifers; +but, according to Carruthers, entirely made up of the "scalariform" +vessels characteristic of Cryptogams. The size of the pith was +very great, and the bark seems to have been the most durable +portion of the trunk. Thus we have evidence that in many cases +the stumps and "stools" of _Sigillarioe_, standing upright in +the old Carboniferous swamps, were completely hollowed out by +internal decay, till nothing but an exterior shell of bark was +left. Often these hollow stumps became ultimately filled up with +sediment, sometimes enclosing the remains of galley-worms, +land-snails, or Amphibians, which formerly found in the cavity +of the trunk a congenial home; and from the sandstone or shale +now filling such trunks some of the most interesting fossils of +the Coal-period have been obtained. There is little certainty +as to either the leaves or fruits of _Sigillaria_, and there +is equally little certainty as to the true botanical position +of these plants. By Principal Dawson they are regarded as being +probably flowering plants allied to the existing "false palms" +or "_Cycads_," but the high authority of Mr Carruthers is to +be quoted in support of the belief that they are Cryptogamic, +and most nearly allied to the Club-mosses. + +[Illustration: Fig. 112.--_Stigmaria ficoides_. Quarter natural +size. Carboniferous.] + +Leaving the botanical position of _Sigillaria_ thus undecided, we +find that it is now almost universally conceded that the fossils +originally described under the name of _Stigmaria_ are the _roots_ +of _Sigillaria_, the actual connection between the two having been +in numerous instances demonstrated in an unmistakable manner. +The _Stigmarioe_ (fig. 112) ordinarily present themselves in +the form of long, compressed or rounded fragments, the external +surface of which is covered with rounded pits or shallow tubercles, +each of which has a little pit or depression in its centre. From +each of these pits there proceeds, in perfect examples, a long +cylindrical rootlet; but in many cases these have altogether +disappeared. In their internal structure, _Stigmaria_ exhibits +a central pith surrounded by a sheath of scalariform vessels, +the whole enclosed in a cellular envelope. The _Stigmarioe_ are +generally found ramifying in the "under-clay," which forms the +floor of a bed of coal, and which represents the ancient soil +upon which the _Sigillarioe_ grew. + +[Illustration: Fig. 113.--_Trigonocarpon ovatum_. Coal-measures, +Britain. (After Liudley and Hutton.)] + +The _Lepidodendroids and Sigillaroids, though the first were +certainly, and the second possibly, Cryptogamic or flowerless +plants, must have constituted the main mass of the forests of +the Coal period; but we are not without evidence of the existence +at the same time of genuine "trees," in the technical sense of +this term--namely, flowering plants with large woody stems. So +far as is certainly known, all the true trees of the Carboniferous +formation were _Conifers_, allied to the existing Pines and Firs. +They are recognised by the great size and concentric woody rings +of their prostrate, rarely erect trunks, and by the presence +of disc-bearing fibres in their wood, as demonstrated by the +microscope; and the principal genera which have been recognised +are _Dadoxylon, Paloeoxylon, Araucarioxylon_, and _Pinites_. +Their fruit is not known with absolute certainty, unless it be +represented, as often conjectured, by _Trigonocarpon_ (fig. 113). +The fruits known under this name are nut-like, often of considerable +size, and commonly three- or six-angled. They probably originally +possessed a fleshy envelope; and if truly referable to the +_Conifers_, they would indicate that these ancient evergreens +produced berries instead of cones, and thus resembled the modern +Yews rather than Pines. It seems, further, that the great group +of the _Cycads_, which are nearly allied to the _Conifers_, and +which attained such a striking prominence in the Secondary period, +probably commenced its existence during the Coal period; but +these anticipatory forms are comparatively few in number, and +for the most part of somewhat dubious affinities. + + + + +CHAPTER XIII. + +THE CARBONIFEROUS PERIOD--Continued. + +ANIMAL LIFE OF THE CARBONIFEROUS. + +We have seen that there exists a great difference as to the mode +of origin of the Carboniferous sediments, some being purely marine, +whilst others are terrestrial; and others, again, have been formed +in inland swamps and morasses, or in brackish-water lagoons, +creeks, or estuaries. A corresponding difference exists necessarily +in the animal remains of these deposits, and in many regions +this difference is extremely well marked and striking. The great +marine limestones which characterise the lower portion of the +Carboniferous series in Britain, Europe, and the eastern portion +of America, and the calcareous beds which are found high up in +the Carboniferous in the western States of America, may, and +do, often contain the remains of drifted plants; but they are +essentially characterised by marine fossils; and, moreover, they +can be demonstrated by the microscope to be almost wholly composed +of the remains of animals which formerly inhabited the ocean. On +the other hand, the animal remains of the beds accompanying the +coal are typically the remains of air-breathing, terrestrial, +amphibious, or aerial animals, together with those which inhabit +fresh or brackish waters. Marine fossils may be found in the +Coal-measures, but they are invariably confined to special horizons +in the strata, and they indicate temporary depressions of the +land beneath the sea. Whilst the distinction here mentioned is +one which cannot fail to strike the observer, it is convenient +to consider the animal life of the Carboniferous as a whole: and +it is simply necessary, in so doing, to remember that the marine +fossils are in general derived from the inferior portion of the +system; whilst the air-breathing, fresh-water, and brackish-water +forms are almost exclusively derived from the superior portion +of the same. + +[Illustration: Fig. 114.--Transparent slice of Carboniferous +Limestone, from Spergen Hill, Indiana, U.S., showing numerous +shells of _Endothyra_ (_Rotalia_), _Baiteyi_ slightly enlarged. +(Original.)] + +[Illustration: Fig. 115.--_Fusulina cylindrica_, Carboniferous +Limestone, Russia.] + +The Carboniferous _Protozoans_ consist mainly of _Foraminifera_ +and _Sponges_. The latter are still very insufficiently known, +but the former are very abundant, and belong to very varied types. +Thin slices of the limestones of the period, when examined by the +microscope, very commonly exhibit the shells of _Foraminifera_ +in greater or less plenty. Some limestones, indeed, are made up of +little else than these minute and elegant shells, often belonging +to types, such as the Textularians and Rotalians, differing little +or not at all from those now in existence. This is the case, for +example, with the Carboniferous Limestone of Spergen Hill in +Indiana (fig. 114), which is almost wholly made up of the spiral +shells of a species of _Endothyra_. In the same way, though to a +less extent, the black Carboniferous marbles of Ireland, and +the similar marbles of Yorkshire, the limestones of the west +of England and of Derbyshire, and the great "Scar Limestones" of +the north of England, contain great numbers of Foraminiferous +shells; whilst similar organisms commonly occur in the shale-beds +associated with the limestones throughout the Lower Carboniferous +series. One of the most interesting of the British Carboniferous +forms is the _Saccammina_ of Mr Henry Brady, which is sometimes +present in considerable numbers in the limestones of Northumberland, +Cumberland, and the west of Scotland, and which is conspicuous +for the comparatively large size of its spheroidal or pear-shaped +shell (reaching from an eighth to a fifth of an inch in size). +More widely distributed are the generally spindle-shaped shells +of _Fusulina_ (fig. 115), which occur in vast numbers in the +Carboniferous Limestone of Russia, Armenia, the Southern Alps, +and Spain, similar forms occurring in equal profusion in the +higher limestones which are found in the Coal-measures of the +United States, in Ohio, Illinois, Indiana, Missouri, &c. Mr Henry +Brady, lastly, has shown that we have in the _Nummulina Pristina_ +of the Carboniferous Limestone of Namur a genuine _Nummulite_, +precursor of the great and important family of the Tertiary +Nummulites. + +[Illustration: Fig. 116--Corals of the Carboniferous Limestone. +a. _Cyathophyllum paracida_, showing young corallites budded +forth from the disc of the old one; a', One of the corallites +of the same, seen in cross-section; b, Fragment of a mass of +_Lithostrotion irregulare_; b', One of the corallites of the +same, divided transversely; c, Portion of the simple cylindrical +coral of _Amplexus coralloides_; c', Transverse section of the +same species; d, _Zaphrentis vermicularis_, showing the depression +or "fossula" on one side of the cup; e, Fragrent of a mass of +_Syringopora ramulosa_; f, Fragment of _Coetetes tumidus_; f', +Portion of the same of the same, enlarged. From the Carboniferous +Limestone of Britain and Belgium. (After Thomson, De Koninck, +Milne-Edwards and Haime, and the Author.)] + +The sub-kingdom of the _Coelenterates_, so far as certainly known, +is represented only by _Corals_;[19] but the remains of these are +so abundant in many of the limestones of the Carboniferous formation +as to constitute a feature little or not at all less conspicuous +than that afforded by the Crinoids. As is the case in the preceding +period, the Corals belong, almost exclusively, to the groups of +the _Rugosa_ and _Tabulata_; and there is a general and striking +resemblance and relationship between the coral-fauna of the Devonian +as a whole, and that of the Carboniferous. Nevertheless, there +is an equally decided and striking amount of difference between +these successive faunas, due to the fact that the great majority +of the Carboniferous _species_ are new; whilst some of the most +characteristic Devonian _genera_ have nearly or quite disappeared, +and several new genera now make their appearance for the first +time. Thus, the characteristic Devonian types _Heliophyllum, +Pachyphyllum, Chonophyllum, Acervularia, Spongophyllum, Smithia, +Endophyllum_, and _Cystiphyllum_, have now disappeared; and the +great masses of _Favosites_ which are such a striking feature +in the Devonian limestones, are represented but by one or two +degenerate and puny successors. On the other hand, we meet in +the Carboniferous rocks not only with entirely new genera--such +as _Axophyllum, Lophophyllum_, and _Londsdaleia_--but we have an +enormous expansion of certain types which had just begun to exist +in the preceding period. This is especially well seen in the Case +of the genus _Lithostrotion_ (fig. 116, b), which more than any +other may be considered as the predominant Carboniferous group of +Corals. All the species of _Lithostrotion_ are compound, consisting +either of bundles of loosely-approximated cylindrical stems, or of +similar "coral-lites" closely aggregated together into astræiform +colonies, and rendered polygonal by mutual pressure. This genus +has a historical interest, as having been noticed as early as in +the year 1699 by Edward Lhwyd; and it is geologically important +from its wide distribution in the Carboniferous rocks of both the +Old and New Worlds. Many species are known, and whole beds of +limestone are often found to be composed of little else than +the skeletons of these ancient corals, still standing upright +as they grew. Hardly less characteristic of the Carboniferous +than the above is the great group of simple "cup-corals," of +which _Clisiophyllum_ is the central type. Amongst types which +commenced in the Silurian and Devonian, but which are still well +represented here, may be mentioned _Syringopora_ (fig. 116, e), +with its colonies of delicate cylindrical tubes united at intervals +by cross-bars; _Zaphrentis_ (fig. 116, d), with its cup-shaped +skeleton and the well-marked depression (or "fossula") on one side +of the calice; _Amplexus_ (fig. 116, c), with its cylindrical, +often irregularly swollen coral and short septa; _Cyathophyllum_ +(fig. 116, a), sometimes simple, sometimes forming great masses +of star-like corallites; and _Choetetes_, with its branched stems, +and its minute, "tabulate" tubes (fig. 116, f). The above, +together with other and hardly less characteristic forms, combine +to constitute a coral-fauna which is not only in itself perfectly +distinctive, but which is of especial interest, from the fact that +almost all the varied types of which it is composed disappeared +utterly before the close of the Carboniferous period. In the +first marine sediments of a calcareous nature which succeeded to +the Coal-measures (the magnesian limestones of the Permian), the +great group of the _Rugose corals_, which flourished so largely +throughout the Silurian, Devonian, and Carboniferous periods, +is found to have all but disappeared, and it is never again +represented save sporadically and by isolated forms. + +[Footnote 19: A singular fossil has been described by Professor +Martin Duncan and Mr Jenkins from the Carboniferous rocks under +the name of _Paloeocoryne_, and has been referred to the Hydroid +Zoophytes (_Corynida_). Doubt, however, has been thrown by other +observers on the correctness of this reference.] + +[Illustration: Fig. 117.--_Platycrinus tricontadactylus_, Lower +Carboniferous. The left-hand figure shows the calyx, arms, and +upper part of the stem; and the figure next this shows the surface +of one of the joints of the column. The right-hand figure shows +the proboscis. (After M'Coy.)] + +[Illustration: Fig. 118.--A, _Pentremites pyriformis_, side-view +of the body ("calyx"); B, The same viewed from below, showing the +arrangement of the plates; C, Body of _Pentremites conoideus_, +viewed from above. Carboniferous.] + +Amongst the _Echinoderms_, by far the most important forms are +the Sea-lilies and the Sea-urchins--the former from their great +abundance, and the latter from their singular structure; but the +little group of the "Pentremites" also requires to be noticed. +The Sea-lilies are so abundant in the Carboniferous rocks, that it +has been proposed to call the earlier portion of the period the +"Age of Crinoids." Vast masses of the limestones of the period +are "crinoidal," being more or less extensively composed of the +broken columns, and detached plates and joints of Sea-lilies, +whilst perfect "heads" may be exceedingly rare and difficult +to procure. In North America the remains of Crinoids are even +more abundant at this horizon than in Britain, and the specimens +found seem to be commonly more perfect. The commonest of the +Carboniferous Crinoids belong to the genera _Cyathocrinus, +Actinocrinus, Platycrinus_, (fig. 117), _Poteriocrinus, Zeacrinus_, +and _Forbesiocrinus_. Closely allied to the Crinoids, or forming +a kind of transition between these and the Cystideans, is the +little group of the "Pentremites," or _Blastoids_ (fig. 118). +This group is first known to have commenced its existence in +the Upper Silurian, and it increased considerably in numbers +in the Devonian; but it was in the seas of the Carboniferous +period that it attained its maximum, and no certain representative +of the family has been detected in any later deposits. The +"Pentremites" resemble the Crinoids in having a cup-shaped body +(fig. 118, A) enclosed by closely-fitting calcareous plates, +and supported on a short stem or "column," composed of numerous +calcareous pieces flexibly articulated together. They differ from +the Crinoids, however, in the fact that the upper surface of +the body does not support the crown of branched feathery "arms," +which are so characteristic of the latter. On the contrary, the +summit of the cup is closed up in the fashion of a flower-bud, +whence the technical name of _Blastoidea_ applied to the group +(Gr. _blastos_, a bud; _eidos_, form). From the top of the cup +radiate five broad, transversely-striated areas (fig. 118, C), +each with a longitudinal groove down its middle; and along each +side of each of these grooves there seems to have been attached +a row of short jointed calcareous filaments or "pinnules." + +[Illustration: Fig. 119.--_Paloechinus ellipticus_, one of the +Carboniferous Sea-urchins. The left-hand figure shows one of the +"ambulacral areas" enlarged, exhibiting the perforated plates. +The right-land figure exhibits a single plate from one of the +"inter-ambulacral areas." (After M'Coy.)] + +A few Star-fishes and Brittle-stars are known to occur in the +Carboniferous rocks; but the only other Echinodemls of this period +which need be noticed are the Sea-urchins (_Echinoids_). Detached +plates and spines of these are far from rare in the Carboniferous +deposits; but anything like perfect specimens are exceedingly +scarce. The Carboniferous Sea-urchins agree with those of the +present day in having the body enclosed in a shell formed by +an enormous number of calcareous plates articulated together. +The shell may be regarded as, typically, nearly spherical in +shape, with the mouth in the centre of the base, and the excretory +opening or vent at its summit. In both the ancient forms and the +recent ones, the plates of the shell are arranged in ten zones +which generally radiate from the summit to the centre of the base. +In five of these zones--termed the "ambulacral areas"--the plates +are perforated by minute apertures or "pores," through which +the animal can protrude the little water-tubes ("tube-feet") by +which its locomotion is carried on. In the other five zones--the +so-called "inter-ambulacral areas"--the plates are of larger +size, and are not perforated by any apertures. In all the modern +Sea-urchins each of these ten zones, whether perforate or +imperforate, is composed of two rows of plates; and there are +thus twenty rows of plates in all. In the Palæozoic Sea-urchins, +on the other hand, the "ambulacral areas" are often like those of +recent forms, in consisting of _two_ rows of perforated plates +(fig. 119); but the "inter-ambulacral areas" are always quite +peculiar in consisting each of three, four, five, or more rows +of large imperforate plates, whilst there are sometimes four +or ten rows of plates in the "ambulacral areas" also: so that +there are many more than twenty rows of plates in the entire +shell. Some of the Palæozoic Sea-urchins, also, exhibit a very +peculiar singularity of structure which is only known to exist +in a very few recently-discovered modern forms (viz., _Calveria_ +and _Phormosoma_). The plates of the inter-ambulacral areas, +namely, overlap one another in an imbricating manner, so as to +communicate a certain amount of flexibility to the shell; whereas +in the ordinary living forms these plates are firmly articulated +together by their edges, and the shell forms a rigid immovable +box. The Carboniferous Sea-urchins which exhibit this extraordinary +peculiarity belong to the genera _Lepidechinus_ and _Lepidesthes_, +and it seems tolerably certain that a similar flexibility of +the shell existed to a less degree in the much more abundant +genus _Archoeocidaris_. The Carboniferous Sea-urchins, like the +modern ones, possessed movable spines of greater or less length, +articulated to the exterior of the shell; and these structures +are of very common occurrence in a detached condition. The most +abundant genera are _Archoeocidaris_ and _Paloechinus_; but the +characteristic American forms belong principally to _Melonites, +Oligoporus_, and _Lepidechinus_. + +[Illustration: Fig. 120.--_Spirorbis (Microconchus) Carbonarius_, +of the natural size, attached to a fossil plant, and magnified. +Carboniferous Britain and North America. (After Dawson.)] + +Amongst the _Annelides_ it is only necessary to notice the little +spiral tubes of _Spirorbis Carbonarius_ (fig. 120), which are +commonly found attached to the leaves or stems of the Coal-plants. +This fact shows that though the modern species of _Spirorbis_ +are inhabitants of the sea, these old representatives of the +genus must have been capable of living in the brackish waters +of lagoons and estuaries. + +[Illustration: Fig. 121.--_Prestwichia rotundata_, a Limuloid +Crustacean. Coal-measures, Britain. (After Henry Woodward.)] + +[Illustration: Fig. 122.--Crustaceans of the Carboniferous Rocks. +a, _Phillipsia seminifera_, of the natural size--Mountain Limestone, +Europe; b, One valve of the shell of _Estheria tenella_, of the +natural size and enlarged--Coal-measures, Europe; c, Bivalved +shell of _Entomoconchus Scouleri_, of the natural size--Mountain +Limestone, Europe; d, _Dithyrocaris Scouleri_, reduced in +size--Mountain Limestone, Ireland; e, _Paloeocaris typus_, slightly +enlarged--Coal-measures, North America; f, _Anthrapaloemon gracilis_, +of the natural size--Coal-measures, North America. (After De +Koninck, M'Coy, Rupert Jones, and Meek and Worthen.)] + +The _Crustaceans_ of the Carboniferous rocks are numerous, and +belong partly to structural types with which we are already familiar, +and partly to higher groups which come into existence here for the +first time. The gigantic _Eurypterids_ of the Upper Silurian and +Devonian are but feebly represented, and make their final exit +here from the scene of life. Their place, however, is taken by +peculiar forms belonging to the allied group of the _Xiphosura_, +represented at the present day by the King-crabs or "Horse-shoe +Crabs" (_Limulus_). Characteristic forms of this group appear +in the Coal-measures both of Europe and America; and though +constituting three distinct genera (_Prestwichia, Belinurus_, +and _Euproöps_), they are all nearly related to one another. The +best known of them, perhaps, is the _Prestwichia rotundala_ of +Coalbrookdale, here figured (fig. 121). The ancient and formerly +powerful order of the _Trilobites_ also undergoes its final +extinction here, not surviving the deposition of the Carboniferous +Limestone series in Europe, but extending its range in America +into the Coal-measures. All the known Carboniferous forms are +small in size and degraded in point of structure, and they are +referable to but three genera (_Phillipsia, Griffithides_, and +_Brachymetopus_), belonging to a single family. The _Phillipsia +seminifera_ here figured (fig. 122, a) is a characteristic species +in the Old World. The Water-fleas (_Ostracoaa_) are extremely +abundant in the Carboniferous rocks, whole strata being often +made up of little else than the little bivalved shells of these +Crustaceans. Many of them are extremely small, averaging about +the size of a millet-seed; but a few forms, such as _Entomoconchus +Scouleni_ (fig. 122, c), may attain a length of from one to +three quarters of an inch. The old group of the _Phyllopods_ +is is likewise still represented in some abundance, partly by +tailed forms of a shrimp-like appearance, such as _Dithyrocaris_ +(fig. 122, d), and partly by the curious striated _Estherioe_ +and their allies, which present a curious resemblance to the +true Bivalve Molluscs (fig. 122, b). Lastly, we meet for the +first time in the Carboniferous rocks with the remains of the +highest of all the groups of _Crustaceans_--namely, the so-called +"Decapods," in which there are five pairs of walking-limbs, and +the hinder end of the body ("abdomen") is composed of separate +rings, whilst the anterior end is covered by a head-shield or +"carapace." All the Carboniferous Decapods hitherto discovered +resemble the existing Lobsters, Prawns, and Shrimps (the _Macrura_), +in having a long and well-developed abdomen terminated by an +expanded tail-fin. The _Paloeocaris typus_ (fig. 122, e) and the +_Anthrapaloemon gracilis_ (fig. 122, f), from the Coal-measures +of Illinois, are two of the best understood and most perfectly +preserved of the few known representatives of the "Long-tailed" +Decapods in the Carboniferous series. The group of the Crabs +or "Short-tailed" Decapods (_Brachyura_), in which the abdomen +is short, not terminated by a tail-fin, and tucked away out of +sight beneath the body, is at present not known to be represented +at all in the Carboniferous deposits. + +[Illustration: Fig. 123.--_Cyclophthalmus senior_. A fossil Scorpion +from the Coal-measures of Bohemia.] + +[Illustration: Fig. 124.--_Xylobius Sigillarioe_, a Carboniferous +Myriapod. a, A specimen, of the natural size; b, Anterior +portion of the same, enlarged; c, Posterior portion, enlarged. +From the Coal-measures of Nova Scotia. (After Dawson.)] + +[Illustration: Fig. 125--_Haplophlebium Barnesi_, a Carboniferous +insect, from the Coal-meastures of Nova Scotia. (After Dawson.)] + +In addition to the water-inhabiting group of the Crustaceans, we +find the articulate animals to be represented by members belonging +to the air-breathing classes of the _Arachnida, Myriapoda_, and +_Insecta_. The remains of these, as might have been expected, are +not known to occur in the marine limestones of the Carboniferous +series, but are exclusively found in beds associated with the Coal, +which have been deposited in lagoons, estuaries, or marshes, in +the immediate vicinity of the land, and which actually represent +an old land-surface. The _Arachnids_ are at present the oldest +known of their class, and are represented both by true Spiders +and Scorpions. Remains of the latter (fig. 123) have been found +both in the Old and New Worlds, and indicate the existence in +the Carboniferous period of Scorpions differing but very little +from existing forms. The group of the _Myriapoda_, including +the recent Centipedes and Galley-worms, is likewise represented +in the Carboniferous strata, but by forms in many respects very +unlike any that are known to exist at the present day. The most +interesting of these were obtained by Principal Dawson, along +with the bones of Amphibians and the shells of Land-snails, in +the sediment filling the hollow trunks of _Sigillaria_, and they +belong to the genera _Xylobius_ (fig. 124) and Archiulus. Lastly, +the true _insects_ are represented by various forms of Beetles +(_Coleoptera_), _Orthoptera_ (such as Cockroaches), and +_Neuropterous_ insects resembling those which we have seen to +have existed towards the close of the Devonian period. One of the +most remarkable of the latter is a huge May-fly (_Haplophlebium +Barnesi_, fig. 125), with netted wings attaining an expanse of +fully seven inches, and therefore much exceeding any existing +Ephemerid in point of size. + +[Illustration: Fig. 126.--Carboniferous _Polyzoa_. a, Fragment +of _Polypora dendroides_, of the natural size, Ireland; a' Small +portion of the same, enlarged to show the cells; b, Glauconome +pulcherrima_, a fragment, of the natural size, Ireland; b', +Portion of the same, enlarged; c, The central screw-like axis +of _Archimedes Wortheni_, of the natural size--Carboniferous, +America; c', Portion of the exterior of the frond of the same, +enlarged; c'', Portion of the interior of the frond of the +same showing the mouths of the cells, enlarged. (After M'Coy and +Hall.)] + +The lower groups of the _Mollusca_ are abundantly represented +in the marine strata of the Carboniferous series by _Polyzoans_ +and _Brachiopods_. Amongst the former, although a variety of other +types are known, the majority still belong to the old group of +the "Lace-corals" (_Fenestellidoe_), some of the characteristic +forms of which are here figured (fig. 126). The graceful netted +fronds of _Fenestella, Retepora_, and _Polypora_ (fig. 126, a) +are highly characteristic, as are the slender toothed branches +of _Glauconome_ (fig. 126, b). A more singular form, however, +is the curious _Archimedes_ (fig. 126, c), which is so +characteristic of the Carboniferous formation of North America. +In this remarkable type, the colony consists of a succession of +funnel-shaped fronds, essentially similar to _Fenestella_ in +their structure, springing in a continuous spiral from a strong +screw-like vertical axis. The outside of the fronds is simply +striated; but the branches exhibit on the interior the mouths of +the little cells in which the semi-independent beings composing +the colony originally lived. + +[Illustration: Fig. 127.--Carboniferous _Braciopoda. a, _Producta +semireticulata_, showing the slightly concave dorsal valve; a' +Side view of the same, showing the convex ventral valve; b, +_Producta longispina_; c, _Orthis resupinata_; d, _Terebratula +hastata_; e, _Athyris subtilita_; f, _Chonetes Hardrensis_; g, +_Rhynchonella pleurodon_; h, _Spirifera trigonalis_. Most of +these forms are widely distributed in the Carboniferous Limestone +of Britain, Europe, America, &c. All the figures are of the natural +size. (After Davidson, De Koninck, and Meek.)] + +The _Brachiopods_ are extremely abundant, and for the most part +belong to types which are exclusively or principally Palæozoic +in their range. The old genera _Strophomena, Orthis_ (fig. 127, +c), _Athyris_ (fig. 127, e), _Rhynchonella_ (fig. 127, g), +and _Spirifera_ (fig. 127, h), are still well represented--the +latter, in particular, existing under numerous specific forms, +conspicuous by their abundance and sometimes by their size. Along +with these ancient groups, we have representatives--for the first +time in any plenty--of the great genus _Terebratula_ (fig. 127, +d), which underwent a great expansion during later periods, +and still exists at the present day. The most characteristic +Carboniferous Brachiopods, however, belong to the family of the +_Productidoe_, of which the principal genus is _Producta_ itself. +This family commenced its existence in the Upper Silurian with +the genus _Chonetes_, distinguished by its spinose hinge-margin. +This genus lived through the Devonian, and flourished in the +Carboniferous (fig. 127, f). The genus _Producta_ itself, +represented in the Devonian by the nearly allied _Productella_, +appeared first in the Carboniferous, at any rate, in force, and +survived into the Permian; but no member of this extensive family +has yet been shown to have over-lived the Palæozoic period. The +_Productoe_ of the Carboniferous are not only exceedingly abundant, +but they have in many instances a most extensive geographical range, +and some species attain what may fairly be considered-gigantic +dimensions. The shell (fig. 127, a and b) is generally more +or less semicircular, with a straight hinge-margin, and having +its lateral angles produced into larger or smaller ears (hence +its generic name--"_cochlea producta_"). One valve (the ventral) +is usually strongly convex, whilst the other (the dorsal) is flat +or concave, the surface of both being adorned with radiating +ribs, and with hollow tubular spines, often of great length. +The valves are not locked together by teeth, and there is no +sign in the fully-grown shell of an opening in or between the +valves for the emission of a muscular stalk for the attachment +of the shell to foreign objects. It is probable, therefore, that +the _Productoe_, unlike the ordinary Lamp-shells, lived an +independent existence, their long spines apparently serving to +anchor them firmly in the mud or ooze of the sea-bottom; but Mr +Robert Etheridge, jun.; has recently shown that in one species +the spines were actually employed as organs of adhesion, whereby +the shell was permanently attached to some extraneous object, +such as the stem of a Crinoid. The two species here figured are +interesting for their extraordinarily extensive geographical +range--_Producta semireticulata_ (fig. 127, a) being found +in the Carboniferous rocks of Britain, the continent of Europe, +Central Asia, China, India, Australia, Spitzbergen, and North +and South America; whilst _P. Longispina_ (fig. 127, b) has +a distribution little if at all less wide. + +[Illustration: Fig. 128.--_Pupa (Dendropupa) vetusta_, a +Carboniferous Land-snail from the Coal-measures of Nova Scotia. +a, The shell, of the natural size; b, The same, magnified; +c, Apex of the shell, enlarged; d, Portion of the surface, +enlarged. (After Dawson.)] + +The higher _Mollusca_ are abundantly represented in the Carboniferous +rocks by Bivalves (_Lamellibranchs_), Univalves (_Gasteropoda_), +Winged-snails (_Pteropoda_), and _Cephalopods_. Amongst the Bivalves +we may note the great abundance of Scallops (_Aviculopecten_ and +other allied forms), together with numerous other types--some of +ancient origin, others represented here for the first time. Amongst +the Gasteropods, we find the characteristically Palæozoic genera +_Macrocheilus_ and _Loxonema_, the almost exclusively Palæozoic +_Euomphalus_, and the persistent, genus _Pleurotomaria_; whilst +the free-swimming Univalves (_Heteropoda_)are represented by +_Bellerophon_ and _Porcellia_, and the _Pteropoda_ by the old +genus _Conularia_. With regard to the Carboniferous Univalves, +it is also of interest to note here the first appearance of true +air-breathing or terrestrial Molluscs, as discovered by Dawson +and Bradley in the Coal-measures of Nova Scotia and Illinois. Some +of these (_Conulus priscus_) are true Land-snails, resembling the +existing _Zonites_; whilst others (_Pupa vetusta_, fig. 128) appear +to be generically inseparable from the "Chrysalis-shells" (_Pupa_) +of the present day. All the known forms--three in number--are of +small size, and appear to have been local in their distribution +or in their preservation. More important, however, than any of +the preceding, are the _Cephalopoda_, represented, as before, +exclusively by the chambered shells of the Tetrabranchiates. +The older and simpler type of these, with simple plain septa, +and mostly a central siphuncle, is represented by the straight +conical shells of the ancient genus Orthoceras, and the bow-shaped +shells of the equally ancient _Cyrtoceras_--some of the former +attaining a great size. The spirally-curved discoidal shells +of the persistent genus _Nautilus_ are also not unknown, and +some of these likewise exhibit very considerable dimensions. +Lastly, the more complex family of the _Ammonitidoe_, with lobed +or angulated septa, and a dorsally-placed siphuncle (situated on +the convex side of the curved shells), now for the first time +commences to acquire a considerable prominence. The principal +representative of this group is the genus _Goniatites_ (fig. +129), which commenced its existence in the Upper Silurian, is well +represented in the Devonian, and attains its maximum here. In this +genus, the shell is spirally curved, the septa are strongly lobed +or angulated, though not elaborately frilled as in the Ammonites, +and the siphuncle is dorsal. In addition to _Goniatites_, the +shells of true _Ammonites_, so characteristic of the Secondary +period, have been described by Dr Waagen as occurring in the +Carboniferous rocks of India. + +[Illustration: Fig. 129.--_Goniatites (Aganides) Fossoe_. +Carboniferous Limestone.] + +[Illustration: Fig. 130.--_Amblypterus macropterus_. Carboniferous.] + +Coming finally to the _Vertebrata_, we have in the first place +to very briefly consider the Carboniferous _fishes_. These are +numerous; but, with the exception of the still dubious "Conodonts," +belong wholly to the groups of the _Ganoids_ and the _Placoids_ +(including under the former head remains which perhaps are truly +referable to the group of the _Dipnoi_ or Mud-fishes). Amongst the +_Ganoids_, the singular buckler-headed fishes of the Upper Silurian +and Devonian (_Cephalaspidoe_) have apparently disappeared; and +the principal types of the Carboniferous belong to the groups +respectively represented at the present day by the Gar pike +(_Lepidosteus_) of the North American lakes, and the _Polypterus_ +of the rivers of Africa. Of the former, the genera _Paloeoniscus_ +and _Amblypterus_ (fig. 130), with their small rhomboidal and +enamelled scales, and their strongly unsymmetrical tails, are +perhaps the most abundant. Of the latter, the most important are +species belonging to the genera _Megalichthys_ and _Rhizodus_, +comprising large fishes, with rhomboidal scales, unsymmetrical +("heterocercal") tails, and powerful conical teeth. These fishes +are sometimes said to be "sauroid," from their presenting some +Reptilian features in their organisation, and they must have been +the scourges of the Carboniferous seas. The remains of _Placoid_ +fishes in the Carboniferous strata are very numerous, but consist +wholly of teeth and fin-spines, referable to forms more or less +closely allied to our existing Port Jackson Sharks, Dog-fishes, +and Rays. The teeth are of very various shapes and sizes,--some +with sharp, cutting edges (_Petalodus, Cladodus_, &c.); others in +the form of broad crushing plates, adapted, like the teeth of the +existing Port Jackson Shark (_Cestracion Philippi_), for breaking +down the hard shells of Molluscs and Crustaceans. Amongst the many +kinds of these latter, the teeth of _Psammodus_ and _Cochliodus_ +(fig. 131) may be mentioned as specially characteristic. The +fin-spines are mostly similar to those so common in the Devonian +deposits, consisting of hollow defensive spines implanted in +front of the pectoral or other fins, usually slightly curved, +often superficially ribbed or sculptured, and not uncommonly +serrated or toothed. The genera _Ctenacanthus, Gyracanthus, +Homacanthus_, &c., have been founded for the reception of these +defensive weapons, some of which indicate fishes of great size +and predaceous habits. + +[Illustration: Fig. 131.--Teeth of _Cochliodus contortus_. +Carboniferous Limestone, Britain.] + +[Illustration: Fig. 132.--a, Upper surface of the skull of +_Anthracosaurus Russelli_, one-sixth of the natural size: b, +Part of one of the teeth cut across, and highly magnified to +show the characteristic labyrinthine structure; c, One of the +integumentary shields or scales, one-half of the natural size. +Coal-measures, Northumberland. (After Atthey.)] + +In the Devonian rocks we meet with no other remains of +Vertebrated animals save fishes only; but the Carboniferous +deposits have yielded remains of the higher group +of the _Amphibians_. This class, comprising our existing +Frogs, Toads, and Newts, stands to some extent in a position midway +between the class of the fishes and that of the true +reptiles, being distinguished from the latter by the fact +that its members invariably possess gills in their early +condition, if not throughout life; whilst they are separated from +the former by always possessing true lungs when adult, and +by the fact that the limbs (when present at all) are never in +the form of fins. The Amphibians, therefore, are all +water-breathers when young, and have respiratory organs adapted +for an aquatic mode of life; whereas, when grown up, they +develop lungs, and with these the capacity for breathing air +directly. Some of them, like the Frogs and Newts, lose their +gills altogether on attaining the adult condition; but others, +such as the living _Proteus_ and _Menobranchus_, retain +their gills even after acquiring their lungs, and are thus fitted +indifferently for an aquatic or terrestrial existence. The name of +"Amphibia," though applied to the whole class, is thus not +precisely appropriate except to these last-mentioned forms +(Gr. _amphi_, both; _bios_, life). The Amphibians also +differ amongst themselves according as to whether they keep +permanently the long tail which they all possess when young (as +do the Newts and Salamanders), or lose this appendage when +grown up (as do the Frogs and Toads). Most of them have +naked skins, but a few living and many extinct forms have +hard structures in the shape of scales developed in the integument. +All of them have well-ossified skeletons, though some +fossil types are partially deficient in this respect; and all of +them which possess limbs at all have these appendages supported +by bones essentially similar to those found in the limbs +of the higher Vertebrates. All the Carboniferous Amphibians +belong to a group which has now wholly passed away--namely, +that of the _Labyrinthodonts_. In the marine strata which +form the base of the Carboniferous series these creatures have only +been recognised by their curious hand-shaped footprints, similar +in character to those which occur in the Triassic rocks, and which +will be subsequently spoken of under the name of _Cheirotherium_. +In the Coal-measures of Britain, the continent of Europe, and +North America, however, many bones of these animals have +been found, and we are now tolerably well acquainted with a +considerable number of forms. All of them seem to have +belonged to the division of Amphibians in which the long tail +of the young is permanently retained; and there is evidence +that some of them kept the gills also throughout life. The skull +is of the characteristic Amphibian type (fig. 132, a), with +two occipital condyles, and having its surface singularly pitted +and sculptured; and the vertebræ are hollowed out at both +ends. The lower surface of the body was defended by an armour +of singular integumentary shields or scales (fig. 132, c); +and an extremely characteristic feature (from which the entire +group derives its name) is, that the walls of the teeth are deeply +folded, so as to give rise to an extraordinary "labyrinthine" +pattern when they are cut across (fig. 132, b). Many of the +Carboniferous Labyrinthodonts are of no great size, some of +them very small, but others attain comparatively gigantic +dimensions, though all fall short in this respect of the huge +examples of this group which occur in the Trias. One of the +largest, and at the same time most characteristic, forms of the +Carboniferous series, is the genus _Anthracosaurus_, the +skull of which is here figured. + +No remains of true Reptiles, Birds, or Quadrupeds have as yet +been certainly detected in the Carboniferous deposits in any part +of the world. It should, however, be mentioned, that Professor +Marsh, one of the highest authorities on the subject, has described +from the Coal-formation of Nova Scotia certain vertebræ which +he believes to have belonged to a marine reptile (_Eosaurus +Acadianus_), allied to the great _Ichthyosauri_ of the Lias. Up to +this time no confirmation of this determination has been obtained +by the discovery of other and more unquestionable remains, and +it therefore remains doubtful whether these bones of _Eosaurus_ +may not really belong to large Labyrinthodonts. + + +LITERATURE. + +The following list contains some of the more important of the +original sources of information to which the student of Carboniferous +rocks and fossils may refer:-- + + (1) 'Geology of Yorkshire,' vol. ii.; 'The Mountain Limestone + District.' John Phillips. + (2) 'Siluria.' Sir Roderick Murchison. + (3) 'Memoirs of the Geological Survey of Great Britain and Ireland.' + (4) 'Geological Report on Londonderry,' &c. Portlock. + (5) 'Acadian Geology.' Dawson. + (6) 'Geology of Iowa,' vol. i. James Hall. + (7) 'Reports of the Geological Survey of Illinois' (Geology and + Palæontology). Meek, Worthen, &c. + (8) 'Reports of the Geological Survey of Ohio' (Geology and + Palæontology). Newberry, Cope, Meek, Hall, &c. + (9) 'Description des Animaux fossiles qui se trouvent dans le + Terrain Carbonifère de la Belgique,' 1843; with subsequent + monographs on the genera _Productus_ and _Chonetes_, + on _Crinoids_, on _Corals_, &c. De Koninck. +(10) 'Synopsis of the Carboniferous Fossils of Ireland.' M'Coy. +(11) 'British Palæozoic Fossils.' M'Coy. +(12) 'Figures of Characteristic British Fossils.' Baily. +(13) 'Catalogue of British Fossils.' Morris. +(14) 'Monograph of the Carboniferous Brachiopoda of Britain' + (Palæontographical Society). Davidson. +(15) 'Monograph of the British Carboniferous Corals' + (Palæontographical Society). Milne-Edwards and Haime. +(16) 'Monograph of the Carboniferous Bivalve Entomostraca of + Britain' (Palæontographical Society). Rupert Jones, Kirkby, and + George S. Brady. +(17) 'Monograph of the Carboniferous Foraminifera of Britain' + (Palæontographical Society). H. B. Brady. +(18) "On the Carboniferous Fossils of the West of Scotland"--'Trans. + Geol. Soc.,' of Glasgow, vol. iii., Supplement. Young and + Armstrong. +(19) 'Poissons Fossiles.' Agassiz. +(20) "Report on the Labyrinthodonts of the Coal-measures"--'British + Association Report,' 1873. L. C. Miall. +(21) 'Introduction to the Study of Palæontological Botany.' John + Hutton Balfour. +(22) 'Traité de Paléontologie Végétale.' Schimper. +(23) 'Fossil Flora.' Lindley and Hutton. +(24) 'Histoire des Végétaux Fossiles.' Brongniart. +(25) 'On Calamites and Calamodendron' (Monographs of the + Palæontographical Society). Binney. +(26) 'On the Structure of Fossil Plants found in the Carboniferous + Strata' (Palæontographical Society). Binney. + +Also numerous memoirs by Huxley, Davidson, Martin Duncan, Professor +Young, John Young, R. Etheridge, jun., Baily, Carruthers, Dawson, +Binney, Williamson, Hooker, Jukes, Geikie, Rupert Jones, Salter, +and many other British and foreign observers. + + + + +CHAPTER XIV. + +THE PERMIAN PERIOD. + +The Permian formation closes the long series of the Palæozoic +deposits, and may in some respects be considered as a kind of +appendix to the Carboniferous system, to which it cannot be compared +in importance, either as regards the actual bulk of its sediments +or the interest and variety of its life-record. Consisting, as +it does, largely of red rocks--sandstones and marls--for the +most part singularly destitute of organic remains, the Permian +rocks have been regarded as a lacustrine or fluviatile deposit; +but the presence of well-developed limestones with indubitable +marine remains entirely negatives this view. It is, however, +not improbable that we are presented in the Permian formation, +as known to us at present, with a series of sediments laid down +in inland seas of great extent, due to the subsidence over large +areas of the vast land-surfaces of the Coal-measures. This view, +at any rate, would explain some of the more puzzling physical +characters of the formation, and would not be definitely negatived +by any of its fossils. + +A large portion of the Permian series, as already remarked, consists +of sandstones and marls, deeply reddened by peroxide of iron, and +often accompanied by beds of gypsum or deposits of salt. In strata +of this nature few or no fossils are found; but their shallow-water +origin is sufficiently proved by the presence of the footprints +of terrestrial animals, accompanied in some cases by well-defined +"ripple-marks." Along with these are occasionally found massive +breccias, holding larger or smaller blocks derived from the older +formations; and these have been supposed to represent an old +"boulder-clay," and thus to indicate the prevalence of an arctic +climate. Beds of this nature must also have been deposited in +shallow water. In all regions, however, where the Permian formation +is well developed, one of its most characteristic members is a +Magnesian limestone, often highly and fantastically concretionary, +but containing numerous remains of genuine marine animals, and +clearly indicating that it was deposited beneath a moderate depth +of salt water. + +It is not necessary to consider here whether this formation can +be retained as a distinct division of the geological series. The +name of _Permian_ was given to it by Sir Roderick Murchison, +from the province of Perm in Russia, where rocks of this age are +extensively developed. Formerly these rocks were grouped with +the succeeding formation of the Trias under the common name of +"New Red Sandstone." This name was given them because they contain +a good deal of red sandstone, and because they are superior to the +Carboniferous rocks, while the Old Red Sandstone is inferior. +Nowadays, however, the term "New Red Sandstone" is rarely employed, +unless it be for red sandstones and associated rocks, which are +seen to overlie the Coal-measures, but which contain no fossils by +which their exact age may be made out. Under these circumstances, +it is sometimes convenient to employ the term "New Red Sandstone." +The New Red, however, of the older geologists, is now broken up +into the two formations of the Permian and Triassic rocks--the +former being usually considered as the top of the Palæozoic series, +and the latter constituting the base of the Mesozoic. + +In many instances, the Permian rocks are seen to repose unconformably +upon the underlying Carboniferous, from which they can in addition +be readily separated by their lithological characters. In other +instances, however, the Coal-measures terminate upwards in red +rocks, not distinguishable by their mineral characters from the +Permian; and in other cases no physical discordance between the +Carboniferous and Permian strata can be detected. As a general +rule, also, the Permian rocks appear to pass upwards conformably +into the Trias. The division, therefore, between the Permian +and Triassic rocks, and consequently between the Palæozoic and +Mesozoic series, is not founded upon any conspicuous or universal +physical break, but upon the difference in life which is observed +in comparing the marine animals of the Carboniferous and Permian +with those of the Trias. It is to be observed, however, that +this difference can be solely due to the fact that the Magnesian +Limestone of the Permian series presents us with only a small, +and not a typical, portion of the marine deposits which must have +been accumulated in some area at present unknown to us during the +period which elapsed between the formation of the great marine +limestones of the Lower Carboniferous and the open-sea and likewise +calcareous sediments of the Middle Trias. + +The Permian rocks exhibit their most typical features in Russia +and Germany, though they are very well developed in parts of +Britain, and they occur in North America. When well developed, +they exhibit three main divisions: a lower set of sandstones, +a middle group, generally calcareous, and an upper series of +sandstones, constituting respectively the Lower, Middle, and Upper +Permians. + +In Russia, Germany, and Britain, the Permian rocks consist of +the following members:-- + +1. The _Lower Permians_, consisting mainly of a great series +of sandstones, of different colours, but usually red. The base +of this series is often constituted by massive breccias with +included fragments of the older rocks, upon which they may happen +to repose; and similar breccias sometimes occur in the upper +portion of the series as well. The thickness of this group varies +a good deal, but may amount to 3000 or 4000 feet. + +2. The _Middle Permians_, consisting, in their typical development, +of laminated marls, or "marl-slate," surmounted by beds of magnesian +limestone (the "Zechstein" of the German geologists). Sometimes +the limestones are degenerate or wholly deficient, and the series +may consist of sandy shales and gypsiferous clays. The magnesian +limestone, however, of the Middle Permians is, as a rule, so well +marked a feature that it was long spoken of as _the_ Magnesian +Limestone. + +3. The _Upper Permians_, consisting of a series of sandstones +and shales, or of red or mottled marls, often gypsiferous, and +sometimes including beds of limestone. + +In North America, the Permian rocks appear to be confined to the +region west of the Mississippi, being especially well developed +in Kansas. Their exact limits have not as yet been made out, +and their total thickness is not more than a few hundred feet. +They consist of sandstones, conglomerates, limestones, marls, +and beds of gypsum. + +The following diagrammatic section shows the general sequence of +the Permian deposits in the north of England, where the series +is extensively developed (fig. 133):-- + +[Illustration: Fig. 133. GENERALISED SECTION OF THE PERMIAN ROCKS +IN THE NORTH OF ENGLAND.] + +The record of the _life_ of the Permian period is but a scanty +one, owing doubtless to the special peculiarities of such of the +deposits of this age with which we are as yet acquainted. Red rocks +are, as a general rule, more or less completely unfossiliferous, and +sediments of this nature are highly characteristic of the Permian. +Similarly, magnesian limestones are rarely as highly charged with +organic remains as is the case with normal calcareous deposits, +especially when they have been subjected to concretionary action, +as is observable to such a marked extent in the Permian limestones. +Nevertheless, much interest is attached to the organic remains, +as marking a kind of transition-period between the Palæozoic +and Mesozoic epochs. + +[Illustration: Fig. 134.--_Walchia piniformis_, from the Permian +of Saxony, a, Branch; b, Twig, (After Gutbier.)] + +The _plants_ of the Permian period, as a whole, have a distinctly +Palæozoic aspect, and are far more nearly allied to those of the +Coal-measures than they are to those of the earlier Secondary +rocks; though the Permian _species_ are mostly distinct from +the Carboniferous, and there are some new genera. Thus, we find +species of _Lepidodendron, Calamites, Equisetites, Asterophyllites, +Annularia_, and other highly characteristic Carboniferous genera. +On the other hand, the _Sigillariods_ of the Coal seem to have +finally disappeared at the close of the Carboniferous period. Ferns +are abundant in the Permian rocks, and belong for the most part to +the well-known Carboniferous genera _Alethopteris, Neuropteris, +Sphenopteris_, and _Pecopteris_. There are also Tree-ferns referable +to the ancient genus _Psaronius_. The _Conifers_ of the Permian +period are numerous, and belong in part to Carboniferous genera. +A characteristic genus, however, is _Walchia_ (fig. 134), +distinguished by its lax short leaves. This genus, though not +exclusively Permian, is mainly so, the best-known species being +the _W. Piniformis_. Here, also, we meet with Conifers which +produce true cones, and which differ, therefore, in an important +degree from the Taxoid Conifers of the Coal-measures. Besides +_Walchia_, a characteristic form of these is the _Ullmania +selaginoides_, which occurs in the Magnesian Limestone of Durham, +the Middle Permian of Westmorland, and the "Kupfer-schiefer" of +Germany. The group of the _Cycads_, which we shall subsequently +find to be so characteristic of the vegetation of the Secondary +period, is, on the other hand, only doubtfully represented in +the Permian deposits by the singular genus _Noeggerathia_. + +The _Protozoans_ of the Permian rocks are few in number, and +for the most part imperfectly known. A few _Foraminifera_ have +been obtained from the Magnesian Limestone of England, and the +same formation has yielded some ill-understood Sponges. It does +not seem, however, altogether impossible that some of the singular +"concretions" of this formation may ultimately prove to have an +organic structure, though others would appear to be clearly of +purely inorganic origin. From the Permian of Saxony, Professor +Geinitz has described two species of _Spongillopsis_, which he +believes to be most nearly allied to the existing fresh-water +Sponges (_Spongilla_). This observation has an interest as bearing +upon the mode of deposition and origin of the Permian sediments. + +The _Coelenterates_ are represented in the Permian by but a few +Corals. These belong partly to the _Tabulate_ and partly to the +_Rugose_ division; but the latter great group, so abundantly +represented in Silurian, Devonian, and Carboniferous seas, is +now extraordinarily reduced in numbers, the British strata of +this age yielding only species of the single genus _Polycoelia_. +So far, therefore, as at present known, all the characteristic +genera of the Rugose Corals of the Carboniferous had become extinct +before the deposition of the limestones of the Middle Permian. + +The _Echinoderms_ are represented by a few _Crinoids_, and by a +Sea-urchin belonging to the genus _Eocidaris_. The latter genus +is nearly allied to the _Archoeocidaris_ of the Carboniferous, so +that this Permian form belongs to a characteristically Palæozoic +type. + +A few _Annelides_ (_Spirorbis, Vermilia_, &c.) have been described, +but are of no special importance. Amongst the _Crustaceans_, +however, we have to note the total absence of the great Palæozoic +group of the _Trilobites_; whilst the little _Ostracoda_ and +_Phyllopods_ still continue to be represented. We have also to +note the first appearance here of the "Short-tailed" Decapods or +Crabs (_Brachyura_), the highest of all the groups of _Crustacea_, +in the person of _Hemitrochiscus paradoxus_, an extremely minute +Crab from the Permian of Germany. + +[Illustration: Fig. 135.--Brachiopods of the Permian formation. +a, _Producta horrida_; b, _Lingula Credneri_; c, _Terebratula +elongata_; d and e, _Camarophoria globulina_. (After King.)] + +Amongst the _Mollusca_, the remains of _Polyzoa_ may fairly be +said to be amongst the most abundant of all the fossils of the +Permian formation, The principal forms of these are the fronds +of the Lace-corals (_Fenestella, Retepora_, and _Synocladia_), +which are very abundant in the Magnesian Limestone of the north +of England, and belong to various highly characteristic species +(such as _Fenestella retiformis, Retepora Ehrenbergi_, and +_Synocladia virgulacea_). The _Brachiopoda_ are also represented +in moderate numbers in the Permian. Along with species of the +persistent genera _Discina, Crania_, and _Lingula_, we still +meet with representatives of the old groups _Spirifera, Athyris_, +and _Streptorhynchus_; and the Carboniferous _Productoe_ yet +survive under well-marked and characteristic types, though in +much-diminished numbers. The species of Brachiopods here figured +(fig. 135) are characteristic of the Magnesian Limestone in Britain +and of the corresponding strata on the Continent. Upon the whole, +the most characteristic Permian _Brachiopods_ belong to the genera +_Producta, Strophalosia_, and _Camarophoria_. + +The _Bivalves_ (_Lamellibranchiata_) have a tolerably varied +development in the Permian rocks; but nearly all the old types, +except some of those which occur in the Carboniferous, have now +disappeared. The principal Permian Bivalves belong to the groups +of the Pearl Oysters (_Aviculidoe_) and the _Trigoniadoe_, +represented by genera such as _Bakewellia_ and _Schizodus_; the +true Mussels (_Mytilidoe_), represented by species which have +been referred to _Mytilus_ itself; and the Arks (_Arcadoe_), +represented by species of the genera _Arca_ (fig. 136) and +_Byssoarca_. The first and last of these three families have a +very ancient origin; but the family of the _Trigoniadoe_, though +feebly represented at the present day, is one which attained +its maximum development in the Mesozoic period. + +[Illustration: Fig. 136.--_Arca antiqua_. Permian.] + +The _Univalves_ (_Gasteropoda_) are rare, and do not demand special +notice. It may be observed, however, that the Palæozoic genera +_Euomphalus, Murchisonia, Loxonema_, and _Macrocheilus_ are still +in existence, together with the persistent genus _Pleurotomaria_. +_Pteropods_ of the old genera _Theca_ and _Conularia_ have been +discovered; but the first of these characteristically Palæozoic +types finally dies out here, and the second only survives but a +short time longer. Lastly, a few _Cephalopods_ have been found, +still wholly referable to the Tetrabranchiate group, and belonging +to the old genera _Orthoceras_ and _Cyrtoceras_ and the long-lived +_Nautilus_. + +[Illustration: Fig. 137.--_Platysomus gibbosus_, a "heterocercal" +Ganoid, from the Middle Permian of Russia.] + +Amongst _Vertebrates_, we meet in the Permian period not only +with the remains of Fishes and Amphibians, but also, for the +first time, with true Reptiles. The _Fishes_ are mainly _Ganoids_, +though there are also remains of a few Cestraciont Sharks. Not +only are the _Ganoids_ still the predominant group of Fishes, but +all the known forms possess the unsymmetrical ("heterocercal") +tail which is so characteristic of the Palæozoic Ganoids. Most +of the remains of the Permian Fishes have been obtained from the +"Marl-slate" of Durham and the corresponding "Kupfer-schiefer" of +Germany, on the horizon of the Middle Permian; and the principal +genera of the Ganoids are _Paloeoniscus_ and _Platysomus_ (fig. +137). + +The _Amphibians_ of the Permian period belong principally to the +order of the _Labyrinthodonts_, which commenced to be represented +in the Carboniferous, and has a large development in the Trias. +Under the name, however, of _Paloeosiren Beinerti_, Professor +Geinitz has described an Amphibian from the Lower Permian of +Germany, which he believes to be most nearly allied to the existing +"Mud-eel" (_Siren lacertina_) of North America, and therefore +to be related to the Newts and Salamanders (_Urodela_). + +[Illustration: Fig. 138.--_Protorosaurus Speneri_, Middle Permian, +Thuringia, reduced in size. (After Von Meyer.) [Copied from Dana.]] + +Finally, we meet in the Permian deposits with the first undoubted +remains of true _Reptiles_. These are distinguished, as a class, +from the _Amphibians_, by the fact that they are air-breathers +throughout the whole of their life, and therefore are at no time +provided with gills; whilst they are exempt from that metamorphosis +which all the _Amphibia_ undergo in early life, consequent upon +their transition from an aquatic to a more or less purely aerial +mode of respiration. Their skeleton is well ossified; they usually +have horny or bony plates, singly or in combination, developed +in the skin; and their limbs (when present) are never either +in the form of _fins_ or _wings_, though sometimes capable of +acting in either of these capacities, and liable to great +modifications of form and structure. Though there can be no doubt +whatever as to the occurrence of genuine Reptiles in deposits of +unquestionable Permian age, there is still uncertainty as to the +precise number of types which may have existed at this period. +This uncertainty arises partly from the difficulty of deciding +in all cases, whether a given bone be truely Labyrinthodont or +Reptilian, but more especially from the confusion which exists at +present between the Permian and the overlying Triassic deposits. +Thus there are various deposits in different regions which have +yielded the remains of Reptiles, and which cannot in the meanwhile +be definitely referred either to the Permian series or to the +Trias by clear stratigraphical or palæontological evidence. All +that can be done in such cases is to be guided by the characters +of the Reptiles themselves, and to judge by their affinities to +remains from known Triassic or Permian rocks to which of these +formations the beds containing them should be referred; but it +is obvious that this method of procedure is seriously liable +to lead to error. In accordance, however, with this, the only +available mode of determination in some cases, the remains of +_Thecodontosaurus_ and _Palæosaurus_ discovered in the dolomitic +conglomerates near Bristol will be considered as Triassic, thus +leaving _Protorosaurus_[20] as the principal and most important +representative of the Permian Reptiles.[21] The type-species of +the genus _Protorusaurus_ is the _P. Speneri_(fig. 138) of the +"Kupfer-schiefer" of Thuringia, but other allied species have +been detected in the Middle Permian of Germany and the north +of England. This Reptile attained a length of from three to four +feet; and it has been generally referred to the group of the +Lizards (_Lacertilia_), to which it is most nearly allied in +its general structure, at the same time that it differs from +all existing members of this group in the fact that its numerous +conical and pointed teeth were implanted in distinct sockets in +the jaws--this being a Crocodilian character. In other respects, +however, _Protorosaurus_ approximates closely to the living Monitors +(_Varanidoe_); and the fact that the bodies of the vertebræ are +slightly cupped or hollowed out at the ends would lead to the +belief that the animal was aquatic in its habits. At the same +time, the structure of the hind-limbs and their bony supports +proves clearly that it must have also possessed the power of +progression upon the land. Various other Reptilian bones have +been described from the Permian formation, of which some are +probably really referable to Labyrinthodonts, whilst others are +regarded by Professor Owen as referable to the order of the +"Theriodonts," in which the teeth are implanted in sockets, and +resemble those of carnivorous quadrupeds in consisting of three +groups in each jaw (namely, incisors, canines, and molars). Lastly, +in red sandstones of Permian age in Dumfriesshire have been +discovered the tracks of what would appear to have been _Chelonians_ +(Tortoises and Turtles); but it would not be safe to accept this +conclusion as certain upon the evidence of footprints alone. The +_Chelichnus Duncani_, however, described by Sir William Jardine +in his magnificent work on the 'Ichnology of Annandale,' bears +a great resemblance to the track of a Turtle. + +[Footnote 20: Though commonly spelt as above, it is probable +that the name of this Lizard was really intended to have been +_Proterosaurus_--from the Greek _proteros_, first; and _saura_, +lizard: and this spelling is followed by many writers.] + +[Footnote 21: In an extremely able paper upon the subject (Quart. +Journ. Geol. Soc., vol. xxvi.), Mr Etheridge has shown that there +are good physical grounds for regarding the dolomitie conglomerate +of Bristol as of Triassic age, and as probably corresponding in +time with the Muschelkalk of the Continent.] + +No remains of Birds or Quadrupeds have hitherto been detected +in deposits of Permian age. + + +LITERATURE. + +The following works may be consulted by the student with regard +to the Permian formation and its fossils:-- + + (1) "On the Geological Relations and Internal Structure of the + Magnesian Limestone and the Lower Portions of the New Red + Sandstone Series, &c."--'Trans. Geol. Soc.,' ser. 2, vol. iii. + Sedgwick. + (2) 'The Geology of Russia in Europe.' Murchison, De Verneuil, and + Von Keyserling. + (3) 'Siluria,' Murchison. + (4) 'Permische System in Sachsen.' Geinitz and Gutbier. + (5) 'Die Versteinerungen des Deutschen Zechsteingebirges,' Geinitz. + (6) 'Die Animalischen Ueberreste der Dyas.' Geinitz. + (7) 'Monograph of the Permian Fossils of England' (Palæontographical + Society). King. + (8) 'Monograph of the Permian Brachiopoda of Britain' + (Palæontographical Society). Davidson. + (9) "On the Permian Rocks of the North-West of England and their + Extension into Scotland"--'Quart. Journ. Geol. Soc.,' vol. xx. + Murchison and Harkness. +(10) 'Catalogue of the Fossils of the Permian System of the Counties + of Northumberland and Durham.' Howse. +(11) 'Petrefacta Germaniæ.' Goldfuss. +(12) 'Beiträge zur Petrefaktenkunde.' Munster. +(13) 'Ein Beitrag zur Palæontologie des Deutschen Zechsteingebirges.' + Von Schauroth. +(14) 'Saurier aus dem Kupfer-schiefer der Zechstein-formation.' Von + Meyer. +(15) 'Manual of Palæontology.' Owen. +(16) 'Recherches sur les Poissons Fossiles.' Agassiz. +(17) 'Ichnology of Annandale.' Sir William Jardine. +(18) 'Die Fossile Flora der Permischen Formation.' Goeppert. +(19) 'Genera et Species Plantarum Fossilium.' Unger. +(20) "On the Red Rocks of England of older Date than the Trias" + --'Quart. Journ. Geol. Soc.,' vol. xxvii. Ramsay. + + + + +CHAPTER XV. + +THE TRIASSIC PERIOD. + +We come now to the consideration of the great _Mesozoic_, or +Secondary series of formations, consisting, in ascending order, +of the Triassic, Jurassic, and Cretaceous systems. The Triassic +group forms the base of the Mesozoic series, and corresponds +with the higher portion of the New Red Sandstone of the older +geologists. Like the Permian rocks, and as implied by its name, +the _Trias_ admits of a subdivision into three groups--a Lower, +Middle, and Upper Trias. Of these sub-divisions the middle one +is wanting in Britain; and all have received German names, being +more largely and typically developed in Germany than in any other +country. Thus, the Lower Trias is known as the _Bunter Sandstein_; +the Middle Trias is called the _Muschelkalk_; and the Upper Trias +is known as the _Keuper_. + +I. The lowest division of the Trias is known as the _Bunter +Sandstein_ (the _Grès bigarré_ of the French), from the generally +variegated colours of the beds which compose it (German, _bunt_, +variegated). The Bunter Sandstein of the continent of Europe +consists of red and white sandstones, with red clays, and thin +limestones, the whole attaining a thickness of about 1500 feet. +The term "marl" is very generally employed to designate the clays +of the Lower and Upper Trias; but the term is inappropriate, as +they may contain no lime, and are therefore not always genuine +marls. In Britain the Bunter Sandstein consists of red and mottled +sandstones, with unconsolidated conglomerates, or "pebble-beds," +the whole having a thickness of 1000 to 2000 feet. The Bunter +Sandstein, as a rule, is very barren of fossils. + +II. The Middle Trias is not developed in Britain, but it is largely +developed in Germany, where it constitutes what is known as the +_Muschelkalk_ (Germ. _Muschel_, mussel; _kalk_, limestone), from +the abundance of fossil shells which it contains. The Muschelkalk +(the _Calcaire coquillier_ of the French) consists of compact +grey or yellowish limestones, sometimes dolomitic, and including +occasional beds of gypsum and rock-salt. + +III. The Upper Trias, or _Keuper_ (the _Marnes irisées_ of the +French), as it is generally called, occurs in England; but is +not so well developed as it is in Germany. In Britain, the Keuper +is 1000 feet or more in thickness, and consists of white and +brown sandstones, with red marls, the whole topped by red clays +with rock-salt and gypsum. + +The Keuper in Britain is extremely unfossiliferous; but it passes +upwards with perfect conformity into a very remarkable group of +beds, at one time classed with the Lias, and now known under the +names of the Penarth beds (from Penarth, in Glamorganshire), the +Rhætic beds (from the Rhætic Alps), or the _Avicula contorta_ beds +(from the occurrence in them of great numbers of this peculiar +Bivalve). These singular beds have been variously regarded as the +highest beds of the Trias, or the lowest beds of the Lias, or as +an intermediate group. The phenomena observed on the Continent, +however, render it best to consider them as Triassic, as they +certainly agree with the so-called Upper St Cassian or Kössen +beds which form the top of the Trias in the Austrian Alps. + +The Penarth beds occur in Glamorganshire, Gloucestershire, +Warwickshire, Staffordshire, and the north of Ireland; and they +generally consist of a small thickness of grey marls, white +limestones, and black shales, surmounted conformably by the lowest +beds of the Lias. The most characteristic fossils which they contain +are the three Bivalves _Cardium Rhoeticum, Avicula contorta_, and +_Pecten Valoniensis_; but they have yielded many other fossils, +amongst which the most important are the remains of Fishes and +small Mammals (_Microlestes_). + +In the Austrian Alps the Trias terminates upwards in an extraordinary +series of fossiliferous beds, replete with marine fossils. Sir +Charles Lyell gives the following table of these remarkable +deposits:-- + +_Strata below the Lias in the Austrian Alps, in descending order._ + + / Grey and black limestone, with calcareous + | marls having a thickness of about 50 + | feet. Among the fossils, Brachiopoda +1. Koessen beds. | very numerous; some few species common + (Synonyms, Upper | to the genuine Lias; many peculiar. + St Cassian beds of < _Avicula contorta, Pecten Valoniensis_, + Escher and Merian.) | _Cardium Rhoeticum, Avicula_ + | _inoequivalvis, Spirifer Münsteri_, + | Dav. Strata containing the above fossils + | alternate with the Dachstein beds, lying + \ next below. + + / White or greyish limestone, often in beds + | three or four feet thick. Total thickness + | of the formation above 2000 feet. Upper + | part fossiliferous, with some strata +2. Dachstein beds. < composed of corals (_Lithodendron_.) + | Lower portion without fossils. Among the + | characteristic shells are _Hemicardium_ + | _Wulfeni, Megalodon triqueler_, and + \ other large bivalves. + + / Red, pink, or white marbles, from 800 to + | 1000 feet in thickness, containing more + | than 800 species of marine fossils, for +3. Hallstadt beds | the most part mollusca. Many species of + (or St Cassian). < _Orthoceras_. True _Ammonites_, + | besides _Ceratites_ and + | _Goniatites, Belemnites_ (rare), + | _Porcellia, Pleurotomania, Trochus_, + \ _Monotis salinaria_, &c. + + / A. Black and grey \ Among the fossils +4. A. Guttenstein beds. | limestone 150 feet | are _Ceratites_ + B. Werfen beds, base | thick, alternating | _cassianus_, + of Upper Trias? | with the underlying | _Myacites_ + Lower Trias of < Werfen beds. > _fassaensis_, + some geologists. | B. Red and green | _Naticella_ + | shale and sandstone, | _costata_, &c. + \ with salt and gypsum./ + +In the United States, rocks of Triassic age occur in several +areas between the Appalachians and the Atlantic seaboard; but +they show no such triple division as in Germany, and their exact +place in the system is uncertain. The rocks of these areas consist +of red sandstones, sometimes shaly or conglomeratic, occasionally +with beds of impure limestone. Other more extensive areas where +Triassic rocks appear at the surface, are found west of the +Mississippi, on the slopes of the Rocky Mountains, where the +beds consist of sandstones and gypsiferous marls. The American +Trias is chiefly remarkable for having yielded the remains of a +small Marsupial (_Dromatherium_), and numerous footprints, which +have generally been referred to Birds (_Brontozoum_), along with +the tracks of undoubted Reptiles (_Otozoum, Anisopus_, &c.) + +The subjoined section (fig. 139) expresses, in a diagrammatic +manner, the general sequence of the Triassic rocks when fully +developed, as, for example, in the Bavarian Alps:-- + +[Illustration: Fig. 139. GENERALIZED SECTION OF THE TRIASSIC ROCKS +OF CENTRAL EUROPE.] + +With regard to the _life_ of the Triassic period, we have to +notice a difference as concerns the different members of the group +similar to that which has been already mentioned in connection +with the Permian formation. The arenaceous deposits of the series, +namely, resemble those of the Permian, not only in being commonly +red or variegated in their colour, but also in their conspicuous +paucity of organic remains. They for the most part are either +wholly unfossiliferous, or they contain the remains of plants or +the bones of reptiles, such as may easily have been drifted from +some neighbouring shore. The few fossils which may be considered +as properly belonging to these deposits are chiefly Crustaceans +(_Estheria_) or Fishes, which may well have lived in the waters +of estuaries or vast inland seas. We may therefore conclude, +with considerable probability, that the barren sandy and marly +accumulations of the Bunter Sandstein and Lower Keuper were not +laid down in an open sea, but are probably brackish-water deposits, +formed in estuaries or land-locked bodies of salt water. This at +any rate would appear to be the case as regards these members +of the series as developed in Britain and in their typical areas +on the continent of Europe; and the origin of most of the North +American Trias would appear to be much the same. Whether this view +be correct or not, it is certain that the beds in question were laid +down in _shallow_ water, and in the immediate vicinity of _land_, +as shown by the numerous drifted plants which they contain and +the common occurrence in them of the footprints of air-breathing +animals (Birds, Reptiles, and Amphibians). On the other hand, the +middle and highest members of the Trias are largely calcareous, +and are replete with the remains of undoubted marine animals. There +cannot, therefore, be the smallest doubt but that the Muschelkalk +and the Rhætic or Kössen beds were slowly accumulated in an open +sea, of at least a moderate depth; and they have preserved for +us a very considerable selection from the marine fauna of the +Triassic period. + +[Illustration: Fig. 140.--_Zamia spiralis_, a living Cycad. +Australia.] + +The _plants_ of the Trias are, on the whole, as distinctively +Mesozoic in their aspect as those of the Permian are Palæozoic. +In spite, therefore, of the great difficulty which is experienced +in effecting a satisfactory stratigraphical separation between +the Permian and the Trias, we have in this fact a proof that the +two formations were divided by an interval of time sufficient +to allow of enormous changes in the terrestrial vegetation of the +world. The _Lepidodendroids, Asterophyllites_, and _Annularioe_, +of the Coal and Permian formations, have now apparently wholly +disappeared: and the Triassic flora consists mainly of Ferns, +Cycads, and Conifers, of which only the two last need special +notice. The _Cycads_ (fig. 140) are true exogenous plants, which +in general form and habit of growth present considerable resemblance +to young Palms, but which in reality are most nearly related to +the Pines and Firs (_Coniferoe_). The trunk is unbranched, often +much shortened, and bears a crown of feathery pinnate fronds. +The leaves are usually "circinate"--they unroll in expanding, +like the fronds of ferns. The seeds are not protected by a +seed-vessel, but are borne upon the edge of altered leaves, or +are carried on the scales of a cone. All the living species of +Cycads are natives of warm countries, such as South America, the +West Indies, Japan, Australia, Southern Asia, and South Africa. +The remains of Cycads, as we have seen, are not known to occur +in the Coal formation, or only to a very limited extent towards +its close; nor are they known with certainty as occurring in +Permian deposits. In the Triassic period, however, the remains +of Cycads belonging to such genera as _Pterophyllum_ (fig. 141, +b), _Zamites_, and _Podozamites_ (fig. 141, c), are sufficiently +abundant to constitute quite a marked feature in the vegetation; +and they continue to be abundantly represented throughout the +whole Mesozoic series. The name "Age of Cycads," as applied to +the Secondary epoch, is therefore, from a botanical point of +view, an extremely appropriate one. The _Conifers_ of the Trias +are not uncommon, the principal form being _Veltzia_ (fig. 141, +a), which possesses some peculiar characters, but would appear +to be most nearly related to the recent Cypresses. + +[Illustration: Fig. 141.--Triassic Conifers and Cycads. a, _Voltzia_ +(_Schizoneura_) _heterophylla_, portion of a branch, Europe and +America; b, Part of the frond of _Pterophyllum Joegeri_, Europe; +c, Part of the frond of _Podozamites lanceolatus_, America.] + +As regards the _Invertebrate animals_ of the Trias, our knowledge +is still principally derived from the calcareous beds which +constitute the centre of the system (the Muschelkalk) on the +continent of Europe, and from the St Cassain and Rhætic beds +still higher in the series; whilst some of the Triassic strata +of California and Nevada have likewise yielded numerous remains +of marine Invertebrates. The _Protozoans_ are represented by +_Foraminifera_ and _Sponges_, and the _Coelenterates_ by a small +number of _Corals_; but these require no special notice. It may be +mentioned, however, that the great Palæozoic group of the _Rugose_ +corals has no known representative here, its place being taken +by corals of Secondary type (such as _Montlivaltia, Synastoea_, +&c.) + +The _Echinoderms_ are represented principally by _Crinoids_, +the remains of which are extremely abundant in some of the +limestones. The best-known species is the famous "Lily-Encrinite" +(_Encrinus liliiformis_, fig. 142), which is characteristic of the +Muschelkalk. In this beautiful species, the flower-like head is +supported upon a rounded stem, the joints of which are elaborately +articulated with one another; and the fringed arms are composed +each of a double series of alternating calcareous pieces. The +Palæozoic Urchins, with their supernumerary rows of plates, the +Cystideans, and the Pentremites have finally disappeared; but +both Star-fishes and Brittle-stars continue to be represented. +One of the latter--namely, the _Aspidura loricata_ of Goldfuss +(fig. 143)--is highly characteristic of the Muschelkalk. + +[Illustration: Fig. 142.--Head and upper part of the column of +_Encrinus liliiformis_. The lower figure shows the articulating +surface of one of the joints of the column. Muschelkalk, Germany.] + +[Illustration: Fig. 143.--_Aspidura loricata_, a Triassic Ophiuroid. +Muschelkalk, Germany.] + +The remains of _Articulate Animals_ are not very abundant in the +Trias, if we except the bivalved cases of the little Water-fleas +(_Ostracoda_), which are occasionally very plentiful. There are +also many species of the horny, concentrically-striated valves +of the _Estherioe_ (see fig. 122, b), which might easily be +taken for small Bivalve Molluscs. The "Long-tailed" Decapods +of the type of the Lobster, are not without examples but they +become much more numerous in the succeeding Jurassic period. +Remains of insects have also been discovered. + +Amongst the _Mollusca_ we have to note the disappearance, amongst +the lower groups, of many characteristic Palæozoic types. Amongst +the _Polyzoans_, the characteristic "Lace-corals," _Fenestella, +Retepora_,[22] _Synocladia, Polypora_, &c., have become apparently +extinct. The same is true of many of the ancient types of +_Brachiopods_, and conspicuously so of the great family of the +_Productidoe_, which played such an important part in the seas +of the Carboniferous and Permian periods. + +[Footnote 22: The genus _Retefora_ is really a recent one, +represented by living forms; and the so-called _Reteporoe_ of the +Palæozoic rocks should properly receive another name (_Phyllopora_), +as being of a different nature. The name _Retepora_ has been here +retained for these old forms simply in accordance with general +usage.] + +[Illustraton: Fig. 144. Triassic Lamellibranchs. a, _Daonella_ +(_Halobia_) _Lommelli_; b, _Pecten Valoniensis_; c, _Myophoria +lineata_; d. _Cardium Rhoeticum_; e. _Avicula contorta_; f. _Avicula +socialis_.] + +_Bivalves_ (_Lamellibranchiata_) and _Univalves_ (_Gasteropoda_) +are well represented in the marine beds of the Trias, and some of the +former are particularly characteristic either of the formation as a +whole or of minor subdivisions of it. A few of these characteristic +species are figured in the accompanying illustration (fig. 144). +Bivalve shells of the genera _Daonella_ (fig. 144, a) and _Halobia_ +(_Monotis_) are very abundant, and are found in the Triassic +strata of almost all regions. These groups belong to the family +of the Pearl-oysters (_Aviculidoe_), and are singular from the +striking resemblance borne by some of their included forms to +the _Strophomenoe amongst the Lamp-shells, though, of course, no +real relation exists between the two. The little Pearl-oyster, +_Avicula socialis_ (fig. 144, f), is found throughout the greater +part of the Triassic series, and is especially abundant in the +Muschelkalk. The genus _Myophoria_ (fig. 144, c), belonging +to the _Trigoniadoe_, and related therefore to the Permian +_Schizodus_, is characteristically Triassic, many species of the +genus being known in deposits of this age. Lastly, the so-called +"Rhætic" or "Kössen" beds are characterised by the occurrence +in them of the Scallop, _Pecten Valoniensis_ (fig. 144, b); +the small Cockle, _Cardium Rhoeticum_ (fig. 144, d); and the +curiously-twisted Pearl-oyster, _Avicula contorta_ (fig. 144, +e)--this last Bivalve being so abundant that the strata in +question are often spoken of as the "Avicula contorta beds." + +[Illustration: Fig. 145.--_Ceratites nodosus_, viewed from the +side and from behind. Muschelkalk.] + +Passing over the groups of the _Heteropods_ and _Pteropods_, we +have to notice the _Cephalopoda_, which are represented in the +Trias not only by the chambered shells of _Tetrabranchiates_, but +also, for the first time, by the internal skeletons of _Dibranchiate_ +forms. The Trias, therefore, marks the first recognised appearance +of true Cuttle-fishes. All the known examples of these belong +to the great Mesozoic group of the _Belemnitidoe_; and as this +family is much more largely developed in the succeeding Jurassic +period, the consideration of its characters will be deferred till +that formation is treated of. Amongst the chambered _Cephalopods_ +we find quite a number of the Palæozoic _Orthoceratites_, some of +them of considerable size, along with the ancient _Cyrtoceras_ +and _Goniatites_; and these old types, singularly enough, occur +in the higher portion of the Trias (St Cassian beds), but have, +for some unexplained reason, not yet been recognised in the lower +and equally fossiliferous formation of the Muschelkalk. Along +with these we meet for the first time with true _Ammonites_, +which fill such an extensive place in the Jurassic seas, and +which will be spoken of hereafter. The form, however, which is +most characteristic of the Trias is _Ceratites_ (fig. 145). In +this genus the shell is curved into a flat spiral, the volutions of +which are in contact; and it further agrees with both _Goniatites_ +and _Ammonites_ in the fact that the septa or partitions between +the air-chambers are not simple and plain (as in the _Nautilus_ +and its allies), but are folded and bent as they approach the +outer wall of the shell. In the _Goniatite_ these foldings of +the septa are of a simply lobed or angulated nature, and in the +_Ammonite_ they are extremely complex; whilst in the _Ceratite_ +there is an intermediate state of things, the special feature +of which is, that those foldings which are turned towards the +mouth of the shell are merely rounded, whereas those which are +turned away from the mouth are characteristically toothed. The +genus _Ceratites_, though principally Triassic, has recently +been recognised in strata of Carboniferous age in India. + +From the foregoing it will be gathered that one of the most important +points in connection with the Triassic _Mollusca_ is the remarkable +intermixture of Palæozoic and Mesozoic types which they exhibit. +It is to be remembered, also, that this intermixture has hitherto +been recognised, not in the Middle Triassic limestones of the +Muschelkalk, in which--as the oldest Triassic beds with marine +fossils--we should naturally expect to find it, but in the St +Cassian beds, the age of which is considerably later than that +of the Muschelkalk. The intermingling of old and new types of +Shell-fish in the Upper Trias is well brought out in the annexed +table, given by Sir Charles Lyell in his 'Student's Elements of +Geology' (some of the less important forms in the table being +omitted here):-- + +GENERA OF FOSSIL MOLLUSCA IN THE ST CASSIAN AND HALLSTADT BEDS. + + Common to | Characteristic of | Common to + Older Rocks. | Triassic Rocks | Newer Rocks. + | | + Orthoceras. | Ceratites. | Ammonites. + Bactrites. | Cochloceras. | Chemnitzia. + Macrocheilus. | Rhabdoceras. | Cerithium. + Loxonema. | Aulacoceras. | Monodonta. + Holopella. | Naticella. | Sphoera. + Murchisonia. | Platystoma. | Cardita. + Porcellia. | Halobia. | Myoconcha. + Athyris. | Hörnesia. | Hinnites. + Retzia. | Koninckia. | Monotis. + Cyrtina. | Scoliostoma. | Plicatula. + Euomphalus. | Myophoria. | Pachyrisma. + |(The last two are | Thecidium. + |principally but not | + |exclusively Triassic.)| + +Thus, to emphasise the more important points alone, the Trias +has yielded, amongst the Gasteropods, the characteristically +Palæozoic _Loxonema, Holopella, Murchisonia, Euomphalus_, and +_Porcellia_, along with typically Triassic forms like _Platystoma_ +and _Scoliostoma_, and the great modern groups _Chemnitzia_ and +_Cerithium_. Amongst the Bivalves we find the Palæozoic _Megalodon_ +side by side with the Triassic _Halobia_ and _Myophoria_, these +being associated with the _Carditoe, Hinnites, Plicatuloe_, and +_Trigonioe_ of later deposits. The Brachiopods exhibit the Palæozoic +_Athyris, Retzia_, and _Cyrtina_, with the Triassic _Koninckia_ +and the modern _Thecidium_. Finally, it is here that the ancient +genera _Orthoceras, Cyrtoceras_, and _Goniatites_ make their last +appearance upon the scene of life, the place of the last of these +being taken by the more complex and almost exclusively Triassic +_Ceratites_, whilst the still more complex genus _Ammonites_ first +appears here in force, and is never again wanting till we reach +the close of the Mesozoic period. The first representatives of +the great Secondary family of the _Belemnites_ are also recorded +from this horizon. + +[Illustration: Fig. 146.--a, Dental plate of _Ceratodus serratus_, +Keuper; b, Dental plate of _Ceratodus altus_, Keuper; (After +Agassiz.)] + +[Illustration: Fig 147.--_Ceratodus Fosteri_, the Australian +Mud-fish, reduced in size.] + +Amongst the _Vertebrate Animals_ of the Trias, the _Fishes_ are +represented by numerous forms belonging to the _Ganoids_ and the +_Placoids_. The Ganoids of the period are still all provided +with unsymmetrical ("heterocercal") tails, and belong principally +to such genera as _Paloeoniscus_ and _Catopterus_. The remains of +Placoids are in the form of teeth and spines, the two principal +genera being the two important Secondary groups _Acrodus_ and +_Hybodus_. Very nearly at the summit of the Trias in England, in +the Rhætic series, is a singular stratum, which is well known as the +"bone-bed," from the number of fish-remains which it contains. More +interesting, however, than the above, are the curious palate-teeth +of the Trias, upon which Agassiz founded the genus _Ceratodus_. +The teeth of Ceratodus (fig. 146) are singular flattened plates, +composed of spongy bone beneath, covered superficially with a +layer of enamel. Each plate is approximately triangular, one +margin (which we now know to be the outer one) being prolonged +into prongs or conical prominences, whilst the surface is more or +less regularly undulated. Until recently, though the master-mind +of Agassiz recognised that these singular bodies were undoubtedly +the teeth of fishes, we were entirely ignorant as to their precise +relation to the animal, or as to the exact affinities of the fish +thus armed. Lately, however, there has been discovered in the +rivers of Queensland (Australia) a living species of _Ceratodus_ +(_C. Fosteri_, fig. 147), with teeth precisely similar to those +of its Triassic predecessor; and we thus have become acquainted +with the use of these structures and the manner in which they +were implanted in the mouth. The palate carries two of these +plates, with their longer straight sides turned towards each +other, their sharply-sinuated sides turned outwards, and their +short straight sides or bases directed backwards. Two similar +plates in the lower jaw correspond to the upper, their undulated +surfaces fitting exactly to those of the opposite teeth. There +are also two sharp-edged front teeth, which are placed in the +front of the mouth in the upper jaw; but these have not been +recognised in the fossil specimens. The living _Ceratodus_ feeds +on vegetable matters, which are taken up or tom off from plants +by the sharp front teeth, and then partially crushed between +the undulated surfaces of the back teeth (Günther); and there +need be little doubt but that the Triassic _Ceratodi_ followed +a similar mode of existence. From the study of the living +_Ceratodus_, it is certain that the genus belongs to the same +group as the existing Mud-fishes (_Dipnoi_); and we therefore +learn that this, the highest, group of the entire class of Fishes +existed in Triassic times under forms little or not at all different +from species now alive; whilst it has become probable that the +order can be traced back into the Devonian period. + +[Illustration: Fig. 148.--Footprints of a Labyrinthodont +(_Cheirotherium_), from the Triassic Sandstones of Hessberg, near +Hildburghausen, Germany, reduced one-eighth. The lower figure +shows a slab, with several prints, and traversed by reticulated +sun-cracks: the upper figure shows the impression of one of the +hind-feet, one-half of the natural size. (After Sickler.)] + +[Illustration: Fig. 149.--Section of the tooth of _Labryinthodon +(Mastodonsaurus) Joegeri_, showing the microscopic structure. +Greatly enlarged. Trias.] + +[Illustration: Fig. 150.--a, Skull of _Labyrinthodon Joegeri_, +much reduced in size; b, Tooth of the same. Trias Württemberg.] + +The _Amphibians_ of the Trias all belong to the old order of +the _Labyrinthodonts_, and some of them are remarkable for their +gigantic dimensions. They were first known by their footprints, +which were found to occur plentifully in the Triassic sandstones +of Britain and the continent of Europe, and which consisted of +a double series of alternately-placed pairs of hand-shaped +impressions, the hinder print of each pair being much larger +than the one in front (fig. 148). So like were these impressions +to the shape of the human hand, that the at that time unknown +animal which produced them was at once christened _Cheirotherium_, +or "Hand-beast." Further discoveries, however, soon showed that +the footprints of _Cheirotherium_ were really produced by species +of Amphibians which, like the existing Frogs, possessed hind-feet +of a much larger size than the fore-feet, and to which the name +of _Labyrinthodonts_ was applied in consequence of the complex +microscopic structure of the teeth (fig. 149). In the essential +details of their structure, the Triassic Labyrinthodonts did not +differ materially from their predecessors in the Coal-measures +and Permian rocks. They possessed the same frog-like skulls (fig. +150), with a lizard-like body, a long tail, and comparatively +feeble limbs. The hind-limbs were stronger and longer than the +fore-limbs, and the lower surface of the body was protected by an +armour of bony plates. Some of the Triassic Labyrinthodonts must +have attained dimensions utterly unapproached amongst existing +Amphibians, the skull of _Labyrinthodon Joegeri_ (fig. 150) being +upwards of three feet in length and two feet in breadth. Restorations +of some of these extraordinary creatures have been attempted in +the guise of colossal Frogs; but they must in reality have more +closely resembled huge Newts. + +Remains of _Reptiles_ are very abundant in Triassic deposits, +and belong to very varied types. The most marked feature, in +fact, connected with the Vertebrate fauna of the Trias, and of +the Secondary rocks in general, is the great abundance of Reptilian +life. Hence the Secondary period is often spoken of as the "Age +of Reptiles." Many of the Triassic reptiles depart widely in +their structure from any with which we are acquainted as existing +on the earth at the present day, and it is only possible here to +briefly note some of the more important of these ancient forms. +Amongst the group of the Lizards (_Lacertilia_), represented by +_Protorosaurus_ in the older Permian strata, three types more +or less certainly referable to this order may be mentioned. One +of these is a small reptile which was found many years ago in +sandstones near Elgin, in Scotland, and which excited special +interest at the time in consequence of the fact that the strata +in question were believed to belong to the Old Red Sandstone +formation. It is, however, now certain that the Elgin sandstones +which contain _Telerpeton Elginense_, as this reptile is termed, +are really to be regarded as of Triassic age. By Professor Huxley, +_Telerpeton_ is regarded as a Lizard, which cannot be considered +as "in any sense a less perfectly-organised creature than the +Gecko, whose swift and noiseless run over walls and ceilings +surprises the traveller in climates warmer than our own." The +"Elgin Sandstones" have also yielded another Lizard, which was +originally described by Professor Huxley under the name of +_Hyperodapedon_, the remains of the same genus having been +subsequently discovered in Triassic strata in India and South +Africa. The Lizards of this group must therefore have at one +time enjoyed a very wide distribution over the globe; and the +living _Sphenodon_ of New Zealand is believed by Professor Huxley +to be the nearest living ally of this family. The _Hyperodapedon_ +of the Elgin Sandstones was about six feet in length, with limbs +adapted for terrestrial progression, but with the bodies of the +vertebræ slightly biconcave, and having two rows of palatal teeth, +which become worn down to the bone in old age. Lastly, the curious +_Rhynchosaurus_ of the Trias is also referred, by the eminent +comparative anatomist above mentioned, to the order of the Lizards. +In this singular reptile (fig. 151) the skull is somewhat bird-like, +and the jaws appear to have been destitute of teeth, and to have +been encased in a horny sheath like the beak of a Turtle or a +Bird. It is possible, however, that the palate was furnished +with teeth. + +[Illustration: Fig. 151.--Skull of _Rhynchosaurus articeps_. Trias. +(After Owen.)] + +The group of the Crocodiles and Alligators (_Crocadilia_), +distinguished by the fact that the teeth are implanted in distinct +sockets and the skin more or less extensively provided with bony +plates, is represented in the Triassic rocks by the _Stagonolepis_ +of the Elgin Sandstones. The so-called "Thecodont" reptiles (such +as _Belodon, Thecodontosaurus_, and _Paloeosaurus_, fig. 152, +c, d, e) are also nearly related to the Crocodiles, though +it is doubtful if they should be absolutely referred to this +group. In these reptiles, the teeth are implanted in distinct +sockets in the jaws, their crowns being more or less compressed +and pointed, "with trenchant and finely serrate margins" (Owen). +The bodies of the vertebræ are hollowed out at both ends, but +the limbs appear to be adapted for progression on the land. The +genus _Belodon_ (fig. 152, c) is known to occur in the Keuper +of Germany and in America; and _Paloeosaurus_ (fig. 153. e) +has also been found in the Trias of the same region. Teeth of the +latter, however, are found, along with remains of _Thecodontosaurus_ +(fig. 153, d), in a singular magnesian conglomerate near Bristol, +which was originally believed to be of Permian age, but which +appears to be undoubtedly Triassic. + +[Illustration: Fig. 152.--Triassic Reptiles. a, Skull of +_Nothosaurus mirabilis_, reduced in size--Muschelkalk, Germany; b, +Tooth of _Simosaurus Gaillardoti_, of the natural size--Muschelkalk, +Germany; c, Tooth of _Beladon Carolinensis_--Trias, America; d, +Tooth of _Thecodontosaurus antiquus_, slightly enlarged--Britain; +e, Tooth of _Paloeosaurus platyodon_, of the natural +size--Britain.] + +The Trias has also yielded the remains of the great marine reptiles +which are often spoken of collectively as the "Enaliosaurians" +or "Sea-lizards," and which will be more particularly spoken +of in treating of the Jurassic period, of which they are more +especially characteristic. In all these reptiles the limbs are +flattened out, the digits being enclosed in a continuous skin, +thus forming powerful swimming-paddles, resembling the "flippers" +of the Whales and Dolphins both in their general structure and +in function. The tail is also long, and adapted to act as a +swimming-organ; and there can be no doubt but that these +extraordinary and often colossal reptiles frequented the sea, +and only occasionally came to the land. The Triassic Enaliosaurs +belong to a group of which the later genus _Plesiosaurus_ is +the type (the _Sauropterygia_). One of the best known of the +Triassic genera is _Nothosaurus_ (fig. 152, a), in which the +neck was long and bird-like, the jaws being immensely elongated, +and carrying numerous powerful conical teeth implanted in distinct +sockets. The teeth in _Simosaurus_ (152, b) are of a similar +nature; but the orbits are of enormous size, indicating eyes of +corresponding dimensions, and perhaps pointing to the nocturnal +habits of the animal. In the singular _Placodus_, again, the +teeth are in distinct sockets, but resemble those of many fishes +in being rounded and obtuse (fig. 153), forming broad crushing +plates adapted for the comminution of shell-fish. There is a +row of these teeth all round the upper jaw proper, and a double +series on the palate, but the lower jaw has only a single row of +teeth. _Placodus_ is found in the Muschelkalk, and the characters +of its dental apparatus indicate that it was much more peaceful +in its habits than its associates the Nothosaur and Simosaur. + +[Illustration: Fig. 153.--Under surface of the upper jaw and palate +of _Placodus gigas_. Muschelkalk, Germany.] + +The Triassic rocks of South Africa and India have yielded the +remains of some extraordinary Reptiles, which have been placed by +Professor Owen in a separate order under the name of _Anomodontia_. +The two principal genera of this group are _Dicynodon_ and +_Oudenodon_, both of which appear to have been large Reptiles, +with well-developed limbs, organised for progression upon the +dry land. In _Oudenodon_ (fig. 154, B) the jaws seem to have +been wholly destitute of teeth, and must have been encased in +a horny sheath, similar to that with which we are familiar in +the beak of a Turtle. In _Dicynodon_ (fig. 154, A), on the other +hand, the front of the upper jaw and the whole of the lower jaw +were destitute of teeth, and the front of the mouth must have +constituted a kind of beak; but the upper jaw possessed on each +side a single huge conical tusk, which is directed downwards, +and must have continued to grow during the life of the animal. + +[Illustration: Fig. 154.--Triassic Anomodont Reptiles. A, Skull +of _Dicynodon lacerticeps_, showing one of the great maxillary +tusks; B, Skull of _Oudenodon Bainii_, showing the toothless, +beak-like jaws. From the Trias of South Africa. (After Owen.)] + +It may be mentioned that the above-mentioned Triassic sandstones +of South Africa have recently yielded to the researches of Professor +Owen a new and unexpected type of Reptile, which exhibits some +of the structural peculiarities which we have been accustomed +to regard as characteristic of the Carnivorous quadrupeds. The +Reptile in question has been named _Cyanodraco_, and it is looked +upon by its distinguished discoverer as the type of a new order, +to which he has given the name of _Theriodontia_. The teeth of +this singular form agree with those of the Carnivorous quadrupeds +in consisting of three distinct groups--namely, front teeth or +_incisors_, eye teeth or _canines_, and back teeth or _molars_. +The canines also are long and pointed, very much compressed, and +having their lateral margins finely serrated, thus presenting a +singular resemblance to the teeth of the extinct "Sabre-toothed +Tiger" (_Machairodus_). The bone of the upper arm (humerus) further +shows some remarkable resemblances to the same bone in the +Carnivorous Mammals. As has been previously noticed, Professor +Owen is of opinion that some of the Reptilian remains of the +Permian deposits will also be found to belong to this group of +the "Theriodonts." + +[Illustration: Fig. 155.--Supposed footprint of a Bird, from +the Triassic Sandstones of the Connecticut River. The slab shows +also numerous "rain-prints."] + +Lastly, we find in the Triassic rocks the remains of Reptiles +belonging to the great Mesozoic order of the _Deinosauria_. This +order attains its maximum at a later period, and will be spoken of +when the Jurassic and Cretaceous deposits come to be considered. +The chief interest of the Triassic Reptiles of this group arises +from the fact that they are known by their footprints as well as +by their bones; and a question has arisen whether the supposed +footprints of _birds_ which occur in the Trias have not really +been produced by Deinosaurs. This leads us, therefore, to speak +at the same time as to the evidence which we have of the existence +of the class of Birds during the Triassic period. No actual bones +of any bird have as yet been detected in any Triassic deposit; +but we have tolerably clear evidence of their existence at this +time in the form of _footprints_. The impressions in question +are found in considerable numbers in certain red sandstones of +the age of the Trias in the valley of the Connecticut River, in +the United States. They vary much in size, and have evidently been +produced by many different animals walking over long stretches of +estuarine mud and sand exposed at low water. The footprints now +under consideration form a double series of _single_ prints, and +therefore, beyond all question, are the tracks of a _biped_--that +is, of an animal which walked upon two legs. No living animals, +save Man and the Birds, walk habitually on two legs; and there +is, therefore, a _primâ facie_ presumption that the authors of +these prints were Birds. Moreover, each impression consists of +the marks of three toes turned forwards (fig. 155), and therefore +are precisely such as might be produced by Wading or Cursorial +Birds. Further, the impressions of the toes show exactly the +same numerical progression in the number of the joints as is +observable in living Birds--that is to say, the innermost of the +three toes consists of three joints, the middle one of four, and +the outer one of five joints. Taking this evidence collectively, +it would have seemed, until lately, quite certain that these +tracks could only have been formed by Birds. It has, however, +been shown that the Deinosaurian Reptiles possess, in some cases +at any rate, some singularly bird-like characters, amongst which +is the fact that the animal possessed the power of walking, +temporarily at least, on its hind-legs, which were much longer and +stronger than the fore-limbs, and which were sometimes furnished +with no more than three toes. As the bones and teeth of Deinosaurs +have been found in the Triassic deposits of North America, it +may be regarded as certain that _some_ of the bipedal tracks +originally ascribed to Birds must have really been produced by +these Reptiles. It seems at the same time almost a certainty +that others of the three-toed impressions of the Connecticut +sandstones were in truth produced by Birds, since it is doubtful +if the bipedal mode of progression was more than an occasional +thing amongst the Deinosaurs, and the greater number of the many +known tracks exhibit no impressions of fore-feet. Upon the whole, +therefore, we may, with much probability, conclude that the great +class of Birds (_Aves_) was in existence in the Triassic period. +If this be so, not only must there have been quite a number of +different forms, but some of them must have been of very large +size. Thus the largest footprints hitherto discovered in the +Connecticut sandstones are 22 inches long and 12 inches wide, +with a proportionate length of stride. These measurements indicate +a foot four times as large as that of the African Ostrich; and the +animal which produced them--whether a Bird or a Deinosaur--must +have been of colossal dimensions. + +[Illustration: Fig. 156.--Lower jaw of _Dromatherium sylvestre_. +Trias, North Carolina. (After Emmons.)] + +[Illustration: Fig. 157.--a, Molar tooth of _Micro estes antiquus_, +magnified; b, Crown of the same, magnified still further. Trias, +Germany.] + +[Illustration: Fig. 158.--The Banded Ant-eater (_Myrmecobius +fasciatus_) of Australia.] + +Finally, the Trias completes the tale of the great classes of the +Vertebrate sub-kingdom by presenting us with remains of the first +known of the true Quadrupeds or _Mammalia_. These are at present only +known by their teeth, or, in one instance, by one of the halves of +the lower jaw; and these indicate minute Quadrupeds, which present +greater affinities with the little Banded Anteater (_Myrmecobius +fasciatus_, fig. 158) of Australia than with any other living form. +If this conjecture be correct, these ancient Mammals belonged to +the order of the Marsupials or Pouched Quadrupeds (_Marsupialia_), +which are now exclusively confined to the Australian province, +South America, and the southern portion of North America. In the +Old World, the only known Triassic Mammals belong to the genus +_Microlestes_, and to the probably identical _Hypsiprymnopsis_ of +Professor Boyd Dawkins. The teeth of _Microlestes_ (fig. 157) +were originally discovered by Plieninger in 1847 in the "bone-bed" +which is characteristic of the summit of the Rhætic series both +in Britain and on the continent of Europe; and the known remains +indicate two species. In Britain, teeth of _Microlestes_ have been +discovered by Mr Charles Moore in deposits of Upper Triassic age, +filling a fissure in the Carboniferous limestone near Frome, in +Somersetshire; and a molar tooth of _Hypsiprymnopsis_ was found +by Professor Boyd Dawkins in Rhætic marls below the "bone-bed" at +Watchet, also in Somersetshire. In North America, lastly, there +has been found in strata of Triassic age one of the branches +of the lower jaw of a small Mammal, which has been described +under the name of _Dromatherium sylvestre_ (fig. 156). The fossil +exhibits ten small molars placed side by side, one canine, and +three incisors, separated by small intervals, and it indicates +a small insectivorous animal, probably most nearly related to +the existing _Myrmecobius_. + + +LITERATURE. + +The following list comprises a few of the more important sources of +information as to the Triassic strata and their fossil contents:-- + + (1) 'Geology of Oxford and the Valley of the Thames.' Phillips. + (2) 'Memoirs of the Geological Survey of Great Britain and Ireland.' + (3) 'Report on the Geology of Londonderry,' &c. Portlock. + (4) "On the Zone of Avicula contorta," &c.--'Quart. Journ. Geol. + Soc.,' vol. xvi., 1860. Dr Thomas Wright. + (5) "On the Zones of the Lower Lias and the Avicula contorta + Zone"--'Quart. Journ. Geol. Soc.,' vol. xvii., 1861. Charles + Moore. + (6) "On Abnormal Conditions of Secondary Deposits," &c.--'Quart. + Journ. Geol. Soc.,' vol. xxiii., 1876-77. Charles Moore. + (7) 'Geognostische Beschreibung des Bayerischen Alpengebirges.' + Gümbel. + (8) 'Lethæa Rossica.' Pander. + (9) 'Lethæa Geognostica.' Bronn. +(10) 'Petrefacta Germaniæ.' Goldfuss. +(11) 'Petrefaktenkunde.' Quenstedt. +(12) 'Monograph of the Fossil Estheriæ' (Palæontographical Society). + Rupert Jones. +(13) "Fossil Remains of Three Distinct Saurian Animals, recently + discovered in the Magnesian Conglomerate near Bristol"--'Trans. + Geol. Soc.,' ser. 2, vol. v., 1840. Riley and Stutchbury. +(14) 'Die Saurier des Muschekalkes.' Von Meyer. +(15) 'Beiträge zur Palæontologie Württembergs.' Von Meyer and + Plieninger. +(16) 'Manual of Palæontology.' Owen. +(17) 'Odontography:' Owen. +(18) 'Report on Fossil Reptiles' (British Association, 1841). Owen. +(19) "On Dicynodon"--'Trans. Geol. Soc.,' vol. iii., 1845. Owen. +(20) 'Descriptive Catalogue of Fossil Reptilia and Fishes in the + Museum of the Royal College of Surgeons, England.' Owen. +(21) "On Species of Labyrinthodon from Warwickshire"--'Trans. Geol. + Soc.,' ser. 2, vol. vi. Owen. +(22) "On a Carnivorous Reptile" (Cynodraco major), &c.--'Quart. + Journ. Geol. Soc.,' vol. xxxii., 1876. Owen. +(23) "On Evidences of Theriodonts in Permian Deposits," &c.--'Quart. + Journ. Geol. Soc.,' vol. xxxii., 1876. Owen. +(24) "On the Stagonolepis Robertsoni," &c.--'Quart. Journ. Geol. + Soc.,' vol. xv., 1859. Huxley. +(25) "On a New Specimen of Telerpeton Elginense"--'Quart. Journ. + Geol. Soc.,' vol. xxiii., 1866. Huxley. +(26) "On Hyperodapedon"--'Quart. Journ. Geol. Soc.,' vol. xxv., + 1869. Huxley. +(27) "On the Affinities between the Deinosaurian Reptiles and + Birds"--'Quart. Journ. Geol. Soc.,' vol. xxvi., 1870. Huxley. +(28) "On the Classification of the Deinosauria," &c.--'Quart. Journ. + Geol. Soc.,' vol. xxvi., 1870. Huxley. +(29) "Palæontologica Indica"--'Memoirs of the Geol. Survey of India.' +(30) "On the Geological Position and Geographical Distribution of the + Dolomitic Conglomerate of the Bristol Area"--'Quart. Journ. + Geol. Soc.,' vol. xxvi., 1870. R. Etheridge, sen. +(31) "Remains of Labyrinthodonta from the Keuper Sandstone of + Warwick"--'Quart. Journ. Geol. Soc.,' vol. xxx., 1874 Miall. +(32) 'Manual of Geology.' Dana. +(33) 'Synopsis of Extinct Batrachia and Reptilia of North America.' + Cope. +(34) 'Fossil Footmarks.' Hitchcock. +(35) 'Ichnology of New England.' Hitchcock. +(36) 'Traité de Paléontologie Végétale.' Schimper. +(37) 'Histoire des Végétaux Fossiles.' Brongniart. +(38) 'Monographie der Fossilen Coniferen.' Goeppert. + + + + +CHAPTER XVI. + +THE JURASSIC PERIOD. + +Resting upon the Trias, with perfect conformity, and with an almost +undeterminable junction, we have the great series of deposits +which are known as the _Oolitic Rocks_, from the common occurrence +in them of oolitic limestones, or as the _Jurassic Rocks_, from +their being largely developed in the mountain-range of the Jura, +on the western borders of Switzerland. Sediments of this series +occupy extensive areas in Great Britain, on the continent of +Europe, and in India. In North America, limestones and marls +of this age have been detected in "the Black Hills, the Laramie +range, and other eastern ridges of the Rocky Mountains; also +over the Pacific slope, in the Uintah, Wahsatch, and Humboldt +Mountains, and in the Sierra Nevada" (Dana); but in these regions +their extent is still unknown, and their precise subdivisions +have not been determined. Strata belonging to the Jurassic period +are also known to occur in South America, in Australia, and in +the Arctic zone. When fully developed, the Jurassic series is +capable of subdivision into a number of minor groups, of which +some are clearly distinguished by their mineral characters, whilst +others are separated with equal certainty by the differences of +the fossils that they contain. It will be sufficient for our +present purpose, without entering into the more minute subdivisions +of the series, to give here a very brief and general account +of the main sub-groups of the Jurassic rocks, as developed in +Britain--the arrangement of the Jura-formation of the continent +of Europe agreeing in the main with that of England. + +I. THE LIAS.--The base of the Jurassic series of Britain is formed +by the great calcareo-argillaceous deposit of the "Lias," which +usually rests conformably and almost inseparably upon the Rhætic +beds (the so-called "White Lias"), and passes up, generally +conformably, into the calcareous sandstones of the Inferior Oolite. +The Lias is divisible into the three principal groups of the Lower, +Middle, and Upper Lias, as under, and these in turn contain many +well-marked "zones;" so that the Lias has some claims to be +considered as an independent formation, equivalent to all the +remaining Oolitic rocks. The _Lower Lias_ (_Terrain Sinemurien_ of +D'Orbigny) sometimes attains a thickness of as much as 600 feet, +and consists of a great series of bluish or greyish laminated +clays, alternating with thin bands of blue or grey limestone--the +whole, when seen in quarries or cliffs from a little distance, +assuming a characteristically striped and banded appearance. By +means of particular species of _Ammonites_, taken along with +other fossils which are confined to particular zones, the Lower +Lias may be subdivided into several well-marked horizons. The +_Middle Lias_, or _Marlstone Series_ (_Terrain Liasien_ of +D'Orbigny), may reach a thickness of 200 feet, and consists of +sands, arenaceous marls, and argillaceous limestones, sometimes +with ferruginous beds. The _Upper Lias_ (_Terrain Toarcien_ of +D'Orbigny) attains a thickness of 300 feet, and consists principally +of shales below, passing upwards into arenaceous strata. + +II. THE LOWER OOLITES.--Above the Lias comes a complex series of +partly arenaceous and argillaceous, but principally calcareous +strata, of which the following are the more important groups: +a, The _Inferior Oolite_ (_Terrain Bajocien_ of D'Orbigny), +consisting of more than 200 feet of oolitic limestones, sometimes +more or less sandy; b, The _Fuller's Earth_, a series of shales, +clays, and marls, about 120 feet in thickness; c, The _Great +Oolite_ or _Bath Oolite_ (_Terrain Bathonien_ of D'Orbigny), +consisting principally of oolitic limestones, and attaining a +thickness of about 130 feet. The well-known "Stonesfield Slates" +belong to this horizon; and the locally developed "Bradford Clay," +"Corn brash," and "Forest-marble" may be regarded as constituting +the summit of this group. + +III. THE MIDDLE OOLITES.--The central portion of the Jurassic +series of Britain is formed by a great argillaceous deposit, +capped by calcareous strata, as follows: a, The _Oxford Clay_ +(_Terrain Callovien_ and _Terrain Oxfordien_ of D'Orbigny), +consisting of dark-coloured laminated clays, sometimes reaching +a thickness of 700 feet, and in places having its lower portion +developed into a hard calcareous sandstone ("Kelloway Rock"); +b, The Coral-Rag (_Terrain Corallien_ of D'Orbigny, "Nerinean +Limestone" of the Jura, "Diceras Limestone" of the Alps), consisting, +when typically developed, of a central mass of oolitic limestone, +underlaid and surmounted by calcareous grits. + +IV. THE UPPER OOLITES.--a, The base of the Upper Oolites of +Britain is constituted by a great thickness (600 feet or more) +of laminated, sometimes carbonaceous or bituminous clays, which +are known as the _Kimmeridge Clay_ (_Terrain Kimméridgien_ of +D'Orbigny); b, The _Portland Beds_ (_Terrain Portlandien_ of +D'Orbigny) succeed the Kimmeridge clay, and consist inferiorly of +sandy beds surmounted by oolitic limestones ("Portland Stone"), +the whole series attaining a thickness of 150 feet or more, and +containing marine fossils; c, The _Purbeck_ Beds are apparently +peculiar to Great Britain, where they form the summit of the entire +Oolitic series, attaining a total thickness of from 150 to 200 +feet. The Purbeck beds consist of arenaceous, argillaceous, and +calcareous strata, which can be shown by their fossils to consist +of a most remarkable alternation of fresh-water, brackish-water, +and purely marine sediments, together with old land-surfaces, +or vegetable soils, which contain the upright stems of trees, +and are locally known as "Dirt-beds." + +One of the most important of the Jurassic deposits of the continent +of Europe, which is believed to be on the horizon of the Coral-rag +or of the lower part of the Upper Oolites, is the "_Solenhofen +Slate_" of Bavaria, an exceedingly fine-grained limestone, which +is largely used in lithography, and is celebrated for the number +and beauty of its organic remains, and especially for those of +Vertebrate animals. + +The subjoined sketch-section (fig. 159) exhibits in a diagrammatic +form the general succession of the Jurassic rocks of Britain. + +Regarded as a whole, the Jurassic formation is essentially marine; +and though remains of drifted plants, and of insects and other +air-breathing animals, are not uncommon, the fossils of the formation +are in the main marine. In the Purbeck series of Britain, +anticipatory of the great river-deposit of the Wealden, there are +fresh-water, brackish-water, and even terrestrial strata, indicating +that the floor of the Oolitic ocean was undergoing upheaval, and +that the marine conditions which had formerly prevailed were nearly +at an end. In places also, as in Yorkshire and Sutherlandshire, +are found actual beds of coal: but the great bulk of the formation +is an indubitable sea-deposit; and its limestones, oolitic as +they commonly are, nevertheless are composed largely of the +comminuted skeletons of marine animals. Owing to the enormous +number and variety of the organic remains which have been yielded +by the richly fossiliferous strata of the Oolitic series, it will +not be possible here to do more than to give an outline-sketch +of the principal forms of life which characterise the Jurassic +period as a whole. It is to be remembered, however, that every +minor group of the Jurassic formation has its own peculiar fossils, +and that by the labours of such eminent observers as Quenstedt, +Oppel, D'Orbigny, Wright, De la Beche, Tate, and others, the +entire series of Jurassic sediments admits of a more complete +and more elaborate subdivision into zones characterised by special +life-forms than has as yet been found practicable in the case +of any other rock-series. + +[Illustration: Fig. 159. GENERALIZED SECTION OF THE JURASSIC ROCKS +OF ENGLAND.] + +[Illustration: Fig. 160.--_Mantellia_ (_Cycadeoidea_) _megalophylla_, +a Cycad from the Purbeck "dirt-bed." Upper Oolites, England.] + +The _plants_ of the Jurassic period consist principally of Ferns, +Cycads, and Conifers--agreeing in this respect, therefore, with +those of the preceding Triassic formation. The _Ferns_ are very +abundant, and belong partly to old and partly to new genera. The +_Cycads_ are also very abundant, and, on the whole, constitute the +most marked feature of the Jurassic vegetation, many genera of this +group being known (_Pterophyllum, Otozamites, Zamites, Crossozamia, +Williamsonia, Bucklandia,_ &c.) The so-called "dirt-bed" of the +Purbeck series consists of an ancient soil, in which stand erect +the trunks of Conifers and the silicified stools of Cycads of +the genus _Mantellia_ (fig.160). The _Coniferoe_ of the Jurassic +are represented by various forms more or less nearly allied to +the existing _Araucarioe_; and these are known not only by their +stems or branches, but also in some cases by their cones. We +meet, also, with the remains of undoubted Endogenous plants, +the most important of which are the fruits of forms allied to +the existing Screw-pines (_Pandaneoe_), such as _Podocarya_ and +_Kaidacarpum_. So far, however, no remains of Palms have been +found; nor are we acquainted with any Jurassic plants which could +be certainly referred to the great "Angiospermous" group of the +Exogens, including the majority of our ordinary plants and trees. + +Amongst animals, the _Protozoans_ are well represented in the +Jurassic deposits by numerous _Foraminifers_ and _Sponges_; as +are the _Coelenterates_ by numerous _Corals_. Remains of these +last-mentioned organisms are extremely abundant in some of the +limestones of the formation, such as the "Coral-rag" and the +Great Oolite; and the former of these may fairly be considered +as an ancient "reef." The _Rugose Corals_ have not hitherto been +detected in the Jurassic rocks; and the "_Tabulate Corals_," +so-called, are represented only by examples of the modern genus +_Millepora_. With this exception, all the Jurassic Corals belong +to the great group which predominates in recent seas (_Zoantharia +sclerodermata_); and the majority belong to the important +reef-building family of the "Star-corals" (_Astroeidoe_). The +form here figured (_Thecosmilia annularis_, fig. 161) is one +of the characteristic species of the Coral-rag. + +[Illustration: Fig. 161.--_Thecosmilia annularis_, Coral-rag, +England.] + +[Illustration: Fig. 162.--_Pentacrinus fasciculos_, Lias. The +left-hand figure shows a few or the joints of the column; the +middle figure shows the arms, and the summit of the column with +its side-arms; and the right-hand figure shows the articulating +surface of one of the column-joints.] + +The _Echinoderms_ are very numerous and abundant fossils in the +Jurassic series, and are represented by Sea-lilies, Sea-urchins, +Star-fishes, and Brittle-stars. The _Crinoids_ are still common, +and some of the limestones of the series are largely composed +of the _débris_ of these organisms. Most of the Jurassic forms +resemble those with which we are already familiar, in having +the body permanently attached to some foreign object by means +of a longer or shorter jointed stalk or "column." One of the +most characteristic Jurassic genera of these "stalked" Crinoids +(though not exclusively confined to this period) is _Pentacrinus_ +(fig. 162). In this genus, the column is five-sided, with whorls +of "side-arms;" and the arms are long, slender, and branched. +The genus is represented at the present day by the beautiful +"Medusa-head Pentacrinite" (_Pentacrinus caput-medusoe_). Another +characteristic Oolitic genus is _Apiocrinus_, comprising the +so-called "Pear Encrinites." In this group the column is long +and rounded, with a dilated base, and having its uppermost joints +expanded so as to form, with the cup itself, a pear-shaped mass, +from the summit of which spring the comparatively short arms. +Besides the "stalked" Crinoids, the Jurassic rocks have yielded +the remains of the higher group of the "free" Crinoids, such as +_Saccosoma_. These forms resemble the existing "Feather-stars" +(_Comatula_) in being attached when young to some foreign body by +means of a jointed stem, from which they detach themselves when +fully grown to lead an independent existence. In this later stage +of their life, therefore, they closely resemble the Brittle-stars +in appearance. True Star-fishes (_Asteroids_) and Brittle-stars +(_Ophiuroids_) are abundant in the Jurassic rocks, and the +Sea-urchins (_Echinoids_) are so numerous and so well preserved +as to constitute quite a marked feature of some beds of the series. +All the Oolitic urchins agree with the modern _Echinoids_ in +having the shell composed of no more than twenty rows of plates. +Many different genera are known, and a characteristic species +of the Middle Oolites (_Hemicidaris crenularis_, fig. 163) is +here figured. + +[Illustration: Fig. 163.--_Hemicidaris crenularis_, showing the +great tubercles on which the spines were supported. Middle Oolites.] + +Passing over the _Annelides_, which, though not uncommon, are +of little special interest, we come to the _Articulates_, which +also require little notice. Amongst the _Crustaceans_, whilst +the little Water-fleas (_Ostracoda_) are still abundant, the +most marked feature is the predominance which is now assumed by +the _Decapods_--the highest of the known groups of the class. +True Crabs (_Brachyura_) are by no means unknown; but the principal +Oolitic Decapods belonged to the "Long-tailed" group (_Macrura_), +of which the existing Lobsters, Prawns, and Shrimps are members. +The fine-grained lithographic slates of Solenhofen are especially +famous as a depot for the remains of these Crustaceans, and a +characteristic species from this locality (_Eryon arctiformis_, +fig. 164) is here represented. Amongst the air-breathing +_Articulates_, we meet in the Oolitic rocks with the remains of +Spiders (_Arachnida_), Centipedes (_Myriapoda_), and numerous +true Insects (_Insecta_). In connection with the last-mentioned +of these groups, it is of interest to note the occurrence of +the oldest known fossil Butterfly--the _Paloeontina Oolitica_ +of the Stonesfield slate--the relationships of which appear to +be with some of the living Butterflies of Tropical America. + +[Illustration: Fig. 164.--_Eryon arctiformis_, a "Long-tailed +Decapod," from the Middle Oolites (Solenhofen Slate).] + +Coming to the _Mollusca_, the _Polyzoans_, numerous and beautiful +as they are, must be at once dismissed; but the _Brachiopods_ +deserve a moment's attention. The Jurassic Lamp-shells (fig. +165) do not fill by any means such a predominant place in the +marine fauna of the period, as in many Palæozoic deposits, but +they are still individually numerous. The two ancient genera +_Leptoena_ (fig. 165, a) and _Spirifera_ (fig. 165, b), dating +the one from the Lower and the other from the Upper Silurian, +appear here for the last time upon the scene, but they have not +hitherto been recognised in deposits later than the Lias. The +great majority of the Jurassic _Brachiopods_, however, belong to +the genera _Terebratula_ (fig. 165, c, e, f) and _Rhynchonella_ +(fig. 165. d), both of which are represented by living forms +at the present day. The _Terebratuloe_, in particular, are very +abundant, and the species are often confined to special horizons +in the series. + +[Illustration: Fig. 165.--Jurassic Brachiopod. a. _Leptoena +Liassica_, enlarged, the small cross below the figure indicating +the true size of the shell--Lias; b, _Spirifera rostrata_, Lias; +c, _Terebratula quadrifida_, Lias; d, d', _Rhynchonella varians_, +Fulter's Earth and Kelloway Rock; e, _Terebratula sphoeroidalis_, +Inferior Oolite; f, _Terebratula digona_, Bradford Clay, +Forest-marble, and Great Oolite. (After Davidson).] + +[Illustration: Fig. 166.--_Ostrea Marshii_. Middle and Lower +Oolites.] + +[Illustration: Fig. 167.--_Gryphoea incurva_. Lias.] + +Remains of _Bivalves_ (_Lamellibranchiata_) are very numerous in +the Jurassic deposits, and in many cases highly characteristic. +In the marine beds of the Oolites, which constitute by far the +greater portion of the whole formation, the Bivalyes are of course +marine, and belong to such genera as _Trigonia, Lima, Pholadomya, +Cardinia, Avicula, Hippopodium_, &c.; but in the Purbeck beds, at +the summit of the series, we find bands of Oysters alternating +with strata containing fresh-water or brackish-water Bivalves, +such as _Cyrenoe_ and _Corbuloe_. The predominant Bivalves of +the Jurassic, however, are the _Oysters_, which occur under many +forms, and often in vast numbers, particular species being commonly +restricted to particular horizons. Thus of the true Oysters, +_Ostrea distorta_ is characteristic of the Purbeck series, where +it forms a bed twelve feet in thickness, known locally as the +"Cinder-bed;" _Ostrea expansa_ abounds in the Portland beds; +_Ostrea deltoidea_ is characteristic of the Kimmeridge clay; +_Ostrea gregaria_ predominates in the Coral-rag; _Ostrea acuminata_ +characterises the small group of the Fuller's Earth; whilst the +plaited _Ostrea Marshii_ (fig. 166) is a common shell in the +Lower and Middle Oolites. Besides the more typical Oysters, the +Oolitic rocks abound in examples of the singularly unsymmetrical +forms belonging to the genera _Exogyra_ and _Gryphoea_ (fig. +167). In the former of these are included Oysters with the beaks +"reversed"--that is to say, turned towards the hinder part of +the shell; whilst in the latter are Oysters in which the lower +valve of the shell is much the largest, and has a large incurved +beak, whilst the upper valve is small and concave. One of the +most characteristic _Exogyroe_ is the _E. Virgula_ of the Oxford +Clay, and of the same horizon on the Continent; and the _Gryphoea +incurva_ (fig. 167) is equally abundant in, and characteristic +of, the formation of the Lias. Lastly, we may notice the +extraordinary shells belonging to the genus _Diceras_ (fig. 168), +which are exclusively confined to the Middle Oolites. In this +formation in the Alps they occur in such abundance as to give +rise to the name of "Calcaire à Dicerates," applied to beds of +the same age as the Coral-rag of Britain. The genus _Diceras_ +belongs to the same family as the "Thorny Clams" (Chama) of the +present day--the shell being composed of nearly equally-sized +valves, the beaks of which are extremely prominent and twisted +into a spiral. The shell was attached to some foreign body by +the beak of one of its valves. + +[Illustration: Fig. 168.--_Diceras arietina_. Middle Oolite.] + +[Illustration: Fig. 169.--_Nerinoea Goodhallii_, one-fourth of the +natural size. The left-hand figure shows the appearance presented +by the shell when vertically divided. Coral-rag, England.] + +Amongst the Jurassic Univalves (_Gasteropoda_) there are many +examples of the ancient and long-lived _Pleurotomaria_; but on +the whole the Univalves begin to have a modern aspect. The +round-mouthed ("holostomatous"), vegetable-eating Sea-snails, +such as the Limpets (_Patellidoe_), the Nerites (_Nerita_), the +_Turritelloe, Chemnitzioe_, &c., still hold a predominant place. +The two most noticeable genera of this group are _Cerithium_ +and _Nerinoea_--the former of these attaining great importance +in the Tertiary and Recent seas, whilst the latter (fig. 169) +is highly characteristic of the Jurassic series, though not +exclusively confined to it. One of the limestones of the Jura, +believed to be of the age of the Coral-rag (Middle Oolite) of +Britain, abounds to such an extent in the turreted shells of +_Nerinoea_ as to have gained the name of "Calcaire à Nérinées." +In addition to forms such as the preceding, we now for the first +time meet, in any force, with the Carnivorous Univalves, in which +the mouth of the shell is notched or produced into a canal, giving +rise to the technical name of "siphonostomatous" applied to the +shell. Some of the carnivorous forms belong to extinct types, +such as the _Purpuroidea_ of the Great Oolite; but others are +referable to well-known existing genera. Thus we meet here with +species of the familiar groups of the Whelks (_Buccinum_), the +Spindle-shells (_Fusus_), the Spider-shells (_Pteroceras_), _Murex, +Rostellaria_, and others which are not at present known to occur +in any earlier formation. + +Amongst the Wing-shells (_Pteropoda_), it is sufficient to mark +the final appearance in the Lias of the ancient genus _Conularia_. + +[Illustration: Fig. 170.--_Ammonites Humphresianus_. Inferior +Oolite.] + +[Illustration: Fig. 171.--_Ammonites bifrons_. Lias.] + +Lastly, the order of the _Cephalopoda_, in both its Tetrabranchiate +and Dibranchiate sections, undergoes a vast development in the +Jurassic period. The old and comparatively simple genus _Nautilus_ +is still well represented, one species being very similar to the +living Pearly Nautilus (_N. Pompilius_); but the _Orthocerata_ +and _Goniatites_ of the Trias have finally disappeared; and the +great majority of the Tetrabranchiate forms are referable to +the comprehensive genus _Ammonites_, with its many sub-genera +and its hundreds of recorded species. The shell in _Ammonites_ +is in the form of a flat spiral, all the coils of which are in +contact (figs. 170 and 171). The innermost whorls of the shell +are more or less concealed; and the body-chamber is elongated +and narrow, rather than expanded towards the mouth. The tube or +siphuncle which runs through the air-chambers is placed on the +dorsal or _convex_ side of the shell; but the principal character +which distinguishes _Ammonites_ from _Goniatites_ and _Ceratites_ is +the wonderfully complex manner in which the _septa_, or partitions +between the air-chambers, are folded and undulated. To such an +extent does this take place, that the edges of the septa, when +exposed by the removal of the shell-substance, present in an +exaggerated manner the appearance exhibited by an elaborately-dressed +shirt-frill when viewed edgewise. The species of _Ammonites_ range +from the Carboniferous to the Chalk; but they have not been found +in deposits older than the Secondary, in any region except India; +and they are therefore to be regarded as essentially Mesozoic +fossils. Within these limits, each formation is characterised by +particular species, the number of individuals being often very +great, and the size which is sometimes attained being nothing short +of gigantic. In the Lias, particular species of _Ammonites_ may +succeed one another regularly, each having a more or less definite +horizon, which it does not transgress. It is thus possible to +distinguish a certain number of zones, each characterised by +a particular Ammonite, together with other associated fossils. +Some of these zones are very persistent and extend over very +wide areas, thus affording valuable aid to the geologist in his +determination of rocks. It is to be remembered, however, that +there are other species which are not thus restricted in their +vertical range, even in the same formations in which definite +zones occur. + +[Illustartion: Fig. 172.--_Beloteuthis subcostata_ Jurassic (Lias).] + +The Cuttle-fishes or _Dibranchiate Cephalopods_ constitute a +feature in the life of the Jurassic period little less conspicuous +and striking than that afforded by the multitudinous and varied +chambered shells of the _Ammonitidoe_. The remains by which these +animals are recognised are necessarily less perfect, as a rule, +than those of the latter, as no external shell is present (except +in rare and more modern groups), and the internal skeleton is +not necessarily calcareous. Nevertheless, we have an ample record +of the Cuttle-fishes of the Jurassic period, in the shape of +the fossilised jaws or beak, the ink-bag, and, most commonly +of all, the horny or calcareous structure which is embedded in +the soft tissues, and is variously known as the "pen" or "bone." +The beaks of Cuttle-fishes, though not abundant, are sufficiently +plentiful to have earned for themselves the general title of +"Rhyncholites;" and in their form and function they resemble +the horny, parrot-like beak of the existing Cephalopods. The +ink-bag or leathery sac in which the Cuttle-fishes store up the +black pigment with which they obscure the water when attacked, +owes its preservation to the fact that the colouring-matter which +it contains is finely-divided carbon, and therefore nearly +indestructible except by heat. Many of these ink-bags have been +found in the Lias; and the colouring-matter is sometimes so well +preserved that it has been, as an experiment, employed in painting +as a fossil "sepia." The "pens" of the Cuttle-fishes are not +commonly preserved, owing to their horny consistence, but they +are not unknown. The form here figured (_Beloteuthis subcostata_, +fig. 172) belonged to an old type essentially similar to our modern +Calamaries, the skeleton of which consists of a horny shaft and +two lateral wings, somewhat like a feather in general shape. When, +on the other hand, the internal skeleton is calcareous, then it is +very easily preserved in a fossil condition; and the abundance of +remains of this nature in the Secondary rocks, combined with their +apparent total absence in Palæozoic strata, is a strong presumption +in favour of the view that the order of the Cuttle-fishes did +not come into existence till the commencement of the Mesozoic +period. The great majority of the skeletons of this kind which are +found in the Jurassic rocks belong to the great extinct family +of the "Belemnites" (_Belemnitidoa_), which, so far as known, is +entirely confined to rocks of Secondary age. From its pointed, +generally cylindro-conical form, the skeleton of the Belemnite is +popularly known as a "thunderbolt". (fig. 173, C). In its perfect +condition--in which it is, however, rarely obtainable--the skeleton +consists of a chambered conical shell (the "phragmacone"), the +partitions between the chambers of which are pierced by a marginal +tube or "siphuncle." This conical shell--curiously similar in its +structure to the _external_ shell of the Nautilus--is extended +forwards into a horny "pen," and is sunk in a corresponding conical +pit (fig. 173, B), excavated in the substance of a nearly cylindrical +fibrous body or "guard," which projects backwards for a longer or +shorter distance, and is the part most usually found in a fossil +condition. Many different kinds of _Belemnites_ are known, and +their guards literally swarm in many parts of the Jurassic series, +whilst some specimens attain very considerable dimensions. Not +only is the internal skeleton known, but specimens of _Belemnites_ +and the nearly allied _Belemnoteuthis_ have been found in some +of the fine-grained sediments of the Jurassic formation, from +which much has been learnt even as to the anatomy of the soft +parts of the animal. Thus we know that the Belemnites were in +many respects comparable with the existing Calamaries or Squids, +the body being furnished with lateral fins, and the head carrying +a circle of ten "arms," two of which were longer than the others +(fig. 173, A). The suckers on the arms were provided, further, +with horny hooks; there was a large ink-sac; and the mouth was +armed with horny mandibles resembling in shape the beak of a +parrot. + +[Illustration: Fig. 173.--A, Restoration of the animal of the +Belemnite; B, Diagram showing the complete skeleton of a Belemnite, +consisting of the chambered phragmacone (a), the guard (b), and +the horny pen (c); C, Specimen of _Belemnites canaliculatus_, +from the Inferior Oolite. (After Phillips.)] + +[Illustration: Fig. 174.--_Tetragonolepis (restored), and scales +of the same. Lias.] + +Coming next to the _Vertebrates_, we find that the Jurassic _Fishes_ +are still represented by _Ganoids_ and _Placoids_. The Ganoids, +however, unlike the old forms, now for the most part possess +nearly or quite symmetrical ("homocercal") tails. A characteristic +genus is _Tetragonolepis_ (fig. 174), with its deep compressed +body, its rhomboidal, closely-fitting scales, and its single +long dorsal fin. Amongst the _Placoids_ the teeth of true Sharks +(_Notidanus_) occur for the first time; but by far the greater +number of remains referable to this group are still the fin-spines +and teeth of "Cestracionts," resembling the living Port-Jackson +Shark. Some of these teeth are pointed (_Hybodus_); but others +are rounded, and are adapted for crushing shell-fish. Of these +latter, the commonest are the teeth of _Acrodus_ (fig. 175), of +which the hinder ones are of an elongated form, with a rounded +surface, covered with fine transverse striæ proceeding from a +central longitudinal line. From their general form and striation, +and their dark colour, these teeth are commonly called "fossil +leeches" by the quarrymen. + +[Illustration: Fig. 175.--Tooth of _Acrodus nobilis_. Lias.] + +The Amphibian group of the _Labyrinthodonts_, which was so +extensively developed in the Trias, appears to have become extinct, +no representative of the order having hitherto been detected in +rocks of Jurassic age. + +[Illustration: Fig. 176.--_Ichthyosaurus communis. Lias.] + +Much more important than the Fishes of the Jurassic series are +the _Reptiles_, which are both very numerous, and belong to a +great variety of types, some of these being very extraordinary +in their anatomical structure. The predominant group is that +of the "Enaliosaurs" or "Sea-lizards," divided into two great +orders, represented respectively by the _Ichthyosaurus_ and the +_Plesiosaurus_. + +The _Ichthyosauri_ or "Fish-Lizards" are exclusively Mesozoic +in their distribution, ranging from the Lias to the Chalk, but +abounding especially in the former. They were huge Reptiles, of +a fish-like form, with a hardly conspicuous neck (fig. 176), +and probably possessing a simply smooth or wrinkled skin, since +no traces of scales or bony integumentary plates have ever been +discovered. The tail was long, and was probably furnished at its +extremity with a powerful expansion of the skin, constituting a +tail-fin similar to that possessed by the Whales. The limbs are +also like those of Whales in the essentials of their structure, +and in their being adapted to act as swimming-paddles. Unlike +the Whales, however, the Ichthyosaurs possessed the hind-limbs +as well as the fore-limbs, both pairs having the bones flattened +out and the fingers completely enclosed in the skin, the arm +and leg being at the same time greatly shortened. The limbs are +thus converted into efficient "flippers," adapting the animal +for an active existence in the sea. The different joints of the +backbone (vertebræ) also show the same adaptation to an aquatic +mode of life, being hollowed out at both ends, like the biconcave +vertebræ of Fishes. The spinal column in this way was endowed +with the flexibility necessary for an animal intended to pass +the greater part of its time in water. Though the _Ichthyosaurs_ +are undoubtedly marine animals, there is, however, reason to +believe that they occasionally came on shore, as they possess +a strong bony arch, supporting the fore-limbs, such as would +permit of partial, if laborious, terrestrial progression. The +head is of enormous size, with greatly prolonged jaws, holding +numerous powerful conical teeth lodged in a common groove. The +nature of the dental apparatus is such as to leave no doubt as +to the rapacious and predatory habits of the Ichthyosaurs--an +inference which is further borne out by the examination of their +petrified droppings, which are known to geologists as "coprolites," +and which contain numerous fragments of the bones and scales +of the Ganoid fishes which inhabited the same seas. The orbits +are of huge size; and as the eyeball was protected, like that +of birds, by a ring of bony plates in its outer coat, we even +know that the pupils of the eyes were of correspondingly large +dimensions. As these bony plates have the function of protecting +the eye from injury under sudden changes of pressure in the +surrounding medium, it has been inferred, with great probability, +that the Ichthyosaurs were in the habit of diving to considerable +depths in the sea. Some of the larger specimens of _Ichthyosaurus_ +which have been discovered in the Lias indicate an animal of +from 20 to nearly 40 feet in length; and many species are known +to have existed, whilst fragmentary remains of their skeletons +are very abundant in some localities. We may therefore safely +conclude that these colossal Reptiles were amongst the most +formidable of the many tyrants of the Jurassic seas. + +[Illustration: Fig. 177.--_Plesiosaurus dolichodeirus_, restored. +Lias.] + +The _Plesiosaurus_ (fig. 177) is another famous Oolitic Reptile, +and, like the preceding, must have lived mainly or exclusively in +the sea. It agrees with the Ichthyosaur in some important features +of its organisation, especially in the fact that both pairs of +limbs are converted into "flippers" or swimming-paddles, whilst +the skin seems to have been equally destitute of any scaly or bony +investiture. Unlike the _Ichthyosaur_, however, the Plesiosaur +had the paddles placed far back, the tail being extremely short, +and the neck greatly lengthened out, and composed of from twenty +to forty vertebræ. The bodies of the vertebræ, also, are not +deeply biconcave, but are flat, or only slightly cupped. The +head is of relatively small size, with smaller orbits than those +of the _Ichthyosaur_, and with a snout less elongated. The jaws, +however, were armed with numerous conical teeth, inserted in +distinct sockets. As regards the habits of the Plesiosaur, Dr +Conybeare arrives at the following conclusions: "That it was +aquatic is evident from the form of its paddles; that it was +marine is almost equally so from the remains with which it is +universally associated; that it may have occasionally visited +the shore, the resemblance of its extremities to those of the +Turtles may lead us to conjecture: its movements, however, must +have been very awkward on land; and its long neck must have impeded +its progress through the water, presenting a strong contrast to +the organisation which so admirably fits the _Ichthyosaurus_ +to cut through the waves." As its respiratory organs were such +that it must of necessity have required to obtain air frequently, +we may conclude "that it swam upon or near the surface, arching +back its long neck like a swan, and occasionally darting it down +at the fish which happened to float within its reach. It may +perhaps have lurked in shoal water along the coast, concealed +amongst the sea-weed; and raising its nostrils to a level with +the surface from a considerable depth, may have found a secure +retreat from the assaults of powerful enemies; while the length +and flexibility of its neck may have compensated for the want +of strength in its jaws, and its incapacity for swift-motion +through the water." + +About twenty species of _Plesiosaurus_ are known, ranging from +the Lias to the Chalk, and specimens have been found indicating +a length of from eighteen to twenty feet. The nearly related +"_Pliosaurs_," however, with their huge heads and short necks, +must have occasionally reached a length of at least forty feet--the +skull in some species being eight, and the paddles six or seven +feet long, whilst the teeth are a foot in length. + +[Illustration: Fig. 178.--_Pterodactylus crassirostis_. From the +Lithographic Slates of Solenhofen (Middle Oolite). The figure is +"restored," and it seems certain that the restoration is incorrect +in the comparatively unimportant particular, that the hand should +consist of no more than four fingers, three short and one long, +instead of five, as represented.] + +Another extraordinary group of Jurassic Reptiles is that of the +"Winged Lizards" or _Pterosauria_. These are often spoken of +collectively as "Pterodactyles," from _Pterodactylus_, the type-genus +of the group. As now restricted, however, the genus _Pterodactylus_ +is more Cretaceous than Jurassic, and it is associated in the +Oolitic rocks with the closely allied genera _Dimorphodon_ and +_Rhamphorhynchus_. In all three of these genera we have the same +general structural organisation, involving a marvellous combination +of characters, which we are in the habit of regarding as peculiar +to Birds on the one hand, to Reptiles on another hand, and to the +Flying Mammals or Bats in a third direction. The "Pterosaurs" +are "Flying" Reptiles, in the true sense of the term, since they +were indubitably possessed of the power of active locomotion +in the air, after the manner of Birds. The so-called "Flying" +Reptiles of the present day, such as the little _Draco volans_ +of the East Indies and Indian Archipelago, possess, on the other +hand, no power of genuine flight, being merely able to sustain +themselves in the air through the extensive leaps which they take +from tree to tree, the wing-like expansions of the skin simply +exercising the mechanical function of a parachute. The apparatus +of flight in the "Pterosaurs" is of the most remarkable character, +and most resembles the "wing" of a Bat, though very different in +some important particulars. The "wing" of the Pterosaurs is like +that of Bats, namely, in consisting of a thin leathery expansion of +the skin which is attached to the sides of the body, and stretches +between the fore and hind limbs, being mainly supported by an +enormous elongation of certain of the digits of the hand. In +the Bats, it is the four outer fingers which are thus lengthened +out; but in the Pterosaurs, the wing-membrane is borne by a single +immensely-extended finger (fig. 178). No trace of the actual +wing-membrane itself has, of course, been found fossilised; but +we could determine that the "Pterodactyles" possessed the power +of flight, quite apart from the extraordinary conformation of +the hand. The proofs of this are to be found partly in the fact +that the breast-bone was furnished with an elevated ridge or +keel, serving for the attachment of the great muscles of flight, +and still more in the fact that the bones were hollow and were +filled with air--a peculiarity wholly confined amongst living +animals to Birds only. The skull of the Pterosaurs is long, light, +and singularly bird-like in appearance--a resemblance which is +further increased by the comparative length of the neck and the +size of the vertebræ of this region (fig. 178). The jaws, however, +unlike those of any existing Bird, were, with one exception to be +noticed hereafter, furnished with conical teeth sunk in distinct +sockets; and there was always a longer or shorter tail composed +of distinct vertebræ; whereas in all existing Birds the tail +is abbreviated, and the terminal vertebræ are amalgamated to +form a single bone, which generally supports the great feathers +of the tail. + +Modern naturalists have been pretty generally agreed that the +_Pterosaurs_ should be regarded as a peculiar group of the Reptiles; +though they have been and are still regarded by high authorities, +like Professor Seeley, as being really referable to the Birds, or +as forming a class by themselves. The chief points which separate +them from Birds, as a class, are the character of the apparatus +of flight, the entirely different structure of the fore-limb, the +absence of feathers, the composition of the tail out of distinct +vertebræ, and the general presence of conical teeth sunk in distinct +sockets in the jaws. The gap between the Pterosaurs and the Birds +has, however, been greatly lessened of late by the discovery +of fossil animals (_Ichthyornis_ and _Hesperornis_) with the +skeleton proper to Birds combined with the presence of teeth +in the jaws, and by the still more recent discovery of other +fossil animals (_Pteranodon_) with a Pterosaurian skeleton, but +without teeth; whilst the undoubtedly feathered _Archoeopteryx_ +possessed a long tail composed of separate vertebræ. Upon the +whole, therefore, the relationships of the Pterosaurs cannot +be regarded as absolutely settled. It seems certain, however, +that they did not possess feathers--this implying that they were +cold-blooded animals; and their affinities with Reptiles in this, +as in other characters, are too strong to be overlooked. + +[Illustration: Fig. 179--_Rhamphorhynchus Bucklandi_, restored. +Bath Oolite, England. (After the late Professor Phillips.)] + +The _Pterosaurs_ are wholly Mesozoic, ranging from the Lias to +the Chalk inclusive; and the fine-grained Lithographic Slate of +Solenhofen has proved to be singularly rich in their remains. +The genus _Pterodactylus_ itself has the jaws toothed to the +extremities with equal-sized conical teeth, and its species range +from the Middle Oolites to the Cretaceous series, in connection +with which they will be again noticed, together with the toothless +genus _Pteranodon_. The genus _Dimorphodon_ is Liassic, and is +characterised by having the front teeth long and pointed, whilst +the hinder teeth are small and lancet-shaped. Lastly, the singular +genus _Rhamphorhynchus_, also from the Lower Oolites, is +distinguished by the fact that there are teeth present in the +hinder portions of both jaws; but the front portions are toothless, +and may have constituted a horny beak. Like most of the other +Jurassic Pterosaurs, _Rhamphorhynchus_ (fig. 179) does not seem +to have been much bigger than a pigeon, in this respect falling +far below the giant "Dragons" of the Cretaceous period. It differed +from its relatives, not only in the armature of the mouth, but +also in the fact that the tail was of considerable length. With +regard to its habits and mode of life, Professor Phillips remarks +that, "gifted with ample means of flight, able at least to perch +on rocks and scuffle along the shore, perhaps competent to dive, +though not so well as a Palmiped bird, many fishes must have +yielded to the cruel beak and sharp teeth of Rhamphorhynchus. +If we ask to which of the many families of Birds the analogy of +structure and probable way of life would lead us to assimilate +Rhamphorhynchus, the answer must point to the swimming races with +long wings, clawed feet, hooked beak, and habits or violence and +voracity; and for preference, the shortness of the legs, and other +circumstances, may be held to claim for the Stonesfield fossil a +more than fanciful similitude to the groups of Cormorants, and +other marine divers, which constitute an effective part of the +picturesque army of robbers of the sea." + +Another extraordinary and interesting group of the Mesozoic Reptiles +is constituted by the _Deinosauria_, comprising a series of mostly +gigantic forms, which range from the Trias to the Chalk. All the +"Deinosaurs" are possessed of the two pairs of limbs proper to +Vertebrate animals, and these organs are in the main adapted for +walking on the dry land. Thus, whilst the Mesozoic seas swarmed +with the huge Ichthyosaurs and Plesiosaurs, and whilst the air +was tenanted by the Dragon-like Pterosaurs, the land-surfaces of +the Secondary period were peopled by numerous forms of Deinosaurs, +some of them of even more gigantic dimensions than their marine +brethren. The limbs of the _Deinosaurs_ are, as just said, adapted +for progression on the land; but in some cases, at any rate, the +hind-limbs were much longer and stronger than the fore-limbs; +and there seems to be no reason to doubt that many of these forms +possessed the power of walking, temporarily or permanently, on their +hind-legs, thus presenting a singular resemblance to Birds. Some +very curious and striking points connected with the structure of +the skeleton have also been shown to connect these strange Reptiles +with the true Birds; and such high authorities as Professors Huxley +and Cope are of opinion that the Deinosaurs are distinctly related +to this class, being in some respects intermediate between the +proper Reptiles and the great wingless Birds, like the Ostrich +and Cassowary. On the other hand, Professor Owen has shown that the +Deinosaurs possess some weighty points of relationship with the +so-called "Pachydermatous" Quadrupeds, such as the Rhinoceros and +Hippopotamus. The most important Jurassic genera of _Deinosauria_ +are _Megalosaurus_ and _Cetiosaurus_, both of which extend their +range into the Cretaceous period, in which flourished, as we +shall see, some other well-known members of this order. + +[Illustration: Fig. 180.--Skull of _Megalosaurus_, on a scale +one-tenth of nature. Restored. (After Professor Phillips.)] + +_Megalosaurus_ attained gigantic dimensions, its thigh and shank +bones measuring each about three feet in length, and its total +length, including the tail, being estimated at from forty to +fifty feet. As the head of the thigh-bone is set on nearly at +right angles with the shaft, whilst all the long bones of the +skeleton are hollowed out internally for the reception of the +marrow, there can be no doubt as to the terrestrial habits of +the animal. The skull (fig. 180) was of large size, four or five +feet in length, and the jaws were armed with a series of powerful +pointed teeth. The teeth are conical in shape, but are strongly +compressed towards their summits, their lateral edges being finely +serrated. In their form and their saw-like edges, they resemble +the teeth of the "Sabre-toothed Tiger" (_Machairodus_), and they +render it certain that the Megalosaur was in the highest degree +destructive and carnivorous in its habits. So far as is known, the +skin was not furnished with any armour of scales or bony plates; +and the fore-limbs are so disproportionately small as compared +with the hind-limbs, that this huge Reptile--like the equally +huge Iguanodon--may be conjectured to have commonly supported +itself on its hind-legs only. + +The _Cetiosaur_ attained dimensions even greater than those of +the Megalosaur, one of the largest thigh-bones measuring over +five feet in length and a foot in diameter in the middle, and +the total length of the animal being probably not less than fifty +feet. It was originally regarded as a gigantic Crocodile, but +it has been shown to be a true Deinosaur. Having obtained a +magnificent series of remains of this reptile, Professor Phillips +has been able to determine many very interesting points as to +the anatomy and habits of this colossal animal, the total length +of which he estimates as being probably not less than sixty or +seventy feet. As to its mode of life, this accomplished writer +remarks:-- + +"Probably when 'standing at ease' not less than ten feet in height, +and of a bulk in proportion, this creature was unmatched in magnitude +and physical strength by any of the largest inhabitants of the +Mesozoic land or sea. Did it live in the sea, in fresh waters, +or on the land? This question cannot be answered, as in the case +of Ichthyosaurus, by appeal to the accompanying organic remains; +for some of the bones lie in marine deposits, others in situations +marked by estuarine conditions, and, out of the Oxfordshire district, +in Sussex, in fluviatile accumulations. Was it fitted to live +exclusively in water? Such an idea was at one time entertained, +in consequence of the biconcave character of the caudal vertebræ, +and it is often suggested by the mere magnitude of the creature, +which would seem to have an easier life while floating in water, +than when painfully lifting its huge bulk, and moving with slow +steps along the ground. But neither of these arguments is valid. The +ancient earth was trodden by larger quadrupeds than our elephant; +and the biconcave character of vertebræ, which is not uniform +along the column in Cetiosaurus, is perhaps as much a character +of a geological period as of a mechanical function of life. Good +evidence of continual life in water is yielded in the case of +Ichthyosaurus and other Enaliosaurs, by the articulating surfaces +of their limb-bones, for these, all of them, to the last phalanx, +have that slight and indefinite adjustment of the bones, with much +intervening cartilage, which fits the leg to be both a flexible +and forcible instrument of natation, much superior to the ordinary +oar-blade of the boatman. On the contrary, in Cetiosaur, as well as +in Megalosaur and Iguanodon, all the articulations are definite, +and made so as to correspond to determinate movements in particular +directions, and these are such as to be suited for walking. In +particular, the femur, by its head projecting freely from the +acetabulum, seems to claim a movement of free stepping more parallel +to the line of the body, and more approaching to the vertical than +the sprawling gait of the crocodile. The large claws concur in this +indication of terrestrial habits. But, on the other hand, these +characters are not contrary to the belief that the animal may have +been amphibious; and the great vertical height of the anterior +part of the tail seems to support this explanation, but it does +not go further.... We have therefore a marsh-loving or river-side +animal, dwelling amidst filicine, cycadaceous, and coniferous +shrubs and trees full of insects and small mammalia. What was +its usual diet? If _ex ungue leonem_, surely _ex dente cibum_. +We have indeed but one tooth, and that small and incomplete. It +resembles more the tooth of Iguanodon than that of any other +reptile; for this reason it seems probable that the animal was +nourished by similar vegetable food which abounded in the vicinity, +and was not obliged to contend with Megalosaurus for a scanty +supply of more stimulating diet." + +All the groups of Jurassic Reptiles which we have hitherto been +considering are wholly unrepresented at the present day, and +do not even pass upwards into the Tertiary period. It may be +mentioned, however, that the Oolitic deposits have also yielded +the remains of Reptiles belonging to three of the existing orders +of the class-namely, the Lizards (_Lacertilia_), the Turtles +(_Chelonia_), and the Crocodiles (_Crocodilia_). The Lizards +occur both in the marine strata of the Middle Oolites and also +in the fresh-water beds of the Purbeck series; and they are of +such a nature that their affinities with the typical Lacertilians +of the present day cannot be disputed. The Chelonians, up to +this point only known by the doubtful evidence of footprints +in the Permian and Triassic sandstones, are here represented by +unquestionable remains, indicating the existence of marine Turtles +(the _Chelone planiceps_ of the Portland Stone). No remains of +Serpents (_Ophidians_) have as yet been detected in the Jurassic; +but strata of this age have yielded the remains of numerous +_Crocodilians_, which probably inhabited the sea. The most important +member of this group is _Teleosaurus_, which attained a length of +over thirty feet, and is in some respects allied to the living +Gavials of India. + +[Illustration: Fig. 181.--_Archoeopteryx macrura_, showing tail +and tail-feathers, with detached bones. Reduced. From the +Lithographic Slate of Solenhofen.] + +[Illustration: Fig. 182.--Restoration of _Archoeopteryx macrura_. +(After Owen.)] + +The great class of the Birds, as we have seen, is represented +in rocks earlier than the Oolites simply by the not absolutely +certain evidence of the three-toed footprints of the Connecticut +Trias. In the Lithographic Slate of Solenhofen (Middle Oolite), +there has been discovered, however, the at present unique skeleton +of a Bird well known under the name of the _Archoeopteryx macrura_ +(figs. 181, 182). The only known specimen--now in the British +Museum--unfortunately does not exhibit the skull; but the +fine-grained matrix has preserved a number of the other bones +of the skeleton, along with the impressions of the tail and wing +feathers. From these remains we know that _Archoeopteryx_ differed +in some remarkable peculiarities of its structure from all existing +members of the class of Birds. This extraordinary Bird (fig. +182) appears to have been about as big as a Rook--the tail being +long and extremely slender, and composed of separate vertebræ, +each of which supports a single pair of quill-feathers. In the +flying Birds of the present day, as before mentioned, the terminal +vertebræ of the tail are amalgamated to form a single bone +("ploughshare-bone"), which supports a cluster of tail-feathers; +and the tail itself is short. In the embryos of existing Birds +the tail is long, and is made up of separate vertebræ, and the +same character is observed in many existing Reptiles. The tail +of _Archoeopteryx_, therefore, is to be regarded as the permanent +retention of an embryonic type of structure, or as an approximation +to the characters of the Reptiles. Another remarkable point in +connection with _Archoeopteryx_, in which it differs from all +known Birds, is, that the wing was furnished with two free claws. +From the presence of feathers, _Archoeopteryx_ may be inferred to +have been hot-blooded; and this character, taken along with the +structure of the skeleton of the wing, may be held as sufficient +to justify its being considered as belonging to the class of +Birds. In the structure of the tail, however, it is singularly +Reptilian; and there is reason to believe that its jaws were +furnished with teeth sunk in distinct sockets, as is the case +in no existing Bird. This conclusion, at any rate, is rendered +highly probable by the recent discovery of "Toothed Birds" +(_Odonturnithes_) in the Cretaceous rocks of North America. + +[Illustration: Fig. 183.--Lower jaw of _Amphitherium_ +(_Thylacotherium_) _Prevostii_. Stonesfield Slate (Great Oolite.)] + +[Illustration: Fig. 184. Oolitic Mammals.--1, Lower jaw and teeth +of _Phascolotherium_, Stonesfield Slate; 2, Lower jaw and teeth +of _Amphitherium_, Stonesfield Slate; 3, Lower jaw and teeth of +_Triconodon_, Purbeck beds; 4, Lower jaw and teeth of _Plagiaulax_, +Purbeck beds. All the figures are of the natural size.] + +The _Mammals_ of the Jurassic period are known to us by a number +of small forms which occur in the "Stonesfield Slate" (Great +Oolite) and in the Purbeck beds (Upper Oolite). The remains of +these are almost exclusively separated halves of the lower jaw, +and they indicate the existence during the Oolitic period in +Europe of a number of small "Pouched animals" (_Marsupials_). +In the horizon of the Stonesfield Slate four genera of these +little Quadrupeds have been described--viz., _Amphilestes, +Amphitherium, Phascolotherium_, and _Stereognathus_. In +_Amphitherium_ (fig. 183), the molar teeth are furnished with +small pointed eminences or "cusps;" and the animal was doubtless +insectivorous. By Professor Owen, the highest living authority on +the subject, _Amphitherium_ is believed to be a small Marsupial, +most nearly allied to the living Banded Ant-eater (_Myrmecobius_) +of Australia (fig. 158). _Amphilestes_ and _Phascolotherium_ +(fig. 184) are also believed by the same distinguished anatomist +and palæontologist to have been insect-eating Marsupials, and +the latter is supposed to find its nearest living ally in the +Opossums (_Didelphys_) of America. Lastly, the _Stereognathus_ of +the Stonesfield Slate is in a dubious position. It may have been +a Marsupial; but, upon the whole, Professor Owen is inclined to +believe that it must have been a hoofed and herbivorous Quadruped +belonging to the series of the higher Mammals (_Placentalia_). +In the Middle Purbeck beds, near to the close of the Oolitic +period, we have also evidence of the existence of a number of +small Mammals, all of which are probably Marsupials. Fourteen +species are known, all of small size, the largest being no bigger +than a Polecat or Hedgehog. The genera to which these little +quadrupeds have been referred are _Plagiaulax, Spalacotherium, +Triconodon_, and _Galestes_. The first of these (fig. 184, 4) +is believed by Professor Owen to have been carnivorous in its +habits; but other authorities maintain that it was most nearly +allied to the living Kangaroo-rats (_Hypsiprymnus_) of Australia, +and that it was essentially herbivorous. The remaining three +genera appear to have been certainly insectivorous, and find +their nearest living representatives in the Australian Phalangers +and the American Opossums. + +Finally, it is interesting to notice in how many respects the +Jurassic fauna of Western Europe approached to that now inhabiting +Australia. At the present day, Australia is almost wholly tenanted +by Marsupials; upon its land-surface flourish _Araucarioe_ and +Cycadaceous plants, and in its seas swims the Port-Jackson Shark +(_Cestracion Philippi_); whilst the Molluscan genus _Trigonia_ +is nowadays exclusively confined to the Australian coasts. In +England, at the time of the deposition of the Jurassic rocks, +we must have had a fauna and flora very closely resembling what +we now see in Australia. The small Marsupials, _Amphitherium, +Phascolotherium_, and others, prove that the Mammals were the same +in order; cones of Araucarian pines, with tree-ferns and fronds +of Cycads, occur throughout the Oolitic series; spine-bearing +fishes, like the Port-Jackson Shark, are abundantly represented +by genera such as _Acrodus_ and _Strophodus_; and lastly, the +genus _Trigonia_, now exclusively Australian, is represented +in the Oolites by species which differ little from those now +existing. Moreover, the discovery during recent years of the +singular Mud-fish, the _Ceratodus Fosteri_ in the rivers of +Queensland, has added another and a very striking point of +resemblance to those already mentioned; since this genus of Fishes, +though preeminently Triassic, nevertheless extended its range +into the Jurassic. Upon the whole, therefore, there is reason +to conclude that Australia has undergone since the close of the +Jurassic period fewer changes and vicissitudes than any other +known region of the globe; and that this wonderful continent +has therefore succeeded in preserving a greater number of the +characteristic life-features of the Oolites than any other country +with which we are acquainted. + + +LITERATURE. + +The following list comprises some of the more important sources of +information as to the rocks and fossils of the Jurassic series:-- + + (1) 'Geology of Oxford and the Thames Valley.' Phillips. + (2) 'Geology of Yorkshire,' vol. ii. Phillips. + (3) 'Memoirs of the Geological Survey of Great Britain.' + (4) 'Geology of Cheltenham.' Murchison, 2d ed. Buckman. + (5) 'Introduction to the Monograph of the Oolitic Asteriadæ' + (Palæontographical Society). Wright. + (6) "Zone of Avicula contorta and the Lower Lias of the South of + England"--'Quart. Journ. Geol. Soc.,' vol. xvi., 1860. Wright. + (7) "Oolites of Northamptonshire"--'Quart. Journ. Geol. Soc.,' + vols. Xxvi. and xxix. Sharp. + (8) 'Manual of Geology.' Dana. + (9) 'Der Jura.' Quenstedt. +(10) 'Das Flötzgebirge Württembergs.' Quenstedt. +(11) 'Jura Formation.' Oppel. +(12) 'Paléontologie du Département de la Moselle.' Terquem. +(13) 'Cours élémentaire de Paléontologie.' D'Orbigny. +(14) 'Paléontologie Française.' D'Orbigny. +(15) 'Fossil Echinodermata of the Oolitic Formation' + (Palæontographical Society). Wright. +(16) 'Brachiopoda of the Oolitic Formation' (Palæontographical + Society). Davidson. +(17) 'Mollusca of the Great Oolite' (Palæontographical Society). + Morris and Lycett. +(18) 'Monograph of the Fossil Trigoniæ' (Palæontographical Society). + Lycett. +(19) 'Corals of the Oolitic Formation' (Palæontographical Society). + Edwards and Haime. +(20) 'Supplement to the Corals of the Oolitic Formation' + (Palæontographical Society). Martin Duncan. +(21) 'Monograph of the Belemnitidæ' (Palæontographical Society). + Phillips. +(22) 'Structure of the Belemnitidæ' (Mem. Geol. Survey). Huxley. +(23) 'Sur les Belemnites.' Blainville. +(24) 'Cephalopoden.' Quenstedt. +(25) 'Mineral Conchology.' Sowerby. +(26) 'Jurassic Cephalopoda' (Palæontologica Indica). Waagen. +(27) 'Manual of the Mollusca.' Woodward. +(28) 'Petrefaktenkunde.' Schlotheim. +(29) 'Bridgewater Treatise.' Buckland. +(30) 'Versteinerungen des Oolithengebirges.' Roemer. +(31) 'Catalogue of British Fossils.' Morris. +(32) 'Catalogue of Fossils in the Museum of Practical Geology.' + Etheridge. +(33) 'Beiträge zur Petrefaktenkunde.' Münster. +(34) 'Petrefacta Germaniæ.' Goldfuss. +(35) 'Lethæa Rossica.' Eichwald. +(36) 'Fossil Fishes' (Decades of the Geol. Survey). Sir Philip Egerton. +(37) 'Manual of Palæontology.' Owen. +(38) 'British Fossil Mammals and Birds.' Owen. +(39) 'Monographs of the Fossil Reptiles of the Oolitic Formation' + (Palæontographical Society). Owen. +(40) 'Fossil Mammals of the Mesozoic Formations' (Palæontographical + Society). Owen. +(41) 'Catalogue of Ornithosauria.' Seeley. +(42) "Classification of the Deinosauria"--'Quart. Journ. Geol. Soc.,' + vol. xxvi., 1870. Huxley. + + + + +CHAPTER XVII. + +THE CRETACEOUS PERIOD. + +The next series of rocks in ascending order is the great and +important series of the Cretaceous Rocks, so called from the +general occurrence in the system of chalk (Lat. _creta_, chalk). +As developed in Britain and Europe generally, the following leading +subdivisions may be recognised in the Cretaceous series:-- + + 1. Wealden, \_ Lower Cretaceous. + 2. Lower Greensand or Neocomian, / + 3. Gault, \ + 4. Upper Greensand, |_ Upper Cretaceous. + 5. Chalk, | + 6. Maestricht beds, / + +I. _Wealden_.--The _Wealden_ formation, though of considerable +importance, is a local group, and is confined to the southeast +of England, France, and some other parts of Europe. Its name is +derived from the _Weald_, a district comprising parts of Surrey, +Sussex, and Kent, where it is largely developed. Its lower portion, +for a thickness of from 500 to 1000 feet, is arenaceous, and is +known as the Hastings Sands. Its Upper portion, for a thickness +of 150 to nearly 300 feet, is chiefly argillaceous, consisting of +clays with sandy layers, and occasionally courses of limestone. +The geological importance of the Wealden formation is very great, +as it is undoubtedly the delta of an ancient river, being composed +almost wholly of fresh-water beds, with a few brackish-water +and even marine strata, intercalated in the lower portion. Its +geographical extent, though uncertain, owing to the enormous +denudation to which it has been subjected, is nevertheless great, +since it extends from Dorsetshire to France, and occurs also in +North Germany. Still, even if it were continuous between all +these points, it would not be larger than the delta of such a +modern river as the Ganges. The river which produced the Wealden +series must have flowed from an ancient continent occupying what +is now the Atlantic Ocean; and the time occupied in the formation +of the Wealden must have been very great, though we have, of +course, no data by which we can accurately calculate its duration. + +The fossils of the Wealden series are, naturally, mostly the +remains of such animals as we know at the present day as inhabiting +rivers. We have, namely, fresh-water Mussels (_Unio_), River-snails +(_Paludina_), and other fresh-water shells, with numerous little +bivalved Crustaceans, and some fishes. + +II. _Lower Greensand_ (_Néocomien_ of D'Orbigny).--The Wealden +beds pass upward, often by insensible gradations, into the Lower +Greensand. The name Lower Greensand is not an appropriate one, +for green sands only occur sparingly and occasionally, and are +found in other formations. For this reason it has been proposed +to substitute for Lower Greensand the name _Neocomian_, derived +from the town of Neufchâtel--anciently called _Neocomum_--in +Switzerland. If this name were adopted, as it ought to be, the +Wealden beds would be called the Lower Neocomian. + +The Lower Greensand or Neocomian of Britain has a thickness of +about 850 feet, and consists of alternations of sands, sandstones, +and clays, with occasional calcareous bands. The general colour +of the series is dark brown, sometimes red; and the sands are +occasionally green, from the presence of silicate of iron. + +The fossils of the Lower Greensand are purely marine, and among +the most characteristic are the shells of _Cephalopods_. + +The most remarkable point, however, about the fossils of the +Lower Cretaceous series, is their marked divergence from the +fossils of the Upper Cretaceous rocks. Of 280 species of fossils +in the Lower Cretaceous series, only 51, or about 18 per cent, pass +on into the Upper Cretaceous. This break in the life of the two +periods is accompanied by a decided physical break as well; for the +Gault is often, if not always, unconformably superimposed on the +Lower Greensand. At the same time, the Lower and Upper Cretaceous +groups form a closely-connected and inseparable series, as shown +by a comparison of their fossils with those of the underlying +Jurassic rocks and the overlying Tertiary beds. Thus, in Britain +no marine fossil is known to be common to the marine beds of +the Upper Oolites and the Lower Greensand; and of more than 500 +species of fossils in the Upper Cretaceous rocks, almost everyone +died out before the formation of the lowest Tertiary strata, the +only survivors being one Brachiopod and a few _Foraminifera_. + +III. _Gault_ (_Aptien_ of D'Orbigny).--The lowest member of the +Upper Cretaceous series is a stiff, dark-grey, blue, or brown +clay, often worked for brick-making, and known as the _Gault_, +from a provincial English term. It occurs chiefly in the south-east +of England, but can be traced through France to the flanks of +the Alps and Bavaria. It never exceeds 100 feet in thickness; +but it contains many fossils, usually in a state of beautiful +preservation. + +IV. _Upper Greensand_ (_Albien_ of D'Orbigny; _Unterquader_ and +_Lower Plänerkalk_ of Germany).--The Gault is succeeded upward by +the _Upper Greensand_, which varies in thickness from 3 up to 100 +feet, and which derives its name from the occasional occurrence +in it of green sands. These, however, are local and sometimes +wanting, and the name "Upper Greensand" is to be regarded as a +_name_ and not a description. The group consists, in Britain, +of sands and clays, sometimes with bands of calcareous grit or +siliceous limestone, and occasionally containing concretions of +phosphate of lime, which are largely worked for agricultural +purposes. + +V. _White Chalk_.--The top of the Upper Greensand becomes +argillaceous, and passes up gradually into the base of the great +formation known as the true _Chalk_, divided into the three +subdivisions of the chalk-marl, white chalk without flints, and +white chalk with flints. The first of these is simply argillaceous +chalk, and passes up into a great mass of obscurely-stratified +white chalk in which there are no flints (_Turonien_ of D'Orbigny; +_Mittelquader_ of Germany). This, in turn, passes up into a great +mass of white chalk, in which the stratification is marked by +nodules of black flint arranged in layers (_Sénonien_ of D'Orbigny; +_Oberquader_ of Germany). The thickness of these three subdivisions +taken together is sometimes over 1000 feet, and their geographical +extent is very great. White Chalk, with its characteristic +appearance, may be traced from the north of Ireland to the Crimea, +a distance of about 1140 geographical miles; and, in an opposite +direction, from the south of Sweden to Bordeaux, a distance of +about 840 geographical miles. + +VI. In Britain there occur no beds containing Chalk fossils, or +in any way referable to the Cretaceous period, above the true +White Chalk with flints. On the banks of the Maes, however, near +Maestricht in Holland, there occurs a series of yellowish limestones, +of about 100 feet in thickness, and undoubtedly superior to the White +Chalk. These _Maestricht beds_ (_Danien_ of D'Orbigny) contain a +remarkable series of fossils, the characters of which are partly +Cretaceous and partly Tertiary. Thus, with the characteristic +Chalk fossils, _Belemnites, Baculites_, Sea-Urchins, &c., are +numerous Univalve Molluscs, such as Cowries and Volutes, which +are otherwise exclusively Tertiary or Recent. + +Holding a similar position to the Maestricht beds, and showing +a similar intermixture of Cretaceous forms with later types, are +certain beds which occur in the island of Seeland, in Denmark, +and which are known as the _Faxöe Limestone_. + +Of a somewhat later date than the Maestricht beds is the _Pisolitic +Limestone_ of France, which rests unconformably on the White +Chalk, and contains a large number of Tertiary fossils along with +some characteristic Cretaceous types. + +The subjoined sketch-section exhibits the general succession of +the Cretaceous deposits in Britain:-- + +[Illustration: Fig. 185. GENERALIZED SECTION OF THE CRETACEOUS +SERIES OF BRITAIN.] + +In North America, strata of Lower Cretaceous age are well represented +in Missouri, Wyoming, Utah, and in some other areas; but the greater +portion of the American deposits of this period are referable to +the Upper Cretaceous. The rocks of this series are mostly sands, +clays, and limestones--_Chalk_ itself being unknown except in +Western Arkansas. Amongst the sandy accumulations, one of the +most important is the so-called "marl" of New Jersey, which is +truly a "Greensand," and contains a large proportion of glauconite +(silicate of iron and potash). It also contains a little phosphate +of lime, and is largely worked for agricultural purposes. The +greatest thickness attained by the Cretaceous rocks of North +America is about 9000 feet, as in Wyoming, Utah, and Colorado. +According to Dana, the Cretaceous rocks of the Rocky Mountain +territories pass upwards "without interruption into a coal-bearing +formation, several thousand feet thick, on which the following +Tertiary strata lie unconformably." The lower portion of this +"Lignitic formation" appears to be Cretaceous, and contains one +or more beds of Coal; but the upper part of it perhaps belongs +to the Lower Tertiary. In America, therefore, the lowest Tertiary +strata appear to rest conformably upon the highest Cretaceous; +whereas in Europe, the succession at this point is invariably an +unconformable one. Owing, however, to the fact that the American +"Lignitic formation" is a shallow-water formation, it can hardly +be expected to yield much material whereby to bridge over the +great palæontological gap between the White Chalk and Eocene +in the Old World. + +Owing to the fact that so large a portion of the Cretaceous formation +has been deposited in the sea, much of it in deep water, the _plants_ +of the period have for the most part been found special members +of the series, such as the Wealden beds, the Aix-la-Chapelle +sands, and the Lignitic beds of North America. Even the purely +marine strata, however, have yielded plant-remains, and some of +these are peculiar and proper to the deep-sea deposits of the +series. Thus the little calcareous discs termed "coccoliths," which +are known to be of the nature of calcareous sea-weeds (_Algoe_) +have been detected in the White Chalk; and the flints of the same +formation commonly contain the spore-cases of the microscopic +_Desmids_ (the so-called Xanthidia), along with the siliceous +cases of the equally diminutive _Diatoms_. + +The plant-remains of the Lower Cretaceous greatly resemble those +of the Jurassic period, consisting mainly of Ferns, Cycads, and +Conifers. The Upper Cretaceous rocks, however, both in Europe and +in North America, have yielded an abundant flora which resembles +the existing vegetation of the globe in consisting mainly of +Angiospermous Exogens and of Monocotyledons.[23] In Europe the +plant-remains in question have been found chiefly in certain +sands in the neighbourhood of Aix-la-Chapelle, and they consist +of numerous Ferns, Conifers (such as _Cycadopteris_), Screw Pines +(_Pandanus_), Oaks (_Quercus_), Walnut (_Juglans_), Fig (_Ficus_), +and many _Proteaceoe_, some of which are referred to existing +genera (_Dryandra, Banksia, Grevillea_, &c.) + +[Footnote 23: The "Flowering plants" are divided into the two +great groups of the Endogens and Exogens. The _Endogens_ (such +as Grasses, Palms, Lilies, &c.) have no true bark, nor rings of +growth, and the stem is said to be "endogenous;" the young plant +also possesses but a single seed-leaf or "cotyledon." Hence these +plants are often simply called "_Monocotyledons_." The _Exogens_, +on the other hand, have a true bark; and the stem increases by +annual additions to the outside, so that rings of growth are +produced. The young plant has two seed-leaves or "cotyledons," +and these plants are therefore called "_Dicotyledons_." Amongst the +Exogens, the Pines (_Conifers_) and the Cycads have seeds which +are unprotected by a seed-vessel, and they are therefore called +"_Gymnosperms_." All the other Exogens, including the ordinary +trees, shrubs, and flowering plants, have the seeds enclosed in +a seed-vessel, and are therefore called "_Angiosperms_." The +derivation of these terms will be found in the Glossary at the +end of the volume.] + +In North America, the Cretaceous strata of New Jersey, Alabama, +Nebraska, Kansas, &c., have yielded the remains of numerous plants, +many of which belong to existing genera. Amongst these may be +mentioned Tulip-trees (_Liriodendron_), Sassafras (fig. 186), +Oaks (_Quercus_), Beeches (_Fagus_), Plane-trees (_Platanus_), +Alders (_Alnus_), Dog-wood (_Cornus_), Willows (_Salix_), Poplars +(_Populus_), Cypresses (_Cupressus_), Bald Cypresses (_Taxodium_), +Magnolias, &c. Besides these, however, there occur other forms +which have now entirely disappeared from North America--as, for +example, species of _Cinnamomum_ and _Araucaria_. + +It follows from the above, that the Lower and Upper Cretaceous +rocks are, from a botanical point of view, sharply separated +from one another. The Palæozoic period, as we have seen, is +characterised by the prevalance of "Flowerless" plants +(_Cryptogams_), its higher vegetation consisting almost exclusively +of Conifers. The Mesozoic period, as a whole, is characterised +by the prevalence of the Cryptogamic group of the Ferns, and +the Gymnospermic groups of the Conifers and the Cycads. Up to +the close of the Lower Cretaceous, no Angiospermous Exogens are +certainly known to have existed, and Monocotyledonous plants or +Endogens are very poorly represented. With the Upper Cretaceous, +however, a new era of plant-life, of which our present is but +the culmination, commenced, with a great and apparently sudden +development of new forms. In place of the Ferns, Cycads, and +Conifers of the earlier Mesozoic deposits, we have now an +astonishingly large number of true Angiospermous Exogens, many +of them belonging to existing types; and along with these are +various Monocotyledonous plants, including the first examples of +the great and important group of the Palms. It is thus a matter +of interest to reflect that plants closely related to those now +inhabiting the earth, were in existence at a time when the ocean +was tenanted by Ammonites and Belemnites, and when land and sea +and air were peopled by the extraordinary extinct Reptiles of +the Mesozoic period. + +[Illustration: Fig. 186.--Cretaceous Angiosperms. a. _Sassafras +Cretaceum; b, Liriodendron Meekii; c, Leguminosites Marcouanus; +d, Salix Meekii_. (After Dana.)] + +As regards animal life, the _Protozoans_ of the Cretaceous period +are exceedingly numerous, and are represented by _Foraminifera_ +and _Sponges_. As we have already seen, the White Chalk itself is +a deep-sea deposit, almost entirely composed of the microscopic +shells of _Foraminifers_, along with Sponge-spicules, and organic +_débris_ of different kinds (see fig. 7). The green grains which +are so abundant in several minor subdivisions of the Cretaceous, +are also in many instances really casts in glauconite of the +chambered shells of these minute organisms. A great many species +of _Foraminifera_ have been recognised in the Chalk; but the +three principal genera are _Globigerina, Rotalia_ (fig. 187), +and _Textularia_--groups which are likewise characteristic of +the "ooze" of the Atlantic and Pacific Oceans at great depths. +The flints of the Chalk also commonly contain the shells of +_Foraminifera_. The Upper Greensand has yielded in considerable +numbers the huge _Foraminifera_ described by Dr Carpenter under +the name of _Parkeria_, the spherical shells of which are composed +of sand-grains agglutinated together, and sometimes attain a +diameter of two and a quarter inches. The Cretaceous Sponges are +extremely numerous, and occur under a great number of varieties +of shape and structure; but the two most characteristic genera +are _Siphonia_ and _Ventriculites_, both of which are exclusively +confined to strata of this age. The _Siphonioe_ (fig. 188) consist +of a pear-shaped, sometimes lobed head, supported by a longer +or shorter stern, which breaks up at its base into a number of +root-like processes of attachment. The water gained access to the +interior of the Sponge by a number of minute openings covering +the surface, and ultimately escaped by a single, large, +chimney-shaped aperture at the summit. In some respects these +sponges present a singular resemblance to the beautiful "Vitreous +Sponges" (_Holtenia_ or _Pheronema_) of the deep Atlantic; and, +like these, they were probably denizens of a deep sea, The +_Ventriculites_ of the Chalk (fig. 189) is, however, a genus +still more closely allied to the wonderful flinty Sponges, which +have been shown, by the researches of the Porcupine, Lightning, +and Challenger expeditions, to live half buried in the Calcareous +ooze of the abysses of our great oceans. Many forms of this genus +are known, having "usually the form of graceful vases, tubes, or +funnels, variously ridged or grooved, or otherwise ornamented +on the surface, frequently expanded above into a cup-like lip, +and continued below into a bundle of fibrous roots. The minute +structure of these bodies shows an extremely delicate tracery +of fine tubes, sometimes empty, sometimes filled with loose +calcareous matter dyed with peroxide of iron."--(Sir Wyville +Thomson.) Many of the Chalk sponges, originally calcareous, have +been converted into flint subsequently; but the Ventriculites +are really composed of this substance, and are therefore genuine +"Siliceous Sponges," like the existing Venus's Flower-Basket +(_Euplectella_). Like the latter, the skeleton was doubtless +originally composed, in the young state, of disconnected six-rayed +spicules, which ultimately become fixed together to constitute +a continuous frame-work. The sea-water, as in the recent forms, +must have been admitted to the interior of the Sponge by numerous +apertures on its exterior, subsequently escaping by a single +large opening at its summit. + +[Illustration: Fig. 187--_Kotalia Boueana_.] + +[Illustration: Fig. 188.--_Siphonia ficus. Upper Greensand. Europe.] + +[Illustration: Fig. 189.--_Ventriculites simplex_. White Chalk. +Britain.] + +Amongst the _Coelenterates_, the "Hydroid Zoophytes" are represented +by a species of the encrusting genus _Hydractinia_, the horny +polypary of which is so commonly found at the present day adhering +to the exterior of shells. The occurrence of this genus is of +interest, because it is the first known instance in the entire +geological series of the occurrence of an unquestionable Hydroid of +a modern type, though many of the existing forms of these animals +possess structures which are perfectly fitted for preservation in +the fossil condition. The corals of the Cretaceous series are not +very numerous, and for the most part are referable to types such +as _Trochocyathus, Stephanophyllia, Parasmilia, Synhelia_ (fig. +190), &c., which belong to the same great group of corals as the +majority of existing forms. We have also a few "Tabulate Corals" +(_Polytremacis_), hardly, if at all, generically separable from very +ancient forms (_Heliolites_); and the Lower Greensand has yielded +the remains of the little _Holocystis elegans_, long believed to +be the last of the great Palæozoic group of the _Rugosa_. + +[Illustration: Fig. 190.--_Synhelia Sharpeana_. Chalk, England.] + +As regards the _Echinoderms_, the group of the _Crinoids_ now +exhibits a marked decrease in the number and variety of its types. +The "stalked" forms are represented by _Pentacrinus_ and +_Bourgueticrinus_, and the free forms by Feather-stars like our +existing _Comatuloe_; whilst a link between the stalked and free +groups is constituted by the curious "Tortoise Encrinite +(_Marsupites_). By far the most abundant Cretaceous Echinoderms, +however, are Sea-urchins (_Echinoids_); though several Star-fishes +are known as well. The remains of Sea-urchins are so abundant +in various parts of the Cretaceous series, especially in the +White Chalk, and are often so beautifully preserved, that they +constitute one of the most marked features of the fauna of the +period. From the many genera of Sea-urchins which occur in strata +of this age, it is difficult to select characteristic types; +but the genera _Galerites_ (fig. 191), _Discoidea_ (fig. 192), +_Micraster, Ananchytes, Diadema, Salenia_, and _Cidaris_, may +be mentioned as being all important Cretaceous groups. + +Coming to the _Annulose Animals_ of the Cretaceous period, there +is little special to remark. The _Crustaceans_ belong for the +most part to the highly-organised groups of the Lobsters and the +Crabs (the Macrurous and Brachyurous Decapods); but there are +also numerous little _Ostracodes_, especially in the fresh-water +strata of the Wealden. It should further be noted that there +occurs here a great development of the singular _Crustaceous_ +family of the Barnacles (_Lepadidoe_), whilst the allied family +of the equally singular Acorn-shells (_Balanidoe_) is feebly +represented as well. + +[Illustration: Fig. 191.--_Galerites albogalerus_, viewed from +below, from the side, and from above. White Chalk.] + +[Illustration: Fig. 192.--_Discoidea cylindrica_; under, side, +and upper aspect. Upper Greensand.] + +Passing on to the _Mollusca_, the class of the Sea-mats and +Sea-mosses (_Polyzoa_) is immensely developed in the Cretaceous +period, nearly two hundred species being known to occur in the +Chalk. Most of the Cretaceous forms belong to the family of the +_Escharidoe_, the genera _Eschara_ and _Escharina_ (fig. 193) +being particularly well represented. Most of the Cretaceous +_Polyzoans_ are of small size, but some attain considerable +dimensions, and many simulate Corals in their general form and +appearance. + +The Lamp-shells (_Brachiopods_) have now reached a further stage +of the progressive decline, which they have been undergoing ever +since the close of the Palæozoic period. Though individually not +rare, especially in certain minor subdivisions of the series, +the number of generic types has now become distinctly diminished, +the principal forms belonging to the genera _Terebratula, +Terebratella_ (fig. 194), _Terebratulina, Rhynchonella_, and +_Crania_ (fig. 195). In the last mentioned of these, the shell +is attached to foreign bodies by the substance of one of the +valves (the ventral), whilst the other or free valve is more +or less limpet-shaped. All the above-mentioned genera are in +existence at the present day; and one _species_--namely, +_Terebratulina striata_--appears to be undistinguishable from +one now living--the _Terebratulina caputserpentis_. + +[Illustration: Fig. 193.--A small fragment of _Escharina Oceani_, +of the natural size; and a portion of the same enlarged. Upper +Greensand.] + +[Illustration: Fig. 194.--_Terebratella Astieriana_. Gault.] + +Whilst the Lamp-shells are slowly declining, the Bivalves +(_Limellibranchs_) are greatly developed, and are amongst the +most abundant and characteristic fossils of the Cretaceous period. +In the great river-deposit of the Wealden, the Bivalves are forms +proper to fresh water, belonging to the existing River-mussels +(_Unio_), _Cyrena_ and _Cyclas_; but most of the Cretaceous +Lamellibranchs are marine. Some of the most abundant and +characteristic of these belong to the great family of the Oysters +(_Ostreidoe_). Amongst these are the genera _Gryphtoea_ and +_Exogyra_, both of which we have seen to occur abundantly in the +Jurassic; and there are also numerous true Oysters (_Ostrea_, +fig. 196) and Thorny Oysters (_Spondylus_, fig. 197). The genus +_Trigonia_, so characteristic of the Mesozoic deposits in general, +is likewise well represented in the Cretaceous strata. No single +genus of Bivalves is, however, so highly characteristic of the +Cretaceous period as _Inoceramus_, a group belonging to the family +of the Pearl-mussels (_Aviculidoe_). The shells of this genus +(fig. 198) have the valves unequal in size, the larger valve often +being much twisted, and both valves being marked with radiating +ribs or concentric furrows. The hinge-line is long and straight, +with numerous pits for the attachment of the ligament which serves +to open the shell. Some of the _Inocerami_ attain a length of +two or three feet, and fragments of the shell are often found +perforated by boring Sponges. Another extraordinary family of +Bivalves, which is exclusively confined to the Cretaceous rocks, +is that of the _Hippuritidoe_. All the members of this group +(fig. 199) were attached to foreign objects, and lived associated +in beds, like Oysters. The two valves of the shell are always +altogether unlike in sculpturing, appearance, shape, and size; +and the cast of the interior of the shell is often extremely +unlike the form of the outer surface. The type-genus of the family +is _Hippurites_ itself (fig. 199), in which the shell is in the +shape of a straight or slightly-twisted horn, sometimes a foot +or more in length, constituted by the attached lower valve, and +closed above by a small lid-like free upper valve. About a hundred +species of the family of the _Hippuritidoe_ are known, all of these +being Cretaceous, and occurring in Britain (one species only), in +Southern Europe, the West Indies, North America, Algeria, and +Egypt. Species of this family occur in such numbers in certain +compact marbles in the south of Europe, of the age of the Upper +Cretaceous (Lower Chalk), as to have given origin to the name +of "Hippurite Limestones," applied to these strata. + +[Illustration: Fig. 195.--_Crania Ignabergensis_. The left-hand +figure shows the perfect shell, attached by its ventral valve +to a foreign body; the middle figure shows the exterior of the +limpet-shaped dorsal valve; and the right-hand figure represents +the interior of the attached valve. White Chalk.] + +[Illustration: Fig. 196.--_Ostrea Couloni_. Lower Greensand.] + +[Illustration: Fig. 197.--_Spondylus spinosus_. White Chalk.] + +[Illustration: Fig. 198.--_Inoceramus sulcatus_. Gault.] + +The Univalves (_Gasteropods_) of the Cretaceous period are not +very numerous, nor particularly remarkable. Along with species of +the persistent genus _Pleurotomaria_ and the Mesozoic _Nerinoea_, +we meet with examples of such modern types as _Turritella_ and +_Natica_, the Staircase-shells (_Solarium_), the Wentle-traps +(_Scalaria_), the Carrier-shells (_Phorus_), &c. Towards the close +of the Cretaceous period, and especially in such transitional strata +as the Maestricht beds, the Faxöe Limestone, and the Pisolitic +Limestone of France, we meet with a number of carnivorous +("siphonostomatous") Univalves, in which the mouth of the shell is +notched or produced into a canal. Amongst these it is interesting +to recognise examples of such existing genera as the Volutes +(_Voluta_, fig. 200), the Cowries (_Cyproea_), the Mitre-shells +(_Mitra_), the Wing - shells (_Strombus_), the Scorpion-shells +(_Pteroceras_), &c. + +[Illustration: Fig. 199.--_Hippurites Toucasiana_. A large +individual, with two smaller ones attached to it. Upper Cretaceous, +South of Europe.] + +[Illustration: Fig. 200.--_Voluta elongata_. White Chalk.] + +Upon the whole, the most characteristic of all the Cretaceous +Molluscs are the _Cephalopods_, represented by the remains of +both _Tetrabranchiate_ and _Dibranchiate_ forms. Amongst the +former, the long-lived genus _Nautilus_ (fig. 201) again reappears, +with its involute shell, its capacious body-chamber, its simple +septa between the air-chambers, and its nearly or quite central +siphuncle. The majority of the chambered _Cephalopods_ of the +Cretaceous belong, however, to the complex and beautiful family +of the _Ammonitidoe_, with their elaborately folded and lobed +septa and dorsally-placed siphuncle. This family disappears wholly +at the close of the Cretaceous period; but its approaching +extinction, so far from being signalised by any slow decrease +and diminution in the number of specific or generic types, seems +to have been attended by the development of whole series of new +forms. The genus _Ammonites_ itself, dating from the Carboniferous, +has certainly passed its prime, but it is still represented by +many species, and some of these attained enormous dimensions +(two or three feet in diameter). The genus _Ancyloceras_ (fig. +202), though likewise of more ancient origin (Jurassic), is +nevertheless very characteristic of the Cretaceous. In this genus +the first portion of the shell is in the form of a flat spiral, +the coils of which are not in contact; and its last portion is +produced at a tangent, becoming ultimately bent back in the form +of a crosier. Besides these pre-existent types, the Cretaceous +rocks have yielded a great number of entirely new forms of the +_Ammonitidoe_, which are not known in any deposits of earlier or +later date. Amongst the more important of these may be mentioned +_Crioceras, Turrilites, Scaphites, Hamites, Ptychoceras_, and +_Baulites_. In the genus _Crioceras_ (fig. 204, d), the shell +consists of an open spiral, the volutions of which are not in +contact, thus resembling a partially-unrolled _Ammonite_ or the +inner portion of an _Ancyloceras_. In _Turrilites_ (fig. 203), the +shell is precisely like that of the _Ammonite_ in its structure; +but instead of forming a flat spiral, it is coiled into an elevated +turreted shell, the whorls of which are in contact with one another. +In the genus _Scaphites_ (fig. 204, e), the shell resembles that +of _Ancyloceras_ in consisting of a series of volutions coiled +into a flat spiral, the last being detached from the others, +produced, and ultimately bent back in the form of a crosier; but +the whorls of the enrolled part of the shell are in contact, +instead of being separate as in the latter. In the genus _Hamites_ +(fig. 204, f), the shell is an extremely elongated cone, which +is bent upon itself more than once, in a hook-like manner, all +the volutions being separate. The genus _Ptychoteras_ (fig. 204, +a) is very like _Hamites_, except that the shell is only bent +once; and the two portions thus bent are in contact with one +another. Lastly, in the genus _Baculites_ (fig. 204, b and +c) the shell is simply a straight elongated cone, not bent +in any way, but possessing the folded septa which characterise +the whole Ammonite family. The _Baculite_ is the simplest of +all the forms of the _Ammonitidoe_; and all the other forms, +however complex, may be regarded as being simply produced by the +bending or folding of such a conical septate shell in different +ways. The _Baculite_, therefore, corresponds, in the series of +the _Ammonitidoe_, to the _Orthoceras_ in the series of the +_Nautilidoe_. All the above-mentioned genera are characteristically, +or exclusively, Cretaceous, and they are accompanied by a number +of other allied forms, which cannot be noticed here. Not a single +one of these genera, further, has hitherto been detected in any +strata higher than the Cretaceous. We may therefore consider that +these wonderful, varied, and elaborate forms of _Ammonitidoe_ +constitute one of the most conspicuous features in the life of +the Chalk period. + +[Illustration: Fig. 201.--Different views of _Nautilus Danicus_. +Faxöe Limestone (Upper Cretaceous), Denmark.] + +[Illustration: Fig. 202.--_Ancyloceras Matheronianus_. Gault.] + +The _Dibranchiate Cephalopods_ are represented partly by the +beak-like jaws of unknown species of Cuttle-fishes and partly +by the internal skeletons of Belemnites. Amongst the latter, +the genus _Belemnites_ itself holds its place in the lower part +of the Cretaceous series; but it disappears in the upper portion +of the series, and its place is taken by the nearly-allied genus +_Belemnitella_ (fig. 205), distinguished by the possession of +a straight fissure in the upper end of the guard. This also +disappears at the close of the Cretaceous period; and no member +of the great Mesozoic family of the _Belemnitidoe_ has hitherto +been discovered in any Tertiary deposit, or is known to exist +at the present day. + +[Illustration: Fig. 203.--_Turrilites catenatus_. The lower figure +represents the entire shell; the upper figure represents the +base of the shell seen from below. Gault.] + +[Illustration: Fig. 204.--a, _Ptychoceras Emericianum_, +reduced--Lower Greensand; b, _Baculites anceps_, reduced--Chalk; +c, Portion of the same, showing the folded edges of the septa; +d, _Crioceras cristatum_, reduced--Gault; e, _Scaphites oequalis_, +natural size--Chalk; f, _Hamites rotundus_, restored--Gault.] + +Passing on next to the _Vertebrate Animals_ of the Cretaceous +period, we find the _Fishes_ represented as before by the Ganoids +and the Placoids, to which, however, we can now add the first +known examples of the great group of the _Bony Fishes_ or +_Teleosteans_, comprising the great majority of existing forms. +The _Ganoid_ fishes of the Cretaceous (_Lepidotus, Pycnodus_, +&c.) present no features of special interest. Little, also, need +be said about the _Placoid_ fishes of this period. As in the +Jurassic deposits, the remains of these consist partly of the +teeth of genuine Sharks (_Lamna, Odontaspis_, &c.) and partly +of the teeth and defensive spines of Cestracionts, such as the +living Port-Jackson Shark. The pointed and sharp-edged teeth of +true Sharks are very abundant in some beds, such as the Upper +Greensand, and are beautifully preserved. The teeth of some forms +(_Carcharias_, &c.) attain occasionally a length of three or four +inches, and indicate the existence in the Cretaceous seas of +huge predaceous fishes, probably larger than any existing Sharks. +The remains of _Cestracionts_ consist partly of the flattened +teeth of genera such as _Acrodus_ and _Ptychodus_ (the latter +confined to rocks of this age), and partly of the pointed teeth +of _Hybodus_, a genus which dates from the Trias. In this genus +the teeth (fig. 206) consist of a principal central cone, flanked +by minor lateral cones; and the fin-spines (fig. 207) are +longitudinally grooved, and carry a series of small spines on +their hinder or concave margin. Lastly, the great modern order +of the Bony Fishes or _Teleosteans_ makes its first appearance +in the Upper Cretaceous rocks, where it is represented by forms +belonging to no less than three existing groups--namely, the +Salmon family (_Salmonidoe_), the Herring family (_Clupeidoe_), +and the Perch family (_Percidoe_). All these fishes have thin, +horny, overlapping scales, symmetrical ("homocercal") tails, +and bony skeletons. The genus _Beryx_ (fig. 208, 1) is one +represented by existing species at the present day, and belongs +to the Perch family. The genus _Osmeroides_, again (fig. 208, +2), is supposed to be related to the living Smelts (_Osmerus_), +and, therefore, to belong to the Salmon tribe. + +[Illustration: Fig. 205.--Guard of _Belemnitella mucronata_. White +Chalk.] + +[Illustration: Fig. 206.--Tooth of _Hybodus_.] + +[Illustration: Fig. 207.--Fin-spine of _Hybodus_. Lower Greensand.] + +[Illustration: Fig. 208.--1, _Beryx Lewesiensis_, a Percoid fish +from the Chalk; 2, _Osmeroides Mantelli_, a Salmonoid fish from +the Chalk.] + +No remains of _Amphibians_ have hitherto been detected in any part +of the Cretaceous series; but _Reptiles_ are extremely numerous, +and belong to very varied types. As regards the great extinct groups +of Reptiles which characterise the Mesozoic period as a whole, the +huge "Enaliosaurs" or "Sea-Lizards" are still represented by the +_Ichthyosaur_ and the _Plesiosaur_. Nearly allied to the latter +of these is the _Elasmosaurus_ of the American Cretaceous, which +combined the long tail of the Ichthyosaur with the long neck +of the Plesiosaur. The length of this monstrous Reptile could not +have been less than fifty feet, the neck consisting of over sixty +vertebræ and measuring over twenty feet in length. The extraordinary +Flying Reptiles of the Jurassic are likewise well represented in +the Cretaceous rocks by species of the genus _Pterodactylus_ +itself, and these later forms are much more gigantic in their +dimensions than their predecessors. Thus some of the Cretaceous +Pterosaurs seem to have had a spread of wing of from twenty to +twenty-five feet, more than realising the "Dragons" of fable in +point of size. The most remarkable, however, of the Cretaceous +_Pterosaurs_ are the forms which have recently been described +by Professor Marsh under the generic title of _Pteranodon_. In +these singular forms--so far only known as American--the animal +possessed a skeleton in all respects similar to that of the typical +Pterodactyles, except that the jaws are completely destitute of +teeth. There is, therefore, the strongest probability that the +jaws were encased in a horny sheath, thus coming to resemble the +beak of a Bird. Some of the recognised species of _Pteranodon_ +are very small; but the skull of one species (_P. Longiceps_) +is not less than a yard in length, and there are portions of +the skull of another species which would indicate a length of +four feet for the cranium. These measurements would point to +dimensions larger than those of any other known Pterosaurs. + +The great Mesozoic order of the _Deinosaurs_ is largely represented +in the Cretaceous rocks, partly by genera which previously existed +in the Jurassic period, and partly by entirely new types. The great +delta-deposit of the Wealden, in the Old World, has yielded the +remains of various of these huge terrestrial Reptiles, and very +many others have been found in the Cretaceous deposits of North +America. One of the most celebrated of the Cretaceous Deinosaurs +is the _Iguanodon_, so called from the curious resemblance of +its teeth to those of the existing but comparatively diminutive +_Iguana_. The teeth (fig. 209) are soldered to the inner face +of the jaw, instead of being sunk in distinct sockets; and they +have the form of somewhat flattened prisms, longitudinally ridged +on the outer surface, with an obtusely triangular crown, and +having the enamel crenated on one or both sides. They present +the extraordinary feature that the crowns became worn down flat +by mastication, showing that the _Iguanodon_ employed its teeth +in actually chewing and triturating the vegetable matter on which +it fed. There can therefore be no doubt but that the _Iguanodon_, +in spite of its immense bulk, was an herbivorous Reptile, and lived +principally on the foliage of the Cretaceous forests amongst which +it dwelt. Its size has been variously estimated at from thirty to +fifty feet, the thigh-bone in large examples measuring nearly +five feet in length, with a circumference of twenty-two inches +in its smallest part. With the strong and massive hind-limbs are +associated comparatively weak and small fore-limbs; and there +seems little reason to doubt that the _Iguanodon_ must have walked +temporarily or permanently upon its hind-limbs, after the manner of +a Bird. This conjecture is further supported by the occurrence in +the strata which contain the bones of the _Iguanodon_ of gigantic +three-toed foot-prints, disposed _singly_ in a double track. These +prints have undoubtedly been produced by some animal walking on +two legs; and they can hardly, with any probability, be ascribed +to any other than this enormous Reptile. Closely allied to the +_Iguanodon_ is the _Hadrosaurus_ of the American Cretaceous, the +length of which is estimated at twenty-eight feet. _Iguanodon_ +does not appear to have possessed any integumentary skeleton; but +the great _Hyloeosaurus_ of the Wealden seems to have been furnished +with a longitudinal crest of large spines running down the back, +similar to that which is found in the comparatively small Iguanas +of the present day. The _Megalosaurus_ of the Oolites continued +to exist in the Cretaceous period; and, as we have previously +seen, it was carnivorous in its habits. The American _Loelaps_ +was also carnivorous, and, like the Megalosaur, which it very +closely resembles, appears to have walked upon its hind-legs, +the fore-limbs being disproportionately small. + +[Illustration: Fig. 209.--Teeth of Iguanodon Mantellii. Wealden, +Britain.] + +Another remarkable group of Reptiles, exclusively confined to +the Cretaceous series, is that of the _Mosasauroids_, so called +from the type-genus _Mosasaurus_. The first species of _Mosasaurus_ +known to science was the _M. Camperi_ (fig. 210), the skull of +which--six feet in length--was discovered in 1780 in the Maestricht +Chalk at Maestricht. As this town stands on the river Meuse, +the name of _Mosasaurus_ ("Lizard of the Meuse") was applied +to this immense Reptile. Of late years the remains of a large +number of Reptiles more or less closely related to _Mosasaurus_, or +absolutely belonging to it, have been discovered in the Cretaceous +deposits of North America, and have been described by Professors +Cope and Marsh. All the known forms of this group appear to have +been of large size--one of them, _Mosasaurus princeps_, attaining +the length of seventy-five or eighty feet, and thus rivalling +the largest of existing Whales in its dimensions. The teeth in +the "Mosasauroids" are long, pointed, and slightly curved; and +instead of being sunk in distinct sockets, they are firmly +amalgamated with the jaws, as in modern Lizards. The palate also +carried teeth, and the lower jaw was so constructed as to allow +of the mouth being opened to an immense width, somewhat as in the +living Serpents. The body was long and snake-like, with a very +long tail, which is laterally compressed, and must have served as +a powerful swimming-apparatus. In addition to this, both pairs +of limbs have the bones connecting them with the trunk greatly +shortened; whilst the digits were enclosed in the integuments, +and constituted paddles, closely resembling in structure the +"flippers" of Whales and Dolphins. The neck is sometimes moderately +long, but oftener very short, as the great size and weight of +the head would have led one to anticipate. Bony plates seem in +some species to have formed an at any rate partial covering to +the skin; but it is not certain that these integumentary appendages +were present in all. Upon the whole, there can be no doubt but +that the Mosasauroid Reptiles--the true "Sea-serpents" of the +Cretaceous period--were essentially aquatic in their habits, +frequenting the sea, and only occasionally coming to the land. + +[Illustration: Fig. 210.--Skull of _Mosasaurus Camperi_, greatly +reduced. Maestricht Chalk.] + +The "Mosasauroids" have generally been regarded as a greatly +modified group of the Lizards (_Lacertilia_). Whether this reference +be correct or not--and recent investigations render it dubious--the +Cretaceous rocks have yielded the remains of small Lizards not widely +removed from existing forms. The recent order of the _Chelonians_ +is also represented in the Cretaceous rocks, by forms closely +resembling living types. Thus the fresh-water deposits of the +Wealden have yielded examples of the "Terrapins" or "Mud-Turtles" +(_Emys_); and the marine Cretaceous strata have been found to +contain the remains of various species of Turtles, one of which +is here figured (fig. 211). No true Serpents (_Ophidia_) have +as yet been detected in the Cretaceous rocks; and this order +does not appear to have come into existence till the Tertiary +period. Lastly, true Crocodiles are known to have existed in +considerable numbers in the Cretaceous period. The oldest of +these occur in the fresh-water deposit of the Wealden; and they +differ from the existing forms of the group in the fact that the +bodies of the vertebræ, like those of the Jurassic Crocodiles, +are bi-concave, or hollowed out at both ends. In the Greensand +of North America, however, occur the remains of Crocodiles which +agree with all the living species in having the bodies of the +vertebræ in the region of the back hollowed out in front and +convex behind. + +[Illustration: Fig. 211.--Carapace of _Chelone Benstedi_. Lower +Chalk. (After Owen.)] + +_Birds_ have not hitherto been shown, with certainty, to have +existed in Europe during the Cretaceous period, except in a few +instances in which fragmentary remains belonging to this class +have been discovered. The Cretaceous deposits of North America +have, however, been shown by Professor Marsh to contain a +considerable number of the remains of Birds, often in a state +of excellent preservation. Some of these belong to Swimming or +Wading Birds, differing in no point of special interest from +modern birds of similar habits. Others, however, exhibit such +extraordinary peculiarities that they merit more than a passing +notice. One of the forms in question constitutes the genus +_Ichthyornis_ of Marsh, the type-species of which (_I. Dispar_) +was about as large as a Pigeon. In two remarkable respects, this +singular Bird differs from all known living members of the class. +One of these respects concerns the jaws, both of which exhibit the +Reptilian character of being armed with numerous small pointed +_teeth_ (fig. 212, a), sunk in distinct sockets. No existing +bird possesses teeth; and this character forcibly recalls the +Bird-like Pterosaurs, with their toothed jaws. _Ichthyornis_, +however, possessed fore-limbs constructed strictly on the type +of the "wing" of the living Birds; and it cannot, therefore, be +separated from this class. Another extraordinary peculiarity +of _Ichthyornis_ is, that the bodies of the _vertebrie_ (fig. +212, c) were _bi-concave_, as is the case with many extinct +Reptiles and almost all Fishes, but as does not occur in any +living Bird. There can be little doubt that _Ichthyornis_ was +aquatic in its habits, and that it lived principally upon fishes; +but its powerful wings at the same time indicate that it was +capable of prolonged flight. The tail of _Ichthyornis_ has, +unfortunately, not been discovered; and it is at present impossible +to say whether this resembled the tail of existing Birds, or +whether it was elongated and composed of separate vertebræ, as +in the Jurassic _Archoeopteryx_. + +Still more wonderful than _Ichthyornis_ is the marvellous bird +described by Marsh under the name of _Hesperornis regalis_. This +presents us with a gigantic diving bird, somewhat resembling the +existing "Loons" (_Colymbus_), but agreeing with _Ichthyornis_ +in having the jaws furnished with conical, recurved, pointed +teeth (fig. 212, b). Hence these forms are grouped together in +a new sub-class, under the name of _Odontornithes_ or "Toothed +Birds." The teeth of _Hesperornis_ (fig. 212, d) resemble those +of _Ichthyornis_ in their general form; but instead of being +sunk in distinct sockets, they are simply implanted in a deep +continuous groove in the bony substance of the jaw. The front of +the upper jaw does not carry teeth, and was probably encased in +a horny beak. The breast-bone is entirely destitute of a central +ridge or keel, and the wings are minute and quite rudimentary; so +that _Hesperornis_, unlike _Ichthyornis_, must have been wholly +deprived of the power of flight, in this respect approaching the +existing Penguins. The tail consists of about twelve vertebræ, +of which the last three or four are amalgamated to form a flat +terminal mass, there being at the same time clear indications +that the tail was capable of up and down movement in a vertical +plane, this probably fitting it to serve as a swimming-paddle or +rudder. The legs were powerfully constructed, and the feet were +adapted to assist the bird in rapid motion through the water. The +known remains of _Hesperornis regalis_ prove it to have been a +swimming and diving bird, of larger dimensions than any of the +aquatic members of the class of Birds with which we are acquainted +at the present day. It appears to have stood between five and six +feet high, and its inability to fly is fully compensated for by the +numerous adaptations of its structure to a watery life. Its teeth +prove it to have been carnivorous in its habits, and it probably +lived upon fishes. It is a curious fact that two Birds agreeing +with one another in the wholly abnormal character of possessing +teeth, and in other respects so entirely different, should, like +_Ichthyornis_ and _Hesperornis_, have lived not only in the same +geological period, but also in the same geographical area; and +it is equally curious that the area inhabited by these toothed +Birds should at the same time have been tenanted by winged and +bird-like Reptiles belonging to the toothed genus _Pterodactylus_ +and the toothless genus _Pteranodon_. + +[Illustration: Fig. 212.--Toothed Birds (_Odontornithes_) of the +Cretaceous Rocks of America. a. Left lower jaw of _Ichthyornis +dispar_, slightly enlarged; b, Left lower jaw of _Hesperornis +regalis_, reduced to nearly one-fourth of the natural size; c. +Cervical vertebra of _Ichthyornis dispar_, front view, twice +the natural size; c', Side view of the same; d, Tooth of +_Hesperornis regalis_, enlarged to twice the natural size. (After +Marsh.)] + +No remains of _Mammals_, finally, have as yet been detected in +any sedimentary accumulations of Cretaceous age. + + +LITERATURE. + +The following list comprises some of the more important works and +memoirs which may be consulted with reference to the Cretaceous +strata and their fossil contents:-- + + (1) 'Memoirs of the Geological Survey of Great Britain.' + (2) 'Geology of England and Wales.' Conybeare and Phillips. + (3) 'Geology of Yorkshire,' vol. ii. Phillips. + (4) 'Geology of Oxford and the Thames Valley.' Phillips. + (5) 'Geological Excursions through the Isle of Wight.' Mantell. + (6) 'Geology of Sussex.' Mantell. + (7) 'Report on Londonderry,' &c. Portlock. + (8) 'Recherches sur le Terrain Crétacé Supérieur de l'Angleterre + et de l'Irlande.' Barrois. + (9) "Geological Survey of Canada"--'Report of Progress, 1872-73.' +(10) 'Geological Survey of California.' Whitney. +(11) 'Geological Survey of Montana, Idaho, Wyoming, and Utah.' + Hayden and Meek. +(12) 'Report on Geology,' &c. (British North American Boundary + Commission). G. M. Dawson. +(13) 'Manual of Geology.' Dana. +(14) 'Lethæa Rossica.' Eichwald. +(15) 'Petrefacta Germaniæ.' Goldfuss. +(16) 'Fossils of the South Downs.' Mantell. +(17) 'Medals of Creation.' Mantell. +(18) 'Mineral Conchology.' Sowerby. +(19) 'Lethæa Geognostica.' Bronn. +(20) 'Malacostracous Crustacea of the British Cretaceous Formation' + (Palæontographical Society). Bell. +(21) 'Brachiopoda of the Cretaceous Formation' (Palæontographical + Society). Davidson. +(22) 'Corals of the Cretaceous Formation' (Palæontographical + Society). Milne-Edwards and Haime. +(23) 'Supplement to the Fossil Corals' (Palæontographical Society). + Martin Duncan. +(24) 'Echinodermata or the Cretaceous Formation' (Palæontographical + Society). Wright. +(25) 'Monograph of the Belemnitidæ' (Palæontographical Society). + Phillips. +(26) 'Monograph of the Trigoniæ' (Palæontographical Society). + Lycett. +(27) 'Fossil Cirripedes' (Palæontographical Society). Darwin. +(28) 'Fossil Mollusca of the Chalk of Britain' (Palæontographical + Society). Sharpe. +(29) 'Entomostraca of the Cretaceous Formation' (Palæontographical + Society). Rupert Jones. +(30) 'Monograph of the Fossil Reptiles of the Cretaceous Formation' + (Palæontographical Society). Owen. +(31) 'Manual of Palæontology.' Owen. +(32) 'Synopsis of Extinct Batrachia and Reptilia.' Cope. +(33) "Structure of the Skull and Limbs in Mosasauroid + Reptiles"--'American Journ. Sci. and Arts, 1872.' Marsh. +(34) "On Odontornithes"--'American Journ. Sci. and Arts, 1875.' + Marsh. +(35) 'Ossemens Fossiles.' Cuvier. +(36) 'Catalogue of Ornithosauria.' Seeley. +(37) 'Paléontologie Française.' D'Orbigny. +(38) 'Synopsis des Echinides fossiles.' Desor. +(39) 'Cat. Raisonné des Echinides.' Agassiz and Desor. +(40) "Echinoids"--'Decades of the Geol. Survey of Britain.' + E. Forbes. +(41) 'Paléontologie Française.' Cotteau. +(42) 'Versteinerungen der Böhmischen Kreide-formation.' Reuss. +(43) "Cephalopoda, Gasteropoda, Pelecypoda, Brachiopoda; &c., of the + Cretaceous Rocks of India"--'Palæontologica Indica,' ser. i., + iii., v., vi., viii. Stoliczka. +(44) "Cretaceous Reptiles of the United States"--'Smithsonian + Contributions to Knowledge,' vol. xiv. Leidy. +(45) 'Invertebrate Cretaceous, and Tertiary Fossils of the Upper + Missouri Country,' 1876. Meek. + + + + +CHAPTER XVIII. + +THE EOCENE PERIOD. + +Before commencing the study of the subdivisions of the Kainozoic +series, there are some general considerations to be noted. In +the first place, there is in the Old World a complete and entire +physical break between the rocks of the Mesozoic and Kainozoic +periods. In no instance in Europe are Tertiary strata to be found +resting conformably upon any Secondary rock. The Chalk has invariably +suffered much erosion and denudation before the lowest Tertiary +strata were deposited upon it. This is shown by the fact that the +actually eroded surface of the Chalk can often be seen; or, failing +this, that we can point to the presence of the chalk-flints in the +Tertiary strata. This last, of course, affords unquestionable proof +that the Chalk must have been subjected to enormous denudation +prior to the formation of the Tertiary beds, all the chalk itself +having been removed, and nothing left but the flints, while these +are all rolled and rounded. In the continent of North America, +on the other hand, the lowest Tertiary strata have been shown +to graduate downwards conformably with the highest Cretaceous +beds, it being a matter of difficulty to draw a precise line +of demarcation between the two formations. + +In the second place, there is a marked break in the _life_ of +the Mesozoic and Kainozoic periods. With the exception of a few +_Foraminifera_, and one _Brachiopod_ (the latter doubtful), no +Cretaceous species is known to have survived the Cretaceous period; +while several characteristic _families_, such as the _Ammonitidoe, +Belemnitidoe_, and _Hippuritidoe_, died out entirely with the +close of the Cretaceous rocks. In the Tertiary rocks, on the +other hand, not only are all the animals and plants more or less +like existing types, but we meet with a constantly-increasing +number of _living species_ as we pass from the bottom of the +Kainozoic series to the top. Upon this last fact is founded the +modern classification of the Kainozoic rocks, propounded by Sil +Charles Lyell. + +The absence in strata of Tertiary age of the chambered Cephalopods, +the Belemnites, the _Hippurites_, the _Inocerami_, and the +diversified types of Reptiles which form such conspicuous features +in the Cretaceous fauna, render the palæontological break between +the Chalk and the Eocene one far too serious to be overlooked. At +the same time, it is to be remembered that the evidence afforded +by the explorations carried out of late years as to the animal +life of the deep sea, renders it certain that the extinction +of marine forms of life at the close of the Cretaceous period +was far less extensive than had been previously assumed. It is +tolerably certain, in fact, that we may look upon some of the +inhabitants of the depths of our existing oceans as the direct, +if modified, descendants of animals which were in existence when +the Chalk was deposited. + +It follows from the general want of conformity between the Cretaceous +and Tertiary rocks, and still more from the great difference in +life, that the Cretaceous and Tertiary periods are separated, in +the Old World at any rate, by an enormous lapse of unrepresented +time. How long this interval may have been, we have no means of +judging exactly, but it very possibly was as long as the whole +Kainozoic epoch itself. Some day we shall doubtless find, at some +part of the earth's surface, marine strata which were deposited +during this period, and which will contain fossils intermediate +in character between the organic remains which respectively +characterise the Secondary and Tertiary periods. At present, we +have only slight traces of such deposits--as, for instance, the +Maestricht beds, the Faxöe Limestone, and the Pisolitic Limestone +of France. + +CLASSIFICATION OF THE TERTIARY ROCKS.--The classification of the +Tertiary rocks is a matter of unusual difficulty, in consequence +of their occurring in disconnected basins, forming a series of +detached areas, which hold no relations of superposition to one +another. The order, therefore, of the Tertiaries in point of +time, can only be determined by an appeal to fossils; and in +such determination Sir Charles Lyell proposed to take as the +basis of classification the _proportion of living or existing +species of Mollusca which occurs in each stratum or group of +strata_. Acting upon this principle, Sir Charles Lyell divides +the Tertiary series into four groups:-- + +I. The _Eocene_ formation (Gr. _eos_, dawn; _kainos_, new), +containing the smallest proportion of existing species, and being, +therefore, the oldest division. In this classification, only +the _Mollusca_ are taken into account; and it was found that of +these about three and a half per cent were identical with existing +species. + +II. The _Miocene_ formation (Gr. _meion_, less; _kainos_, new), +with more recent species than the Eocene, but _less_ than the +succeeding formation, and less than one-half the total number +in the formation. As before, only the _Mollusca_ are taken into +account, and about 17 per cent of these agree with existing species. + +III. The _Pliocene_ formation (Gr. _pleion_, more; _kainos_, new), +with generally _more_ than half the species of shells identical +with existing species--the proportion of these varying from 35 +to 50 per cent in the lower beds of this division, up to 90 or +95 per cent in its higher portion. + +IV. The _Post-Tertiary Formations_, in which all _the shells +belong to existing species_. This, in turn, is divided into two +minor groups--the _Post-Pliocene_ and _Recent Formations_. In +the _Post-Pliocene_ formations, while all the _Mollusca_ belong +to existing species, most of the _Mammals_ belong to extinct +species. In the Recent period, the quadrupeds, as well as the +shells, belong to living species. + +The above, with some modifications, was the original classification +proposed by Sir Charles Lyell for the Tertiary rocks, and now +universally accepted. More recent researches, it is true, have +somewhat altered the proportions of existing species to extinct, +as stated above. The general principle, however, of an increase +in the number of living species, still holds good; and this is as +yet the only satisfactory basis upon which it has been proposed +to arrange the Tertiary deposits. + + +EOCENE FORMATION. + +The Eocene rocks are the lowest of the Tertiary series, and comprise +all those Tertiary deposits in which there is only a small proportion +of existing _Mollusca_--from three and a half to five per cent. +The Eocene rocks occur in several basins in Britain, France, +the Netherlands, and other parts of Europe, and in the United +States. The subdivisions which have been established are extremely +numerous, and it is often impossible to parallel those of one +basin with those of another. It will be sufficient, therefore, +to accept the division of the Eocene formation into three great +groups--Lower, Middle, and Upper Eocene--and to consider some of +the more important beds comprised under these heads in Europe +and in North America. + +I. EOCENE OF BRITAIN. (1.) LOWER EOCENE.--The base of the Eocene +series in Britain is constituted by about 90 feet of light-coloured, +sometimes argillaceous sands (_Thanet Sands_), which are of marine +origin. Above these, or forming the base of the formation where these +are wanting, come mottled clays and sands with lignite (_Woolwich +and Reading series_), which are estuarine or fluvio-marine in +origin. The highest member of the Lower Eocene of Britain is the +"London Clay," consisting of a great mass of dark-brown or blue +clay, sometimes with sandy beds, or with layers of "septaria," +the whole attaining a thickness of from 200 to as much as 500 +feet. The London Clay is a purely marine deposit, containing +many marine fossils, with the remains of terrestrial animals and +plants; all of which indicate a high temperature of the sea and +tropical or sub-tropical conditions of the land. + +(2.) MIDDLE EOCENE.--The inferior portion of the Middle Eocene +of Britain consists of marine beds, chiefly consisting of sand, +clays, and gravels, and attaining a very considerable thickness +(_Bag-shot and Bracklesham beds_). The superior portion of the +Middle Eocene of Britain, on the other hand, consists of deposits +which are almost exclusively fresh-water or brackish-water in +origin (_Headon and Osborne series_). + +The chief Continental formations of Middle Eocene age are the +"Calcaire grossier" of the Paris basin, and the "Nummulitic +Limestone" of the Alps. + +(3.) UPPER EOCENE.--If the Headon and Osborne beds of the Isle +of Wight be placed in the Middle Eocene, the only British +representatives of the Upper Eocene are the _Bembridge beds_. +These strata consist of limestones, clays, and marls, which have +for the most part been deposited in fresh or brackish water. + +II. EOCENE BEDS OF THE PARIS BASIN.--The Eocene strata are very +well developed in the neighbourhood of Paris, where they occupy +a large area or basin scooped out of the Chalk. The beds of this +area are partly marine, partly freshwater in origin; and the +following table (after Sir Charles Lyell) shows their subdivisions +and their parallelism with the English series:-- + + GENERAL TABLE OF FRENCH EOCENE STRATA. + + UPPER EOCENE. + + _French Subdivisions._ _English Equivalents._ + A. 1. Gypseous series of Mont 1. Bembridge series. + Montmartre. + A. 2. Calcaire silicieux, or 2. Osborne and Headon series. + Travertin Inférieur. + A. 3. Grès de Beauchamp, or 3. White sand and clay of + Sables Moyens. Barton Cliff, Hants. + + MIDDLE EOCENE. + + B. 1. Calcaire Grossier. 1. Bagshot and Bracklesham beds. + B. 2. Soissonnais Sands, or 2. Wanting. + Lits Coquilliers. + + LOWER EOCENE. + + C. 1. Argile de Londres at base 1. London clay. + of Hill of Cassel, near + Dunkirk. + C. 2. Argile plastique and 2. Plastic clay and sand with + lignite. lignite (Woolwich and Reading + series). + C. 3. Stables de Bracheux. 3. Thanet sands. + +III. EOCENE STRATA OF THE UNITED STATES.--The lowest member of +the Eocene deposits of North America is the so-called "_Lignitic +Formation_," which is largely developed in Mississippi, Tennessee, +Arkansas, Wyoming, Utah, Colorado, and California, and sometimes +attains a thickness of several thousand feet. Stratigraphically, +this formation exhibits the interesting point that it graduates +downwards insensibly and conformably into the Cretaceous, whilst +it is succeeded _uncomformably_ by strata of Middle Eocene age. +Lithologically, the series consists principally of sands and +clays, with beds of lignite and coal, and its organic remains +show that it is principally of fresh-water origin with a partial +intermixture of marine beds. These marine strata of the "Lignitic +formation" are of special interest, as showing such a commingling +of Cretaceous and Tertiary types of life, that it is impossible +to draw any rigid line in this region between the Mesozoic and +Kainozoic systems. Thus the marine beds of the Lignitic series +contain such characteristic Cretaceous forms as _Inoceramus_ +and _Ammonites_, along with a great number of Univalves of a +distinctly Tertiary type (Cones, Cowries, &c.) Upon the whole, +therefore, we must regard this series of deposits as affording a +kind of transition between the Cretaceous and the Eocene, holding +in some respects a position which may be compared with that held +by the Purbeck beds in Britain as regards the Jurassic and +Cretaceous. + +The Middle Eocene of the United States is represented by the +_Claiborne_ and _Jackson_ beds. The _Claiborne series_ is extensively +developed at Claiborne, Alabama, and consists of sands, clays, +lignites, marls, and impure limestones, containing marine fossils +along with numerous plant-remains. The _Jackson series_ is +represented by lignitic clays and marls which occur at Jackson, +Mississippi. Amongst the more remarkable fossils of this series +are the teeth and bones of Cetaceans of the genus _Zeuglodon_. + +Strata of Upper Eocene age occur in North America at Vicksburg, +Mississippi, and are known as the _Vicksburg series_. They consist +of lignites, clays, marls, and limestones. Freshwater deposits +of Eocene age are also largely developed in parts of the Rocky +Mountain region. The most remarkable fossils of these beds are +Mammals, of which a large number of species have been already +determined. + + +LIFE OF THE EOCENE PERIOD. + +The fossils of the Eocene deposits are so numerous that nothing +more can be attempted here than to give a brief and general sketch +of the life of the period, special attention being directed to some +of the more prominent and interesting types, amongst which--as +throughout the Tertiary series--the Mammals hold the first place. +It is not uncommon, indeed, to speak of the Tertiary period as a +whole under the name of the "Age of Mammals," a title at least +as well deserved as that of "Age of Reptiles" applied to the +Mesozoic, or "Age of Molluscs" applied to the Palæozoic epoch. + +As regards the _plants_ of the Eocene, the chief point to be +noticed is, that the conditions which had already set in with +the commencement of the Upper Cretaceous, are here continued, +and still further enforced. The _Cycads_ of the Secondary period, +if they have not totally disappeared, are exceedingly rare; and +the _Conifers_, losing the predominance which they enjoyed in the +Mesozoic, are now relegated to a subordinate though well-defined +place in the terrestrial vegetation. The great majority of the +Eocene plants are referable to the groups of the Angiospermous +Exogens and the Monocotyledons; and the vegetation of the period, +upon the whole, approximates closely to that now existing upon +the earth. The plants of the European Eocene are, however, in the +main most closely allied to forms which are now characteristic +of tropical or sub-tropical regions. Thus, in the London Clay +are found numerous fruits of Palms (_Napdites_, fig. 213), along +with various other plants, most of which indicate a warm climate +as prevailing in the south of England at the commencement of the +Eocene period. In the Eocene strata of North America occur numerous +plants belonging to existing types--such as Palms, Conifers, +the Magnolia, Cinnamon, Fig. Dog-wood, Maple, Hickory, Poplar, +Plane, &c. Taken as a whole, the Eocene flora of North America +is nearly related to that of the Miocene strata of Europe, as +well as to that now existing in the American area. We conclude, +therefore, that "the forests of the American Eocene resembled +those of the European Miocene, and even of modern America" (Dana). + +[Illustration: Fig. 213.--_Napadites ellipticus_, the fruit of +a fossil Palm. London Clay, Isle of Sheppey.] + +As regards the _animals_ of the Eocene period, the _Protozoans_ +are represented by numerous _Foraminifera_, which reach here their +maximum of development, both as regards the size of individuals and +the number of generic types. Many of the Eocene Foraminifers are of +small size; but even these not uncommonly form whole rock-masses. +Thus, the so-called "Miliolite Limestone" of the Paris basin, largely +used as a building-stone, is almost wholly composed of the shells +of a small species of _Miliola_. The most remarkable, however, of +the many members of this group of animals which flourished in +Eocene times, are the "Nummulites" (_Nummulina_), so called from +their resemblance in shape to coins (Lat. _nummus_, a coin). The +Nummulites are amongst the largest of all known _Foraminifera_, +sometimes attaining a size of three inches in circumference; +and their internal structure is very complex (fig. 214). Many +species are known, and they are particularly characteristic of +the Middle and Upper of these periods--their place being sometimes +taken by _Orbitoides_, a form very similar to the Nummulite in +external appearance, but differing in its internal details. In +the Middle Eocene, the remains of Nummulites are found in vast +numbers in a very widely-spread and easily-recognised formation +known as the "Nummulitic Limestone" (fig. 10). According to Sir +Charles Lyell, "the Nummulitic Limestone of the Swiss Alps rises +to more than 10,000 feet above the level of the sea, and attains +here and in other mountain-chains a thickness of several thousand +feet. It may be said to play a far more conspicuous part than +any other Tertiary group in the solid framework of the earth's +crust, whether in Europe, Asia, or Africa. It occurs in Algeria +and Morocco, and has been traced from Egypt, where it was largely +quarried of old for the building of the Pyramids, into Asia Minor, +and across Persia by Bagdad to the mouths of the Indus. It has +been observed not only in Cutch, but in the mountain-ranges which +separate Scinde from Persia, and which form the passes leading +to Cabul; and it has been followed still further eastward into +India, as far as Eastern Bengal and the frontiers of China." +The shells of Nummulites have been found at an elevation of 16,500 +feet above the level of the sea in Western Thibet; and the +distinguished and philosophical geologist just quoted, further +remarks, that "when we have once arrived at the conviction that +the Nummulitic formation occupies a middle and upper place in the +Eocene series, we are struck with the comparatively modern date to +which some of the greatest revolutions in the physical geography +of Europe, Asia, and Northern Africa must be referred. All the +mountain-chains--such as the Alps, Pyrenees, Carpathians, and +Himalayas--into the composition of whose central and loftiest parts +the Nummulitic strata enter bodily, could have had no existence +till after the Middle Eocene period. During that period, the +sea prevailed where these chains now rise; for Nummulites and +their accompanying Testacea were unquestionably inhabitants of +salt water." + +[Illustration: Fig. 214.--_Nummulina loevigata_. Middle Eocene.] + +The _Coelenterates_ of the Eocene are represented principally +by _Corals_, mostly of types identical with or nearly allied to +those now in existence. Perhaps the most characteristic group +of these is that of the _Turbinolidoe_, comprising a number of +simple "cup-corals," which probably lived in moderately deep +water. One of the forms belonging to this family is here figured +(fig. 215). Besides true Corals, the Eocene deposits have yielded +the remains of the "Sea-pens" (_Pennatulidoe_) and the branched +skeletons of the "Sea-shrubs" (_Gorgontidoe_). + +The _Echinoderms_ are represented principally by Sea-urchins, and +demand nothing more than mention. It is to be observed, however, +that the great group of the Sea-lilies (_Crinoids_) is now verging +on extinction, and is but very feebly represented. + +Amongst the _Mollusca_, the _Polyzoans_ and _Brachiopods_ also +require no special mention, beyond the fact that the latter are +greatly reduced in numbers, and belong principally to the existing +genera _Terebratula_ and _Rhynchonella_. The Bivalves +(_Lamellibranchs_) and the Univalves (_Gasteropods_) are exceedingly +numerous, and almost all the principal existing genera are now +represented; though less than five percent of the Eocene _species_ +are identical with those now living. It is difficult to make any +selection from the many Bivalves which are known in deposits of +this age; but species of _Cardita, Crassatella, Leda, Cyrena, Mactra, +Cardium, Psammobia_, &c., may be mentioned as very characteristic. +The _Caradita planicosta_ here figured (fig. 216) is not only very +abundant in the Middle Eocene, but is very widely distributed, +ranging from Europe to the Pacific coast of North America. The +_Univalves_ of the Eocene are extremely numerous, and generally +beautifully preserved. The majority of them belong to that great +section of the _Gasteropods_ in which the mouth of the shell +is notched or produced into a canal (when the shell is said to be +"siphonostomatous")--this section including the carnivorous and +most highly-organized groups of the class. Not only is this the +case, but a large number of the Eocene Univalves belong to types +which now attain their maximum of development in the warmer regions +of the globe. Thus we find numerous species of Cones (_Conus_), +Volutes (_Voluta_), Cowries (_Cyproea_, fig. 218), Olives and +Rice-shells (_Oliva_), Mitre-shells (_Mitra_), Trumpet-shells +(_Triton_), Auger-shells (_Terebra_), and Fig-shells (_Pyrula_). +Along with these are many forms of _Pleurotoma, Rostellaria_, +Spindle-shells (_Fusus_), Dog-whelks (_Nassa_), _Murices_, and +many round-mouthed ("holostomatous") species, belonging to such +genera as _Turritella, Nerita, Natica, Scalaria_, &c. The genus +_Cerithium_ (fig. 219), most of the living forms of which are found +in warm regions, inhabiting fresh or brackish waters, undergoes a +vast development in the Eocene period, where it is represented +by an immense number of specific forms, some of which attain +very large dimensions. In the Eocene strata of the Paris basin +alone, nearly one hundred and fifty species of this genus have been +detected. The more strictly fresh-water deposits of the Eocene +period have also yielded numerous remains of Univalves such as +are now proper to rivers and lakes, together with the shells of +true Land-snails. Amongst these may be mentioned numerous species +of _Limnoea_ (fig. 220), _Physa_ (fig. 221), _Melania, Paludina, +Planorbis, Helix, Bulimus_, and _Cyclostoma_ (fig. 222). + +[Illustration: Fig. 215.--_Turbinolia sulcata_, viewed from one +side, and from above. Eocene.] + +[Illustration: Fig. 216.--_Cardita planicosta_. Middle Eocene.] + +[Illustration: Fig. 217.--_Typhis tubifer_, a "siphonostomatous" +Univalve. Eocene.] + +[Illustration: Fig. 218.--Cyproea elegans. Eocene.] + +[Illustration: Fig. 219.--_Cerithium hexagonum_. Eocene.] + +With regard to the _Cephalopods_, the chief point to be noticed +is, that all the beautiful and complex forms which peculiarly +characterised the Cretaceous period have here disappeared. We no +longer meet with a single example of the Turrilite, the Baculite, +the Hamite, the Scaphite, or the Ammonite. The only exception +to this statement is the occurrence of one species of Ammonite +in the so-called "Lignitic Formation" of North America; but the +beds containing this may possibly be rather referable to the +Cretaceous--and this exception does not affect the fact that +the _Ammonitidoe_, as a family, had become extinct before the +Eocene strata were deposited. The ancient genus _Nautilus_ still +survives, the sole representative of the once mighty order of the +Tetrabranchiate Cephalopods. In the order of the _Dibranchiates_, +we have a like phenomenon to observe in the total extinction +of the great family of the "Belemnites." No form referable to +this group has hitherto been found in any Tertiary stratum; but +the internal skeletons of Cuttle-fishes (such as _Belosepia_) +are not unknown. + +[Illustration: Fig. 220.--_Limnoea pyramidalis_. Eocene.] + +[Illustration: Fig. 221.--_Physa columnaris_. Eocene.] + +[Illustration: Fig. 222.--_Cyclostoma Arnoudii_. Eocene.] + +Remains of _Fishes_ are very abundant in strata of Eocene age, +especially in certain localities. The most famous depot for the +fossil fishes of this period is the limestone of Monte Bolca, +near Verona, which is interstratified with beds of volcanic ashes, +the whole being referable to the Middle Eocene. The fishes here +seem to have been suddenly destroyed by a volcanic eruption, +and are found in vast numbers. Agassiz has described over one +hundred and thirty species of Fishes from this locality, belonging +to seventy-seven genera. All the _species_ are extinct; but about +one-half of the _genera_ are represented by living forms. The +great majority of the Eocene Fishes belong to the order of the +"Bony Fishes" (_Teleosteans_), so that in the main the forms +of Fishes characterising the Eocene are similar to those which +predominate in existing seas. In addition to the above, a few +_Ganoids_ and a large number of _Placoids_ are known to occur +in the Eocene rocks. Amongst the latter are found numerous teeth +of true Sharks, such as _Otodus_ (fig. 224) and _Carcharodon_. +The pointed and serrated teeth of the latter sometimes attain +a length of over half a foot, indicating that these predaceous +fishes attained gigantic dimensions; and it is interesting to +note that teeth, in external appearance very similar to those +of the early Tertiary genus _Carcharodon_, have been dredged +from great depths during the recent expedition of the Challenger. +There also occur not uncommonly the flattened teeth of Rays (fig. +225), consisting of flat bony pieces placed close together, and +forming "a kind of mosaic pavement on both the upper and lower +jaws" (Owen). + +[Illustration: Fig. 223.--_Rhombus minimus_, a small fossil Turbot +from the Eocene Tertiary, Monte Bolca.] + +[Illustration: Fig. 224.--Tooth of _Otodus obliquus_. Eocene.] + +[Illustration: Fig. 225.--Flattened dental plates of a Ray +(_Myliobatis Edwardsii_). Eocene.] + +In the class of the _Reptiles_, the disappearance of the +characteristic Mesozoic types is as marked a phenomenon as the +introduction of new forms. The Ichthyosaurs, the Plesiosaurs, +the Pterosaurs, and the Mosasaurs of the Mesozoic, find no +representatives in the Eocene Tertiary; and the same is true of the +Deinosaurs, if we except a few remains from the doubtfully-situated +"Lignitic formation" of the United States, On the other hand, all +the modern orders of Reptiles are known to have existed during +the Eocene period. The _Chelonians_ are represented by true marine +Turtles, by "Terrapins" (_Emydidoe_), and by "Soft Tortoises" +(_Trionycidoe_). The order of the Snakes and Serpents (_Ophidia_) +makes its appearance here, for the first time under several +forms--all of which, however, are referable to the non-venomous +group of the "Constricting Serpents" (_Boidoe_). The oldest of +these is the _Paloeophis toliapicus_ of the London Clay of Sheppey, +first made known to science by the researches of Professor Owen. +The nearly-allied _Paloeophis typhoeus_ of the Eocene beds of +Bracklesham appears to have been a Boa-constrictor-like Snake +of about twenty feet in length. Similar Python-like Snakes +(_Paloeophis, Dinophis_, &c.) have been described from the Eocene +deposits of the United States. True Lizards (_Lacertilians_) +are found in some abundance in the Eocene deposits,--some being +small terrestrial forms, like the common European lizards of the +present day; whilst others equal or exceed the living Monitors +in size. Lastly, the modern order of the _Crocodilia_ is largely +represented in Eocene times, by species belonging to all the +existing genera, together with others referable to extinct types. +As pointed out by Owen, it is an interesting fact that in the +Eocene rocks of the south-west of England, there occur fossil +remains of all the three living types of Crocodilians--namely, the +Gavials, the true Crocodiles, and the Alligators (fig. 226)--though +at the present day these forms are all geographically restricted +in their range, and are never associated together. + +[Illustration: Fig. 226.--Upper jaw of Alligator. Eocene Tertiary, +Isle of Wight.] + +Almost all the existing orders of _Birds_, if not all, are +represented in the Eocene deposits by remains often very closely +allied to existing types. Thus, amongst the Swimming Birds +(_Natatores_) we find examples of forms allied to the living +Pelicans and Mergansers; amongst the Waders (_Grallatores_) we +have birds resembling the Ibis (the _Numenius gypsorum_ of the +Paris basin); amongst the Running Birds (_Cursores_) we meet with +the great _Gastornis Parisiensis_, which equalled the African +Ostrich in height, and the still more gigantic _Dasornis +Londinensis_; remains of a Partridge represent the Scratching +Birds (_Rasores_); the American Eocene has yielded the bones of +one of the Climbing Birds (_Scansores_), apparently referable +to the Woodpeckers; the _Protornis Glarisiensis_ of the Eocene +Schists of Glaris is the oldest known example of the Perching +Birds (_Insessores_); and the Birds of Prey (_Raptores_) are +represented by Vultures, Owls, and Hawks. The toothed Birds of +the Upper Cretaceous are no longer known to exist; but Professor +Owen has recently described from the London Clay the skull of a very +remarkable Bird, in which there is, at any rate, an approximation +to the structure of _Ichthyornis_ and _Hesperornis_. The bird +in question has been named the _Odontopteryx totiapicus_, its +generic title being derived from the very remarkable characters +of its jaws. In this singular form (fig. 227) the margins of +both jaws are furnished with tooth-like denticulations, which +differ from true teeth in being actually portions of the bony +substance of the jaw itself, with which they are continuous, and +which were probably encased by extensions of the horny sheath +of the bill. These tooth-like processes are of two sizes, the +larger ones being comparable to canines; and they are all directed +forwards, and have a triangular or compressed conical form. From +a careful consideration of all the discovered remains of this +bird, Professor Owen concludes that "_Odontopteryx_ was a +warm-blooded feathered biped, with wings; and further, that it +was web-footed and a fish-eater, and that in the catching of +its slippery prey it was assisted by this Pterosauroid armature +of its jaws." Upon the whole, _Odontopteryx_ would appear to be +most nearly related to the family of the Geese (_Anserinoe_) +or Ducks (_Anatidoe_); but the extension of the bony substance +of the jaws into tooth-like processes is an entirely unique +character, in which it stands quite alone. + +[Illustration: Fig. 227.--Skull of _Odontopteryx toliapicus restored. +(After Owen.)] + +The known _Mammals_ of the Mesozoic period, as we have seen, +are all of small size; and with one not unequivocal exception, +they appear to be referable to the order of the Pouched Quadrupeds +(_Marsupials_), almost the lowest group of the whole class of +the Mammalia. In the Eocene rocks, on the other hand, numerous +remains of Quadrupeds have been brought to light, representing +most of the great Mammalian orders now in existence upon the +earth, and in many cases indicating animals of very considerable +dimensions. We are, in fact, in a position to assert that the +majority of the great groups of Quadrupeds with which we are +familiar at the present day were already in existence in the +Eocene period, and that their ancient root-stocks were even in +this early time separated by most of the fundamental differences +of structure which distinguish their living representatives. +At the same time, there are some amongst the Eocene quadrupeds +which have a "generalised" character, and which may be regarded +as structural types standing midway between groups now sharply +separated from one another. + +The order of the _Marsupials_--including the existing Kangaroos, +Wombats, Opossums, Phalangers, &c.--is poorly represented in +deposits of Eocene age. The most celebrated example of this group +is the _Didelphys gypsorum_ of the Gypseous beds of Montmartre, +near Paris, an Opossum very nearly allied to the living Opossums +of North and South America. + +No member of the _Edenates_ (Sloths, Ant-eaters, and Armadillos) +has hitherto been detected in any Eocene deposit. The aquatic order +of the _Sirenians_ (Dugongs and Manatees), with their fish-like +bodies and tails, paddle-shaped forelimbs, and wholly deficient +hind-limbs, are represented in strata of this age by remains of +the ancient "Sea-Cows," to which the name of _Halitherium_ has +been applied. Nearly allied to the preceding is the likewise aquatic +order of the Whales and Dolphins (_Cetaceans_), in which the body +is also fish-like, the hind-limbs are wanting, the fore-limbs are +converted into powerful "flippers" or swimming-paddles, and the +terminal extremity of the body is furnished with a horizontal, +tail-fin. Many existing Cetaceans (such as the Whalebone Whales) +have no true teeth; but others (Dolphins, Porpoises, Sperm Whales) +possess simple conical teeth. In strata of Eocene age, however, we +find a singular group of Whales, constituting the genus _Zeuglodon +(fig. 228), in which the teeth differed from those of all existing +forms in being of two kinds,--the front ones being conical incisors, +whilst the back teeth or molars have serrated triangular crowns, +and are inserted in the jaw by two roots. Each molar (fig. 228, +A) looks as if it were composed of two separate teeth united on +one side by their crowns; and it is this peculiarity which is +expressed by the generic name (Gr. _zeugle_, a yoke; _odous_, +tooth). The best-known species of the genus is the _Zeuglodon +cetoides_ of Owen, which attained a length of seventy feet. Remains +of these gigantic Whales are very common in the "Jackson Beds" of +the Southern United States. So common are they that, according +to Dana, "the large vertebræ, some of them a foot and a half +long and a foot in diameter, were formerly so abundant over the +country, in Alabama, that they were used for making walls, or +were burned to rid the fields of them." + +[Illustration: Fig. 228.--_Zeuglodon cetoides_. A, Molar tooth of +the natural size; B, Vertebra, reduced in size. From the Middle +Eocene of the United States. (After Lyell.)] + +The great and important order of the Hoofed Quadrupeds (_Ungulata_) +is represented in the Eocene by examples of both of its two principal +sections--namely, those with an uneven number of toes (one or three) +on the foot (_Perissodactyle Ungulates_), and those with an even +number of toes (two or four) to each foot (_Artiodactyle Ungulates_). +Amongst the Odd-toed Ungulates, the living family of the Tapirs +(_Tapirdoe_) is represented by the genus _Coryphodon_ of Owen. +Nearly related to the preceding are the species of _Paloeotherium_, +which have a historical interest as being amongst the first of +the Tertiary Mammals investigated by the illustrious Cuvier. +Several species of _Paloeothere_ are known, varying greatly in +size, the smallest being little bigger than a hare, whilst the +largest must have equalled a good-sized horse in its dimensions. The +species of _Paloeotherium_ appear to have agreed with the existing +Tapirs in possessing a lengthened and flexible nose, which formed +a short proboscis or trunk (fig. 229), suitable as an instrument +for stripping off the foliage of trees--the characters of the +molar teeth showing them to have been strictly herbivorous in +their habits. They differ, however, from the Tapirs, amongst +other characters, in the fact that both the fore and the hind +feet possessed three toes each; whereas in the latter there are +four toes on each fore-foot, and the hind-feet alone are three-toed. +The remains of _Paloeotheria_ have been found in such abundance in +certain localities as to show that these animals roamed in great +herds over the fertile plains of France and the south of England +during the later portion of the Eocene period. The accompanying +illustration (fig. 229) represents the notion which the great +Cuvier was induced by his researches to form as to the outward +appearance of _Paloeotherium magnum_. Recent discoveries, however, +have rendered it probable that this restoration is in some important +respects inaccurate. Instead of being bulky, massive, and more +or less resembling the living Tapirs in form, it would rather +appear that _Paloeotherium magnum_ was in reality a slender, +graceful, and long-necked animal, more closely resembling in +general figure a Llama, or certain of the Antelopes. + +[Illustration: Fig. 229.--Outline of _Paloeotherium magnum_, +restored. Upper Eocene, Europe. (After Cuvier.)] + +The singular genus _Anchitherium_ forms a kind of transition +between the _Paloeotheria_ and the true Horses (_Equidoe_). The +Horse (fig. 230, D) possesses but one fully-developed toe to +each foot, this being terminated by a single broad hoof, and +representing the _middle_ toe--the _third_ of the typical +five-fingered or five-toed limb of Quadrupeds in general. In +addition, however, to this fully-developed toe, each foot in the +horse carries two rudimentary toes which are concealed beneath the +skin, and are known as the "splint-bones." These are respectively +the _second_ and _fourth_ toes, in an aborted condition; and the +first and fifth toes are wholly wanting. In _Hipparion_ (fig. +230, C), the foot is essentially like that of the modern Horses, +except that the second and fourth toes no longer are mere +"splint-bones," hidden beneath the skin; but have now little +hoofs, and hang freely, but uselessly, by the side of the great +middle toe, not being sufficiently developed to reach the ground. +In _Anchitherium_, again (fig. 230, B), the foot is three-toed, +like that of _Hipparion_; but the two lateral toes (the second +and fourth) are so far developed that they now reach the ground. +The _first_ digit (thumb or great toe) is still wanting; as also +is the _fifth_ digit (little finger or little toe). Lastly, the +Eocene rocks have yielded in North America the remains of a small +Equine quadruped, to which Marsh has given the name of _Orohippus_. +In this singular form--which was not larger than a fox--the foot +(fig. 230, A) carries _four_ toes, all of which are hoofed and touch +the ground, but of which the _third_ toe is still the largest. The +_first_ toe (thumb or great toe) is still wanting; but in this +ancient representative of the Horses, the _fifth_ or "little" +toe appears for the first time. As all the above-mentioned forms +succeed one another in point of time, it may be regarded as probable +that we shall yet be able to point, with some certainty, to some +still older example of the _Equidoe_, in which the first digit +is developed, and the foot assumes its typical five-fingered +condition. + +[Illustration: Fig. 230.--Skeleton of the foot in various forms +belonging to the family of the _Equidoe_. A, Foot of _Orohippus_, +Eocene; B, Foot of _Anchitherium</>, Upper Eocene and Lower Miocene; +C, Foot of _Hipparion_, Upper Miocene and Pliocene: D, Foot of +Horse (_Equus_), Pliocene and Recent. The figures indicate the +numbers of the digits in the typical five-fingered hand of Mammals. +(After Marsh.)] + +Passing on to the Even-toed or _Artiodactyle Ungulates_, no +representative of the _Hippotamus_ seems yet to have existed, but +there are several forms (_Choeropotamus, Hyopotamus_, &c.) more +or less closely allied to the Pigs (_Suida_); and the singular +group of the _Anoplotheridoe_ may be regarded as forming a kind of +transition between the Swine and the Ruminants. The _Anoplotheria_ +(fig. 231) were slender in form, the largest not exceeding a +donkey in size, with long tails, and having the feet terminated +by two hoofed toes each, sometimes with a pair of small accessory +hoofs as well. The teeth exhibit the peculiarity that they are +arranged in a continuous series, without any gap or interval +between the molars and the canines; and the back teeth, like +those of all the Ungulates, are adapted for grinding vegetable +food, their crowns resembling in form those of the true Ruminants. +The genera _Dichobune_ and _Xiphodon_, of the Middle and Upper +Eocene, are closely related to _Anoplotherium_, but are more +slender and deer-like in form. No example of the great Ruminant +group of the Ungulate Quadrupeds has as yet been detected in +deposits of Eocene age. + +[Illustration: Fig. 231.--_Anoplotherium commune_. Eocene Tertiary, +France. (After Cuvier.)] + +Whilst true Ruminants appear to be unknown, the Eocene strata +of North America have yielded to the researches of Professor +Marsh examples of an extraordinary group (_Dinocerata_), which +may be considered as in some respects intermediate between the +Ungulates and the Proboscideans. In _Dinoceras_ itself (fig. +232) we have a large animal, equal in dimensions to the living +Elephants, which it further resembles in the structure of the +massive limbs, except that there are only four toes to each foot. +The upper jaw was devoid of front teeth, but there were two very +large canine teeth, in the form of tusks directed perpendicularly +downwards; and there was also a series of six small molars on each. +Each upper jaw-bone carried a bony projection, which was probably +of the nature of a "horn-core," and was originally sheathed in +horn. Two similar, but smaller, horn-cores are carried on the +nasal bones; and two much larger projections, also probably of +the nature of horn-cores, were carried upon the forehead. We may +thus infer that _Dinoceras_ possessed three pairs of horns, all +of which resembled the horns of the Sheep and Oxen in consisting +of a central bony "core," surrounded by a horny sheath. The nose +was not prolonged into a proboscis or "trunk," as in the existing +Elephants; and the tail was short and slender. Many forms of +the _Dinocerata_ are known; but all these singular and gigantic +quadrupeds appear to have been confined to the North American +continent, and to be restricted to the Eocene period. + +[Illustration: Fig. 232.--Skull of _Dinoceras mirabilis_, greatly +reduced. Eocene, North America. (After Marsh.)] + +The important order of the Elephants (_Proboscidea_) is also not +known to have come into existence during the Eocene period. On the +other hand, the great order of the Beasts of Prey (_Carnivora_) +is represented in Eocene strata by several forms belonging to +different types. Thus the _Ardocyon_ presents us with an Eocene +Carnivore more or less closely allied to the existing Racoons; +the _Paloeonyctis_ appears to be related to the recent Civet-cats; +the genus _Hyoenodon_ is in some respects comparable to the living +Hyænas; and the _Canis Parisiensis_ of the gypsum-bearing beds +of Montmartre may perhaps be allied to the Foxes. + +[Illustration: Fig. 233.--Portion of the skeleton of _Vespertilio +Parisienis_. Eocene Tertiary, France.] + +The order of the Bats (_Cheiroptera_) is represented in Eocene +strata of the Paris basin (Gypseous series of Montmartre) by +the _Vespertilio Parisiensis_ (fig. 233), an insect-eating Bat +very similar to some of the existing European forms. Lastly, the +Eocene deposits have yielded more or less satisfactory evidence +of the existence in Europe at this period of examples of the +orders of the Gnawing Mammals (_Rodentia_), the Insect-eating +Mammals (_Insectivora_), and the Monkeys (_Quadrumana_).[24] + +[Footnote 24: A short list of the more important works relating to +the Eocene rocks and fossils will be given after all the Tertiary +deposits have been treated of.] + + + + +CHAPTER XIX. + +THE MIOCENE PERIOD. + +The Miocene rocks comprise those Tertiary deposits which contain +less than about 35 per cent of existing species of shells +(_Mollusca_), and more than 5 per cent--or those deposits in +which the proportion of living shells is less than of extinct +species. They are divisible into a _Lower Miocene_ (_Oligocene_) +and an _Upper Miocene_ series. + +In _Britain_, the Miocene rocks are very poorly developed, one +of their leading developments being at Bovey Tracy in Devonshire, +where there occur sands, clays, and beds of lignite or imperfect +coal. These strata contain numerous plants, amongst which are +Vines, Figs, the Cinnamon-tree, Palms, and many Conifers, especially +those belonging to the genus Sequoia (the "Red-Foods"). These +Bovey Tracy lignites are of Lower Miocene age, and they are +lacustrine in origin. Also of Lower Miocene age are the so-called +"Hempstead Beds" of Yarmouth in the Isle of Wight. These attain a +thickness of less than 200 feet, and are shown by their numerous +fossils to be principally a true marine formation. Lastly, the +Duke of Argyll, in 1851, showed that there existed at Ardtun, in +the island of Mull, certain Tertiary strata containing numerous +remains of plants; and these also are now regarded as belonging +to the Lower Miocene. + +In _France_, the Lower Miocene is represented in Auvergne, Cantal, +and Velay, by a great thickness of nearly horizontal strata of +sands, sandstone, clays, marls, and limestones, the whole of +fresh-water origin. The principal fossils of these lacustrine +deposits are _Mammalia_, of which the remains occur in great +abundance. In the valley of the Loire occur the typical European +deposits of Upper Miocene age. These are known as the "Faluns," +from a provincial term applied to shelly sands, employed to spread +upon soils which are deficient in lime; and the Upper Miocene +is hence sometimes spoken of as the "Falunian" formation. The +Faluns occur in scattered patches, which are rarely more than 50 +feet in thickness, and consist of sands and marls. The fossils +are chiefly marine; but there occur also land and fresh-water +shells, together with the remains of numerous Mammals. About 25 +per cent of the shells of the Faluns are identical with existing +species. The sands, limestones, and marls of the Department of +Gers, near the base of the Pyrenees, rendered famous by the number +or Mammalian remains exhumed from them by M. Lartet, also belong +to the age of the Faluns. + +In _Switzerland_, between the Alps and the Jura, there occurs +a great series of Miocene deposits, known collectively as the +"Molasse," from the soft nature of a greenish sandstone, which +constitutes one of its chief members. It attains a thickness of +many thousands of feet, and rises into lofty mountains, some +of which--as the Rigi--are more than 6000 feet in height. The +middle portion of the Molasse is of marine origin, and is shown +by its fossils to be of the age of the Faluns; but the lower +and upper portions of the formation are mainly or entirely of +fresh-water origin. The Lower Molasse (of Lower Miocene age) +has yielded about 500 species of plants, mostly of tropical or +sub-tropical forms. The Upper Molasse has yielded about the same +number of plants, with about 900 species of Insects, such as +wood-eating Beetles Water-beetles, White Ants, Dragon-flies, &c. + +In _Belgium_, strata of both Lower and Upper Miocene age are +known,--the former (_Rupelian Clays_) containing numerous marine +fossils; whilst the latter (_Bolderberg Sands_) have yielded +numerous shells corresponding with those of the Faluns. + +In _Austria_, Miocene strata are largely developed, marine beds +belonging to both the Lower and Upper division of the formation +occurring extensively in the Vienna basin. The well-known Brown +Coals of Radaboj, in Croatia, with numerous plants and insects, +are also of Lower Miocene age. + +In _Germany_, deposits belonging to both the Lower and Upper +division of the Miocene formation are extensively developed. +To the former belong the marine strata of the Mayence basin, +and the marine _Rupelian Clay_ near Berlin; whilst a celebrated +group of strata belonging to the Upper Miocene occurs near +Epplesheim, in Hesse-Darmstadt, and is well known for the number +of its Mammalian remains. + +In _Greece_, at Pikermé, near Athens, there occurs a celebrated +deposit of Upper Miocene age, well known to palæontologists through +the researches of M. M. Wagner, Roth, and Gaudry upon the numerous +Mammalia which it contains. In _Italy_, also, strata of both Lower +and Upper Miocene age are well developed in the neighbourhood +of Turin. + +In the _Siwâlik Hills_, in India, at the southern foot of the +Himalayas, occurs a series of Upper Miocene strata, which have +become widely celebrated through the researches of Dr Falconer +and Sir Proby Cautley upon the numerous remains of Mammals and +Reptiles which they contain. Beds of corresponding age, with +similar fossils, are known to occur in the island of Perim in +the Gulf of Cambay. + +Lastly, Miocene deposits are found in _North America_, in New +Jersey, Maryland, Virginia, Missouri, California, Oregon, &c., +attaining a thickness of 1500 feet or more. They consist principally +of clays, sands, and sandstones, sometimes of marine and sometimes +of fresh-water origin. Near Richmond, in Virginia, there occurs a +remarkable stratum, wrongly called "Infusorial Earth," which is +occasionally 30 feet in thickness, and consists almost wholly of +the siliceous envelopes of certain low forms of plants (Diatoms), +along with the spicules of Sponges and other siliceous organisms +(see fig. 16). The _White River Group_ of Hayden occurs in the +Upper Missouri region, and is largely exposed over the barren +and desolate district known as the "Mauvaises Terres." They have +a thickness of 1000 feet or more, and contain numerous remains +of Mammals. They are of lacustrine origin, and are believed to +be of the age of the Lower Miocene. Upon the whole, about from +15 to 30 per cent of the _Mollusca_ of the American Miocene are +identical with existing species. + +In addition to the regions previously enumerated, Miocene strata +are known to be developed in _Greenland, Iceland, Spitzbergen_, +and in other areas of less importance. + +The _life_ of the Miocene period is extremely abundant, and, from +the nature of the deposits of this age, also extremely varied +in its character. The marine beds of the formation have yielded +numerous remains of both Vertebrate and Invertebrate sea-animals; +whilst the fresh-water deposits contain the skeletons of such +shells, fishes, &c., as now inhabit rivers or lakes. Both the +marine and the lacustrine beds have been shown to contain an +enormous number of plants, the latter more particularly; whilst +the Brown Coals of the formation are made up of vegetable matter +little altered from its original condition. The remains of +air-breathing animals, such as Insects, Reptiles, Birds, and +Mammals, are also abundantly found, more especially in the +fresh-water beds. + +The _plants_ of the Miocene period are extraordinarily numerous, +and only some of the general features of the vegetation of this +epoch can be indicated here. Our chief sources of information as +to the Miocene plants are the Brown Coals of Germany and Austria, +the Lower and Upper Molasse of Switzerland, and the Miocene strata +of the Arctic regions. The lignites of Austria have yielded very +numerous plants, chiefly of a tropical character--one of the +most noticeable forms being a Palm of the genus _Sabal_ (fig. +234, B), now found in America. The plants of the Lower Miocene of +Switzerland are also mostly of a tropical character, but include +several forms now found in North America, such as a Tulip-tree +(_Liriodendron_) and a Cypress (_Taxodium_). Amongst the more +remarkable forms from these beds may be mentioned Fan-Palms +(_Chamoerops_, fig 234, A), numerous tropical ferns, and two +species of Cinnamon. The plant-remains of the Upper Molasse of +Switzerland indicate an extraordinarily rank and luxuriant +vegetation, composed mainly of plants which now live in warm +countries. Among the commoner plants of this formation may be +enumerated many species of Maple (_Acer_), Plane-trees (_Platanus_ +fig. 235), Cinnamon-trees (fig. 236), and other members of the +_Lauraceoe_, many species of _Proteaccoe_ (_Banksia, Grevillea_, +&c.), several species of Sarsaparilla (_Smilax_), Palms, Cypresses, +&c. + +[Illustration: Fig. 234.--Miocene Palms A, _Chamoerops Helvetica_; +B, _Sabal major_. Lower Miocene of Switzerland and France.] + +[Illustration: Fig. 235.--_Platanus aceroides_, an Upper Miocene +Plane-tree. a, Leaf; b, The core of a bundle of fruits; c, +A single fruit.] + +[Illustration: Fig. 236.--_Cinnamomum polymorphum_. a, Leaf; +b, Flower. Upper Miocene.] + +In Britain, the Lower Miocene strata of Bovey Tracy have yielded +remains of Ferns, Vines, Fig, Cinnamon, _Proteaccoe_, &c., along +with numerous Conifers. The most abundant of these last is a +gigantic pine--the _Sequoia Couttsioe_--which is very nearly +allied to the huge _Sequoia_ (_Wellingtonia_) _gigantea_ of +California. A nearly-allied form (_Sequoia Langsdorffi_) has been +detected in the leaf-bed of Ardtun, in the Hebrides. + +In Greenland, as well as in other parts of the Arctic regions, +Miocene strata have been discovered which have yielded a great +number of plants, many of which are identical with species found +in the European Miocene. Amongst these plants are found many +trees, such as Conifers, Beeches, Oaks, Maples, Plane-trees, +Walnuts, Magnolias, &c., with numerous shrubs, ferns, and other +smaller plants. With regard to the Miocene flora of the Arctic +regions, Sir Charles Lyell remarks that "more than thirty species +of Coniferæ have been found, including several Sequoias (allied +to the gigantic Wellingtonia of California), with species of +_Thujopsis_ and _Salisburia_, now peculiar to Japan. There are +also beeches, oaks, planes, poplars, maples, walnuts, limes, and +even a magnolia, two cones of which have recently been obtained, +proving that this splendid evergreen not only lived but ripened +its fruit within the Arctic circle. Many of the limes, planes, +and oaks were large-leaved species; and both flowers and fruits, +besides immense quantities of leaves, are in many cases preserved. +Among the shrubs are many evergreens, as _Andromeda_, and two +extinct genera, _Daphnogene_ and _M'Clintockia_, with fine leathery +leaves, together with hazel, blackthorn, holly, logwood, and +hawthorn. A species of Zamia (_Zimites_) grew in the swamps, +with _Potamogeton, Sparganium_, and _Menyanthes_; while ivy and +villes twined around the forest-trees, and broad-leaved ferns +grew beneath their shade. Even in Spitzbergen, as far north as +lat. 78° 56', no less than ninety-five species of fossil plants +have been obtained, including _Taxodium_ of two species, hazel, +poplar, alder, beech, plane-tree, and lime. Such a vigorous growth +of trees within 12° of the pole, where now a dwarf willow and a +few herbaceous plants form the only vegetation, and where the +ground is covered with almost perpetual snow and ice, is truly +remarkable." + +Taking the Miocene flora as a whole, Dr Heer concludes from his +study of about 3000 plants contained in the European Miocene +alone, that the Miocene plants indicate tropical or sub-tropical +conditions, but that there is a striking inter-mixture of forms +which are at present found in countries widely removed from one +another. It is impossible to state with certainty how many of the +Miocene plants belong to existing species, but it appears that +the larger number are extinct. According to Heer, the American +types of plants are most largely represented in the Miocene flora, +next those of Europe and Asia, next those of Africa, and lastly +those of Australia. Upon the whole, however, the Miocene flora +of Europe is mostly nearly allied to the plants which we now +find inhabiting the warmer parts of the United States; and this +has led to the suggestion that in Miocene times the Atlantic +Ocean was dry land, and that a migration of American plants to +Europe was thus permitted. This view is borne out by the fact +that the Miocene plants of Europe are most nearly allied to the +living plants of the eastern or Atlantic seaboard of the United +States, and also by the occurrence of a rich Miocene flora in +Greenland. As regards Greenland, Dr Heer has determined that +the Miocene plants indicate a temperate climate in that country, +with a mean annual temperature at least 30° warmer than it is +at present. + +The present limit of trees is the isothermal which gives the +mean temperature of 500 Fahr. in July, or about the parallel of +67° N. latitude. In Miocene times, however, the Limes, Cypresses, +and Plane-trees reach the 79th degree of latitude, and the Pines +and Poplars must have ranged even further north than this. + +The _Invertebrate Animals_ of the Miocene period are very numerous, +but they belong for the most part to existing types, and they +can only receive scanty consideration here. The little shells of +_Foraminifera_ are extremely abundant in some beds, the genera +being in many cases such as now flourish abundantly in our seas. +The principal forms belong to the genera _Textularia_ (fig. 237), +_Robulina, Glandulina, Polystomella, Amplistegina_, &c. Corals +are very abundant, in many instances forming regular "reefs;" +but all the more important groups are in existence at the present +day. The Red Coral (_Corallium_), so largely sought after as an +ornamental material, appears for the first time in deposits of +this age. Amongst the _Echinoderms_, we meet with Heart-Urchins +(_Spatangus_), Cake-Urchins (_Scutella_; fig. 238), and various +other forms, the majority of which are closely allied to forms +now in existence. + +[Illustration: Fig. 237.--_Textularia Meyeriana_, greatly enlarged. +Miocene Tertiary.] + +Numerous Crabs and Lobsters represent the _Crustacea_; but the most +important of the Miocene Articulate Animals are the _Insects_. Of +these, more than thirteen hundred species have been determined by +Dr Heer from the Miocene strata of Switzerland alone. They include +almost all the existing orders of insects, such as numerous and +varied forms of Beetles (_Coleoptera_), Forest-bugs (_Hemiptera_), +Ants (_Hymenoptera_), Flies (_Diptera_), Termites and Dragon-flies +(_Neuroptera_), Grasshoppers (_Orthoptera_), and Butterflies +(_Lepidoptera_). One of the latter, the well-known _Vanessa Pluto_ +of the Brown Coals of Croatia, even exhibits the pattern of the +wing, and to some extent its original coloration; whilst the more +durably-constructed insects are often in a state of exquisite +preservation. + +[Illustration: Fig. 238.--Different views of _Scutella subrotunda_, +a Miocene "Cake-Urchin" from the south of France.] + +The _Mollusca_ of the Miocene period are very numerous, but call +for little special comment. Upon the whole, they are generically +very similar to the Shell-fish of the present day; whilst, as +before stated, from fifteen to thirty per cent of the _species_ +are identical with those now in existence. So far as the European +area is concerned, the Molluscs indicate a decidedly hotter climate +than the present one, though they have not such a distinctly +tropical character as is the case with the Eocene shells. Thus we +meet with many Cones, Volutes, Cowries, Olive-shells, Fig-shells, +and the like, which are decidedly indicative of a high temperature +of the sea. _Polyzoans_ are abundant, and often attain considerable +dimensions; whilst _Brachiopods_, on the other hand, are few in +number. Bivalves and _Univalves_ are extremely plentiful; and +we meet here with the shells of Winged-Snails (_Pteropods_), +belonging to such existing genera as _Hyalea_ (fig. 239) and +_Cleodora_. Lastly, the _Cephalopods_ are represented both by +the chambered shells of _Nautili_ and by the internal skeletons +of Cuttle-fishes (_Spirulirostra_.) + +[Illustration: Fig. 239.--Different views of the shell of _Hyalea +Orbignyana_, a Miocene Pteropod.] + +The _Fishes_ of the Miocene Period are very abundant but of little +special importance. Besides the remains of Bony Fishes, we meet +in the marine deposits of this age with numerous pointed teeth +belonging to different kinds of Sharks. Some of the genera of +these--such as _Carcharodon_ (fig. 241), _Oxyrhina_ (fig. 240), +_Lamna_, and _Galeocerdo_--are very widely distributed, ranging +through both the Old and New Worlds; and some of the species +attain gigantic dimensions. + +Amongst the _Amphibians_ we meet with distinctly modern types, +such as Frogs (_Rana_) and Newts or Salamanders. The most celebrated +of the latter is the famous _Andrias Scheuchzeri_ (fig. 242), +discovered in the year 1725 in the fresh-water Miocene deposits +of OEningen, in Switzerland. The skeleton indicates an animal +nearly five feet in length; and it was originally described by +Scheuchzer, a Swiss physician, in a dissertation published in 1731, +as the remains of one of the human beings who were in existence +at the time of the Noachian Deluge. Hence he applied to it the +name of _Homo diluvii testis_. In reality, however, as shown by +Cuvier, we have here the skeleton of a huge Newt, very closely +allied to the Giant Salamander (_Menopoma maxima_) of Java. + +[Illustration: Fig. 240.--Tooth of _Oxyrhina xiphodon_. Miocene.] + +[Illustration: Fig. 241.--Tooth of _Carcharodon productus_. Miocene.] + +The remains of _Reptiles_ are far from uncommon in the Miocene +rocks, consisting principally of Chelonians and Crocodilians. +The Land-tortoises (_Testudinidoe_) make their first appearance +during this period. The most remarkable form of this group is +the huge _Colossochelys Atlas_ of the Upper Miocene deposits +of the Siwâlik Hills in India, described by Dr Falconer and Sir +Proby Cautley. Far exceeding any living Tortoise in its dimensions, +this enormous animal is estimated as having had a length of about +twenty feet, measured from the tip of the snout to the extremity +of the tail, and to have stood upwards of seven feet high. All the +details of its organisation, however, prove that it must have been +"strictly a land animal, with herbivorous habits, and probably +of the most inoffensive nature." The accomplished palæontologist +just quoted, shows further that some of the traditions of the +Hindoos would render it not improbable that this colossal Tortoise +had survived into the earlier portion of the human period. + +Of the _Birds_ of the Miocene period it is sufficient to remark +that though specifically distinct, they belong, so far as known, +wholly to existing groups, and therefore present no points of +special palæontological interest. + +The _Mammals_ of the Miocene are very numerous, and only the more +important forms can be here alluded to. Amongst the _Marsupials_, +the Old World still continued to possess species of Opossum +(_Didephys_), allied to the existing American forms. The _Edentates_ +(Sloths, Armadillos, and Ant-eaters), at the present day mainly +South American, are represented by two large European forms. One +of these is the large _Macrotherium giganteum_ of the Upper Miocene +of Gers in Southern France, which appears to hare been in many +respects allied to the existing Scaly Ant-eaters or Pangolins, +at the same time that the disproportionately long fore-limbs would +indicate that it possessed the climbing habits of the Sloths. +The other is the still more gigantic _Ancylotherium Pentelici_ +of the Upper Miocene of Pikermé, which seems to have been as +large as, or larger than, the Rhinoceros, and which must have +been terrestrial in its habits. This conclusion is further borne +out by the comparative equality of length which subsists between +the fore and hind limbs, and is not affected by the curvature and +crookedness of the claws, this latter feature being well marked +in such existing terrestrial Edentates as the Great Ant-eater. + +[Illustration: Fig. 242.--Front portion of the skeleton of _Andrias +Scheuchzeri_, a Giant Salamander from the Miocene Tertiary of +Oeningen, in Switzerland. Reduced in size.] + +The aquatic _Sirenians_ and _Cetaceans_ are represented in Miocene +times by various forms of no special importance. Amongst the +former, the previously existing genus _Halitherium_ continued to +survive, and amongst the latter we meet with remains of Dolphins +and of Whales of the "Zeuglodont" family. We may also note here +the first appearance of true "Whalebone Whales," two species +of which, resembling the living "Right Whale" of Arctic seas, +and belonging to the same genus (_Baloena_), have been detected +in the Miocene beds of North America. + +The great order of the _Ungulates_ or Hoofed Quadrupeds is very +largely developed in strata of Miocene age, various new types +of this group making their appearance here for the first time, +whilst some of the characteristic genera of the preceding period +are still represented under new shapes. Amongst the Odd-toed +or "Perissodactyle" Ungulates, we meet for the first time with +representatives of the family _Rhinoceridoe_ comprising only +the existing Rhinoceroses. In India in the Upper Miocene beds +of the Siwâlik Hills, and in North America, several species of +Rhinoceros have been detected, agreeing with the existing forms +in possessing three toes to each foot, and in having one or two +solid fibrous "horns" carried upon the front of the head. On +the other hand, the forms of this group which distinguish the +Miocene deposits of Europe appear to have been for the most part +hornless, and to have resembled the Tapirs in having three-toed +hind-feet, but four-toed fore-feet. + +The family of the Tapirs is represented, both in the Old and +New Worlds, by species of the genus _Lophiodon_, some of which +were quite diminutive in point of size, whilst others attained +the dimensions of a horse. Nearly allied to this family, also, +is the singular group of quadrupeds which Marsh has described +from the Miocene strata of the United States under the name of +_Brontotheridoe_. These extraordinary animals, typified by +_Brontotherium_ (fig. 243) itself, agree with the existing Tapirs +of South America and the Indian Archipelago in having the fore-feet +four-toed, whilst the hind-feet are three-toed; and a further +point of resemblance is found in the fact (as shown by the form +of the nasal bones) that the nose was long and flexible, forming +a short movable proboscis or trunk, by means of which the animal +was enabled to browse on shrubs or trees. They differ, however, +from the Tapirs, not only in the apparent presence of a long tail, +but also in the possession of a pair of very large "horn-cores," +carried upon the nasal bones, indicating that the animal possessed +horns of a similar structure to those of the "Hollow-horned" +Ruminants (_e.g._, Sheep and Oxen). _Brontotherium gigas_ is +said to be nearly as large as an Elephant, whilst _B. Ingens_ +appears to have attained dimensions still more gigantic. The +well-known genus _Titanotherium_ of the American Miocene would +also appear to belong to this group. + +[Illustration: Fig. 243.--Skull of _Brontotherium ingens_. Miocene +Tertiary, United States. (After Marsh.)] + +The family of the Horses (_Equidoe_) appears under various forms +in the Miocene, but the most important and best known of these +is _Hipparion_. In this genus the general conformation of the +skeleton is extremely similar to that of the existing Horses, +and the external appearance of the animal must have been very +much the same. The foot of _Hipparion_, however, as has been +previously mentioned, differed from that of the Horse in the +fact that whilst both possess the middle toe greatly developed +and enclosed in a broad hoof, the former, in addition, possessed +two lateral toes, which were sufficiently developed to carry +hoofs, but were so far rudimentary that they hung idly by the +side of the central toe without touching the ground (see fig. +230). In the Horse, on the other hand, these lateral toes, though +present, are not only functionally useless, but are concealed +beneath the skin. Remains of the _Hipparion_ have been found +in various regions in Europe and in India; and from the immense +quantities of their bones found in certain localities, it may +be safely inferred that these Middle Tertiary ancestors of the +Horses lived, like their modern representatives, in great herds, +and in open grassy plains or prairies. + +Amongst the Even-toed or _Artiodactyle_ Ungulates, we for the +first time meet with examples of the _Hippopotamus_, with its +four-toed feet, its massive body, and huge tusk-like lower canine +teeth. The Miocene deposits of Europe have not hitherto yielded +any remains of _Hippopotamus_; but several species have been +detected in the Upper Miocene of the Siwâlik Hills by Dr Falconer +and Sir Proby Cautley. These ancient Indian forms, however, differ +from the existing _Hippopotamus amphibius_ of Africa in the fact +that they possessed six incisor teeth in each jaw (fig. 244), +whereas the latter has only four. + +[Illustration: Fig. 244.--a, Skull of _Hippopotamus Sivalensis_, +viewed from below, one-eighth of the natural size; b, Molar +tooth of the same, showing the surface of the crown, one-half +of the natural size: c, Front of the lower jaw of the same, +showing the six incisors and the tusk-like canines, one-eighth of +the natural size. Upper Miocene, Siwâlik Hills; (After Falconer +and Cautley.)] + +Amongst the other Even-toed Ungulates, the family of the Pigs +(_Suida_) is represented by true Swine (_Sus Erymanthius_), Peccaries +(_Dicotyles antiquus_), and by forms which, like the great +_Elotherium_ of the American Miocene, have no representative at +the present day. The Upper Miocene of India has yielded examples +of the Camels. Small Musk-deer (_Amphitragulus_ and _Dremotherium_) +are known to have existed in France and Greece; and the true Deer +(_Cervidoe_), with their solid bony antlers, appear for the first +time here in the person of species allied to the living Stags +(_Cervus_), accompanied by the extinct genus _Dorcatherium_. The +Giraffes (_Camelopardalidoe_), now confined to Africa, are known to +have lived in India and Greece; and the allied _Helladotherium_, in +some respects intermediate between the Giraffes and the Antelopes, +ranged over Southern Europe from Attica to France. The great +group of the "Hollow-horned" Ruminants (_Cavicornia_), lastly, +came into existence in the Miocene period; and though the typical +families of the Sheep and Oxen are apparently wanting, there are +true Antelopes, together with forms which, if systematically +referable to the _Antilopidoe_, nevertheless are more or less +clearly transitional between this and the family of the Sheep and +Goats. Thus the _Paloeoreas_ of the Upper Miocene of Greece may +be regarded as a genuine Antelope; but the _Tragoceras_ of the +same deposit is intermediate in its characters between the typical +Antelopes and the Goats. Perhaps the most remarkable, however, +of these Miocene Ruminants is the _Sivatherium giganteum_ (fig. +245) of the Siwâlik Hills, in India. In this extraordinary animal +there were two pairs of horns, supported by bony "horn-cores," +so that there can be no hesitation in referring _Sivatherium_ +to the Cavicorn Ruminants. If all these horns had been simple, +there would have been no difficulty in considering _Sivatherium_ +as simply a gigantic four-horned Antelope, essentially similar +to the living _Antilope_ (_Tetraceros_) _quadricornis_ of India. +The hinder pair of horns, however, is not only much larger than +the front pair, but each possesses two branches or snags--a +peculiarity not to be paralleled amongst any existing Antelope, +save the abnormal Prongbuck (_Antilocapra_) of North America. +Dr Murie, however, in an admirable memoir on the structure and +relationships of _Sivatherium_, has drawn attention to the fact +that the Prongbuck sheds the _sheath_ of its horns annually, +and has suggested that this may also have been the case with +the extinct form. This conjecture is rendered probable, amongst +other reasons, by the fact that no traces of a horny sheath +surrounding the horn-cores of the Indian fossil have been as +yet detected. Upon the whole, therefore, we may regard the +elephantine _Sivatherium_ as being most nearly allied to the +Prongbuck of Western America, and thus as belonging to the family +of the Antelopes. + +[Illustration: Fig. 245.--Skull of _Sivatherium giganteum_, reduced +in size. Miocene, India. (After Murie.)] + +It is to the Miocene period, again, to which we must refer the +first appearance of the important order of the Elephants and +their allies (_Proboscideans_), all of which are characterised +by their elongated trunk-like noses, the possession of five toes +to the foot, the absence of canine teeth, the development of two +or more of the incisor teeth into long tusks, and the adaptation +of the molar teeth to a vegetable diet. Only three generic groups +of this order are known-namely, the extinct _Deinotherium_, the +equally extinct _Mastodons_, and the _Elephants_; and all these +three types are known to have been in existence as early as the +Miocene period, the first of them being exclusively confined to +deposits of this age. Of the three, the genus _Deinotherium_ +is much the most abnormal in its characters; so much so, that +good authorities regard it as really being one of the Sea-cows +(_Sirenia_)--though this view has been rendered untenable by +the discovery of limb-bones which can hardly belong to any other +animal, and which are distinctly Proboscidean in type. The most +celebrated skull of the Deinothere (fig. 246) is one which was +exhumed from the Upper Miocene deposits of Epplesheim, in +Hesse-Darmstadt, in the year 1836. This skull was four and a half +feet in length, and indicated an animal larger than any existing +species of Elephant. The upper jaw is destitute of incisor or +canine teeth, but is furnished on each side with five molars, +which are opposed to a corresponding series of grinding teeth in +the lower jaw. No canines are present in the lower jaw; but the +front portion of the jaw is abruptly bent downwards, and carries +two huge tusk-like incisor teeth, which are curved downwards and +backwards, and the use of which is rather problematical. Not +only does the Deinothere occur in Europe, but remains belonging +to this genus have also been detected in the Siwâlik Hills, in +India. + +[Illustration: Fig. 246.--Skull of _Deinotherium giganteum_, greatly +reduced. From the Upper Micene of Germany.] + +The true Elephants (_Elephas_) do not appear to have existed +during the Miocene period in Europe, but several species have +been detected in the Upper Miocene deposits of the Siwâlik Hills, +in India. The fossil forms, though in all cases specifically, and +in some cases even sub-generically, distinct, agree with those +now in existence in the general conformation of their skeleton, +and in the principal characters of their dentition. In all, the +canine teeth are wanting in both jaws; and there are no incisor +teeth in the lower jaw, whilst there are two incisors in the +front of the upper jaw, which are developed into two huge "tusks." +There are six molar teeth on each side of both the upper and lower +jaw, but only one, or at most a part of two, is in actual use +at any given time; and as this becomes worn away, it is pushed +forward and replaced by its successor behind it. The molars are of +very large size, and are each composed of a number of transverse +plates of enamel united together by ivory; and by the process +of mastication, the teeth become worn down to a flat surface, +crossed by the enamel-ridges in varying patterns; These patterns +are different in the different species of Elephants, though constant +for each; and they constitute one of the most readily available +means of separating the fossil forms from one another. Of the +seven Miocene Elephants of India, as judged by the characters of +the molar, teeth, two are allied to the existing Indian Elephant, +one is related to the living African Elephant, and the remaining +four are in some respects intermediate between the true Elephants +and the Mastodons. + +[Illustration: Fig. 247.--A, Molar tooth of _Elephas planifrons_, +one-third of the natural size, showing the grinding surface--from +the Upper Miocene of India; B, Profile view of the last upper molar +of _Mastodon Sivalensis_, one-third of the natural size--from +the Upper Miocene of India. (After Falconer.)] + +The _Mastodons_, lastly, though quite elephantine in their general +characters, possess molar teeth which have their crowns furnished +with conical eminences or tubercles placed in pairs (fig. 247, B), +instead of having the approximately flat surface characteristic +of the grinders of the Elephants. As in the latter, there are two +upper incisor teeth, which grow permanently during the life of +the animal, and which constitute great tusks; but the Mastodons, +in addition, often possess two lower incisors, which in some +cases likewise grow into small tusks. Three species of _Mastodon_ +are known to occur in the Upper Miocene of the Siwâlik Hills +of India; and the Miocene deposits of the European area have +yielded the remains of four species, of which the best known are +the _M. Longirostris_ and the _M. Angustidens_. + +Whilst herbivorous Quadrupeds, as we have seen, were extremely +abundant during Miocene times, and often attained gigantic +dimensions, Beasts of Prey (_Carnivora_) were by no means wanting, +most of the principal existing families of the order being +represented in deposits of this age. Thus, we find aquatic Carnivores +belonging to both the living groups of the Seals and Walruses; +true Bears are wanting, but their place is filled by the +closely-allied genus _Amphicyon_, of which various species are +known; Weasels and Otters were not unknown, and the _Hyoenictis_ +and _Iditherium_ of the Upper Miocene of Greece are apparently +intermediate between the Civet-cats and the Hyænas; whilst the great +Cats of subsequent periods are more than adequately represented by +the huge "Sabre-toothed Tiger" (_Machairodus_), with its immense +trenchant and serrated canine teeth. + +Amongst the _Rodent_ Mammals, the Miocene rocks have yielded +remains of Rabbits, Porcupines (such as the _Hystrix primigenius_ +of Greece), Beavers, Mice, Jerboas, Squirrels, and Marmots. All the +principal living groups of this order were therefore differentiated +in Middle Tertiary times. + +The _Cheiroptera_ are represented by small insect-eating Bats; +and the order of the Insectivorous Mammals is represented by +Moles, Shrew-mice, and Hedgehogs. + +[Illustration: Fig. 248.--Lower jaw of _Pliopithcus antiquus_. +Upper Miocene, France.] + +Lastly, the Monkeys (_Quadrumana_) appear to have existed during +the Miocene period under a variety of forms, remains of these +animals having been found both in Europe and in India; but no member +of this order has as yet been detected in the Miocene Tertiary of +the North American continent. Amongst the Old World Monkeys of +the Miocene, the two most interesting are the _Pliopithecus_ +and _Dryopithecus_ of France. The former of these (fig. 248) +is supposed to have been most nearly related to the living +_Semnopitheci_ of Southern Asia, in which case it must have possessed +a long tail. The _Mesopithecus_ of the Upper Miocene of Greece is +also one of the lower Monkeys, as it is most closely allied to +the existing Macaques. On the other hand, the _Dryopithecus_ +of the French Upper Miocene is referable to the group of the +"Anthropoid Apes," and is most nearly related to the Gibbons +of the present day, in which the tail is rudimentary and there +are no cheek-pouches. _Dryopithecus_ was, also, of large size, +equalling Man in stature, and apparently living amongst the trees +and feeding upon fruits. + + + + +CHAPTER XX. + +THE PLIOCENE PERIOD. + +The highest division of the Tertiary deposits is termed the +_Pliocene_ formation, in accordance with the classification proposed +by Sir Charles Lyell. The Pliocene formations contain from 40 to +95 per cent of existing species of _Mollusca_, the remainders +belonging to extinct species. They are divided by Sir Charles +Lyell into two divisions, the Older Pliocene and Newer Pliocene. + +The Pliocene deposits of Britain occur in Suffolk, and are known +by the name of "Crags," this being a local term used for certain +shelly sands, which are employed in agriculture. Two of these +Crags are referable to the Older Pliocene, viz., the White and +Red Crags,--and one belongs to the Newer Pliocene, viz., the +Norwich Crag. + +The _White or Coralline Crag_ of Suffolk is the oldest of the +Pliocene deposits of Britain, and is an exceedingly local formation, +occurring in but a single small area, and having a maximum thickness +of not more than 50 feet. It consists of soft sands, with occasional +intercalations of flaggy limestone. Though of small extent and +thickness, the Coralline Crag is of importance from the number +of fossils which it contains. The name "Coralline" is a misnomer; +since there are few true Corals, and the so-called "Corals" of +the formation are really _Polyzoa_, often of very singular forms. +The shells of the Coralline Crag are mostly such as inhabit the +seas of temperate regions; but there occur some forms usually +looked upon as indicating a warm climate. + +The _Upper_ or _Red Crag_ of Suffolk--like the Coralline Crag--has +a limited geographical extent and a small thickness, rarely exceeding +40 feet. It consists of quartzose sands, usually deep red or +brown in colour, and charged with numerous fossils. + +Altogether more than 200 species of shells are known from the +Red Crag, of which 60 per cent are referable to existing species. +The shells indicate, upon the whole, a temperate or even cold +climate, decidedly less warm than that indicated by the organic +remains of the Coralline Crag. It appears, therefore, that a +gradual refrigeration was going on during the Pliocene period, +commencing in the Coralline Crag, becoming intensified in the Red +Crag, being still more severe in the Norwich Crag, and finally +culminating in the Arctic cold of the Glacial period. + +Besides the _Mollusca_, the Red Crag contains the ear-bones of +Whales, the teeth of Sharks and Rays, and remains of the Mastodon, +Rhinoceros, and Tapir. + +The _Newer Pliocene_ deposits are represented in Britain by the +_Norwich Crag_, a local formation occurring near Norwich. It +consists of incoherent sands, loams, and gravels, resting in +detached patches, from 2 to 20 feet in thickness, upon an eroded +surface of Chalk. The Norwich Crag contains a mixture of marine, +land, and fresh-water shells, with remains of fishes and bones +of mammals; so that it must have been deposited as a local +sea-deposit near the mouth of an ancient river. It contains +altogether more than 100 marine shells, of which 89 per cent +belong to existing species. Of the Mammals, the two most important +are an Elephant (_Elephas meridionalis_), and the characteristic +Pliocene Mastodon (_M. Arvernensis_), which is hitherto the only +Mastodon found in Britain. + +According to the most recent views of high authorities, certain +deposits--such as the so-called "Bridlington Crag" of Yorkshire, +and the "Chillesford beds" of Suffolk--are to be also included +in the Newer Pliocene, upon the ground that they contain a small +proportion of extinct shells. Our knowledge, however, of the +existing Molluscan fauna, is still so far incomplete, that it +may reasonably be doubted if these supposed extinct forms have +actually made their final disappearance, whilst the strata in +question have a strong natural connection with the "Glacial +deposits," as shown by the number of Arctic Mollusca which they +contain. Here, therefore, these beds will be included in the +Post-Pliocene series, in spite of the fact that some of their +species of shells are not known to exist at the present day. + +The following are the more important Pliocene deposits which have +been hitherto recognised out of Britain:-- + +1. In the neighbourhood of Antwerp occur certain "crags," which +are the equivalent of the White and Red Crag in part. The lowest +of these contains less than 50 per cent, and the highest 60 per +cent, of existing species of shells, the remainder being extinct. + +2. Bordering the chain of the Apennines, in Italy, on both sides +is a series of low hills made up of Tertiary strata, which are +known as the Sub-Apennine beds. Part of these is of Miocene age, +part is Older Pliocene, and a portion is Newer Pliocene. The +Older Pliocene portion of the Sub-Apennines consists of blue or +brown marls, which sometimes attain a thickness of 2000 feet. + +3. In the valley of the Arno, above Florence, are both Older +and Newer Pliocene strata. The former consist of blue clays and +lignites, with an abundance of plants. The latter consist of sands +and conglomerates, with remains of large Carnivorous Mammals, +Mastodon, Elephant, Rhinoceros, Hippopotamus, &c. + +4. In Sicily, Newer Pliocene strata are probably more largely +developed than anywhere else in the world, rising sometimes to a +height of 3000 feet above the sea. The series consists of clays, +marls, sands, and conglomerates, capped by a compact limestone, +which attains a thickness of from 700 to 800 feet. The fossils of +these beds belong almost entirely to living species, one of the +commonest being the Great Scallop of the Mediterranean (_Pecten +Jacoboeus_). + +5. Occupying an extensive area round the Caspian, Aral, and Azof +Seas, are Pliocene deposits known as the "Aralo-Caspian" beds. +The fossils in these beds are partly freshwater, partly marine, +and partly intermediate in character, and they are in great part +identical with species now inhabiting the Caspian. The entire +formation appears to indicate the former existence of a great +sheet of brackish water, forming an inland sea, like the Caspian, +but as large as, or larger than, the Mediterranean. + +6. In the United States, strata of Pliocene age are found in +North and South Carolina. They consist of sands and clays, with +numerous fossils, chiefly _Molluscs_ and _Echinoderms_. From 40 +to 60 per cent of the fossils belong to existing species. On +the Loup Fork of the river Platte, in the Upper Missouri region, +are strata which are also believed to be referable to the Pliocene +period, and probably to its upper division. They are from 300 to +400 feet thick, and contain land-shells, with the bones of numerous +Mammals, such as Camels, Rhinoceroses, Mastodons, Elephants, the +Horse, Stag, &c. + +As regards the _life_ of the Pliocene period, there are only +two classes of organisms to which our attention need be +directed--namely, the Shell-fish and the Mammals. So far as the +former are concerned, we have to note in the first place that +the introduction of new species of animals upon the globe went +on rapidly during this period. In the Older Pliocene deposits, +the number of shells of existing species is only from 40 to 60 +per cent; but in the Newer Pliocene the proportion of living +forms rises to as much as from 80 to 95 per cent. Whilst the +Molluscs thus become rapidly modernised, the Mammals still all +belong to extinct species, though modern generic types gradually +supersede the more antiquated forms of the Miocene. In the second +place, there is good evidence to show that the Pliocene period +was one in which the climate of the northern hemisphere underwent +a gradual refrigeration. In the Miocene period, there is evidence +to show that Europe possessed a climate very similar to that +now enjoyed by the Southern United States, and certainly very +much warmer than it is at present. The presence of Palm-trees +upon the land, and of numerous large Cowries, Cones, and other +shells of warm regions in the sea, sufficiently proves this. In +the Older Pliocene deposits, on the other hand, northern forms +predominate amongst the Shells, though some of the types of hotter +regions still survive. In the Newer Pliocene, again, the Molluscs +are such as almost exclusively inhabit the seas of temperate +or even cold regions; whilst if we regard deposits like the +"Bridlington Crag" and "Chillesford beds" as truly referable to +this period, we meet at the close of this period with shells such +as nowadays are distinctively characteristic of high latitudes. It +might be thought that the occurrence of Quadrupeds such as the +Elephant, Rhinoceros, and Hippopotamus, would militate against +this generalisation, and would rather support the view that the +climate of Europe and the United States must have been a hot +one during the later portion of the Pliocene period. We have, +however, reason to believe that many of these extinct Mammals +were more abundantly furnished with hair, and more adapted to +withstand a cool temperature, than any of their living congeners. +We have also to recollect that many of these large herbivorous +quadrupeds may have been, and indeed probably were, more or less +migratory in their habits; and that whilst the winters of the +later portion of the Pliocene period were cold, the summers might +have been very hot. This would allow of a northward migration +of such terrestrial animals during the summer-time, when there +would be an ample supply of food and a suitably high temperature, +and a southward recession towards the approach of winter. + +The chief palæontological interests of the Pliocene deposits, +as of the succeeding Post-Pliocene, centre round the Mammals of +the period; and amongst the many forms of these we may restrict +our attention to the orders of the Hoofed Quadrupeds (_Ungulates_), +the _Proboscideans_, the _Carnivora_, and the _Quadrumana_. Almost +all the other Mammalian orders are more or less fully represented +in Pliocene times, but none of them attains any special interest +till we enter upon the Post-Pliocene. + +Amongst the Odd-toed Ungulates, in addition to the remains of +true Tapirs (_Tapirus Arvernensis_), we meet with the bones of +several species of Rhinoceros, of which the _Rhinoceros Etruscus_ +and _R. Megarhinus_ (fig. 249) are the most important. The former +of these (fig. 249, A) derives its specific name from its abundance +in the Pliocene deposits of the Val d'Arno, near Florence, and +though principally Pliocene in its distribution, it survived +into the earlier portion of the Post-Pliocene period. _Rhinoceros +Etruscus_ agreed with the existing African forms in having two +horns placed one behind the other, the front one being the longest; +but it was comparatively slight and slender in its build, whilst +the nostrils were separated by an incomplete bony partition. In +the _Rhinoceros megarhinus_ (fig. 249, B), on the other hand, no +such partition exists between the nostrils, and the nasal bones +are greatly developed in size. It was a two-horned form, and is +found associated with _Elephas meridionalis_ and _E. Antiquus_ in +the Pliocene deposits of the Val d'Arno, near Florence. Like the +preceding, it survived, in diminished numbers, into the earlier +portion of the Post-Pliocene period. + +[Illustration: Fig. 249.--A. Under surface of the skull of +_Rhinoceros Etruscus_, one-seventh of the natural size--Pliocene, +Italy.; B, Crowns of the three true molars of the upper jaw, left +side, of _Rhinoceros megarhinus_ (_R. Leptorhinus_, Falconer), +one-half of the natural size--Pliocene, France. (After Falconer.)] + +The Horses (_Equidoe_) are represented, both in Europe and America, +by the three-toed Hipparions, which survive from the Miocene, +but are now verging upon extinction. For the first time, also, +we meet with genuine Horses (_Equus_), in which each foot is +provided with a single complete toe only, encased in a single +broad hoof. One of the American species of this period (the _Equus +excelsus_) quite equalled the modern Horse in stature; and it +is interesting to note the occurrence of indigenous horses in +America at such a comparatively late geological epoch, seeing +that this continent certainly possessed none of these animals +when first discovered by the Spaniards. + +Amongst the Even-toed Ungulates, we may note the occurrence of +Swine (_Suida_), of forms allied to the Camels (_Camelidoe_), and +of various kinds of Deer (_Cervidoe_); but the most interesting +Pliocene Mammal belonging to this section is the great _Hippopotamus +major_ of Britain and Europe. This well-known species is very +closely allied to the living _Hippopotamus amphibius_ of Africa, +from which it is separated only by its larger dimensions, and by +certain points connected with the conformation of the skeleton. +It is found very abundantly in the Pliocene deposits of Italy and +France, associated with the remains of the Elephant, Mastodon, +and Rhinoceros, and it survived into the earlier portion of the +Post-Pliocene period. During this last-mentioned period, it extended +its range northwards, and is found associated with the Reindeer, +the Bison, and other northern animals. From this fact it has been +inferred, with great probability, that the _Hippotamus major_ +was furnished with a long coat of hair and fur, thus differing +from its nearly hairless modern representative, and resembling +its associates, the Mammoth and the Woolly Rhinoceros. + +[Illustration: Fig. 250.--Third milk-molar of the left side of +the upper jaw of _Mastodon Arvernensis_, showing the grinding +surface. Pliocene.] + +Passing on to the Pliocene Proboscideans, we find that the great +_Deinotheria_ of the Miocene have now wholly disappeared, and the +sole representatives of the order are Mastodons and Elephants. +The most important member of the former group is the _Mastodon +Arvernensis_ (fig. 250), which ranged widely over Southern Europe +and England, being generally associated with remains of the _Elephas +meridionalis, E. antiquus, Rhinoceros megarhinus_, and _Hippopotamus +major_. The lower jaw seems to have been destitute of incisor +teeth; but the upper incisors are developed into great tusks, +which sometimes reach a length of nine feet, and which have the +simple curvature of the tusks of the existing Elephants. Amongst +the Pliocene Elephants the two most important are the _Elephas +meridionalis_ and the _Elephas antiquus_. Of these, the _Elephas +meridionalis_ (fig. 251) is found abundantly in the Pliocene +deposits of Southern Europe and England, and also survived into +the earlier portion of the Post-Pliocene period. Its molar teeth +are of the type of those of the existing African Elephant, the +spaces enclosed by the transverse enamel-plates being more or +less lozenge-shaped, whilst the curvature of the tusks is simple. +The _Elephas antiquus_ (fig. 252) is very generally associated +with the preceding, and it survived to an even later stage of +the Post-Pliocene period. The molar teeth are of the type of the +existing Indian Elephant, with comparatively thin enamel-ridges, +placed closer together than in the African type; whilst the tusks +were nearly straight. + +[Illustration: Fig. 251.--Molar tooth of _Elephas meridionalis_, +one-third of the natural size. Pliocene and Post-Pliocene.] + +[Illustration: Fig. 252.--Molar tooth of _Elephas antiquus_, +one-third of the natural size. Pliocene and Post-Pliocene.] + +Amongst the Pliocene _Carnivores_, we meet with true Bears (_Ursus +Arvernensis_), Hyænas (such as _Hyoena Hipparionum_), and genuine +Lions (such as the _Felis angustus_ of North America); but the +most remarkable of the beasts of prey of this period is the great +"Sabre-toothed Tiger" (_Machairodus_), species of which existed +in the earlier Miocene, and survived to the later Post-Pliocene. +In this remarkable form we are presented with perhaps the most +highly carnivorous type of all known beasts of prey. Not only +are the jaws shorter in proportion even than those of the great +Cats of the present day, but the canine teeth (fig. 253) are +of enormous size, greatly flattened so as to assume the form +of a poignard, and having their margins finely serrated. A part +from the characters of the skull, the remainder of the skeleton, +so far as known, exhibits proofs that the Sabre-toothed Tiger +was extraordinarily muscular and powerful, and in the highest +degree adapted for a life of rapine. Species of _Machairodus_ +must have been as large as the existing Lion; and the genus is +not only European, but is represented both in South America and +in India, so that the geographical range of these predaceous +beasts must have been very extensive. + +[Illustration: Fig. 253.--A, Skull of _Machairodus cultridens_, +without the lower jaw, reduced in size; B, Canine tooth of the +same, one-half the natural size. Pliocene, France.] + +Lastly, we may note that the Pliocene deposits of Europe have +yielded the remains of Monkeys (_Quadrumana_), allied to the +existing _Semnopitheci_ and Macaques. + + +LITERATURE. + +The following list comprises a small selection of some of the +more important and readily accessible works and memoirs relating +to the Tertiary rocks and their fossils. With few exceptions, +foreign works relating to the Tertiary strata of the continent +of Europe or their organic remains have been omitted:-- + + (1) 'Elements of Geology.' Lyell. + (2) 'Students' Elements of Geology.' Lyell. + (3) 'Manual of Palæontology.' Owen. + (4) 'British Fossil Mammals and Birds.' Owen. + (5) 'Traité de Paléontologie.' Pictet. + (6) 'Cours Elémentaire de Paléontologie.' D'Orbigny. + (7) "Probable Age of the London Clay," &c.--'Quart. Journ. Geol. + Soc.,' vol. iii. Prestwich. + (8) 'Structure and Probable Age of the Bagshot Sands'--Ibid., vol. + iii. Prestwich. + (9) 'Tertiary Formations of the Isle of Wight'--Ibid., vol. ii. + Prestwich. +(10) 'Structure of the Strata between the London Clay and the + Chalk,' &c.--Ibid., vols. vi., viii., and x. Prestwich. +(11) 'Correlation of the Eocene Tertiaries of England, France, + and Belgium'--Ibid., vol. xxvii. Prestwich. +(12) 'On the Fluvio-marine Formations of the Isle of Wight'--Ibid., + vol. ix. Edward Forbes. +(13) 'Newer Tertiary Deposits of the Sussex Coast'--Ibid., vol. + xiii. Godwin-Austen. +(14) 'Kainozoic Formations of Belgium'--Ibid., vol. xxii. + Godwin-Austen. +(15) 'Tertiary Strata of Belgium and French Flanders'--Ibid., + vol. viii. Lyell. +(16) 'On Tertiary Leaf-beds in the Isle of Mull'--Ibid., vol. vii. + The Duke of Argyll. +(17) 'Newer Tertiaries of Suffolk and their Fauna'--Ibid., vol. + xxvi. Ray Lankester. +(18) 'Lower London Tertiaries of Kent'--Ibid., vol. xxii. Whitaker. +(19) "Guide to the Geology of London"--'Mem. Geol. Survey.' + Whitaker. +(20) 'Memoirs of the Geological Survey of Great Britain.' +(21) 'Introductory Outline of the Geology of the Crag District' + (Supplement to Crag Mollusca, Palæontographical Society). S. V. + Wood, jun., and F. w. Harmer. +(22) "Tertiary Fluvio-marine Deposits of the Isle of Wight." Edward + Forbes. Edited by Godwin-Austen; with Descriptions of the + Fossils by Morris, Salter, and Rupert Jones--'Memoirs of the + Geological Survey.' +(23) 'Geological Excursions round the Isle of Wight.' Mantell. +(24) 'Catalogue of British Fossils.' Morris. +(25) 'Catalogue of Fossils in the Museum of Practical Geology.' + Etheridge. +(26) 'Monograph of the Crag Polyzoa' (Palæontographical Society). Busk. +(27) 'Monograph of the Tertiary Brachiopoda' (Ibid.) Davidson. +(28) 'Monograph of the Tertiary Malacostracous Crustacea' (Ibid.) + Bell. +(29) 'Monograph of the Tertiary Corals' (Ibid.) Milne-Edwards and + Haime. +(30) 'Supplement to the Tertiary Corals' (Ibid.) Martin Duncan. +(31) 'Monograph of the Eocene Mollusca' (Ibid.) Fred. E. Edwards. +(32) 'Monograph of the Eocene Mollusca' (Ibid.) Searles V. Wood. +(33) 'Monograph of the Crag Mollusca' (Ibid.) Searles V. Wood. +(34) 'Monograph of the Tertiary Entomostraca' (Ibid.) Rupert Jones. +(35) 'Monograph of the Foraminifera of the Crag' (Ibid.) Rupert Jones, + Parker, and H. B. Brady. +(36) 'Monograph of the Radiaria of the London Clay' (Ibid.) Edward + Forbes. +(37) 'Monograph of the Cetacea of the Red Crag' (Ibid.) Owen. +(38) 'Monograph of the Fossil Reptiles of the London Clay' (Ibid.) + Owen and Bell. +(39) "On the Skull of a Dentigerous Bird from the London Clay of + Sheppey"--'Quart. Journ. Geol. Soc.,' vol. xxix. Owen. +(40) 'Ossemens Fossiles.' Cuvier. +(41) 'Fauna Antiqua Sivalensis.' Falconer and Sir Proby Cautley. +(42) 'Palæontological Memoirs.' Falconer. +(43) 'Animaux Fossiles et Géologie de l'Attique.' Gaudry. +(44) "Principal Characters of the Dinocerata"--'American Journ. of + Science and Arts,' vol. xi. Marsh. +(45) 'Principal Characters of the Brontotheridæ' (Ibid.) Marsh. +(46) 'Principal Characters of the Tillodontia' (Ibid.) Marsh. +(47) "Extinct Vertebrata of the Eocene of Wyoming"--'Geological + Survey of Montana,' &c., 1872. Cope. +(48) "Ancient Fauna of Nebraska"--'Smithsonian Contributions to + Knowledge,' vol. vi. Leidy. +(49) 'Manual of Geology.' Dana. +(50) "Palæontology and Evolution" (Presidential Address to the + Geological Society of London, 1870)--'Quart. Journ. Geol. + Soc.,' vol. xxvi. Huxley.' +(51) 'Mineral Conchology.' Sowerby. +(52) 'Description des Coquilles Fossiles,' &c. Deshayes. +(53) 'Description des Coquilles Tertiaires de Belgique.' Nyst. +(54) 'Fossilen Polypen des Wiener Tertiär-beckens.' Reuss. +(55) 'Palæontologische Studien über die älteren Tertiär-schichten + der Alpen.' Reuss. +(56) 'Land und Süss-wasser Conchylien der Vorwelt.' Sandberger. +(57) 'Flora Tertiaria Helvetica.' Heer. +(58) 'Flora Fossilis Arctica.' Heer. +(59) 'Recherches sur le Climat et la Végétation du Pays + Tertiaire.' Heer. +(60) 'Fossil Flora of Great Britain.' Lindley and Hutton. +(61) 'Fossil Fruits and Seeds of the London Clay.' Bowerbank. +(62) "Tertiary Leaf-beds of the Isle of Mull"--'Quart. Journ. + Geol. Soc.,' vol. vii. Edward Forbes. +(63) 'The Geology of England and Wales.' Horace B. Woodward.[25] + +[Footnote 25: This work--published whilst these sheets were going +through the press--gives to the student a detailed view of all the +strata of England and Wales, with their various sub-divisions, +from the base of the Palæozoic to the top of the Tertiary.] + + + + +CHAPTER XXI. + +THE QUATERNARY PERIOD. + +THE POST-PLIOCENE PERIOD. + +Later than any of the Tertiary formations are various detached +and more or less superficial accumulations, which are generally +spoken of as the _Post-Tertiary formations_, in accordance with +the nomenclature of Sir Charles Lyell--or as the _Quaternary +formations_, in accordance with the general usage of Continental +geologists. In all these formations we meet with no _Mollusca_ +except such as are now alive--with the partial and very limited +exception of some of the oldest deposits of this period, in which +a few of the shells occasionally belong to species not known +to be in existence at the present day. Whilst the _Shell-fish_ +of the Quaternary deposits are, generally speaking, identical +with existing forms, the _Mammals_ are sometimes referable to +living, sometimes to extinct species. In accordance with this, +the Quaternary formations are divided into two groups: (1) The +_Post-Pliocene_, in which the shells are almost invariably referable +to existing species, but some of the _Mammals are extinct_; and +(2) the _Recent_, in which _the shells and the Mammals alike +belong to existing species_. The Post-Pliocene deposits are often +spoken of as the Pleistocene formations (Gr. _pleistos_, most; +_kainos_, new or recent), in allusion to the fact that the great +majority of the living beings of this period belong to the species +characteristic of the "new" or Recent period. + +The _Recent_ deposits, though of the highest possible interest, +do not properly concern the palæontologist strictly so-called, but +the zoologist, since they contain the remains of none but existing +animals. They are "Pre-historic," but they belong entirely to +the existing terrestrial order. The _Post-Pliocene_ deposits, on +the other hand, contain the remains of various extinct Mammals; +and though Man undoubtedly existed in, at any rate, the later +portion of this period, if not throughout the whole of it, they +properly form part of the domain of the palæontologist. + +The Post-Pliocene deposits are extremely varied, and very widely +distributed; and owing to the mode of their occurrence, the ordinary +geological tests of age are in their case but very partially +available. The subject of the classification of these deposits +is therefore an extremely complicated one; and as regards the age +of even some of the most important of them, there still exists +considerable difference of opinion. For our present purpose, it +will be convenient to adopt a classification of the Post-Pliocene +deposits founded on the relations which they bear in time to the +great "Ice-age" or "Glacial period;" though it is not pretended +that our present knowledge is sufficient to render such a +classification more than a provisional one. + +In the early Tertiary period, as we have seen, the climate of the +northern hemisphere, as shown by the Eocene animals and plants, +was very much hotter than it is at present--partaking, indeed, of a +sub-tropical character. In the Middle Tertiary or Miocene period, +the temperature, though not so high, was still much warmer than +that now enjoyed by the northern hemisphere; and we know that the +plants of temperate regions at this time flourished within the +Arctic circle. In the later Tertiary or Pliocene period, again, +there is evidence that the northern hemisphere underwent a further +progressive diminution of temperature; though the climate of Europe +generally seems at the close of the Tertiary period to have been +if anything warmer, or at any rate not colder, than it is at +the present day. With the commencement of the Quaternary period, +however, this diminution of temperature became more decided; and +beginning with a temperate climate, we find the greater portion +of the northern hemisphere to become gradually subjected to all +the rigours of intense Arctic cold. All the mountainous regions +of Northern and Central Europe, of Britain, and of North America, +became the nurseries of huge ice-streams, and large areas of the +land appear to have been covered with a continuous ice-sheet. +The Arctic conditions of this, the well-known "Glacial period," +relaxed more than once, and were more than once re-established +with lesser intensity. Finally, a gradual but steadily progressive +amelioration of temperature took place; the ice slowly gave way, +and ultimately disappeared altogether; and the climate once more +became temperate, except in high northern latitudes. + +The changes of temperature sketched out above took place slowly +and gradually, and occupied the whole of the Post-Pliocene period. +In each of the three periods marked out by these changes--in +the early temperate, the central cold, and the later temperate +period--certain deposits were laid down over the surface of the +northern hemisphere; and these deposits collectively constitute the +Post-Pliocene formations. Hence we may conveniently classify all +the accumulations of this age under the heads of (1) _Pre-Glacial_ +deposits, (2) _Glacial_ deposits, and (3) _Post-Glacial_ deposits, +according as they were formed before, during, or after the "Glacial +period." It cannot by any means be asserted that we can definitely +fix the precise relations in time of all the Post-Pliocene deposits +to the Glacial period. On the contrary, there are some which +hold a very disputed position as regards this point; and there +are others which do not admit of definite allocation in this +manner at all, in consequence of their occurrence in regions +where no "Glacial Period" is known to have been established. +For our present purpose, however, dealing as we shall have to do +principally with the northern hemisphere, the above classification, +with all its defects, has greater advantages than any other that +has been yet proposed. + +I. PRE-GLACIAL DEPOSITS.--The chief pre-glacial deposit of Britain +is found on the Norfolk coast, reposing upon the Newer Pliocene +(Norwich Crag), and consists of an ancient land-surface which +is known as the "Cromer Forest-bed." + +This consists of an ancient soil, having embedded in it the stumps +of many trees, still in an erect position, with remains of living +plants, and the bones of recent and extinct quadrupeds. It is +overlaid by fresh-water and marine beds, all the shells of which +belong to existing species, and it is finally surmounted by true +"glacial drift." While all the shells and plants of the Cromer +Forest-bed and its associated strata belong to existing species, +the Mammals are partly living, partly extinct. Thus we find the +existing Wolf (_Canis lupus_), Red Deer (_Cervus elaphus_), Roebuck +(_Cervus capreolus_), Mole (_Talpa Europtoea_), and Beaver (_Castor +fiber_), living in western England side by side with the +_Hippopotamus major, Elephas antiquus, Elephas meridionalis, +Rhinoceros Etruscus_, and _R. Megarhinus_ of the Pliocene period, +which are not only extinct, but imply an at any rate moderately +warm climate. Besides the above, the Forest-bed has yielded the +remains of several extinct species of Deer, of the great extinct +Beaver (_Trogontherium Cuvieri_), of the Caledonian Bull or "Urus" +(_Bos primigenius_), and of a Horse (_Equus fossilis_), little +if at all distinguishable from the existing form. + +The so-called "Bridlington Crag" of Yorkshire, and the "Chillesford +Beds" of Suffolk, are probably to be regarded as also belonging +to this period; though many of the shells which they contain +are of an Arctic character, and would indicate that they were +deposited in the commencement of the Glacial period itself. Owing, +however, to the fact that a few of the shells of these deposits +are not known to occur in a living condition, these, and some +other similar accumulations, are sometimes considered as referable +to the Pliocene period. + +II. GLACIAL DEPOSITS.--Under this head is included a great series +of deposits which are widely spread over both Europe and America, +and which were formed at a time when the climate of these countries +was very much colder than it is at present, and approached more +or less closely to what we see at the present day in the Arctic +regions. These deposits are known by the general name of the +_Glacial deposits_, or by the more specialised names of the Drift, +the Northern Drift, the Boulder-clay, the Till, &c. + +These glacial deposits are found in Britain as far south as the +Thames, over the whole of Northern Europe, in all the more elevated +portions of Southern and Central Europe, and over the whole of +North America, as far south as the 39th parallel. They generally +occur as sands, clays, and gravels, spread in widely-extended +sheets over all the geological formations alike, except the most +recent, and are commonly spoken of under the general term of +"Glacial drift." They vary much in their exact nature in different +districts, but they universally consist of one, or all, of the +following members:-- + +1. _Unstratified_ clays, or loams, containing numerous angular +or sub-angular blocks of stone, which have often been transported +for a greater or less distance from their parent rock, and which +often exhibit polished, grooved, or striated surfaces. These +beds are what is called _Boulder-clay_, or _Till_. + +2. Sands, gravels, and clays, often more or less regularly +_stratified_, but containing erratic blocks, often of large size, +and with their edges _unworn_, derived from considerable distances +from the place where they are now found. In these beds it is +not at all uncommon to find fossil shells; and these, though of +existing species, are generally of an Arctic character, comprising +a greater or less number of forms which are now exclusively found +in the icy waters of the Arctic seas. These beds are often spoken +of as "Stratified Drift." + +3. _Stratified_ sands and gravels, in which the pebbles are _worn_ +and rounded, and which have been produced by a rearrangement of +ordinary glacial beds by the sea. These beds are commonly known +as "Drift-gravels," or "Regenerated Drift". + +Some of the last-mentioned of these are doubtless post-glacial; +but, in the absence of fossils, it is often impossible to arrive at +a positive opinion as to the precise age of superficial accumulations +of this nature. It is also the opinion of high authorities that a +considerable number of the so-called "cave-deposits," with the +bones of extinct Mammals, truly belong to the Glacial period, +being formed during warm intervals when the severity of the Arctic +cold had become relaxed. It is further believed that some, at +any rate, of the so-called "high-level" river-gravels and +"brick-earths" have likewise been deposited during mild or warm +intervals in the great age of ice; and in two or three instances +this has apparently been demonstrated--deposits of this nature, +with the bones of extinct animals and the implements of man, +having been shown to be overlaid by true Boulder-clay. + +The fossils of the undoubted Glacial deposits are principally +shells, which are found in great numbers in certain localities, +sometimes with _Foraminifera_, the bivalved cases of Ostracode +Crustaceans, &c. Whilst some of the shells of the "Drift" are such +as now live in the seas of temperate regions, others, as previously +remarked, are such as are now only known to live in the seas of +high latitudes; and these therefore afford unquestionable evidence +of cold conditions. Amongst these Arctic forms of shells which +characterise the Glacial beds may be mentioned _Pecten Islandicus_ +(fig. 254), _Pecten Groenlandicus, Scalaria Groenlandica, Leda +truncata, Astarte borealis, Tellina proxima, Nattra clausa_, +&c. + +[Illustration: Fig. 254.--Left valve of _Pecten Islandicus_, Glacial +and Recent.] + +III. POST-GLACIAL DEPOSITS.--As the intense cold of the Glacial +period became gradually mitigated, and temperate conditions of +climate were once more re-established, various deposits were +formed in the northern hemisphere, which are found to contain +the remains of extinct Mammals, and which, therefore, are clearly +of Post-Pliocene age. To these deposits the general name of +_Post-Glacial_ formations is given; but it is obvious that, from +the nature of the case, and with our present limited knowledge, +we cannot draw a rigid line of demarcation between the deposits +formed towards the close of the Glacial period, or during warm +"interglacial" periods, and those laid down after the ice had +fairly disappeared. Indeed it is extremely improbable that any +such rigid line of demarcation should ever have existed; and it +is far more likely that the Glacial and Post-Glacial periods, +and their corresponding deposits, shade into one another by an +imperceptible gradation. Accepting this reservation, we may group +together, under the general head of "Post-Glacial Deposits," +most of the so-called "Valley-gravels," "Brick-earths," and +"Cave-deposits," together with some "raised beaches" and various +deposits of peat. Though not strictly within the compass of this +work, a few words may be said here as to the origin and mode of +formation of the Brick-earths, Valley-gravels, and Cave-deposits, +as the subject will thus be rendered more clearly intelligible. + +Every river produces at the present day beds of fine mud and +loam, and accumulations of gravel, which it deposits at various +parts of its course--the gravel generally occupying the lowest +position, and the finer sands and mud coming above. Numerous +deposits of a similar nature are found in most countries in various +localities, and at various heights above the present channels of +our rivers. Many of these fluviatile (Lat. _fluvius_, a river) +deposits consist of fine loam, worked for brick-making, and known +as "Brick-earths;" and they have yielded the remains of numerous +extinct Mammals, of which the Mammoth (_Elephas primigenius_) is +the most abundant. In the valley of the Rhine these fluviatile +loams (known as "Loess") attain a thickness of several hundred +feet, and contain land and fresh-water shells of existing species. +With these occur the remains of Mammals, such as the Mammoth and +Woolly Rhinoceros. Many of these Brick-earths are undoubtedly +Post-Glacial, but others seem to be clearly "inter-glacial;" and +instances have recently been brought forward in which deposits +of Brick-earth containing bones and shells of fresh-water Molluscs +have been found to be overlaid by regular unstratified boulder-clay. + +The so-called "Valley-gravels," like the Brick-earths, are fluviatile +deposits, but are of a coarser nature, consisting of sands and +gravels. Every river gives origin to deposits of this kind at +different points along the course of its valley; and it is not +uncommon to find that there exist in the valley of a single river +two or more sets of these gravel-beds, formed by the river itself, +but formed at times when the river ran at different levels, and +therefore formed at different periods. These different accumulations +are known as the "high-level" and "low-level" gravels; and a +reference to the accompanying diagram will explain the origin +and nature of these deposits (fig. 255). When a river begins +to occupy a particular line of drainage, and to form its own +channel, it will deposit fluviatile sands and gravels along its +sides. As it goes on deepening the bed or valley through which +it flows, it will deposit other fluviatile strata at a lower +level beside its new bed. In this way have arisen the terms +"high-level" and "low-level" gravels. We find, for instance, a +modern river flowing through a valley which it has to a great +extent or entirely formed itself; by the side of its immediate +channel we may find gravels, sand, and loam (fig. 255, 2 2') +deposited by the river flowing in its present bed. These are +_recent_ fluviatile or alluvial deposits. At some distance from +the present bed of the river, and at a higher level, we may find +other sands and gravels, quite like the recent ones in character +and origin, but formed at a time when the stream flowed at a higher +level, and before it had excavated its valley to its present +depth. These (fig. 255, 3 3') are the so-called "_low-level_ +gravels" of a river. At a still higher level, and still farther +removed from the present bed of the river, we may find another +terrace, composed of just the same materials as the lower one, +but formed at a still earlier period, when the excavation of +the valley had proceeded to a much less extent. These (fig. 255, +4 4') are the so-called "_high-level_ gravels" of a river, and +there may be one or more terraces of these. + +[Illustration: Fig. 255.--Recent and Post-Pliocene Alluvial Deposits. +1, Peat of the recent period; 2, Gravel of the modern river: +2', Loam of the modern river; 3. Lower-level valley-gravel with +bones of extinct Mammals (Post-Pliocene); 3', Loam of the same +age as 3; 4. Higher-level valley-gravel (Post-Pliocene); 4', +Loam of the same age as 4; 5. Upland gravels of various kinds +(often glacial drift); 6, Older rock. (After Sir Charles Lyell.)] + +The important fact to remember about these fluviatile deposits +is this--that here the ordinary geological rule is reversed. The +high-level gravels are, of course, the highest, so far as their +actual elevation above the sea is concerned; but geologically the +lowest, since they are obviously much older than the low-level +gravels, as these are than the recent gravels. How much older +the high-level gravels may be than the low-level ones, it is +impossible to say. They occur at heights varying from 10 to 100 +feet above the present river-channels, and they are therefore +older than the recent gravels by the time required by the river +to dig out its own bed to this depth. How long this period may +be, our data do not enable us to determine accurately; but if +we are to calculate from the observed rate of erosion of the +actually existing rivers, the period between the different +valley-gravels must be a very long one. + +The lowest or recent fluviatile deposits which occur beside the +bed of the present river, are referable to the Recent period, +as they contain the remains of none but living Mammals. The two +other sets of gravels are Post-Pliocene, as they contain the +bones of extinct Mammals, mixed with land and fresh-water shells +of existing species. Among the more important extinct Mammals +of the low-level and high-level valley-gravels may be mentioned +the _Elephas antiquus_, the Mammoth (_Elephas primigenius_), +the Woolly Rhinoceros (_R. Tichorhinus_), the Hippopotamus, the +Cave-lion, and the Cave-bear. Along with these are found +unquestionable traces of the existence of Man, in the form of +rude flint implements of undoubted human workmanship. + +The so-called "Cave-deposits," again, though exhibiting peculiarities +due to the fact of their occurrence in caverns or fissures in the +rocks, are in many respects essentially similar to the older +valley-gravels. Caves, in the great majority of instances, occur +in limestone. When this is not the case, it will generally be +found that they occur along lines of sea-coast, or along lines +which can be shown to have anciently formed the coast-line. There +are many caves, however, in the making of which it can be shown +that the sea has had no hand; and these are most of the caves +of limestone districts. These owe their origin to the solvent +action upon lime of water holding carbonic acid in solution. +The rain which falls upon a limestone district absorbs a certain +amount of carbonic acid from the air, or from the soil. It then +percolates through the rock, generally along the lines of jointing +so characteristic of limestones, and in its progress it dissolves +and carries off a certain quantity of carbonate of lime. In this +way, the natural joints and fissures in the rock are widened, as +can be seen at the present day in any or all limestone districts. +By a continuance of this action for a sufficient length of time, +caves may ultimately be produced. Nothing, also, is commoner +in a limestone district than for the natural drainage to take +the line of some fissure, dissolving the rock in its course. In +this way we constantly meet in limestone districts with springs +issuing from the limestone rock--sometimes as large rivers--the +waters of which are charged with carbonate of lime, obtained by +the solution of the sides of the fissure through which the waters +have flowed. By these and similar actions, every district in which +limestones are extensively developed will be found to exhibit +a number of natural caves, rents, or fissures. The first element, +therefore, in the production of cave-deposits, is the existence +of a period in which limestone rocks were largely dissolved, and +caves were formed in consequence of the then existing drainage +taking the line of some fissure. + +Secondly, there must have been a period in which various deposits +were accumulated in the caves thus formed. These cavern-deposits +are of very various nature, consisting of mud, loam, gravel, +or breccias of different kinds. In all cases, these materials +have been introduced into the cave at some period subsequent to, +or contemporaneous with, the formation of the cave. Sometimes +the cave communicates with the surface by a fissure through which +sand, gravel, &c., may be washed by rains or by floods from some +neighbouring river. Sometimes the cave has been the bed of an +ancient stream, and the deposits have been formed as are fluviatile +deposits at the surface. Or, again, the river has formerly flowed +at a greater elevation than it does at present, and the cave +has been filled with fluviatile deposits by the river at a time +prior to the excavation of its bed to the present depth (fig. +256). In this last case, the cave-deposits obviously bear exactly +the same relation in point of antiquity to recent deposits, as +do the low-level and high-level valley-gravels to recent +river-gravels. In any case, it is necessary for the physical +geography of the district to change to some extent, in order +that the cave-deposits should be preserved. If the materials +have been introduced by a fissure, the cave will probably become +ultimately filled to the roof, and the aperture of admission +thus blocked up. If a river has flowed through the cave, the +surface configuration of the district must be altered so far +as to divert the river into a new channel. And if the cave is +placed in the side of a river-valley, as in fig. 256, the river +must have excavated its channel to such a depth that it can no +longer wash out the contents of the cave even in high floods. + +[Illustration: Fig 256.--Diagrammatic section across a river-valley +and cave. _a a_, Recent valley-gravels near the channel (b) of +the existing river; c, Cavern, partly filled with cave-earth; +_d d_, High-level gravels, filling fissures in the limestone, +which perhaps communicate in some instances with the cave, and +form a channel by which materials of various kinds were introduced +into it; _e e_, Inclined beds of limestone.] + +If the cave be entirely filled, the included deposits generally +get more or less completely cemented together by the percolation +through them of water holding carbonate of lime in solution. If +the cave is only partially filled, the dropping of water from +the roof holding lime in solution, and its subsequent evaporation, +would lead to the formation over the deposits below of a layer of +stalagmite, perhaps several inches, or even feet, in thickness. +In this way cave-deposits, with their contained remains, may +be hermetically sealed up and preserved without injury for an +altogether indefinite period of time. + +In all caves in limestone in which deposits containing bones are +found, we have then evidence of three principal sets of changes. +(1.) A period during which the cave was slowly hollowed out by +the percolation of acidulated water; (2.) A period in which the +cave became the channel of an engulfed river, or otherwise came +to form part of the general drainage-system of the district; (3.) +A period in which the cave was inhabited by various animals. + +As a typical example of a cave with fossiliferous Post-Pliocene +deposits, we may take Kent's Cavern, near Torquay, in which a +systematic and careful examination has revealed the following +sequence of accumulations in descending order:-- + +(a) Large blocks of limestone, which lie on the floor of the +cave, having fallen from the roof, and which are sometimes cemented +together by stalagmite. + +(b) A layer of black mould, from three to twelve inches thick, +with human bones, fragments of pottery, stone and bronze implements, +and the bones of animals now living in Britain. This, therefore, +is a _recent_ deposit. + +(c) A layer of stalagmite, from sixteen to twenty inches thick, +but sometimes as much as five feet, containing the bones of Man, +together with those of extinct Post-Pliocene Mammals. + +(d) A bed of red cave-earth, sometimes four feet in thickness, +with numerous bones of extinct Mammals (Mammoth, Cave-bear, &c.), +together with human implements of flint and horn. + +(e) A second bed of stalagmite, in places twelve feet in thickness, +with bones of the Cave-bear. + +(f) A red-loam and cave-breccia, with remains of the Cave-bear +and human implements. + +The most important Mammals which are found in cave-deposits in +Europe generally, are the Cave-bear, the Cave-lion, the Cave-hyæna, +the Reindeer, the Musk-ox, the Glutton, and the Lemming--of which +the first three are probably identical with existing forms, and +the remainder are certainly so--together with the Mammoth and +the Woolly Rhinoceros, which are undoubtedly extinct. Along with +these are found the implements, and in some cases the bones, of +Man himself, in such a manner as to render it absolutely certain +that an early race of men was truly contemporaneous in Western +Europe with the animals above mentioned. + +IV. UNCLASSIFIED POST-PLIOCENE DEPOSITS.--Apart from any of the +afore mentioned deposits, there occur other accumulations--sometimes +superficial, sometimes in caves--which are found in regions where +a "Glacial period" has not been fully demonstrated, or where +such did not take place; and which, therefore, are not amenable +to the above classification. The most important of these are +known to occur in South America and Australia; and though their +numerous extinct Mammalia place their reference to the Post-Pliocene +period beyond doubt, their relations to the glacial period and +its deposits in the northern hemisphere have not been precisely +determined. + + + + +CHAPTER XXII. + +THE POST-PLIOCENE PERIOD--_Continued_. + +As regards the _life_ of the Post-Pliocene period, we have, in +the first place, to notice the effect produced throughout the +northern hemisphere by the gradual supervention of the Glacial +period. Previous to this the climate must have been temperate or +warm-temperate; but as the cold gradually came on, two results were +produced as regards the living beings of the area thus affected. +In the first place, all those Mammals which, like the Mammoth, the +Woolly Rhinoceros, the Lion, the Hyæna, and the Hippopotamus, +require, at any rate, moderately warm conditions, would be forced +to migrate southwards to regions not affected by the new state +of things. In the second place, Mammals previously inhabiting +higher latitudes, such as the Reindeer, the Musk-ox, and the +Lemming, would be enabled by the increasing cold to migrate +southwards, and to invade provinces previously occupied by the +Elephant and the Rhinoceros. A precisely similar, but more +slowly-executed process, must have taken place in the sea, the +northern Mollusca moving southwards as the arctic conditions of +the Glacial period became established, whilst the forms proper +to temperate seas receded. As regards the readily locomotive +Mammals, also, it is probable that this process was carried on +repeatedly in a partial manner, the southern and northern forms +alternately fluctuating backwards and forwards over the same +area, in accordance with the fluctuations of temperature which +have been shown by Mr James Geikie to have characterised the +Glacial period as a whole. We can thus readily account for the +intermixture which is sometimes found of northern and southern +types of Mammalia in the same deposits, or in deposits apparently +synchronous, and within a single district. Lastly, at the final close +of the arctic cold of the Glacial period, and the re-establishment +of temperate conditions over the northern hemisphere, a reversal +of the original process took place--the northern Mammals retiring +within their ancient limits, and the southern forms pressing +northwards and reoccupying their original domains. + +The _Invertebrate_ animals of the Post-Pliocene deposits require +no further mention--all the known forms, except a few of the shells +in the lowest beds of the formation, being identical with species +now in existence upon the globe. The only point of importance in +this connection has been previously noticed--namely, that in +the true Glacial deposits themselves a considerable number of +the shells belong to northern or Arctic types. + +As regards the _Vertebrate_ animals of the period, no extinct +forms of Fishes, Amphibians, or Reptiles are known to occur, +but we meet with both extinct Birds and extinct Mammals. The +remains of the former are of great interest, as indicating the +existence during Post-Pliocene times, at widely remote points +of the southern hemisphere, of various wingless, and for the +most part gigantic, Birds. All the great wingless Birds of the +order _Cursores_ which are known as existing at the present day +upon the globe, are restricted to regions which are either wholly +or in great part south of the equator. Thus the true Ostriches are +African; the Rheas are South American; the Emeus are Australian; +the Cassowaries are confined to Northern Australia, Papua, and the +Indian Archipelago; the species of _Apteryx_ are natives of New +Zealand; and the Dodo and Solitaire (wingless, though probably +not true _Cursores_), both of which have been exterminated within +historical times, were inhabitants of the islands of Mauritius +and Rodriguez, in the Indian Ocean. In view of these facts, it +is noteworthy that, so far as known, all the Cursorial Birds +of the Post-Pliocene period should have been confined to the +same hemisphere as that inhabited by the living representatives +of the order. It is still further interesting to notice that +the extinct forms in question are only found in geographical +provinces which are now, or have been within historical times, +inhabited by similar types. The greater number of the remains +of these have been discovered in New Zealand, where there now +live several species of the curious wingless genus _Apteryx_; +and they have been referred by Professor Owen to several generic +groups, of which _Dinornis_ is the most important (fig. 257). +Fourteen species of _Dinornis_ have been described by the +distinguished palæontologist just mentioned, all of them being +large wingless birds of the type of the existing Ostrich, having +enormously powerful hind-limbs adapted for running, but with +the wings wholly rudimentary, and the breast-bone devoid of the +keel or ridge which characterises this bone in all birds which +fly. The largest species is the _Dinornis giganteus_, one of +the most gigantic of living or fossil birds, the shank (tibia) +measuring a yard in length, and the total height being at least +ten feet. Another species, the _Dinornis Elephantopus_ (fig. +257), though not standing more than about six feet in height, +was of an even more ponderous construction--"the framework of +the skeleton being the most massive of any in the whole class of +Birds," whilst "the toe-bones almost rival those of the Elephant" +(Owen). The feet in _Dinornis_ were furnished with three toes, +and are of interest as presenting us with an undoubted Bird big +enough to produce the largest of the foot-prints of the Triassic +Sandstones of Connecticut. New Zealand has now been so far explored, +that it seems questionable if it can retain in its recesses any +living example of _Dinornis_; but it is certain that species +of this genus were alive during the human period, and survived +up to quite a recent date. Not only are the bones very numerous +in certain localities, but they are found in the most recent +and superficial deposits, and they still contain a considerable +proportion of animal matter; whilst in some instances bones have +been found with the feathers attached, or with the horny skin of +the legs still adhering to them. Charred bones have been found +in connection with native "ovens;" and the traditions of the +Maories contain circumstantial accounts of gigantic wingless +Birds, the "Moas," which were hunted both for their flesh and +their plumage. Upon the whole, therefore, there can be no doubt +but that the Moas of New Zealand have been exterminated at quite a +recent period--perhaps within the last century--by the unrelenting +pursuit of Man,--a pursuit which their wingless condition rendered +them unable to evade. + +[Illustration: Fig. 257.--Skeleton of _Dinornis elephantopus_, +greatly reduced. Post-Pliocene, New Zealand. (After Owen.)] + +In Madagascar, bones have been discovered of another huge wingless +Bird, which must have been as large as, or larger than, the _Dinornis +giganteus_, and which has been described under the name of _Æpiornis +maximus_. With the bones have been found eggs measuring from +thirteen to fourteen inches in diameter, and computed to have +the capacity of three Ostrich eggs. At least two other smaller +species of _Æpiornis_ have been described by Grandidier and +Milne-Edwards as occurring in Madagascar; and they consider the +genus to be so closely allied to the _Dinornis_ of New Zealand, +as to prove that these regions, now so remote, were at one time +united by land. Unlike New Zealand, where there is the _Apteryx_, +Madagascar is not known to possess any living wingless Birds; +but in the neighbouring island of Mauritius the wingless Dodo +(_Didus ineptus_) has been exterminated less than three hundred +years ago; and the little island of Rodriguez, in the same +geographical province, has in a similar period lost the equally +wingless Solitaire (_Pezophaps_), both of these, however, being +generally referred to the _Rasores_. + +The _Mammals_ of the Post-Pliocene period are so numerous, that +in spite of the many points of interest which they present, only +a few of the more important forms can be noticed here, and that +but briefly. The first order that claims our attention is that +of the _Marsupials_, the headquarters of which at the present +day is the Australian province. In Oolitic times Europe possessed +its small Marsupials, and similar forms existed in the same area +in the Eocene and Miocene periods; but if size be any criterion, +the culminating point in the history of the order was attained +during the Post-Pliocene period in Australia. From deposits of +this age there has been disentombed a whole series of remains of +extinct, and for the most part gigantic, examples of this group +of Quadrupeds. Not to speak of Wombats and Phalangers, two forms +stand out prominently as representatives of the Post-Pliocene +animals of Australia. One of these is _Diprotodon_ (fig. 258), +representing, with many differences, the well-known modern group +of the Kangaroos. In its teeth, _Diprotodon_ shows itself to +be closely allied to the living, grass-eating Kangaroos; but +the hind-limbs were not so disproportionately long. In size, +also, _Diprotodon_ must have many times exceeded the dimensions +of the largest of its living successors, since the skull measures +no less than three feet in length. The other form in question +is _Thylacoleo_ (fig. 259), which is believed by Professor Owen +to belong to the same group as the existing "Native Devil" +(_Dasyurus_) of Van Diemen's Land, and therefore to have been +flesh-eating and rapacious in its habits, though this view is +not accepted by others. The principal feature in the skull of +_Thylacoleo_ is the presence, on each side of each jaw, of a +single huge tooth, which is greatly compressed, and has a cutting +edge. This tooth is regarded by Owen as corresponding to the +great cutting tooth of the jaw of the typical Carnivores, but +Professor Flower considers that _Thylacoleo_ is rather related to +the Kangaroo-rats. The size of the crown of the tooth in question +is not less than two inches and a quarter; and whether carnivorous +or not, it indicates an animal of a size exceeding that of the +largest of existing Lions. + +[Illustration: Fig. 258.--Skull of _Diprotodon Australis_, greatly +reduced. Post-Pliocene, Australia.] + +[Illustration: Fig. 259.--Skull of _Thylacoleo_. Post-Pliocene, +Australia. Greatly reduced. (After Flower.)] + +The order of the _Edentates_, comprising the existing Sloths, +Ant-eaters, and Armadillos, and entirely restricted at the present +day to South America, Southern Asia, and Africa, is one alike +singular for the limited geographical range of its members, their +curious habits of life, and the well-marked peculiarities of +their anatomical structure. South America is the metropolis of +the existing forms; and it is an interesting fact that there +flourished within Post-Pliocene times in this continent, and to +some extent in North America also, a marvellous group of extinct +Edentates, representing the living Sloths and Armadillos, but +of gigantic size. The most celebrated of these is the huge +_Megatherium Cuvieri_ (fig. 260) of the South American Pampas. +The Megathere was a colossal Sloth-like animal which attained a +length of from twelve to eighteen feet, with bones more massive +than those of the Elephant. Thus the thigh-bone is nearly thrice +the thickness of the same bone in the largest of existing Elephants, +its circumference at its narrowest point nearly equalling its +total length; the massive bones of the shank (tibia and fibula) +are amalgamated at their extremities; the heel-bone (calcaneum) +is nearly half a yard in length; the haunch-bones (ilia) are +from four to five feet across at their crests; and the bodies +of the vertebræ at the root of the tail are from five to seven +inches in diameter, from which it has been computed that the +circumference of the tail at this part might have been from five +to six feet. The length of the fore-foot is about a yard, and +the toes are armed with powerful curved claws. It is known now +that the Megathere, in spite of its enormous weight and ponderous +construction, walked, like the existing Ant-eaters and Sloths, +upon the outside edge of the fore-feet, with the claws more or +less bent inwards towards the palm of the hand. As in the great +majority of the Edentate order, incisor and canine teeth are +entirely wanting, the front of the jaws being toothless. The +jaws, however, are furnished with five upper and four lower molar +teeth on each side. These grinding teeth are from seven to eight +inches in length, in the form of four-sided prisms, the crowns of +which are provided with well-marked transverse ridges; and they +continue to grow during the whole life of the animal. There are +indications that the snout was prolonged, and more or less flexible; +and the tongue was probably prehensile. From the characters of +the molar teeth it is certain that the Megathere was purely +herbivorous in its habits; and from the enormous size and weight +of the body, it is equally certain that it could not have imitated +its modern allies, the Sloths, in the feat of climbing, back +downwards, amongst the trees. It is clear, therefore, that the +Megathere sought its sustenance upon the ground; and it was +originally supposed to have lived upon roots. By a masterly piece +of deductive reasoning, however, Professor Owen showed that this +great "Ground-Sloth" must have truly lived upon the foliage of +trees, like the existing Sloths--but with this difference, that +instead of climbing amongst the branches, it actually uprooted +the tree bodily. In this _tour de force_, the animal sat upon its +huge haunches and mighty tail, as on a tripod, and then grasping +the trunk with its powerful arms, either wrenched it up by the +roots or broke it short off above the ground. Marvellous as this +may seem, it can be shown that every detail in the skeleton of the +Megathere accords with the supposition that it obtained its food +in this way. Similar habits were followed by the allied _Mylodon_ +(fig. 261), another of the great "Ground-Sloths," which inhabited +South America during the Post-Pliocene period. In most respects, +the _Mylodon_ is very like the Megathere; but the crowns of the +molar teeth are flat instead of being ridged. The nearly-related +genus _Megalonyx_, unlike the Megathere, but like the Mylodon, +extended its range northwards as far as the United States. + +[Illustration: Fig. 260.--_Megatherium Cuvieri_. Post-Pliocene, +South America.] + +Just as the Sloths of the present day were formerly represented +in the same geographical area by the gigantic Megatheroids, so +the little banded and cuirassed Armadillos of South America were +formerly represented by gigantic species, constituting the genus +_Glyptodon_. The _Glyptodons_ (fig. 262) differed from the living +Armadillos in having no bands in their armour, so that they must +have been unable to roll themselves up. It is rare at the present +day to meet with any Armadillo over two or three feet in length; +but the length of the _Glyptodon clavipes_, from the tip of the +snout to the end of the tail, was more than nine feet. + +[Illustration: Fig. 261.--Skeleton of _Mylodon robustus_. +Post-Pliocene, South America.] + +[Illustration: Fig. 262.--Skeleton of _Glyptodon clavipes_. +Post-Pliocene, South America.] + +There are no canine or incisor teeth in the _Glyptodon_, but +there are eight molars on each side of each jaw, and the crowns +of these are fluted and almost trilobed. The head is covered +by a helmet of bony plates, and the trunk was defended by an +armour of almost hexagonal bony pieces united by sutures, and +exhibiting special patterns of sculpturing in each species. The +tail was also defended by a similar armour, and the vertebræ were +mostly fused together so as to form a cylindrical bony rod. In +addition to the above-mentioned forms, a number of other Edentate +animals have been discovered by the researches of M. Lund in +the Post-Pliocene deposits of the Brazilian bone-caves. Amongst +these are true Ant-eaters, Armadillos, and Sloths, many of them +of gigantic size, and all specifically or generically distinct +from existing forms. + +Passing over the aquatic orders of the _Sirenians_ and _Cetaceans_, +we come next to the great group of the Hoofed Quadrupeds, the +remains of which are very abundant in Post-Pliocene deposits both +in Europe and North America. Amongst the Odd-toed Ungulates the +most important are the Rhinoceroses, of which three species are +known to have existed in Europe during the Post-Pliocene period. +Two of these are the well-known Pliocene forms, the _Rhinoceros +Etruscus_ and the _R. Megarhinus_ still surviving in diminished +numbers; but the most famous is the _Rhinoceros tichorhinus_ +(fig. 263), or so-called "Woolly Rhinoceros." This species is +known not only by innumerable bones, but also by a carcass, at +the time of its discovery complete, which was found embedded in +the frozen soil of Siberia towards the close of last century, +and which was partly saved from destruction by the exertions of +the naturalist Pallas. From this, we know that the Tichorhine +Rhinoceros, like its associate the Mammoth, was provided with +a coating of hair, and therefore was enabled to endure a more +severe climate than any existing species. The skin was not thrown +into the folds which characterise most of the existing forms; +and the technical name of the species refers to the fact that +the nostrils were completely separated by a bony partition. The +head carried two horns, placed one behind the other, the front +one being unusually large. As regards its geographical range, +the Woolly Rhinoceros is found in Europe in vast numbers north +of the Alps and Pyrenees, and it also abounded in Siberia; so +that it would appear to be a distinctly northern form, and to +have been adapted for a temperate climate. It is not known to +occur in Pliocene deposits, but it makes its first appearance +in the Pre-Glacial deposits, surviving the Glacial period, and +being found in abundance in Post-Glacial accumulations. It was +undoubtedly a contemporary of the earlier races of men in Western +Europe; and it may perhaps be regarded as being the actual +substantial kernel of some of the "Dragons" of fable. + +[Illustration: Fig. 263.--Skull of the Tichorhine Rhinoceros, the +horns being wanting. One-tenth of the natural size. Post-Pliocene +deposits of Europe and Asia.] + +The only other Odd-toed Ungulate which needs notice is the so-called +_Equus fossilis_ of the Post-Pliocene of Europe. This made its +appearance before the Glacial period, and appears to be in reality +identical with the existing Horse (_Equus caballus_). True Horses +also occur in the Post-Pliocene of North America; but, from some +cause or another, they must have been exterminated before historic +times. + +[Illustration: Fig. 264--Skeleton of the "Irish Elk" (_Cervus +megaceros_). Post-Pliocene, Britain.] + +Amongst the Even-toed Ungulates, the great _Hippopotamus major_ +of the Pliocene still continued to exist in Post-Pliocene times +in Western Europe; and the existing Wild Boar (_Sus scrofa_), +the parent of our domestic breeds of Pigs, appeared for the first +time. The Old World possessed extinct representatives of its +existing Camels, and lost types of the living Llamas inhabited +South America. Amongst the Deer, the Post-Pliocene accumulations +have yielded the remains of various living species, such as the +Red Deer (_Cervus elaphus_), the Reindeer (_Cervus tarandus_), +the Moose or Elk (_Alces malchis_), and the Roebuck (_Cervus +capreolus_), together with a number of extinct forms. Among the +latter, the great "Irish Elk" (_Cervus megaceros_) is justly +celebrated both for its size and for the number and excellent +preservation of its discovered remains. This extinct species +(fig. 264) has been found principally in peat-mosses and +Post-Pliocene lake-deposits, and is remarkable for the enormous +size of the spreading antlers, which are widened out towards +their extremities, and attain an expanse of over ten feet from +tip to tip. It is not a genuine Elk, but is intermediate between +the Reindeer and the Fallow-deer. Among the existing Deer of the +Post-Pliocene, the most noticeable is the Reindeer, an essentially +northern type, existing at the present day in Northern Europe, +and also (under the name of the "Caribou") in North America. When +the cold of the Glacial period became established, this boreal +species was enabled to invade Central and Western Europe in great +herds, and its remains are found abundantly in cave-earths and +other Post-Pliocene deposits as far south as the Pyrenees. + +[Illustration: Fig. 265.--Skull of the Urns (_Bos primigenius_). +Post-Pliocene and Recent. (After Owen.)] + +In addition to the above, the Post-Pliocene deposits of Europe +and North America have yielded the remains of various Sheep and +Oxen. One of the most interesting of the latter is the "Urus" or +Wild Bull (_Bos primigenius_, fig. 265), which, though much larger +than any of the existing fossils, is believed to be specifically +undistinguishable from the domestic Ox (_Bos taurus_), and to be +possibly the ancestor of some of the larger European varieties +of oxen. In the earlier part of its existence the Urus ranged +over Europe and Britain in company with the Woolly Rhinoceros +and the Mammoth; but it long survived these, and does not appear +to have been finally exterminated till about the twelfth century. +Another remarkable member of the Post-Pliocene Cattle, also to +begin with an associate of the Mammoth and Rhinoceros, is the +European Bison or "Aurochs" (_Bison priscus_). This "maned" ox +formerly abounded in Europe in Post-Glacial times, and was not +rare even in the later periods of the Roman empire, though much +diminished in numbers, and driven back into the wilder and more +inaccessible parts of the country. At present this fine species +has been so nearly exterminated that it no longer exists in Europe +save in Lithuania, where its preservation has been secured by +rigid protective laws. Lastly, the Post-Pliocene deposits have +yielded the remains of the singular living animal which is known +as the Musk-ox or Musk-sheep (_Ovibos moschatus_). At the present +day, the Musk-ox is an inhabitant of the "barren grounds" of +Arctic America, and it is remarkable for the great length of +its hair. It is, like the Reindeer, a distinctively northern +animal; but it enjoyed during the Glacial period a much wider +range than it has at the present day, the conditions suitable +for its existence being then extended over a considerable portion +of the northern hemisphere. Thus remains of the Musk-Ox are found +in greater or less abundance in Post-Pliocene deposits over a +great part of Europe, extending even to the south of France; +and closely-related forms are found in similar deposits in the +United States. + +[Illustration: Fig. 266.--Skeleton of the Mammoth (_Elephas +primigenius_). Portions of the integument still adhere to the +head, and the thick skin of the soles is still attached to the +feet. Post-Pliocene.] + +Coming to the _Proboscideans_, we find that the _Mastodons_ seem +to have disappeared in Europe at the close of the Pliocene period, +or at the very commencement of the Post-Pliocene. In the New World, +on the other hand, a species of Mastodon (_M. Americanus_ or _M. +Ohioticus_) is found abundantly in deposits of Post-Pliocene +age, from Canada to Texas. Very perfect skeletons of this species +have been exhumed from morasses and swamps, and large individuals +attained a length (exclusive of the tusks) of seventeen feet and +a height of eleven feet, the tusks being twelve feet in length. +Remains of _Elephants_ are also abundant in the Post-Pliocene +deposits of both the Old and the New World. Amongst these, we +find in Europe the two familiar Pliocene species _E. Meridionales_ +and _E. Antiquus_ still surviving, but in diminished numbers. +With these are found in vast abundance the remains of the +characteristic Elephant of the Post-Pliocene, the well-known +"Mammoth" (Elephas primigenius_), which is accompanied in North +America by the nearly-allied, but more southern species, the +_Elephas Americanus_. The Mammoth (fig. 266) is considerably +larger than the largest of the living Elephants, the skeleton +being over sixteen feet in length, exclusive of the tusks, and +over nine feet in height. The tusks are bent almost into a circle, +and are sometimes twelve feet in length, measured along their +curvature. In the frozen soil of Siberia several carcasses of +the Mammoth have been discovered with the flesh and skin still +attached to the bones, the most celebrated of these being a Mammoth +which was discovered at the beginning of this century at the +mouth of the Lena, on the borders of the Frozen Sea, and the +skeleton of which is now preserved at St Petersburg (fig. 266). +From the occurrence of the remains of the Mammoth in vast numbers +in Siberia, it might have been safely inferred that this ancient +Elephant was able to endure a far more rigorous climate than its +existing congeners. This inference has, however, been rendered +a certainty by the specimens just referred to, which show that +the Mammoth was protected against the cold by a thick coat of +reddish-brown wool, some nine or ten inches long, interspersed +with strong, coarse black hair more than a foot in length. The +teeth of the Mammoth (fig.267) are of the type of those of the +existing Indian Elephant, and are found in immense numbers in +certain localities. The Mammoth was essentially northern in its +distribution, never passing south of a line drawn through the +Pyrenees, the Alps, the northern shores of the Caspian, Lake +Baikal, Kamschatka, and the Stanovi Mountains (Dawkins). It occurs +in the Pre-Glacial forest-bed of Cromer in Norfolk, survived the +Glacial period, and is found abundantly in Post-Glacial deposits +in France, Germany, Britain, Russia in Europe, Asia, and North +America, being often associated with the Reindeer, Lemming, and +Musk-ox. That it survived into the earlier portion of the human +period is unquestionable, its remains having been found in a +great number of instances associated with implements of human +manufacture; whilst in one instance a recognisable portrait of +it has been discovered, carved on bone. + +[Illustration: Fig. 267.--Molar tooth of the Mammoth (_Elephas +primigenius_), upper jaw, right side, one-third of the natural +size. a, Grinding surface; b, Side view. Post-Pliocene.] + +Amongst other Elephants which occur in Post-Pliocene deposits +may be mentioned, as of special interest, the pigmy Elephants +of Malta. One of these--the _Elephas Melitensis_, or so-called +"Donkey-Elephant"--was not more than four and a half feet in +height. The other--the _Elephas Falconeri_, of Busk--was still +smaller, its average height at the withers not exceeding two +and a half to three feet. + +[Illustration: Fig. 268.--Skull of _Ursus spelpeus_. Post-Pliocene, +Europe. One-sixth of the natural size.] + +Whilst herbivorous animals abounded during the Post-Pliocene, +we have ample evidence of the coexistence with them of a number +of Carnivorous forms, both in the New and the Old World. The +Bears are represented in Europe by at least three species, two +of which--namely, the great Grizzly Bear (_Ursus ferox_) and +the smaller Brown Bear (_Ursus arctos_)--are in existence at the +present day. The third species is the celebrated Cave-bear (_Ursus +speloeus_, fig. 268), which is now extinct. The Cave-bear exceeded +in its dimensions the largest of modern Bears; and its remains, +as its name implies; have been found mainly in cavern-deposits. +Enormous numbers of this large and ferocious species must have +lived in Europe in Post-Glacial times; and that they survived +into the human period, is clearly shown by the common association +of their bones with the implements of man. They are occasionally +accompanied by the remains of a Glutton (the _Gulo speloeus_), +which does not appear to be really separable from the existing +Wolverine or Glutton of northern regions (the _Gulo luscus_). +In addition, we meet with the bones of the Wolf, Fox, Weasel, +Otter, Badger, Wild Cat, Panther, Hyæna, and Lion, &c., together +with the extinct _Machairodus_ or "Sabre-toothed Tiger." The +only two of these that deserve further mention are the Hyæna +and the Lion. The Cave-hyæna (_Hyoena speloea_, fig. 269) is +regarded by high authorities as nothing more than a variety of +the living Spotted Hyæna (_H. Crocuta_) of South Africa. This +well-known species inhabited Britain and a considerable portion +of Europe during a large part of the Post-Pliocene period; and +its remains often occur in great abundance. Indeed, some caves, +such as the Kirkdale Cavern in Yorkshire, were dens inhabited +during long periods by these animals, and thus contain the remains +of numerous individuals and of successive generations of Hyænas, +together with innumerable gnawed and bitten bones of their prey. +That the Cave-hyæna was a contemporary with Man in Western Europe +during Post-Glacial times is shown beyond a doubt by the common +association of its bones with human implements. + +[Illustration: Fig. 269.--Skull of _Hyoena speloea_, one-fourth +of the natural size. Post-Phocene, Europe.] + +Lastly, the so-called Cave-lion (_Felis speloea_), long supposed +to be a distinct species, has been shown to be nothing more than +a large variety of the existing Lion (_Felis leo_). This animal +inhabited Britain and Western Europe in times posterior to the +Glacial period, and was a contemporary of the Cave-hyæna, Cave-bear, +Woolly Rhinoceros, and Mammoth. The Cave-lion also unquestionably +survived into the earlier portion of the human period in Europe. + +The Post-Pliocene deposits of Europe have further yielded the +remains of numerous _Rodents_--such as the Beaver, the Northern +Lemming, Marmots, Mice, Voles, Rabbits, &c.--together with the +gigantic extinct Beaver known as the _Trogontherium Cuvieri_ +(fig. 270). The great _Castoroides Ohioensis_ of the Post-Pliocene +of North America is also a great extinct Beaver, which reached +a length of about five feet. Lastly, the Brazilian bone-caves +have yielded the remains of numerous Rodents of types now +characteristic of South America, such as Guinea-pigs, Capybaras, +tree-inhabiting Porcupines, and Coypus. + +[Illustration: Fig. 270.--Lower jaw of _Trogontherium Cuvieri_, +one-fourth of the natural size. Post-Pliocene, Britain.] + +The deposits just alluded to have further yielded the remains of +various Monkeys, such as Howling Monkeys, Squirrel Monkeys, and +Marmosets, all of which belong to the group of _Quadrumana_ which +is now exclusively confined to the South American continent--namely, +the "Platyrhine" Monkeys. + +We still have very briefly to consider the occurrence of Man +in Post-Pliocene deposits; but before doing so, it will be well +to draw attention to the evidence afforded by the Post-Pliocene +Mammals as to the climate of Western Europe at this period. The +chief point which we have to notice is, that a considerable +revolution of opinion has taken place on this point. It was +originally believed that the presence of such animals as Elephants, +Lions, the Rhinoceros, and the Hippopotamus afforded an irrefragable +proof that the climate of Europe must have been a warm one, at any +rate during Post-Glacial times. The existence, also, of numbers +of Mammoths in Siberia, was further supposed to indicate that +this high temperature extended itself very far north. Upon the +whole, however, the evidence is against this view. Not only is +there great difficulty in supposing that the Arctic conditions of +the Glacial period were immediately followed by anything warmer +than a cold-temperate climate; but there is nothing in the nature +of the Mammals themselves which would absolutely forbid their +living in a temperate climate. The _Hippopotamus major_, though +probably clad in hair, offers some difficulty--since, as pointed +out by Professor Busk, it must have required a climate sufficiently +warm to insure that the rivers were not frozen over in the winter; +but it was probably a migratory animal, and its occurrence may +be accounted for by this. The Woolly Rhinoceros and the Mammoth +are known with certainty to have been protected with a thick +covering of wool and hair; and their extension northwards need +not necessarily have been limited by anything except the absence of +a sufficiently luxuriant vegetation to afford them food. The great +American Mastodon, though not certainly known to have possessed a +hairy covering, has been shown to have lived upon the shoots of +Spruce and Firs, trees characteristic of temperate regions--as +shown by the undigested food which has been found with its skeleton, +occupying the place of the stomach. The Lions and Hyænas, again, +as shown by Professor Boyd Dawkins, do not indicate necessarily +a warm climate. Wherever a sufficiency of herbivorous animals +to supply them with food can live, there they can live also; +and they have therefore no special bearing upon the question of +climate. After a review of the whole evidence, Professor Dawkins +concludes that the nearest approach at the present day to the +Post-Pliocene climate of Western Europe is to be found in the +climate of the great Siberian plains which stretch from the Altai +Mountains to the Frozen Sea. "Covered by impenetrable forests, +for the most part of Birch, Poplar, Larch, and Pines, and low +creeping dwarf Cedars, they present every gradation in climate +from the temperate to that in which the cold is too severe to admit +of the growth of trees, which decrease in size as the traveller +advances northwards, and are replaced by the grey mosses and +lichens that cover the low marshy 'tundras.' The maximum winter +cold, registered by Admiral Von Wrangel at Nishne Kolymsk, on +the banks of the Kolyma, is--65° in January. 'Then breathing +becomes difficult; the Reindeer, that citizen of the Polar region, +withdraws to the deepest thicket of the forest, and stands there +motionless as if deprived of life;' and trees burst asunder with +the cold. Throughout this area roam Elks, Black Bears, Foxes, +Sables, and Wolves, that afford subsistence to the Jakutian and +Tungusian fur-hunters. In the northern part countless herds of +Reindeer, Elks, Foxes, and Wolverines make up for the poverty +of vegetation by the rich abundance of animal life. 'Enormous +flights of Swans, Geese, and Ducks arrive in the spring, and seek +deserts where they may moult and build their nests in safety. +Ptarmigans run in troops amongst the bushes; little Snipes are +busy along the brooks and in the morasses; the social Crows seek +the neighbourhood of new habitations; and when the sun shines +in spring, one may even sometimes hear the cheerful note of the +Finch, and in autumn that of the Thrush.' Throughout this region +of woods, a hardy, middle-sized breed of horses lives under the +mastership and care of man, and is eminently adapted to bear the +severity of the climate.... The only limit to their northern +range is the difficulty of obtaining food. The severity of the +winter through the southern portion of this vast wooded area is +almost compensated for by the summer heat and its marvellous +effect on vegetation."--(Dawkins, 'Monograph of Pleistocene +Mammalia.') + +Finally, a few words must be said as to the occurrence of the +remains of Man in Post-Pliocene deposits. That Man existed in +Western Europe and in Britain during the Post-Pliocene period, is +placed beyond a doubt by the occurrence of his bones in deposits +of this age, along with the much more frequent occurrence of +implements of human manufacture. At what precise point of time +during the Post-Pliocene period he first made his appearance is +still a matter of conjecture. Recent researches would render +it probable that the early inhabitants of Britain and Western +Europe were witnesses of the stupendous phenomena of the Glacial +period; but this cannot be said to have been demonstrated. That +Man existed in these regions during the Post-Glacial division +of Post-Pliocene time cannot be doubted for a moment. As to the +physical peculiarities of the ancient races that lived with the +Mammoth and the Woolly Rhinoceros, little is known compared with +what we may some day hope to know. Such information as we have, +however, based principally on the skulls of the Engis, Neanderthal, +Cro-Magnon, and Bruniquel caverns, would lead to the conclusion that +Post-Pliocene Man was in no respect inferior in his organisation +to, or less highly developed than, many existing races. All the +known skulls of this period, with the single exception of the +Neanderthal cranium, are in all respects average and normal in +their characters; and even the Neanderthal skull possessed a +cubic capacity at least equal to that of some existing races. +The implements of Post-Pliocene Man are exclusively of stone or +bone; and the former are invariably of rude shape and _undressed_. +These "palæolithic" tools (Gr. _palaios_; ancient; _lithos_, +stone) point to a very early condition of the arts; since the +men of the earlier portion of the Recent period, though likewise +unacquainted with the metals, were in the habit of polishing +or dressing the stone implements which they fabricated. + +It is impossible here to enter further into this subject; and +it would be useless to do so without entering as well into a +consideration of the human remains of the Recent period--a period +which lies outside the province of the present work. So far as +Post-Pliocene Man is concerned, the chief points which the +palæontological student has to remember have been elsewhere +summarised by the author as follows:-- + +1. Man unquestionably existed during the later portion of what +Sir Charles Lyell has termed the "Post-Pliocene" period. In other +words, Man's existence dates back to a time when several remarkable +Mammals, previously mentioned, had not yet become extinct; but he +does not date back to a time anterior to the present _Molluscan_ +fauna. + +2. The antiquity of the so-called Post-Pliocene period is a matter +which must be mainly settled by the evidence of Geology proper, +and need not be discussed here. + +3. The extinct Mammals with which man coexisted in Western Europe are +mostly of large size, the most important being the Mammoth (_Elephas +primogenius_), the Woolly Rhinoceros (_Rhinoceros tichorhinus_), +the Cave-lion (_Felis speloea_), the Cave-hyæna(_Hyoena speloea), +and the Cave-bear (_Ursus speloeus_). We do not know the causes +which led to the extinction of these Mammals; but we know that +hardly any Mammalian species has become extinct during the historical +period. + +4. The extinct Mammals with which man coexisted are referable in +many cases to species which presumably required a very different +climate to that now prevailing in Western Europe. How long a +period, however, has been consumed in the bringing about of the +climatic changes thus indicated, we have no means of calculating +with any approach to accuracy. + +5. Some of the deposits in which the remains of man have been +found associated with the bones of extinct Mammals, are such as +to show incontestably that great changes in the physical geography +and surface-configuration of Western Europe have taken place +since the period of their accumulation. We have, however, no +means at present of judging of the lapse of time thus indicated +except by analogies and comparisons which may be disputed. + +6. The human implements which are associated with the remains +of extinct Mammals, themselves bear evidence of an exceedingly +barbarous condition of the human species. Post-Pliocene or +"Palæolithic" Man was clearly unacquainted with the use of any +of the metals. Not only so, but the workmanship of these ancient +races was much inferior to that of the later tribes, who were also +ignorant of the metals, and who also used nothing but weapons +and tools of stone, bone, &c. + +7. Lastly, it is only with the human remains of the Post-Pliocene +period that the palæontologist proper has to deal. When we enter +the "Recent" period, in which the remains of Man are associated +with those of _existing species of Mammals_, we pass out of the +region of pure palæontology into the domain of the Archæologist +and the Ethnologist. + + +LITERATURE. + +The following are some of the principal works and memoirs to which +the student may refer for information as to the Post-Pliocene +deposits and the remains which they contain, as well as to the +primitive races of mankind:-- + + (1) 'Elements of Geology.' Lyell. + (2) 'Antiquity of Man.' Lyell. + (3) 'Palæontological Memoirs.' Falconer. + (4) 'The Great Ice-age.' James Geikie. + (5) 'Manual of Palæontology.' Owen. + (6) 'British Fossil Mammals and Birds.' Owen. + (7) 'Cave-Hunting.' Boyd Dawkins. + (8) 'Prehistoric Times.' Lubbock. + (9) 'Ancient Stone Implements.' Evans. +(10) 'Prehistoric Man.' Daniel Wilson. +(11) 'Prehistoric Races of the United States.' Foster. +(12) 'Manual of Geology.' Dana. +(13) 'Monograph of Pleistocene Mammalia' (Palæontographical + Society). Boyd Dawkins and Sanford. +(14) 'Monograph of the Post-Tertiary Entomostraca of Scotland, &c., + with an Introduction on the Post-Tertiary Deposits of Scotland' + (Ibid.) G. S. Brady, H. W. Crosskey, and D. Robertson. +(15) "Reports on Kent's Cavern"--'British Association Reports.' + Pengelly. +(16) "Reports on the Victoria Cavern, Settle"--'British Association + Reports.' Tiddeman. +(17) 'Ossemens Fossiles.' Cuvier. +(18) 'Reliquiæ Diluvianæ.' Buckland. +(19) "Fossil Mammalia"--'Zoology of the Voyage of the Beagle.' + Owen. +(20) 'Description of the Tooth and Part of the Skeleton of the + _Glyptodon_.' Owen. +(21) "Memoir on the Extinct Sloth Tribe of North + America"--'Smithsonian Contributions to Knowledge.' Leidy. +(22) "Report on Extinct Mammals of Australia"--'British Association,' + 1844. Owen. +(23) 'Description of the Skeleton of an Extinct Gigantic Sloth + (_Mylodon robtutus_).' Owen. +(24) "Affinities and Probable Habits of Thylacoleo"--'Quart. Journ. + Geol. Soc.,' vol. xxiv. Flower. +(25) 'Prodromus of the Palæontology of Victoria.' M'Coy. +(26) 'Les Ossemens Fossiles des Cavernes de Liège.' Schmerling. +(27) 'Die Fauna der Pfahlbauten in der Schweiz.' Rütimeyer. +(28) "Extinct and Existing Bovine Animals of Scandinavia"--'Annals + of Natural History,' ser. 2, vol. iv., 1849. Nilsson. +(29) 'Man's Place in Nature.' Huxley. +(30) 'Les Temps Antéhistoriques en Belgique.' Dupont. +(31) "Classification of the Pleistocene Strata of Britain and the + Continent"--'Quart. Journ. Geol. Soc.,' vol. xxviii. Boyd Dawkins. +(32) 'Distribution of the Post-Glacial Mammalia' (Ibid.), vol. xxv. + Boyd Dawkins. +(33) 'On British Fossil Oxen' (Ibid.), vols. xxii. and xxiii. Boyd + Dawkins. +(34) 'British Prehistoric Mammals' (Congress of Prehistoric + Archæology, 1868). Boyd Dawkins. +(35) 'Reliquiæ Aquitanicæ.' Lartet and Christy. +(36) 'Zoologie et Paléontologie Françaises.' Gervais. +(37) 'Notes on the Post-Pliocene Geology of Canada.' Dawson. +(38) "On the Connection between the existing Fauna and Flora of + Great Britain and certain Geological Changes"--'Mem. Geol. + Survey.' Edward Forbes. +(39) 'Cavern-Researches.' M'Enery. Edited by Vivian. +(40) "Quaternary Gravels"--'Quart. Journ. Geol. Soc.,' vol. xxv. + Tylor. + + + + +CHAPTER XXIII. + +THE SUCCESSION OF LIFE UPON THE GLOBE. + +In conclusion, it may not be out of place if we attempt to summarise, +in the briefest possible manner, some of the principal results +which may be deduced as to the succession of life upon the earth +from the facts which have in the preceding portion of this work +been passed in review. That there was a time when the earth was +void of life is universally admitted, though it may be that the +geological record gives us no direct evidence of this. That the +globe of to-day is peopled with innumerable forms of life whose +term of existence has been, for the most part, but as it were +of yesterday, is likewise an assertion beyond dispute. Can we +in any way connect the present with the remote past, and can we +indicate even imperfectly the conditions and laws under which the +existing order was brought about? The long series of fossiliferous +deposits, with their almost countless organic remains, is the +link between what has been and what is; and if any answer to the +above question can be arrived at, it will be by the careful and +conscientious study of the facts of Palæontology. In the present +state of our knowledge, it may be safely said that anything like +a dogmatic or positive opinion as to the precise sequence of +living forms upon the globe, and still more as to the manner in +which this sequence may have been brought about, is incapable of +scientific proof. There are, however, certain general deductions +from the known facts which may be regarded as certainly established. + +In the first place, it is certain that there has been a _succession_ +of life upon the earth, different specific and generic types +succeeding one another in successive periods. It follows from +this, that the animals and plants with which we are familiar +as living, were not always upon the earth, but that they have +been preceded by numerous races more or less differing from them. +What is true of the species of animals and plants, is true also +of the higher zoological divisions; and it is, in the second +place, quite certain that there has been a similar _succession_ +in the order of appearance of the primary groups ("sub-kingdoms," +"classes," &c.) of animals and vegetables. These great groups +did not all come into existence at once, but they made their +appearance successively. It is true that we cannot be said to +be certainly acquainted with the first _absolute_ appearance of +any great group of animals. No one dare assert positively that +the apparent first appearance of Fishes in the Upper Silurian +is really their first introduction upon the earth: indeed, there +is a strong probability against any such supposition. To whatever +extent, however, future discoveries may push back the first advent +of any or of all of the great groups of life, there is no likelihood +that anything will be found out which will materially alter the +_relative_ succession of these groups as at present known to us. +It is not likely, for example, that the future has in store for +us any discovery by which it would be shown that Fishes were in +existence before Molluscs, or that Mammals made their appearance +before Fishes. The sub-kingdoms of Invertebrate animals were +all represented in Cambrian times--and it might therefore be +inferred that _these_ had all come simultaneously into existence; +but it is clear that this inference, though incapable of actual +disproof, is in the last degree improbable. Anterior to the Cambrian +is the great series of the Laurentian, which, owing to the +metamorphism to which it has been subjected, has so far yielded +but the singular _Eozoön_. We may be certain, however, that others +of the Invertebrate sub-kingdoms besides the Protozoa were in +existence in the Laurentian period; and we may infer from known +analogies that they appeared successively, and not simultaneously. + +When we come to smaller divisions than the sub-kingdoms--such +as classes, orders, and families--a similar succession of groups +is observable. The different classes of any given sub-kingdom, +or the different orders of any given class, do not make their +appearance together and all at once, but they are introduced +upon the earth in _succession_. More than this, the different +classes of a sub-kingdom, or the different orders of a class, +_in the main succeed one another in the relative order of their +zoological rank--the lower groups appearing first and the higher +groups last_. It is true that in the Cambrian formation--the +earliest series of sediments in which fossils are abundant--we +find numerous groups, some very low, others very high, in the +zoological scale, which _appear_ to have simultaneously flashed +into existence. For reasons stated above, however, we cannot +accept this appearance as real; and we must believe that many of +the Cambrian groups of animals really came into being long before +the commencement of the Cambrian period. At any rate, in the long +series of fossiliferous deposits of later date than the Cambrian +the above-stated rule holds good as a broad generalisation--that +the lower groups, namely, precede the higher in point of time; +and though there are apparent exceptions to the rule, there are +none of such a nature as not to admit of explanation. Some of +the leading facts upon which this generalisarion is founded will +be enumerated immediately; but it will be well, in the first +place, to consider briefly what we precisely mean when we speak +of "higher" and "lower" groups. + +It is well known that naturalists are in the habit of "classifying" +the innumerable animals which now exist upon the globe; or, in +other words, of systematically arranging them into groups. The +precise arrangement adopted by one naturalist may differ in minor +details from that adopted by another; but all are agreed as to +the fundamental points of classification, and all, therefore, +agree in placing certain groups in a certain sequence. What, +then, is the principle upon which this sequence is based? Why, +for example, are the Sponges placed below the Corals; these below +the Sea-urchins; and these, again, below the Shell-fish? Without +entering into a discussion of the principles of zoological +classification, which would here be out of place, it must be +sufficient to say that the sequence in question is based upon +the _relative type of organisation_ of the groups of animals +classified. The Corals are placed above the Sponges upon the +ground that, regarded as a whole, the _plan or type of structure_ +of a Coral is more complex than that of a Sponge. It is not in the +slightest degree that the Sponge is in any respect less highly +organised or less perfect, as a Sponge, than is the Coral as a +Coral. Each is equally perfect in its own way; but the structural +pattern of the Coral is the highest, and therefore it occupies a +higher place in the zoological scale. It is upon this principle, +then, that the primary subdivisions of the animal kingdom (the +so-called "sub-kingdoms") are arranged in a certain order. Coming, +again, to the minor subdivisions (classes, orders, &c.) of each +sub-kingdom, we find a different but entirely analogous principle +employed as a means of classification. The numerous animals belonging +to any given sub-kingdom are formed upon the same fundamental +plan of structure; but they nevertheless admit of being arranged +in a regular series of groups. All the Shell-fish, for example, +are built upon a common plan, this plan representing the ideal +Mollusc; but there are at the same time various groups of the +_Mollusca_, and these groups admit of an arrangement in a given +sequence. The principle adopted in this case is simply of _the +relative elaboration of the common type_. The Oyster is built +upon the same ground-plan as the Cuttle-fish; but this plan is +carried out with much greater elaboration, and with many more +complexities, in the latter than in the former: and in accordance +with this, the _Cephalopoda_ constitute a higher group than the +Bivalve Shell-fish. As in the case of superiority of structural +type, so in this case also, it is not in the least that the Oyster +is an _imperfect_ animal. On the contrary, it is just as perfectly +adapted by its organisation to fill its own sphere and to meet +the exigencies of its own existence as is the Cuttle-fish; but +the latter lives a life which is, physiologically, higher than +the former, and its organisation is correspondingly increased +in complexity. + +This being understood, it may be repeated that, in the main, +the succession of life upon the globe in point of _time_ has +corresponded with the relative order of succession of the great +groups of animals in _zoological rank_; and some of the more +striking examples of this may be here alluded to. Amongst the +_Echinoderms_, for instance, the two orders generally admitted to +be the "lowest" in the zoological scale--namely, the _Crinoids_ +and the _Cystoids_--are likewise the oldest, both, appearing in +the Cambrian, the former slowly dying out as we approach the +Recent period, and the latter disappearing wholly before the +close of the Palæozoic period. Amongst the _Crustaceans_, the +ancient groups of the Trilobites, Ostracodes, Phyllopods, +Eurypterids, and Limuloids, some of which exist at the present +day, are all "low" types; whereas the highly-organised Decapods +do not make their appearance till near the close of the Palæozoic +epoch, and they do not become abundant till we reach Mesozoic +times. Amongst the _Mollusca_, those Bivalves which possess +breathing-tubes (the "siphonate" Bivalves) are generally admitted +to be higher than those which are destitute of these organs (the +"asiphonate" Bivalves); and the latter are especially characteristic +of the Palæozoic period, whilst the former abound in Mesozoic +and Kainozoic formations. Similarly, the Univalves with +breathing-tubes and a corresponding notch in the mouth of the +shell ("siphonostomatous" Univalves) are regarded as higher in +the scale than the round-mouthed vegetable-eating Sea-snails, in +which no respiratory siphons exist ("holostomatous" Univalves); +but the latter abound in the Palæozoic rocks--whereas the former +do not make their appearance till the Jurassic period, and their +higher groups do not seem to have existed till the close of the +Cretaceous. The _Cephalopods_, again--the highest of all the groups +of Mollusca--are represented in the Palæozoic rocks exclusively +by Tetrabranchiate forms, which constitute the lowest of the +two orders of this class; whereas the more highly specialised +Dibranchiates do not make their appearance till the commencement +of the Mesozoic. The Palæozoic Tetrabranchiates, also, are of +a much simpler type than the highly complex _Ammonitidoe_ of +the Mesozoic. + +Similar facts are observable amongst the _Vertebrate animals_. +The Fishes are the lowest class of Vertebrates, and they are +the first to appear, their first certain occurrence being in +the Upper Silurian; whilst, even if the Lower Silurian and Upper +Cambrian "Conodonts" were shown to be the teeth of Fishes, there +would still remain the enormously long periods of the Laurentian +and Lower Cambrian, during which there were Invertebrates, but +no Vertebrates. The _Amphibians_, the next class in zoological +order, appears later than the Fishes, and is not represented till +the Carboniferous; whilst its highest group (that of the Frogs +and Toads) does not make its entrance upon the scene till Tertiary +times are reached. The class of the _Reptiles_, again, the next +in order, does not appear till the Permian, and therefore not +till after Amphibians of very varied forms had been in existence +for a protracted period. The _Birds_ seem to be undoubtedly later +than the Reptiles; but, owing to the uncertainty as to the exact +point of their first appearance, it cannot be positively asserted +that they preceded Mammals, as they should have done. Finally, +the Mesozoic types of _Mammals_ are mainly, if not exclusively, +referable to the _Marsupials_, one of the lowest orders of the +class; whilst the higher orders of the "Placental" Quadrupeds +are not with certainty known to have existed prior to the +commencement of the Tertiary period. + +Facts of a very similar nature are offered by the succession +of Plants upon the globe. Thus the vegetation of the Palæozoic +period consisted principally of the lowly-organised groups of +the Cryptogamous or Flowerless plants. The Mesozoic formations, +up to the Chalk, are especially characterised by the naked-seeded +Flowering plants--the Conifers and the Cycads; whilst the higher +groups of the Angiospermous Exogens and Monocotyledons characterise +the Upper Cretaceous and Tertiary rocks. + +Facts of the above nature--and they could be greatly multiplied--seem +to point clearly to the existence of some law of progression, +though we certainly are not yet in a position to formulate this +law, or to indicate the precise manner in which it has operated. +Two considerations, also, must not be overlooked. In the first +place, there are various groups, some of them highly organised, +which make their appearance at an extremely ancient date, but +which continue throughout geological time almost unchanged, and +certainly unprogressive. Many of these "persistent types" are +known--such as various of the _Foraminifera_, the _Linguloe_, the +_Nautili_, &c.; and they indicate that under given conditions, at +present unknown to us, it is possible for a life-form to subsist +for an almost indefinite period without any important modification +of its structure. In the second place, whilst the facts above +mentioned point to some general law of progression of the great +zoological groups, it cannot be asserted that the primeval types +_of any given group_ are necessarily "lower," zoologically speaking, +than their modern representatives. Nor does this seem to be at +all necessary for the establishment of the law in question. It +cannot be asserted, for example, that the Ganoid and Placoid Fishes +of the Upper Silurian are in themselves less highly organised +than their existing representatives; nor can it even be asserted +that the Ganoid and Placoid orders are low _groups_ of the class +_Pisces_. On the contrary, they are high groups; but then it +must be remembered that these are probably not really the first +Fishes, and that if we meet with Fishes at some future time in +the Lower Silurian or Cambrian, these may easily prove to be +representatives of the lower orders of the class. This question +cannot be further entered into here, as its discussion could be +carried out to an almost unlimited length; but whilst there are +facts pointing both ways, it appears that at present we are not +justified in asserting that the earlier types of each group--so far +as these are known to us, or really are without predecessors--are +_necessarily_ or _invariably_ more "degraded" or "embryonic" in +their structure than their more modern representatives. + +It remains to consider very briefly how far Palæontology supports +the doctrine of "Evolution," as it is called; and this, too, is a +question of almost infinite dimensions, which can but be glanced at +here. Does Palæontology teach us that the almost innumerable kinds +of animals and plants which we know to have successively flourished +upon the earth in past times were produced separately and wholly +independently of each other, at successive periods? or does it +point to the theory that a large number of these supposed distinct +forms, have been in reality produced by the slow modification of a +comparatively small number of primitive types? Upon the whole, it +must be unhesitatingly replied that the evidence of Palæontology +is in favour of the view that the succession of life-forms upon +the globe has been to a large extent regulated by some orderly +and constantly-acting law of modification and evolution. Upon +no other theory can we comprehend how the fauna of any given +formation is more closely related to that of the formation next +below in the series, and to that of the formation next above, +than to that of any other series of deposits. Upon no other view +can we comprehend why the Post-Tertiary Mammals of South America +should consist principally of Edentates, Llamas, Tapirs, Peccaries, +Platyrhine Monkeys, and other forms now characterising this +continent; whilst those of Australia should be wholly referable +to the order of Marsupials. On no other view can we explain the +common occurrence of "intermediate" or "transitional" forms of +life, filling in the gaps between groups now widely distinct. + +On the other hand, there are facts which point clearly to the +existence of some law other than that of evolution, and probably +of a deeper and more far-reaching character. Upon no theory of +evolution can we find a satisfactory explanation for the constant +introduction throughout geological time of new forms of life, +which do not appear to have been preceded by pre-existent allied +types; The Graptolites and Trilobites have no known predecessors, +and leave no known successors. The Insects appear suddenly in the +Devonian, and the Arachnides and Myriapods in the Carboniferous, +under well-differentiated and highly-specialised types. The +Dibranchiate Cephalopods appear with equal apparent suddenness in +the older Mesozoic deposits, and no known type of the Palæozoic +period can be pointed to as a possible ancestor. The _Hippuritidoe_ +of the Cretaceous burst into a varied life to all appearance +almost immediately after their first introduction into existence. +The wonderful Dicotyledonous flora of the Upper Cretaceous period +similarly surprises us without any prophetic annunciation from +the older Jurassic. + +Many other instances could be given; but enough has been said +to show that there is a good deal to be said on both sides, and +that the problem is one environed with profound difficulties. +One point only seems now to be universally conceded, and that +is, that the record of life in past time is not interrupted by +gaps other than those due to the necessary imperfections of the +fossiliferous series, to the fact that many animals are incapable +of preservation in a fossil condition, or to other causes of a +like nature. All those who are entitled to speak on this head +are agreed that the introduction of new and the destruction of +old species have been slow and gradual processes, in no sense of +the term "catastrophistic." Most are also willing to admit that +"Evolution" has taken place in the past, to a greater or less +extent, and that a greater or less number of so-called species of +fossil animals are really the modified descendants of pre-existent +forms. _How_ this process of evolution has been effected, to what +extent it has taken place, under what conditions and laws it has +been carried out, and how far it may be regarded as merely auxiliary +and supplemental to some deeper law of change and progress, are +questions to which, in spite of the brilliant generalisations +of Darwin, no satisfactory answer can as yet be given. In the +successful solution of this problem--if soluble with the materials +available to our hands--will lie the greatest triumph that +Palæontology can hope to attain; and there is reason to think +that, thanks to the guiding-clue afforded by the genius of the +author of the 'Origin of Species,' we are at least on the road +to a sure, though it may be a far-distant, victory. + + + + +APPENDIX. + +TABULAR VIEW OF THE CHIEF DIVISIONS OF THE ANIMAL KINGDOM. + +(Extinct groups are marked with an asterisk. Groups not represented +at all as fossils are marked with two asterisks.) + + +INVERTEBRATE ANIMALS. + +SUB-KINGDOM I.--PROTOZOA. + +Animal simple or compound; body composed of "sarcode," not definitely +segmented; no nervous system; and no digestive apparatus, beyond +occasionally a mouth and gullet. + +CLASS I. GREGARINIDÆ.** +CLASS II. RHIZOPODA. + _Order_ 1. _Monera_.** + " 2. _Amoebea_.** + " 3. _Foraminifera_. + " 4. _Radiolaria_ (Polycystines, &c.) + " 5. _Spongida_ (Sponges). +CLASS III. INFUSORIA.** + +SUB-KINGDOM II.--COELENTERATA. + +Animal simple or compound; body-wall composed of two principal +layers; digestive canal freely communicating with the general +cavity of the body; no circulating organs, and no nervous system +or a rudimentary one; mouth surrounded by tentacles, arranged, +like the internal organs, in a "radiate" or star-like manner. + +CLASS I. HYDROZOA. + _Sub-class_ 1. _Hydroida_ ("Hydroid Zoophytes"). _Ex._ + Fresh-water Polypes,** Pipe-corallines (_Tubularia_), Sea-Firs + (_Sertularia_). + _Sub-class_ 2. _Siphonophora_** ("Oceanic Hydrozoa"). + _Ex_. Portuguese Man-of-war (_Physalia_). + _Sub-class_ 3. _Discophora_ ("Jelly-fishes"). Only known as + fossils by impressions of their stranded carcasses. + _Sub-class_ 4. _Lucernarida_ ("Sea-blubbers"). Also only + known as fossils by impressions left in fine-grained strata. + _Sub-class_ 5. _Graptolitidoe_* ("Graptolites"). +CLASS II. ACTINOZOA. + _Order_ 1. _Zoantharia_. _Ex_. Sea-anemones** + (_Actinidoe_), Star-corals (_Astroeidoe_). + _Order_ 2. _Alcyonaria_. _Ex_. Sea-pens + (_Pennatula_), Organ-pipe Coral (_Tubipora_), + Red Coral (_Corallium_). + _Order_ 3. _Rugosa_ ("Rugose Corals"). + " 4. _Ctenophora_.** _Ex_. Venus's Girdle (_Cestum_). + +SUB-KINGDOM III.--ANNULOIDA. + +Animals in which the digestive canal is completely shut off from +the cavity of the body; a distinct nervous system; a system of +branched "water-vessels," which usually communicate with the +exterior. Body of the adult often "radiate," and never composed +of a succession of definite rings. + +CLASS I. ECHINODERMATA. + _Order_ 1. _Crinoidea_ ("Sea-lilies"). _Ex_. + Feather-star (_Comatula_), Stone-lily (_Encrinus_*). + _Order_ 2. _Blastoidea_* ("Pentremites"). + " 3. _Cystoidea_* ("Globe-lilies"). + " 4. _Ophiuroidea_ ("Brittle-stars"). _Ex_. + Sand-stars (_Ophiura_), Brittle-stars (_Ophiocoma_). + _Order_ 5. _Asteroidea_ ("Star-fishes"). Ex. Cross-fish + (_Uraster_), Sun-star (_Solaster_). + _Order_ 6. _Echinoidea_ ("Sea-urchins"). Ex. Sea-eggs + (_Echinus_), Heart-urchins (_Spatangus_). + _Order_ 7. _Holothuroidea_ ("Sea-cucumbers"). _Ex_. + Trepangs (_Holothuria_). +CLASS II. SCOLECIDA** (Intestinal Worms, Wheel Animalcules, &c.) + +SUB-KINGDOM IV.--ANNULOSA. + +Animal composed of numerous definite segments placed one behind +the other; nervous system forming a knotted cord placed along +the lower (ventral) surface of the body. + +_Division A. Anarthropoda_. No jointed limbs. + +CLASS I. GEPHYREA** ("Spoon-worms"). +CLASS II. ANNELIDA. ("Ringed-worms"). _Ex_. Leeches** + (_Hirudinea_), Earthworms** (_Oligochoeta_), + Tube-worms (_Tubicola_), Sea-worms and + Sea-centipedes (_Errantia_). +CLASS III. CHÆTOGNATHA** ("Arrow-worms"). + +_Division B. Arthropoda or Articulata_. Limbs jointed to the body. + +CLASS I. CRUSTACEA ("Crustaceans"). _Ex_. Barnacles and + Acorn-shells (_Cirripedia_), Water-fleas (_Ostracoda_), + Brine-shrimps and Fairy-shrimps (_Phyllopoda_), Trilobites* + (_Trilobita_), King-crabs and Eurypterids* (_Merostomata_), + Wood-lice and Slaters (_Isopoda_), Sand-hoppers + (_Amphipoda_), Lobsters, Shrimps, Hermit-crabs, and + Crabs (_Decapoda_). +CLASS II. ARACHNIDA. _Ex._ Mites (_Acarina_), Scorpions + (_Pedipalpi_), Spiders (_Araneida_). +CLASS III. MYRIAPODA. _Ex._ Centipedes (_Chilopoda_), + Millipedes and Galley-worms (_Chilignatha_). +CLASS IV. INSECTA ("Insects"). _Ex_. Field-bugs (_Hemiptera_); + Crickets, Grasshoppers, &c. (_Orthoptera_); Dragon-flies + and May-flies (_Neuroptera_); Goats and House-flies + (_Diptera_); Butterflies and Moths (_Lepidoptera_); + Bees, Wasps, and Ants (_Hymenoptera_); Beetles + (_Coleoptera_). + +SUB-KINGDOM V.--MOLLUSCA. + +Animal soft-bodied, generally with a hard covering or shell; no +distinct segmentation of the body; nervous system of scattered +masses. + +CLASS I. POLYZOA ("Sea-Mosses"). _Ex_. Sea-mats (_Flustra_), + Lace-corals (_Fenestellidoe_*). +CLASS II. TUNICATA** ("Tunicaries"). _Ex_. Sea-squirts + (_Ascidia_). +CLASS III. BRACHIOPODA ("Lamp-shells"). _Ex_. Goose-bill + Lamp-shell (_Lingula_). +CLASS IV. LAMELLIBRANCHIATA ("Bivalves"). _Ex_. Oyster + (_Ostrea_), Mussel (_Mytilus_), Scallop (_Pecten_), + Cockle (_Cardium_). +CLASS V. GASTEROPODA ("Univalves"). _Ex_. Whelks + (_Buccinum_), Limpets (_Patella_), Sea-slugs** + (_Doris_), Land-snails (_Helix_). +CLASS VI. PTEROPODA ("Winged Snails"). Ex. _Hyalea, Cleodora_. +CLASS VII. CEPHALOPODA ("Cuttle-fishes"). _Ex_. Calamary + (_Loligo_), Poulpe (_Octopus_), Paper Nautilus + (_Arganauta_), Pearly Nautilus (_Nautilus_), Belemnites,* + Orthoceratites,* Ammonites.* + + +VERTEBRATE ANIMALS. + +SUB-KINGDOM VI.--VERTEBRATA. + +Body composed of definite segments arranged longitudinally one +behind the other; main masses of the nervous system placed dorsally; +a backbone or "vertebral column" in the majority. + +CLASS I. PISCES ("Fishes"). _Ex_. Lancelet** (_Amphioxus_); + Lampreys and Hag-fishes (_Marsipobranchii_**); Herring, + Salmon, Perch, &c. (_Teleostei_ or "Bony Fishes"); + Gar-pike, Sturgeon, &c. (_Ganoidei_); Sharks, Dog-fishes, + Rays, &c. (_Elasmobranchii_ or "Placoids"). +CLASS II. AMPHIBIA ("Amphibians"). Ex. _Labyrinthodontia_,* + Cæcilians,** Newts and Salamanders (_Urodela_), Frogs and + Toads (_Anoura_). +CLASS III. REPTILIA ("Reptiles"). Ex. _Deinosauria_,* + _Pterosauria_,* _Anomodontia_,* Plesiosaurs + (_Sauropterygia_*), Ichthyosaurs (_Ichthyopterygia_*), + Tortoises and Turtles (_Chelonia_), Snakes (_Ophidia_), + Lizards (_Lacertilia_), Crocodiles (_Crocodilia_). +CLASS IV. AVES ("Birds"). _Ex_. Toothed Birds + (_Odontornithes_*); Lizard-tailed Birds (_Archoeopteryx_*); + Ducks, Geese, Gulls, &c. (_Natatores_); Storks, Herons, + Snipes, Plovers, &c. (_Grallatores_); Ostrich, Emeu, + Cassowary, Dinornis,* Æpiornis,* &c. (_Cursores_); Fowls, + Game Birds, and Doves (_Rasores_); Cuckoos, Woodpeckers, + Parrots, &c. (_Scansores_); Crows, Starlings, Finches, + Hummingbirds, Swallows, &c. (_Insessores_); Owls, Hawks, + Eagles, Vultures (_Raptores_). +CLASS V. MAMMALIA ("Quadrupeds"). _Ex_. Duck-mole and Spiny + Ant-eater (_Monotremata_**); Kangaroos, Phalangers, + Opossums, Tasmanian Devil, &c. (_Marsupialia_); Sloths, + Ant-eaters, Armadillos (_Edentata_); Manatees and Dugongs + (_Sirenia_); Whales, Dolphins, Porpoises (_Cetacea_); + Rhinoceros, Tapir, Horses, Hippopotamus, Pigs, Camels and + Llamas, Giraffes, Deer, Antelopes, Sheep, Goats, Oxen + (_Ungulata_); Hyrax (_Hyracoidea_**); Elephants, + Mastodon,* Deinotherium* (_Proboscidea_); Seals, + Walrus, Bears, Dogs, Wolves, Cats, Lions, Tigers, &c. + (_Carnivora_); Hares, Rabbits, Porcupines, Beavers, + Rats, Mice, Lemmings, Squirrels, Marmots, &c. (_Rodentia_); + Bats (_Cheiroptera_); Moles, Shrew-mice, Hedgehogs + (_Insectivora_); Lemurs, Spider-monkeys, Macaques, + Baboons, Apes (_Quadrumana_); Man (_Bimana_). + + + + +GLOSSARY. + +ABDOMEN (Lat. _abdo_, I conceal). The posterior cavity of the +body, containing the intestines and others of the viscera. In +many Invertebrates there is no separation of the body-cavity +into thorax and abdomen, and it is only in the higher _Annulosa_ +that a distinct abdomen can be said to exist. + +ABERRANT (Lat. _aberro_, I wander away). Departing from the regular +type. + +ABNORMAL (Lat. _ab_, from; _norma_, a rule). Irregular; deviating +from the ordinary standard. + +ACRODUS (Gr. _akros_, high; _odous_, tooth). A genus of the +Cestraciont fishes, so called from the elevated teeth. + +ACROGENS (Gr. _akros_, high; _gennao_, I produce). Plants which +increase in height by additions made to the summit of the stem +by the union of the bases of the leaves. + +ACROTRETA (Gr. _akros_, high; _tretos_, pierced). A genus of +Brachiopods, so called from the presence of a foramen at the summit +of the shell. + +ACTINOCRINUS (Gr. _aktin_, a ray; _krinon_, a lily). A genus of +Crinoids. + +ACTINOZOA (Gr. _aktin_, a ray; and _zoön_, an animal). That division +of the _Coelenterata_ of which the Sea-anemones may be taken as +the type. + +ÆGLINA (_Æglé_, a sea-nymph). A genus of Trilobites. + +ÆPIORNIS (Gr. _aipus_, huge; _ornis_, bird). A genus of gigantic +Cursorial birds. + +AGNOSTUS (Gr. _a_, not; _gignosko_, I know). A genus of Trilobites. + +ALCES (Lat. _alces_, elk). The European Elk or Moose. + +ALECTO (the proper name of one of the Furies). A genus of _Polyzoa_. + +ALETHOPTERIS (Gr. _alethes_, true; _pteris_, fern). A genus of +Ferns. + +ALGÆ. (Lat. _alga_, a marine plant). The order of plants comprising +the Sea-weeds and many fresh-water plants. + +ALVEOLUS (Lat. _alvus_, belly). Applied to the sockets of the +teeth. + +AMBLYPTERUS (Gr. _amblus_, blunt; _pteron_, fin). An order of +Ganoid Fishes. + +AMBONYCHIA (Gr. _ambon_, a boss; _onux_, claw). A genus of Palæozoic +Bivalves. + +AMBULACRA (Lat. _ambulacrum_, a place for walking). The perforated +spaces or "avenues" through which are protruded the tube-feet, +by means of which locomotion is effected in the _Echinodermata_. + +AMMONITIDÆ. A family of Tetrabranchiate Cephalopods, so called +from the resemblance of the shell of the type-genus, _Ammonites_, +to the horns of the Egyptian God, Jupiter-Ammon. + +AMORPHOZOA (Gr. _a_, without; _morphe_, shape; _zoön_, animal). +A name sometimes used to designate the _Sponges_. + +AMPHIBIA (Gr. _amphi_, both; _bios_, life). The Frogs, Newts, +and the like, which have gills when young, but can always breathe +air directly when adult. + +AMPHICYON (Gr. _amphi_, both--implying doubt; _kuon_, dog). An +extinct genus of _Carnivora_. + +AMPHILESTES (Gr. _amphi_, both; _lestes_, a thief). A genus of +Jurassic Mammals. + +AMPHISPONGIA (Gr. _amphi_, both; _spoggos_, sponge). A genus of +Silurian sponges. + +AMPHISTEGINA (Gr. _amphi_, both; _stegé_, roof). A genus of +_Foraminifera_. + +AMPHITHERIUM (Gr. _amphi_, both; _therion_, beast). A genus of +Jurassic Mammals. + +AMPHITRAGULUS (Gr. _amphi_, both; dim. of _tragos_, goat). An +extinct genus related to the living Musk-deer. + +AMPLEXUS (Lat. an Ambrace). A genus of Rugose Corals. + +AMPYX (Gr. _ampux_, a wreath or wheel). A genus of Trilobites. + +ANARTHROPODA (Gr. _a_, without; _arthros_, a joint; _pous_, foot). +That division of _Annulose_ animals in which there are no articulated +appendages. + +ANCHITHERIUM (Gr. _agchi_, near; _therion_, beast). An extinct +genus of Mammals. + +ANCYLOCERAS (Gr. _agkulos_, crooked; _ceras_, horn). A genus of +_Ammonitidoe_. + +ANCYLOTHERIUM (Gr. _agkulos_, crooked; _therion_, beast). An extinct +genus of Edentate Mammals. + +ANDRIAS (Gr. _andrias_, image of man). An extinct genus of tailed +Amphibians. + +ANGIOSPERMS (Gr. _angeion_, a vessel; _sperma_, seed). Plants +which have their seeds enclosed in a seed-vessel. + +ANNELIDA (a Gallicised form of _Annulata_). The Ringed Worms, +which form one of the divisions of the _Anarthropoda_. + +ANNULARIA (Lat. _annulus_, a ring). A genus of Palæozoic plants, +with leaves in whorls. + +ANNULOSA (Lat. _annulus_). The sub-kingdom comprising the +_Anarthropoda_ and the _Arthropoda_ or _Articulata_, in all of +which the body is more or less evidently composed of a succession +of rings. + +ANOMODONTIA (Gr. _anomos_, irregular; _odous_, tooth). An extinct +order of Reptiles, often called _Dicynodontia_. + +ANOMURA (Gr. _anomos_, irregular; _oura_, tail). A tribe of Decapod +_Crustacea_, of which the Hermit-crab is the type. + +ANOPLOTHERIDÆ (Gr. _anoplos_, unarmed; _ther_, beast). A family +of Tertiary Ungulates. + +ANOURA (Gr. _a_, without; _oura_, tail). The order of _Amphibia_ +comprising the Frogs and Toads, in which the adult is destitute +of a tail. Often, called _Batrachia_. + +ANTENNÆ (Lat. _antenna_, a yard-arm). The jointed horns or feelers +possessed by the majority of the _Articulata_. + +ANTENNULES (dim. of _Antennoe_). Applied to the smaller pair of +antennæ in the _Crustacea_. + +ANTHRACOSAURUS (Gr. _anthrax_, coal; _saura_, lizard). A genus +of Labyrinthodont Amphibians. + +ANTHRAPALÆMON (Gr. _anthrax_, coal; _paloemon_, a prawn--originally +a proper name). A genus of long-tailed Crustaceans from the +Coal-measures. + +ANTLERS. Properly the branches of the horns of the Deer tribe +(_Cervidoe_), but generally applied to the entire horns. + +APIOCRINIDÆ (Gr. _apion_, a pear; _krinon_, lily). A family of +Crinoids--the "Pear-encrinites." + +APTERYX (Gr. _a_, without; _pterux_, a wing). A wingless bird +of New Zealand, belong to the order _Cursores_. + +AQUEOUS (Lat. _aqua_, water). Formed in or by water. + +ARACHNIDA (Gr. _arachne_, a spider). A class of the _Articulata_, +comprising Spiders, Scorpions, and allied animals. + +ARBORESCENT. Branched like a tree. + +ARCHÆOCIDARIS (Gr. _archaios_, ancient; Lat. _cidaris_, a diadem). +A Palæozoic genus of Sea-urchins, related to the existing _Cidaris_. + +ARCHÆOCYATHUS (Gr. _archaios_, ancient; _kuathos_, cup). A genus +of Palæozoic fossils allied to the Sponges. + +ARCHÆOPTERYX (Gr. _archaios_, ancient; _pterux_, a wing). The +singular fossil bird which alone constitutes the order of the +_Saururoe_. + +ARCTOCYON (Gr. _arctos_, bear; _kuon_, dog). An extinct genus +of Carnivora. + +ARENACEOUS. Sandy, or composed of grains of sand. + +ARENICOLITES (Lat. _arena_, sand; _colo_, I inhabit). A genus +founded on burrows supposed to be formed by worms resembling +the living Lobworms (_Arenicola_). + +ARTICULATA (Lat. _articulus_, a joint). A division of the animal +kingdom, comprising Insects, Centipedes, Spiders, and Crustaceans, +characterised by the possession of jointed bodies or jointed +limbs. The term _Arthropoda_ is now more usually employed. + +ARTIODACTYLA (Gr. _artios_, even; _daktulos_, a finger or toe). +A division of the hoofed quadrupeds (_Ungulata_) in which each +foot has an even number of toes (two or four). + +ASAPHUS (Gr. _Asaphes_, obscure). A genus of Trilobites. + +ASCOCERAS (Gr. _askos_, a leather bottle; _keras_, horn). A genus +of Tetrabranchiate Cephalopods. + +ASIPHONATE. Not possessing a respiratory tube or siphon. (Applied +to a division of the _Lamellibranchiate_ Molluscs.) + +ASTEROID (Gr. _aster_, a star; and _eidos_, form). Star-shaped, +or possessing radiating lobes or rays like a star-fish. + +ASTEROIDEA. An order of _Echinodermata_, comprising the Star-fishes, +characterised by their rayed form. + +ASTEROPHYLLITES (Gr. _aster_, a star; _phullon_, leaf). A genus +of Palæozoic plants, with leaves in whorls. + +ASTRÆIDÆ (Gr. _Astroea_, a proper name). The family of the +Star-corals. + +ASTYLOSPONGIA (Gr. _a_, without; _stulos_, a column; _spoggos_, +a sponge). A genus of Silurian Sponges. + +ATHYRIS (Gr. _a_, without; _thura_, door). A genus of Brachiopods. + +ATRYPA (Gr. _a_, without; _trupa_, a hole). A genus of Brachiopods. + +AVES (Lat. _avis_, a bird). The class of the Birds. + +AVICULA (Lat. a little bird). The genus of Bivalve Molluscs +comprising the Pearl-oysters. + +AXOPHYLLUM (Gr. _axon_, a pivot; _phullon_, a leaf). A genus of +Rugose Corals. + +AZOIC (Gr. _a_, without; _zoé_, life). Destitute of traces of +living beings. + + +BACULITES (Lat. _baculum_, a staff). A genus of the _Ammonitidoe_. + +BALÆNA (Lat. a whale). The genus of the Whalebone Whales. + +BALANIDÆ (Gr. _balanos_, an acorn). A family of sessile _Cirripedes_, +commonly called "Acorn-shells." + +BATRACHIA (Gr. _batrachos_, a frog). Often loosely applied to +any of the _Amphibia_, but sometimes restricted to the Amphibians +as a class, or to the single order of the _Anoura_. + +BELEMNITIDÆ (Gr. _belemnon_, a dart). An extinct group of +Dibranchiate Cephalopods, comprising the Belemnites and their +allies. + +BELEMNOTEUTHIS (Gr. _belemnon_, a dart; _teuthis_, a cuttle-fish). +A genus allied to the Belemnites proper. + +BELINURUS (Gr. _belos_, a dart; _oura_, tail). A genus of fossil +King-crabs. + +BELLEROPHON (Gr. proper name). A genus of oceanic Univalves +(_Heteropoda_). + +BELOTEUTHIS (Gr. _belos_, a dart; _teuthis_, a cuttle-fish). An +extinct genus of Dibranchiate Cephalopods. + +BEYRICHIA (named after Prof. Beyrich). A genus of Ostracode +Crustaceans. + +BILATERAL. Having two symmetrical sides. + +BIMANA (Lat. _Bis_, twice; _manus_, a hand). The order of _Mammalia_ +comprising man alone. + +BIPEDAL (Lat. _bis_, twice; _pes_, foot). Walking upon two legs. + +BIVALVE (Lat. _bis_, twice; _valvoe_, folding-doors). Composed of +two plates or valves; applied to the shell of the _Lamellibranchiata_ +and _Brachiopoda_, and to the carapace of certain _Crustacea_. + +BLASTOIDEA (Gr. _blastos_, a bud; and _eidos_, form). An extinct +order of _Echinodermata_, often called _Pentremites_. + +BRACHIOPODA (Gr. _brachion_, an arm; _pous_, the foot). A class +or the _Molluscoida_, often called "Lamp-shells," characterised +by possessing two fleshy arms continued from the sides of the +mouth. + +BRACHYURA (Gr. _brachus_, short; _oura_, tail). A tribe of the +Decapod _Crustaceans_ with short tails (_i.e._, the Crabs). + +BRADYPODIDÆ. (Gr. _bradus_, slow; _podes_, feet). The family of +_Edentata_ comprising the Sloths. + +BRANCHIA (Gr. _bragchia_, the gill of a fish). A respiratory organ +adapted to breathe air dissolved in water. + +BRANCHIATE. Possessing gills or branchiæ. + +BRONTEUS (Gr. _broné_, thunder--an epithet of Jupiter the Thunderer). +A genus of Trilobites. + +BRONTOTHERIUM (Gr. _bronté_, thunder; _therion_ beast). An extinct +genus of Ungulate Quadrupeds. + +BRONTOZOUM (Gr. _bronté_, thunder; _zoön_, animal). A genus founded +on the largest footprints of the Triassic Sandstones of Connecticut. + +BUCCINUM (Lat. _buccinun_, a trumpet). The genus of Univalves +comprising the Whelks. + + +CAINOZOIC (_See_ Kainozoic.) + +CALAMITES (Lat. _calamus_, a reed). Extinct plants with reed-like +stems, believed to be gigantic representatives of the _Equisetaceoe_. + +CALCAREOUS (Lat. _calx_, lime). Composed of carbonate of lime. + +CALICE. The little cup in which the polype of a coralligenous +Zoophyte (_Actinozoön_) is contained. + +CALYMENE (Gr. _kalumené_, concealed). A genus of Trilobites. + +CALYX (Lat. a cup). Applied to the cup-shaped body of a _Crinoid_ +(_Echinodermata_). + +CAMAROPHORIA (Gr. _kamara_, a chamber; _phero_, I carry). A genus +of Brachiopods. + +CAMELOPARDALIDÆ. (Lat. _camelus_, a camel; _pardalis_, a panther). +The family of the Giraffes. + +CANINE (Lat. _canis_, a dog). The eye-tooth of Mammals, or the +tooth which is placed at or close to the præmaxillary suture in +the upper jaw, and the corresponding tooth in the lower jaw. + +CARAPACE. A protective shield. Applied to the upper shell of +Crabs, Lobsters, and many other _Crustacea_. Also the upper half +of the immovable case in which the body of a Chelonian is protected. + +CARCHARODON (Gr. _karcharos_. rough; _odous_, tooth). A genus +of Sharks. + +CARDIOCARPON (Gr. _kardia_, the heart; _karpos_, fruit). A genus +of fossil fruit from the Coal-measures. + +CARDIUM (Gr. _kardia_, the heart). The genus of Bivalve Molluscs +comprising the Cockles. _Cardinia, Cardiola_, and _Cardita_ have +the same derivation. + +CARNIVORA (Lat. _caro_, flesh; _voro_, I devour). An order of +the _Mammalia_. The "Beasts of Prey." + +CARNIVOROUS (Lat. _caro_, flesh; _voro_, I devour). Feeding upon +flesh. + +CARYOCARIS (Gr. _karua_, a nut; _karis_, a shrimp). A genus of +Phyllopod Crustaceans. + +CARYOCRINUS (Gr. _karua_, a nut; _krinon_, a lily). A genus of +Cystideans. + +CAUDAL (Lat. _cauda_, the tail). Belonging to the tail. + +CAVICORNIA (Lat. _cavus_, hollow; _cornu_, a horn). The +"hollow-horned" Ruminants, in which the horn consists of a central +bony "horn-core" surrounded by a horny sheath. + +CENTRUM (Gr. _kentron_, the point round which a circle is described +by a pair of compasses). The central portion or "body" of a vertebra. + +CEPHALASPIDÆ. (Gr. _kephale_, head; _aspis_, shield). A family +of fossil fishes. + +CEPHALIC (Gr. _kephale_, head). Belonging to the head. + +CEPHALOPODA (Gr. _kephale_; and _podes_, feet). A class of the +_Mollusca_, comprising the Cuttle-fishes and their allies, in +which there is a series of arms ranged round the head. + +CERATIOCARIS (Gr. _keras_, a horn; _karis_, a shrimp). A genus +of Phyllopod Crustaceans. + +CERATITES (Gr. _keras_, a horn). A genus of _Ammonitidoe_. + +CERATODUS (Gr. _keras_, a horn; _odous_, tooth). A genus of Dipnoous +fishes. + +CERVICAL (Lat. _cervix_, the neck). Connected with or belonging +to the region of the neck. + +CERVIDÆ (Lat. _cervus_, a stag). The family of the Deer. + +CESTRAPHORI (Gr. _kestra_, a weapon; _phero_, I carry). The group +of the "Cestraciont Fishes," represented at the present day by +the Port-Jackson Shark; so called from their defensive spines. + +CETACEA (Gr. _ketos_, a whale). The order of Mammals comprising +the Whales and the Dolphins. + +CETIOSAURUS (Gr. _ketos_, whale; _saura_, lizard). A genus of +Deinosaurian Reptiles. + +CHEIROPTERA (Gr. _cheir_, hand; _pteron_, wing). The Mammalian +order of the Bats. + +CHEIROTHERIUM (Gr. _cheir_, hand; _therion_, beast). The generic +name applied originally to the hand-shaped footprints of +Labyrinthodonts. + +CHEIRURUS (Gr. _cheir_, hand; _oura_, tail). A genus of Trilobites. + +CHELONIA (Gr. _cheloné_, a tortoise). The Reptilian order of the +Tortoises and Turtles. + +CHONETES (Gr. _choné_ or _choané_, a chamber or box). A genus +of Brachiopods. + +CIDARIS (Lat. a diadem). A genus of Sea-urchins. + +CLADODUS (Gr. _klados_, branch; _odous_, tooth). A genus of Fishes. + +CLATHROPORA (Lat. _clathti_, a trellis; _porus_, a pore). A genus +of Lace-corals (_Polyzoa_). + +CLISIOPHYLLUM (Gr. _klision_, a hut; _phullon_, leaf). A genus +of Rugose Corals. + +CLYMENIA (_Clumene_, a proper name). A genus of Tetrabranchiate +Cephalopods. + +COCCOSTEUS (Gr. _kokkos_, berry; _osteon_, bone). A genus of Ganoid +Fishes. + +COCHLIODUS (Gr. _kochlion_, a snail-shell; _odous_, tooth). A +genus of Cestraciont Fishes. + +COELENTERATA (Gr. _koilos_, hollow; _enteron_, the bowel). The +sub-kingdom which comprises the _Hydrozoa_ and _Actinozoa_. Proposed +by Frey and Leuckhart in place of the old term _Radiata_, which +included other animals as well. + +COLEOPTERA (Gr. _koleos_, a sheath; _pteron_, wing). The order +of Insects (Beetles) in which the anterior pair of wings are +hardened, and serve as protective cases for the posterior pair +of membranous wings. + +COLOSSOCHELYS (Gr. _kolossos_, a gigantic statue; _chelus_, a +tortoise). A huge extinct Land-tortoise. + +COMATULA (Gr. _koma_, the hair). The Feather-star, so called in +allusion to its tress-like arms. + +CONDYLE (Gr. _kondulos_, a knuckle). The surface by which one +bone articulates with another. Applied especially to the articular +surface or surfaces by which the skull articulates with the vertebral +column. + +CONIFERÆ (Lat. _conus_, a cone; _fero_, I carry). The order of +the Firs, Pines, and their allies, in which the fruit is generally +a "cone" or "fir-apple." + +CONULARIA (Lat. _conulus_, a little-cone). An extinct genus of +Pteropods. + +COPRALITES (Gr. _kopros_, dung; _lithos_, stone). Properly applied +to the fossilised excrements of animals; but often employed to +designate phosphatic concretions which are not of this nature. + +CORALLITE. The corallum secreted by an _Actinozoön_ which consists +of a single polype; or the portion of a composite corallum which +belongs to, and is secreted by, an individual polype. + +CORALLUM (from the Latin for Red Coral). The hard structures +deposited in, or by the tissues of an _Actinozoön_,--commonly +called a "coral." + +CORIACEOUS (Lat. _corium_. hide). Leathery. + +CORYPHODON (Gr. _korus_, helmet; _odous_, tooth). An extinct genus +of Mammals, allied to the Tapirs. + +CRANIUM (Gr. _kranion_, the skull). The bony or cartilaginous +case in which the brain is contained. + +CRETACEOUS (Lat. _creta_, chalk). The formation which in Europe +contains white chalk as one of its most conspicuous members. + +CRINOIDEA (Gr. _krinon_, a lily; _eidos_, form). An order of +_Echinodermata_, comprising forms which are usually stalked, and +sometimes resemble lilies in shape. + +CRIOCERAS (Gr. _krios_, a ram; _keras_, a horn). A genus of +_Ammonitidoe_. + +CROCODILIA (Gr. _krokodeilos_, a crocodile). An order of Reptiles. + +CROSSOPTERYGIDÆ. (Gr. _krossotos_, a fringe; _pterux_, a fin). A +sub-order of Ganoids in which the paired fins possess a central +lobe. + +CRUSTACEA (Lat. _crusta_, a crust). A class of Articulate animals, +comprising Crabs, Lobsters, &c., characterised by the possession +of a hard shell or crust, which they cast periodically. + +CRYPTOGAMS (Gr. _kruptos_, concealed; _gamos_, marriage). A division +of plants in which the organs of reproduction are obscure and +there are no true flowers. + +CTENACANTHUS (Gr. _kteis_, a comb; _akantha_, a thorn). A genus +of fossil fishes, named from its fin-spines. + +CTENOID (Gr. _kteis_, a comb; _eidos_, form). Applied to those +scales of fishes the hinder margins of which are fringed with +spines or comb-like projections. + +CURSORES (Lat. _curro_, I run). An order of _Aves_, comprising +birds destitute of the power of flight, but formed for running +vigorously (_e.g._, the Ostrich and Emeu). + +CUSPIDATE. Furnished with small pointed eminences or "cusps." + +CYATHOCRINUS (Gr. _kuathos_, a cup; _krinon_, a lily). A genus +of Crinoids. + +CYATHOPHYLLUM (Gr. _kuathos_, a cup; _phullon_, a leaf). A genus +of Rugose Corals. + +CYCLOID (Gr. _kuklos_, a circle; _eidos_, form). Applied to those +scales of fishes which have a regularly circular or elliptical +outline with an even margin. + +CYCLOPHTHALMUS (Gr. _kuklos_, a circle; _ophthalmos_, eye). A +genus of fossil Scorpions. + +CYCLOSTOMI (Gr. _kuklos_, and _stoma_, mouth). Sometimes used +to designate the Hag-fishes and Lampreys, forming the order +_Marsipobranchii_. + +CYPRÆA (a name of Venus). The genus of Univalve Molluscs comprising +the Cowries. + +CYRTOCERAS (Gr. _kurtos_. crooked; _keras_, horn). A genus of +Tetrabranchiate Cephalopods. + +CYSTIPHYLLUM (Gr. _kustis_, a bladder; _phullon_, a leaf). A genus +of Rugose Corals. + +CYSTOIDEA (Gr. _kustis_, a bladder; _eidos_, form). The +"Globe-crinoids," an extinct order of _Echinodermata_. + + +DADOXYLON (Gr. _dadion_, a torch; _xulon_, wood). An extinct genus +of Coniferous trees. + +DECAPODA (Gr. _deka_, ten; _podes_, feet). The division of +_Crustacea_ which have ten feet; also the family of Cuttle-fishes, +in which there are ten arms or cephalic processes. + +DECIDUOUS (Lat. _decido_, I fall off). Applied to parts which +fall off or are shed during the life of the animal. + +DEINOSAURIA (Gr. _deinos_, terrible; _saura_, lizard). An extinct +order of Reptiles. + +DEINOTHERIUM (Gr. _deinos_, terrible; _therion_, beast). An extinct +genus of Proboscidean Mammals. + +DENDROGRAPTUS (Gr. _dendron_, tree; _grapho_, I write). A genus +of Graptolites. + +DESMIDIÆ. Minute fresh-water plants, of a green colour, without +a siliceous epidermis. + +DIATOMACEÆ (Gr. _diatemno_, I sever). An order of minute plants +which are provided with siliceous envelopes. + +DIBRANCHIATA (Gr. _dis_; twice; _bragchia_, gill). The order +of _Cephalopoda_ (comprising the Cuttle-fishes, &c.) in which +only two gills are present. + +DICERAS (Gr. _dis_, twice; _keras_, horn). An extinct genus of +Bivalve Molluscs. + +DICTYONEMA (Gr. _diktuon_, a net; _nema_, thread). An extinct +genus of _Polyzoa_. + +DICYNODONTIA (Gr. _dis_, twice; _kuon_, dog; _odous_, tooth). +An extinct order of Reptiles. + +DIDYMOGRAPTUS (Gr. _didumos_, twin; _grapho_, I write). A genus +of Graptolites. + +DIMORPHODON (Gr. _dis_, twice; _morphé_, shape; _oduos_, tooth). +A genus of Pterosaurian reptiles. + +DINICHTHYS (Gr. _deinos_, terrible; _ichthus_, fish). An extinct +genus of Fishes. + +DINOCERAS (Gr. _deinos_, terrible; _keras_, horn). An extinct +genus of Mammals. + +DINOPHIS (Gr. _deinos_, terrible; _ophis_, snake). An extinct +genus of Snakes. + +DINORNIS (Gr. _deinos_, terrible; _ornis_, bird). An extinct genus +of Birds. + +DIPLOGRAPTUS (Gr. _diplos_, double; _grapho_, I write). A genus +of Graptolites. + +DIPNOI (Gr. _dis_, twice; _pnoé_, breath). An order of Fishes, +comprising the Mud-fishes, so called in allusion to their double +mode of respiration. + +DIPROTODON (Gr. _dis_, twice; _protos_, first; _odous_, tooth). +A genus of extinct Marsupials. + +DIPTERA (Gr. _dis_, twice; _pteron_, wing). An order of Insects +characterised by the possession of two wings. + +DISCOID (Gr. _diskos_, a quoit; _eidos_, form). Shaped like a +round plate or quoit. + +DOLOMITE (named after M. Dolomieu). Magnesian limestone. + +DORSAL (Lat. _dorsum_, the back). Connected with or placed upon +the back. + +DROMATHERIUM (Gr. _dromaios_, nimble; _therion_, beast). A genus +of Triassic Mammals. + +DRYOPITHECUS (Gr. _drus_, an oak; _pithekos_, an ape). An extinct +genus of Monkeys. + + +ECHINODERMATA (Gr. _echinos_; and _derma_, skin). A class of +animals comprising the Sea-urchins, Star-fishes, and others, most +of which have spiny skins. + +ECHINOIDEA (Gr. _echinos_; and _eidos_, form). An order of +_Echinodermata_, comprising the Sea-urchins. + +EDENTATA (Lat. _e_, without; _dens_, tooth). An order of _Mammalia_ +often called _Bruta_. + +EDENTULOUS. Toothless, without any dental apparatus. Applied to +the mouth of any animal, or to the hinge of the Bivalve Molluscs. + +ELASMOBRANCHII (Gr. _elasma_, a plate; _bragchia_, gill). An order +of Fishes, including the Sharks and Rays. + +ENALIOSAURIA (Gr. _enalios_, marine; _saura_, lizard), Sometimes +employed as a common term to designate the extinct Reptilian +orders of the _Ichthyosauria_ and _Plesiosauria_. + +EOCENE (Gr. _eos_, dawn; _kainos_, new or recent). The lowest +division of the Tertiary rocks, in which species of existing +shells are to a small extent represented. + +EOPHYTON (Gr. _eos_, dawn; _phuton_, a plant). A genus of Cambrian +fossils, supposed to be of a vegetable nature. + +EOZOÖN (Gr. _eos_, dawn; _zoön_, animal). A genus of chambered +calcareous organisms found in the Laurentian and Huronian formations. + +EQUILATERAL (Lat. _oequus_, equal; _latus_, side). Having its +sides equal. Usually applied to the shells of the _Brachiopoda_. +When applied to the spiral shells of the _Foraminifera_, it means +that all the convolutions of the shell lie in the same plane. + +EQUISETACEÆ (Lat. _equus_, horse; _seta_, bristle). A group of +Cryptogamous plants, commonly known as "Horse-tails." + +EQUIVALVE (Lat. _oequus_, equal; _valvoe_, folding-doors). Applied +to shells which are composed of two equal pieces or valves. + +ERRANTIA (Lat. _erro_, I wander). An order of _Annelida_, often +called _Nereidea_, distinguished by their great locomotive powers. + +EUOMPHALUS (Gr. _eu_, well; _omphalos_, navel). An extinct genus +of Univalve Molluscs. + +EURYPTERIDA (Gr. _eurus_, broad; _pteron_, wing). An extinct +sub-order of _Crustacea_. + +EXOGYRA (Gr. _exo_, outside; _guros_, circle). An extinct genus +of Oysters. + + +FAUNA (Lat. _Fauni_, the rural deities of the Romans). The general +assemblage of the animals of any region or district. + +FAVOSITES (Lat. _favus_, a honeycomb). A genus of Tabulate Corals. + +FENESTELLIDÆ. (Lat. _fenestella_, a little window). The +"Lace-corals," a group of Palæozoic Polyzoans. + +FILICES (Lat. _filix_, a fern). The order of Cryptogamic plants +comprising the Ferns. + +FILIFORM (Lat. _filum_, a thread; _forma_, shape). Thread-shaped. + +FLORA (Lat. _Flora_, the goddess of flowers). The general assemblage +of the plants of any region or district. + +FORAMINIFERA (Lat. _foramen_, an aperture; _fero_, I carry). +An order of Protozoa, usually characterised by the possession +of a shell perforated by numerous pseudopodial apertures. + +FRUGIVOROUS (Lat. _frux_, fruit; _voro_, I devour). Living upon +fruits. + +FUCOIDS (Lat. _fucus_, sea-weed; Gr. _eidos_, likeness). Fossils, +often of an obscure nature, believed to be the remains of sea-weeds. + +FUSULINA (Lat. _fusus_, a spindle). An extinct genus of +_Foraminifera_. + + +GANOID (Gr, _ganos_, splendour, brightness). Applied to those +scales or plates which are composed of an inferior layer of true +bone covered by a superior layer of polished enamel. + +GANOIDEI. An order of Fishes. + +GASTEROPODA (Gr. _gaster_, stomach; _pous_, foot). The class +of the Mollusca comprising the ordinary Univalves, in which +locomotion is usually effected by a muscular expansion of the +under surface of the body (the "foot"). + +GLOBIGERINA (Lat. _globus_, a globe; _gero_, I carry). A genus +of _Foraminifera_. + +GLYPTODON (Gr. _glupho_, I engrave; _odous_, tooth). An extinct +genus of Armadillos, so named in allusion to the fluted teeth. + +GONIATITES (Gr. _gonia_, angle). A genus of Tetrabranchiate +Cephalopods. + +GRALLATORES (Lat. _gralloe_, stilts). The order of the long-legged +Wading Birds. + +GRAPTOLITIDÆ. (Gr. _grapho_, I write; _lithos_, stone). An extinct +sub-class of the _Hydrozoa_. + +GYMNOSPERMS (Gr. _gumnos_, naked; _sperma_, seed). The Conifers +and Cycads, in which the seed is not protected within a seed-vessel. + + +HALITHERIUM (Gr. _hals_, sea; _therion_, beast). An extinct genus +of Sea-cows (_Sirenia_). + +HAMITES (Lat. _hamus_, a hook). A genus of the _Ammonitidoe_. + +HELIOPHYLLUM (Gr. _helios_, the sun; _phullon_, leaf). A genus +of Rugose Corals. + +HELLADOTHERIUM (Gr. _Hellas_, Greece; _therion_, beast). An extinct +genus of Ungulate Mammals. + +HEMIPTERA (Gr. _hemi_, and _pteron_, wing). An order of Insects +in which the anterior wings are sometimes "hemelytra." + +HESPERORNIS (Gr. _Hesperos_, the evening star; _ornis_, bird). +An extinct genus of Birds. + +HETEROCERCAL (Gr. _heteros_, diverse; _kerkos_, tail). Applied +to the tail of Fishes when it is unsymmetrical, or composed of +two unequal lobes. + +HETEROPODA (Gr. _heteros_, diverse; _podes_, feet). An aberrant +group of the Gasteropods, in which the foot is modified so as +to form a swimming organ. + +HIPPARION (Gr. _hipparion_, a little horse). An extinct genus +of _Equidoe_. + +HIPPOPOTAMUS (Gr. _hippos_, horse; _potamos_, river). A genus +of Hoofed Quadrupeds--the "River-horses." + +HIPPURITIDÆ. (Gr. _hippos_, horse; _oura_, tail). An extinct family +of Bivalve Molluscs. + +HOLOPTYCHIUS (Gr. _holos_, whole; _ptucé_, wrinkle). An extinct +genus of Ganoid Fishes. + +HOLOSTOMATA (Gr. _holos_, whole; _stoma_, mouth). A division +of _Gasteropodous Molluscs_, in which the aperture of the shell +is rounded, or "entire." + +HOLOTHUROIDEA (Gr. _holothourion_, and _eidos_, form). An order +of _Echinodermata_ comprising the Trepangs. + +HOMOCERCAL (Gr. _homos_, same; _kerkol_, tail). Applied to the +tail of Fishes when it is symmetrical, or composed of two equal +lobes. + +HYBODUNTS (Gr. _hubos_, curved; _odous_, tooth). A group of Fishes +of which _Hybodus_ is the type-genus. + +HYDROIDA (Gr. _hudra_; and _eidos_, form). The sub-class of the +_Hydrozoa_, which comprises the animals most nearly allied to +the Hydra. + +HYDROZOA (Gr. _hudra_; and _zoön_, animal). The class of the +_Coelenterata_ which comprises animals constructed after the type +of the Hydra. + +HYMENOPTERA (Gr. _humen_, a membrane; _pteron_, a wing). An order +of Insects (comprising Bees, Ants, &c.) characterised by the +possession of four membranous wings. + + +ICHTHYODORULITE (Gr. _ichthus_, fish; _dorus_, spear; _lithos_, +stone). The fossil fin-spine of Fishes. + +ICHTHYOPTERYGIA (Gr. _ichthus_; _pterux_, wing). An extinct order +of Reptiles. + +ICHTHYORNIS (Gr. _ichthus_, fish; _ornis_, bird). An extinct genus +of Birds. + +ICHTHYOSAURIA (Gr. _ichthus_; _saura_, lizard). Synonymous with +_Ichthyopterygia_. + +IGUANODON (_Iguana_, a living lizard; Gr. _odous_, tooth). A genus +of Deinosaurian Reptiles. + +INCISOR (Lat. _incido_, I cut). The cutting teeth fixed in the +intermaxillary bones of the _Mammalia_, and the corresponding +teeth in the lower jaw. + +INEQUILATERAL. Having the two sides unequal, as in the case of +the shells of the ordinary bivalves (_Lamellibranchiata_). When +applied to the shells of the _Foraminifera_, it implies that +the convolutions of the shell do not lie in the same plane, but +are obliquely wound round an axis. + +INEQUIVALVE. Composed of two unequal pieces or valves. + +INOCERAMUS (Gr. _is_, a fibre; _keramos_, an earthen vessel). +An extinct genus of Bivalve Molluscs. + +INSECTA (Lat. _inseco_, I cut into). The class of articulate animals +commonly known as Insects. + +INSECTIVORA (Lat. _insectum_, an insect; _voro_, I devour). An +order of Mammals. + +INSECTIVOROUS. Living upon Insects. + +INSESSORES (Lat. _insedeo_, I sit upon). The order of the Perching +Birds, often called _Passeres_. + +INTERAMBULACRA. The rows of plates in an _Echinoid_ which are +not perforated for the emission of the "tube-feet." + +INTERMMAXILLÆ or PRÆMAXILLÆ. The two bones which are situated +between the two superior maxillæ in _Vertebrata_. In man, and +some monkeys, the præmaxillæ anchylose with the maxillæ, so as +to be irrecognisable in the adult. + +INVERTEBRATA (Lat. _in_, without; _vertebra_, a bone of the back). +Animals without a spinal column or backbone. + +ISOPODA. (Gr. _isos_, equal; _podes_, feet). An order of _Crustacea_ +in which the feet are like one another and equal. + + +KAINOZOIC (Gr. _kainos_, recent; _zoe_, life). The Tertiary period +in Geology comprising those formations in which the organic remains +approximate more or less closely to the existing fauna and flora. + + +LABYRINTHODONTIA (Gr. _laburinthos_, a labyrinth; _odous_, tooth). +An extinct order of _Amphibia_, so called from the complex +microscopic structure of the teeth. + +LACERTILIA (Lat. _lacerta_, a lizard). An order of _Reptilia_ +comprising the Lizards and Slow-worms. + +LAMELLIBRANCHIATA (Lat. _lamella_, a plate; Gr. _bragchia_, gill). +The class of _Mollusca_ comprising the ordinary bivalves, +characterised by the possession of lamellar gills. + +LEPIDODENDRON (Gr. _lepis_, a scale; _dendron_, a tree). A genus +of extinct plants, so named from the scale-like scars upon the +stem left by the falling off of the leaves. + +LEPIDOPTERA (Gr. _lepis_, a scale; _pteron_, a wing). An order +of Insects, comprising Butterflies and Moths, characterised by +possessing four wings which are usually covered with minute scales. + +LEPIDOSIREN (Gr. _lepis_, a scale; _seiren_, a siren--the generic +name of the Mud-eel or _Siren lacertina_). A genus of Dipnoous +fishes, comprising the "Mud-fishes." + +LEPIDOSTROBUS (Gr. _lepis_, a scale; _strobilos_, a fir-cone). +A genus founded on the cones of _Lepidodendron_. + +LEPTÆNA (Gr. _leptos_. slender). A genus of Brachiopods. + +LINGULA (Lat. _lingula_, a little tongue). A genus of Brachiopods. + +LYCOPODIACEÆ (Gr. _lupos_, a wolf; _pous_, foot). The group of +Cryptogamic plants generally known as "Club-mosses." + + +MACHÆRACANTHUS (Gr. _machaira_, a sabre; _acantha_, thorn or spine). +An extinct genus of Fishes. + +MACHAIRODUS (Gr. _machaira_, a sabre; _odous_, tooth). An extinct +genus of Carnivora. + +MACROTHERIUM (Gr. _makros_, long; _therion_. beast). An extinct +genus of Edentata. + +MACRURA (Gr. _makros_, long; _oura_, tail). A tribe of Decapod +_Crustaceans_ with long tails (e.g., the Lobster, Shrimp, &c.) + +MAMMALIA (Lat. _mamma_, the breast). The class of Vertebrate animals +which suckle their young. + +MANDIBLE (Lat. _mandibulum_, a jaw). The upper pair of jaws in +Insects; also applied to one of the pairs of jaws in _Crustacea_ +and Spiders, to the beak of Cephalopods, the lower jaw of +Vertebrates, &c. + +MANTLE. The external integument of most of the Mollusca, which +is largely developed, and forms a cloak in which the viscera +are protected. Technically called the "pallium." + +MANUS (Lat. the hand). The hand of the higher Vertebrates. + +MARSIPOBRANCHII (Gr. _marsipos_, a pouch; _bragchia_, gill). +The order of Fishes comprising the Hag-fishes and Lampreys, with +pouch-like gills. + +MARSUPIALIA (Lat. _marsupium_, a pouch). An order of Mammals in +which the females mostly have an abdominal pouch in which the +young are carried. + +MASTODON (Gr. _mastos_, nipple; _odous_, tooth). An extinct genus +of Elephantine Mammals. + +MEGALONYX (Gr. _megas_, great; _onux_, nail). An extinct genus +of Edentate Mammals. + +MEGALOSAURUS (Gr. _megas_, great; _saura_, lizard). A genus of +Deinosaurian Reptiles. + +MEGATHERIUM (Gr. _megas_, great; _therion_, beast). An extinct +genus of Edentata. + +MESOZOIC (Gr. _mesos_, middle; and _zoe_, life). The Secondary +period in Geology. + +MICROLESTES (Gr. _mikros_, little; _lestes_, thief). An extinct +genus of Triassic Mammals. + +MILLEPORA (Lat. _mille_, one thousand; _porus_, a pore). A genus +of "Tabulate Corals." + +MIOCENE (Gr. _meion_, less; _kainol_, new). The Middle Tertiary +period. + +MOLARS (Lat. _mola_, a mill). The "grinders" in man, or the teeth +in diphyodont Mammals which are not preceded by milk-teeth. + +MOLLUSCA (Lat. _mollis_, soft). The sub-kingdom which includes +the Shell-fish proper, the _Polyzoa_, the _Tunicata_, and the +Lamp-shells; so called from the generally soft nature of their +bodies. + +MOLLUSCOIDA (_Mollusca_; Gr. _eidos_, form). The lower division +of the _Mollusca_, comprising the _Polyzoa, Tunicata_, and +_Brachiopoda_. + +MONOGRAPTUS (Gr. _monos_, single; _grapho_, I write). A genus +of Graptolites. + +MYLODON (Gr. _mulos_, a mill; _odous_, tooth). An extinct genus +of Edentate Mammals. + +MYRIAPODA or MYRIOPODA (Gr. _murios_, ten thousand; _podes_, +feet). A class of _Arthropoda_ comprising the Centipedes and their +allies, characterised by their numerous feet. + + +NATATORES (Lat. _nare_, to swim). The order of the Swimming Birds. + +NATATORY (Lat. _nare_, to swim). Formed for swimming. + +NAUTILOID. Resembling the shell of the _Nautilus_ in shape. + +NERVURES (Lat. _nervus_, a sinew). The ribs which support the +membranous wings of insects. + +NEUROPTERA (Gr. _neuron_, a nerve; _pteron_, a wing). An order +of Insects characterised by four membranous wings with numerous +reticulated nervures (_e.g._, Dragon-flies). + +NEUROPTERIS (Gr. _neuron_, a nerve; _pteris_, a fern). An extinct +genus of Ferns. + +NOTHOSAURUS (Gr. _nothos_, spurious; _saura_, lizard). A genus +of _Plesiosaurian_ Reptiles. + +NOTOCHORD (Gr. _notos_, back; _chorde_, string). A cellular rod +which is developed in the embryo of Vertebrates immediately beneath +the spinal cord, and which is usually replaced in the adult by the +vertebral column. Often it is spoken of as the "chorda dorsalis." + +NUDIBRANCHIATA (Lat. _nudus_, naked; and Gr. _bragchia_, gill). +An order of the _Gasteropoda_ in which the gills are naked. + +NUMMULINA (Lat. _nummus_, a coin). A genus of _Foraminifera_, +comprising the coin-shaped "Nummulites." + + +OBOLELLA (Lat. dim. of _obolus_, a small coin). An extinct genus +of Brachiopods. + +OCCIPITAL. Connected with the _occiput_, or the back part of the +head. + +OCEANIC. Applied to animals which inhabit the open ocean (= pelagic). + +ODONTOPTERYX (Gr. _oduos_, tooth; _pterux_, wing). An extinct +genus of Birds. + +ODONTORNITHES (Gr. _oduos_, tooth; _ornis_, bird). The extinct +order of Birds, comprising forms with distinct teeth in sockets. + +OLIGOCENE (Gr. _oligos_, few; _kainos_, new). A name used by +many Continental geologists as synonymous with the Lower Miocene. + +OPHIDIA (Gr. _ophis_, a serpent). The order of Reptiles comprising +the Snakes. + +OPHIUROIDEA (Gr. _ophis_, snake; _oura_, tail; _eidos_, form). +An order of _Echinodermata_, comprising the Brittle-stars and +Sand-stars. + +ORNITHOSCELIDA (Gr. _ornis_, bird; _skelos_, leg). Applied by +Huxley to the Deinosaurian Reptiles, together with the genus +_Compsognathus_, on account of the bird-like character of their +hind-limbs. + +ORTHIS (Gr. _orthos_, straight). A genus of Brachiopods, named +in allusion to the straight hinge-line. + +ORTHOCERATIDÆ (Gr. _orthos_, straight; _keras_, horn). A family +of the _Nautilidoe_, in which the shell is straight, or nearly +so. + +ORTHOPTERA (Gr. _orthos_, straight; _pteron_, wing). An order +of Insects. + +OSTEOLEPIS (Gr. _osteon_, bone; _lepis_, scale). An extinct genus +of Ganoid Fishes. + +OSTRACODA (Gr. _ostrakon_, a shell). An order of small Crustaceans +which are enclosed in bivalve shells. + +OTODUS (Gr. _ota_, ears; _odous_, tooth). An extinct genus of +Sharks. + +OUDENODON (Gr. _ouden_, none; _odous_, tooth). A genus of Dicynodont +Reptiles. + +OVIBUS (Lat. _ovis_, sheep; _bos_, ox). The genus comprising the +Musk-ox. + + +PACHYDERMATA (Gr. _pachus_, thick; _derma_, skin). An old Mammalian +order constituted by Cuvier for the reception of the Rhinoceros, +Hippopotamus, Elephant, &c. + +PALÆASTER (Gr. _palaios_, ancient; _aster_, star). An extinct +genus of Star-fishes. + +PALÆOCARIS (Gr. _palaios_, ancient; _karis_, shrimp). An extinct +genus of Decapod Crustaceans. + +PALÆOLITHIC (Gr. _palaios_, ancient; _lithos_, stone). Applied +to the rude stone implements of the earliest known races of men, +to the men who made these implements, or to the period at which +they were made. + +PALÆONTOLOGY (Gr. _palaios_, ancient; and _logos_, discourse). +The science of fossil remains or of extinct organised beings. + +PALÆOPHIS (Gr. _palaios_, ancient; _ophis_, serpent). An extinct +genus of Snakes. + +PALÆOSAURUS (Gr. _palaios_, ancient; _saura_, lizard). A genus +of Thecodont Reptiles. + +PALÆOTHERIDÆ. (Gr. _palaios_, ancient; _ther_, beast). A group +of Tertiary Ungulates. + +PALÆOZOIC (Gr. _palaios_, ancient; and _zoe_, life). Applied to +the oldest of the great geological epochs. + +PARADOXIDES (Lat. _paradoxus_, marvellous). A genus of Trilobites. + +PATAGIUM (Lat. the border of a dress). Applied to the expansion +of the integument by which Bats, Flying Squirrels, and other +animals support themselves in the air. + +PECOPTERIS (Gr. _peko_, I comb; _pteris_, a fern). An extinct +genus of Ferns. + +PECTEN (Lat. a comb). The genus of Bivalve Molluscs comprising +the Scallops. + +PECTORAL (Lat. _pectus_, chest). Connected with, or placed upon, +the chest. + +PENTACRINUS (Gr. _penta_, five; _krinon_, lily). A genus of Crinoids +in which the column is five-sided. + +PENTAMERUS (Gr. _penta_, five; _meros_, part). An extinct genus +of Brachiopods. + +PENTREMITES (Gr. _penta_, five; _trema_, aperture). A genus of +_Blastoidea_, so named in allusion to the apertures at the summit +of the calyx. + +PERENNIBRANCHIATA (Lat. _perennis_, perpetual; Gr. _bragchia_, +gill). Applied to those Amphibia in which the gills are permanently +retained throughout life. + +PERISSODACTYLA (Gr. _perissos_, uneven; _daktulos_, finger). +Applied to those Hoofed Quadrupeds (_Ungulata_) in which the feet +have an uneven number of toes. + +PETALOID. Shaped like the petal of a flower. + +PHACOPS (Gr. _phaké_, a lentil; _ops_, the eye). A genus of +Trilobites. + +PHALANGES (Gr. _phalanx_, a row). The small bones composing the +digits of the higher _Vertebrata_. Normally each digit has three +phalanges. + +PHANEROGAMS (Gr. _phaneros_, visible; _gamos_, marriage). Plants +which have the organs of reproduction conspicuous, and which +bear true flowers. + +PHARYNGOBRANCHII (Gr. _pharugx_, pharynx; _bragchia_, gill). The +order of Fishes comprising only the Lancelet. + +PHASCOLOTHERIUM (Gr. _phaskolos_, a pouch; _therion_, a beast). +A genus of Oolitic Mammals. + +PHRAGMACONE (Gr. _phragma_, a partition; and _konos_, a cone). +The chambered portion of the internal shell of a _Belemnite_. + +PHYLLOPODA (Gr. _phullon_, leaf; and _pous_, foot). An order of +_Crustacea_. + +PINNATE (Lat. _pinna_, a feather). Feather-shaped; or possessing +lateral processes. + +PINNIGRADA (Lat. _pinna_, a feather; _gradior_, I walk). The +group of _Carnivora_, comprising the Seals and Walruses, adapted +for an aquatic life. Often called _Pinnipedia_. + +PINNULÆ. (Lat. dim. of _pinna_). The lateral processes of the +arms of _Crinoids_. + +PISCES (Lat. _piscis_, a fish). The class of Vertebrates comprising +the Fishes. + +PLACOID (Gr. _plax_, a plate; _eidos_, form). Applied to the +irregular bony plates, grains, or spines which are found in the +skin of various fishes (_Elasmobranchii_). + +PLAGIOSTOMI (Gr. _plagios_, transverse; _stoma_, mouth). The +Sharks and Rays, in which the mouth is transverse, and is placed +on the under surface of the head. + +PLATYCERAS (Gr. _platus_, broad; _keras_, horn). A genus of Univalve +Molluscs. + +PLATYCRINUS (Gr. _platus_, broad; _krinom_, lily). A genus of +Crinoidea. + +PLATYRHINA (Gr. _platus_, broad; _rhines_, nostrils). A group +of the _Quadrumana_. + +PLATYSOMUS (Gr. _platus_, wide; _soma_, body). A genus of Ganoid +Fishes. + +PLEISTOCENE (Gr. _pleistos_, most; _kainos_, new). Often used +as synonymous with "Post-Pliocene." + +PLEUROTOMARIA (Gr. _pleura_, the side; _tomé_, notch). A genus +of Univalve shells. + +PLIOCENE (Gr. _pleion_, more; _kainos_, new). The later Tertiary +period. + +PLIOPITHECUS (Gr. _pleion_, more; _pithekos_, ape). An extinct +genus of monkeys. + +PLIOSAURUS (Gr. _pleion_, more; _saura_, lizard). A genus of +Plesiosaurian Reptiles. + +POLYCYSTINA (Gr. _polus_, many; and _kustis_, a cyst). An order +of _Protozoa_ with foraminated siliceous shells. + +POLYPARY. The hard chitinous covering secreted by many of the +_Hydrozoa_. + +POLYPE (Gr. _polus_, many; _pous_, foot). Restricted to the single +individual of a simple _Actinozoön_, such as a Sea-anemone, or +to the separate zooids of a compound _Actinozoön_. Often applied +indiscriminately to any of the _Coelenterata_, or even to the +Polyzoa. + +POLYPORA (Gr. _polus_, many; _poros_, a passage). A genus of +Lace-corals (_Fenestellidoe_). + +POLYTHALAMOUS (Gr. _polus_; and _thalamos_, chamber). Having +many chambers; applied to the shells of _Foraminifera_ and +_Cephalopoda_. + +POLYZOA (Gr. _polus_; and _zoön_, animal). A division of the +_Molluscoida_ comprising compound animals, such as the +Sea-mat--sometimes called _Bryozoa_. + +PORIFERA (Lat. _porus_, pore; and _fero_, I carry). Sometimes +used to designate the _Foraminifera_, or the _Sponges_. + +PRÆMOLARS (Lat. _proe_, before; _molares_, the grinders). The +molar teeth of Mammals which succeed the molars of the milk-set +of teeth. In man, the bicuspid teeth. + +PROBOSCIDEA (Lat. _proboscis_, the snout). The order of Mammals +comprising the Elephants. + +PROCOELOUS (Gr. _pro_, before; _koilos_, hollow). Applied to vertebræ +the bodies of which are hollow or concave in front. + +PRODUCTA (Lat. _productus_, drawn out or extended). An extinct +genus of Brachiopods, in which the shell is "eared," or has its +lateral angles drawn out. + +PROTICHNITES (Gr. _protos_, first; _ichnos_, footprint). Applied +to certain impressions in the Potsdam sandstone of North America, +believed to have been produced by large Crustaceans. + +PROTOPHYTA (Gr. _protos_; and _phuton_, plant). The lowest division +of plants. + +PROTOPLASM (Gr. _protos_; and _plasso_ I mould). The elementary +basis of organised tissues. Sometimes used synonymously for the +"sarcode" of the _Protozoa_. + +PROTOROSAURUS or PROTEROSAURUS (Gr. _protos_, first; _orao_, I +see or discover; _saura_, lizard: or _proteros_, earlier; _saura_, +lizard). A genus of Permian lizards. + +PROTOZOA (Gr. _protos_; and _zoön_, animal). The lowest division +of the animal kingdom. + +PSAMMODUS (Gr. _psammos_, sand; _odous_, tooth). An extinct genus +of Cestraciont Sharks. + +PSEUDOPODIA (Gr. _pseudos_, falsity; and _pous_, foot). The +extensions of the body-substance which are put forth by the +_Rhizopoda_ at will, and which serve for locomotion and prehension. + +PSILOPHYTON (Gr. _psilos_, bare; _phuton_, plant). An extinct +genus of Lycopodiaceous plants. + +PTERANODON (Gr. _pteron_, wing; _a_, without; _odous_, tooth). +A genus of Pterosaurian Reptiles. + +PTERASPIS (Gr. _pteron_, wing; _aspis_, shield). A genus of Ganoid +Fishes. + +PTERICHTHYS (Gr. _pteron_, wing; _ichthus_, fish). A genus of +Ganoid Fishes. + +PTERODACTYLUS (Gr. _pteron_, wing; _daktulos_, finger). A genus +of Pterosaurian Reptiles. + +PTEROPODA (Gr. _pteron_, wing; and _pous_, foot). A class of the +_Mollusca_ which swim by means of fins attached near the head. + +PTEROSAURIA (Gr. _pteron_, wing; _saura_, lizard). An extinct +order of Reptiles. + +PTILODICTYA (Gr. _ptilon_, a feather; _diktuon_, a net). An extinct +genus of _Polyzoa_. + +PTYCHOCERAS (Gr. _ptucé_, a fold; _keras_, a horn). A genus of +_Ammonitidoe_. + +PULMONATE. Possessing lungs. + +PYRIFORM (Lat. _pyrus_, a pear; and _forma_, form). Pear-shaped. + + +QUADRUMANA (Lat. _quatuor_, four; _manus_, hand). The order of +Mammals comprising the Apes, Monkeys, Baboons, Lemurs, &c. + + +RADIATA (Lat. _radius_, a ray). Formerly applied to a large number +of animals which are now placed in separate sub-kingdoms (e.g., the +_Coelenterata_, the _Echinodermata_, the _Infusoria_, &c.) + +RADIOLARIA (Lat. _radius_, a ray). A division of _Protozoa_. + +RAMUS (Lat. a branch). Applied to each half or branch of the lower +jaw, or mandible, of Vertebrates. + +RAPTORES (Lat. _rapto_, I plunder). The order of the Birds of +Prey. + +RASORES (Lat. _rado_, I scratch). The order of the Scratching +Birds (Fowls. Pigeons, &c.) + +RECEPTACULITES (Lat. _receptaculum_, a storehouse). An extinct +genus of Protozoa. + +REPTILIA (Lat. _repto_, I crawl). The class of the _Vertebrata_ +comprising the Tortoises, Snakes, Lizards, Crocodiles, &c. + +RETEPORA (Lat. _reté_, a net; _porus_, a pore). A genus of +Lace-corals (_Polyzoa_). + +RHAMPHORHYNCHUS (Gr. _rhamphos_, beak; _rhugchos_, nose). A genus +of Pterosaurian Reptiles. + +RHINOCEROS (Gr. _rhis_, the nose; _keras_, horn). A genus of Hoofed +Quadrupeds. + +RHIZOPODA (Gr. _rhiza_, a root; and _pous_, foot). The division +of _Protozoa_ comprising all those which are capable of emitting +pseudopodia. + +RHYNCHOLITES (Gr. _rhugchos_, beak; and _lithos_, stone). Beak-shaped +fossils consisting of the mandibles of _Cephalopoda_. + +RHYNCHONELLA (Gr. _rhugchos_, nose or beak). A genus of Brachiopods. + +RODENTIA (Lat. _rodo_, I gnaw). An order of the Mammals; often +called _Glires_ (Lat. _glis_, a dormouse). + +ROTALIA (Lat. _rota_, a wheel). A genus of _Foraminifera_. + +RUGOSA (Lat. _rugosus_, wrinkled). An order of Corals. + +RUMINANTIA (Lat. _ruminor_, I chew the cud). The group of Hoofed +Quadrupeds (_Ungulata_) which "ruminate" or chew the cud. + + +SARCODE (Gr. _sarx_, flesh; _eidos_, form). The jelly-like substance +of which the bodies of the _Protozoa_ are composed. It is an +albuminous body containing oil-granules, and is sometimes called +"animal protoplasm." + +SAURIA (Gr. _saura_, a lizard). Any lizard-like Reptile is often +spoken of as a "Saurian;" but the term is sometimes restricted +to the Crocodiles alone, or to the Crocodiles and Lacertilians. + +SAUROPTERYGIA (Gr. _sauro_; _pterux_, wing). An extinct order +of Reptiles, called by Huxley _Plesiosauria_, from the typical +genus _Plesiosaurus_. + +SAURURÆ (Gr. _saura_; _oura_, tail). The extinct order of Birds +comprising only the _Archoeopteryx_. + +SCANSORES (Lat. _scando_, I climb). The order of the Climbing +Birds (Parrots, Woodpeckers, &c.) + +SCAPHITES (Lat. _scapha_, a boat). A genus of the _Ammonitidoe_. + +SCOLITHUS (Gr. _skolex_, a worm; _lithos_, a stone). The vertical +burrows of sea-worms in rocks. + +SCUTA (Lat. _scutum_, a shield). Applied to any shield-like plates; +especially to those which are developed in the integument of +many Reptiles. + +SELACHIA or SELACHII (Gr. _selachos_, a cartilaginous fish, probably +a shark). The sub-order of _Elasmobranchii_ comprising the Sharks +and Dog-fishes. + +SEPIOSTAIRE. The internal shell of the Sepia, commonly known as +the "cuttle-bone." + +SEPTA. Partitions. + +SERPENTIFORM. Resembling a serpent in shape. + +SERTULARIDA (Lat. _sertum_, a wreath). An order of _Hydrozoa_. + +SESSILE (Lat. _sedo_, I sit). Not supported upon a stalk or peduncle; +attached by a base. + +SETHÆ (Lat. bristles). Bristles or long stiff hairs. + +SIGILLARIOIDS (Lat. _sigilla_, little images). A group of extinct +plants of which _Sigillaria_ is the type, so called from the +seal-like markings on the bark. + +SILICEOUS (Lat. _silex_, flint). Composed of flint. + +SINISTRAL (Lat. _sinistra_, the left hand). Left-handed; applied +to the direction of the spiral in certain shells, which are said +to be "reversed." + +SIPHON (Gr. a tube). Applied to the respiratory tubes in the +_Mollusca_; also to other tubes of different functions. + +SIPHONIA (Gr. _siphon_, a tube). A genus of fossil Sponges. + +SIPHONOSTOMATA (Gr. _siphon_; and _stoma_, mouth). The division +of _Gasteropodous Molluscs_ in which the aperture of the shell +is not "entire," but possesses a notch or tube for the emission +of the respiratory siphon. + +SIPHUNCLE (Lat. _siphunculus_, a little tube). The tube which +connects together the various chambers of the shell of certain +_Cephalopoda_ (_e.g._, the Pearly Nautilus). + +SIRENIA (Gr. _seiren_. a mermaid). The order of _Mammalia_ comprising +the Dugongs and Manatees. + +SIVATHERIUM (_Siva_, a Hindoo deity; Gr. _therion_, beast). An +extinct genus of Hoofed Quadrupeds. + +SOLIDUNGULA (Lat. _solidus_, solid; _ungula_, a hoof). The group +of Hoofed Quadrupeds comprising the Horse, Ass, and Zebra, in +which each foot has only a single solid hoof. Often called +_Solipedia_. + +SPHENOPTERIS (Gr. _sphen_, a wedge; _pteris_, a fern). An extinct +genus of ferns. + +SPICULA (Lat. _spicidum_, a point). Pointed needle-shaped bodies. + +SPIRIFERA (Lat. _spira_, a spire or coil; _fero_, I carry). An +extinct genus of Brachiopods, with large spiral supports for +the "arms." + +SPIRORBIS (Lat. _spira_, a spire; _orbis_, a circle). A genus +of tube-inhabiting Annelides, in which the shelly tube is coiled +into a spiral disc. + +SPONGIDA (Gr. _spoggos_, a sponge). The division of _Protozoa_ +commonly known as sponges. + +STALACTITES (Gr. _stalasso_, I drop). Icicle-like encrustations +and deposits of lime, which hang from the roof of caverns in +limestone. + +STALAGMITE (Gr. _stalagma_, a drop). Encrustations of lime formed +on the floor of caverns which are hollowed out of limestone. + +STIGMARIA (Gr. _stigma_, a mark made with a pointed instrument). +A genus founded on the roots of various species of _Sigillaria_. + +STRATUM (Lat. _stratus_, spread out; or _stratum_, a thing spread +out). A layer of rock. + +STROMATOPORA (Gr. _stroma_, a thing spread out; _paras_, a passage +or pore). A Palæozoic genus of _Protozoa_. + +STROPHOHENA (Gr. _strophao_, I twist; _mené_, moon). An extinct +genus of Brachiopods. + +SUB-CALCAREOUS. Somewhat calcareous. + +SUB-CENTRAL. Nearly central, but not quite. + +SUTURE (Lat. _suo_, I sew). The line of junction of two parts +which are immovably connected together. Applied to the line where +the whorls of a univalve shell join one another; also to the lines +made upon the exterior of the shell of a chambered _Cephalopod_ +by the margins of the septa. + +SYRINGOPORA (Gr. _surigx_, a pipe; _poros_, a pore). A genus of +Tabulate Corals. + + +TABULÆ. (Lat. _tabula_, a tablet). Horizontal plates or floors +found in some Corals, extending across the cavity of the "theca" +from side to side. + +TEGUMENTARY (Lat. _tegumentum_, a covering). Connected with the +integument or skin. + +TELEOSAURUS (Gr. _teleios_, perfect; _saura_, lizard). An extinct +genus of Crocodilian Reptiles. + +TELEOSTEI (Gr. _teleios_, perfect; _osteon_, bone). The order +of the "Bony Fishes." + +TELSON (Gr. a limit). The last joint in the abdomen of _Crustacea_; +variously regarded as a segment without appendages, or as an +azygous appendage. + +TENTACULITES (Lat. _tentaculum_, a feeler). A genus of _Pteropoda_. + +TEREBRATULA (Lat. _terebratus_, bored or pierced). A genus of +_Brachiopoda_, so called in allusion to the perforated beak of +the ventral valve. + +TEST (Lat. _testa_, shell). The shell of _Mollusca_, which are +for this reason sometimes called "_Testacea_;" also, the calcareous +case of _Echinoderms_; also, the thick leathery outer tunic in +the _Tunicata_. + +TESTACEOUS. Provided with a shell or hard covering. + +TESTUDINIDÆ (Lat. _testudo_, a tortoise). The family of the +Tortoises. + +TETRABRANCHIATA (Gr. _tetra_, four; _bragchia_, gill). The order +of _Cephalopoda_ characterised by the possession of four gills. + +TEXTULARIA. (Lat. _textilis_, woven). A genus of _Foraminifera_. + +THECA (Gr. _theké_, a sheath). A genus of Pteropods. + +THECODONTOSAURUS (Gr. _theké_, a sheath; _odous_, tooth; _saura_, +lizard). A genus of "Thecodont" Reptiles, so named in allusion +to the fact that the teeth are sunk in distinct sockets. + +THERIODONT (Gr. _therion_, a beast; _odous_, tooth). A group of +Reptiles so named by Owen in allusion to the Mammalian character +of their teeth. + +THORAX (Gr. a breastplate). The region of the chest. + +THYLACOLEO (Gr. _thulakos_, a pouch; _leo_, a lion). An extinct +genus of Marsupials. + +TRIGONIA (Gr. _treis_, three; _gonia_, angle). A genus of Bivalve +Molluscs. + +TRIGONOCARPON (Gr. _treis_, three; _gonia_. angle; _karpos_, +fruit). A genus founded on fossil fruits of a three-angled form. + +TRILOBITA (Gr. _treis_, three; _lobos_, a lobe). An extinct order +of _Crustaceans_. + +TRINUCLEUS (Lat. _tris_, three; _nucleus_, a kernel). A genus +of Trilobites. + +TROGONTHERIUM (Gr. _trogo_, I gnaw; _therion_, beast). An extinct +genus of Beavers. + +TUBICOLA (Lat. _tuba_, a tube; and _colo_, I inhabit). The order +of _Annelida_ which construct a tubular case in which they protect +themselves. + +TUBICOLOUS. Inhabiting a tube. + +TUNICATA (Lat. _tunica_, a cloak). A class of _Molluscoida_ which +are enveloped in a tough leathery case or "test." + +TURBINATED (Lat. _turbo_, a top). Top-shaped; conical with a round +base. + +TURRILITES (Lat, _turris_, a tower). A genus of the _Ammonitidoe_. + + +UMBO (Lat. the boss of a shield). The beak of a bivalve shell. + +UNGUICULATE (Lat. _unguis_, nail). Furnished with claws. + +UNGULATA (Lat. _ungula_, hoof). The order of Mammals comprising +the Hoofed Quadrupeds. + +UNGULATE. Furnished with expanded nails constituting hoofs. + +UNILOCULAR (Lat. _unus_, one; and _loculus_. a little purse). +Possessing a single cavity or chamber. Applied to the shells +of _Foraminifera_ and _Mollusca_. + +UNIVALVE (Lat. _unus_, one; _valvoe_, folding-doors). A shell +composed of a single piece or valve. + +URODELA (Gr. _oura_, tail; _delos_, visible). The order of the +Tailed Amphibians (Newts, &c.) + + +VENTRAL (Lat. _venter_, the stomach). Relating to the inferior +surface of the body. + +VENTRICULITES (Lat. _ventriculum_, a little stomach). A genus +of siliceous Sponges. + +VERMIFORM (Lat. _vermis_, worm; and _forma_, form). Worm-like. + +VERTEBRA (Lat. _verto_, I turn). One of the bony segments of the +vertebral column or backbone. + +VERTEBRATA (Lat. _vertebra_, a bone of the back, from _vertere_, +to turn). The division of the Animal Kingdom roughly characterised +by the possession of a backbone. + +VESICLE (Lat. _vesica_, a bladder). A little sac or cyst. + + +WHORL. The spiral turn of a univalve shell. + + +XIPHOSURA (Gr. _xiphos_, a sworn; and _oura_, tail). An order of +_Crustacea_, comprising the _Limuli_ or King-Crabs, characterised +by their long sword-like tails. + +XYLOBIUS (Gr. _xulon_, wood; _bios_, life). An extinct genus of +Myriapods, named in allusion to the fact that the animal lived +on decaying wood. + + +ZAPHRENTIS (proper name). A genus of Rugose Corals. + +ZEUGLODONTIDÆ. (Gr. _zeuglé_, a yoke; _odous_, a tooth). An extinct +family of Cetaceans, in which the molar teeth are two-fanged, +and look as if composed of two parts united by a neck. + +ZOOPHYTE (Gr. _zoön_, animal; _phuton_, plant). Loosely applied +to many plant-like animals, such as Sponges, Corals, Sea-anemones, +Sea-mats, &c. + + + + +INDEX. + +Acadian Group. +_Acer_. +_Acervularia_. +_Acidaspis_. +Acorn-shells. +_Acroculia_. +_Acrodus; nobilis_. +_Acrotreta_. +_Acroura_. +_Actinocrinus_. +_Æglina_. +_Æpiornis_. +_Agnostus; rex_. +_Alces malchis_. +_Alecto_. +_Alethopteris_. +_Algoe_ (_see_ Sea-weeds). +Alligators. +_Alnus_. +_Amblypterus; macropterus_. +_Ambonychia_. +_Ammonites; Humpresianus; bifrons_. +_Ammonitidoe_. +_Amphibia_; of the Carboniferous; of the Permian; of the Trias; + of the Jurassic; of the Miocene. +_Amphicyon_. +_Amphilestes_. +_Amphispongia_. +_Amphistegina_. +_Amphitherium; Prevostii_. +_Amphitragulus_. +_Amplexus; coralloides_. +_Ampyx_. +_Anachytes_. +_Anchitherium_. +_Ancyloceras; Matheronianus_. +_Ancylotherium Pentelici_. +_Andrias Scheuchzeri_. +_Angiosperms_. +Animal Kingdom, divisions of. +_Anisopus_. +_Annelida_, of the Cambrian period; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous. +_Annularia_. +_Anomodontia_. +_Anoplotheridoe_. +_Anoplotherium; commune_. +Ant-eaters. +Antelopes. +_Anthracosaurus Russelli_. +_Anthrapaloemon gracilis_. +_Antilocapra_. +_Antilope quadricornis_. +Antwerp Crag. +Apes. +_Apiocrinus_. +_Apteryx_. +Aqueous rocks. +_Arachnida_ of the Coal-measures. +Aralo-Caspian Beds. +_Araucaria_. +_Araucarioxylon_. +_Arca; antiqua_. +_Archoeocidaris_. +_Archoeocyathus_. +_Archoeopteryx; macrura_. +_Archoeospoerinoe_. +_Archimedes; Wortheni_. +_Archiulus_. +Arctic regions, Miocene flora of. +_Arctocyon_. +Arenaceous rocks. +_Arenicolites; didymus_. +Arenig rocks. +Argillaceous rocks. +Armadillos. +_Artiodactyle Ungulates_. +_Asaphus; tyrannus_. +_Ascoceras_. +_Aspidella_. +_Aspidura loricata_. +_Astarte borealis_. +_Asterophyllites_. +_Asterosteus_. +_Astroeidoe_. +_Astroeospongia_. +_Astylospongia; proemorsa_. +_Athyris; subtilita_. +Atlantic Ooze. +_Atrypa; congesta; hemispoerica; reticularis_. +Auger-shells. +Aurochs. +Aves (_see_ Birds). +_Avicula; cantorta; socialis_. +"Avicula contorta Beds". +_Aviculidoe_. +_Aviculopecten_. +_Axophyllum_. +Aymestry Limestone. +Azoic rocks. + +_Baculites; anceps_. +Bagshot and Bracklesham Beds. +_Bakewellia_. +_Baloena_. +Bala Group. +Bala Limestone. +_Balanidoe_. +_Banksia_. +Barbadoes Earth. +Barnacles. +Bath Oolite. +Bats. +Bears. +Beaver. +Beetles. +_Belemnitella mucronata_. +_Beleminites; canaliculatus_. +_Belemnitidoe_. +_Belemnoteuthis_. +_Belinurus_. +_Bellerophon; Argo_. +_Belodon; Carolinensis_. +_Belosepia_. +_Beloteuthis subcostata_. +Bembridge Beds. +_Beryx; Lewesiensis_. +_Beyrichia; complicata_. +Bird's-eye Limestone. +Birds, of the Trias; of the Jurassic; of the Cretaceous; of + the Eocene; of the Post-Pliocene. +_Bison priscus_. +Bituminous Schists of Caithness. +Bivalves (_see_ Lamellibranchiata). +Black-lead (_see_ Graphite). +Black-River Limestone. +_Blastoidea_; of the Devonian; of the Carboniferous. +_Boidoe_. +Bolderberg Beds. +Bone-bed, of the Upper Ludlow; of the Trias. +Bony Fishes (_see_ Teleostean Fishes). +_Bos primigenius; _taurus_. +Boulder-clay. +_Bourgueticrinus_. +Bovey-Tracy Beds. +_Brachiopoda_; of the Cambrian rocks; of the Lower Silurian; + of the Upper Silurian; of the Devonian; of the Carboniferous; + of the Permian; of the Trias; of the Jurassic; of the + Cretaceous; of the Eocene. +_Brachymetopus_. +Brachyurous Crustaceans. +Bradford Clay. +Breaks in the Geological and Palæontological record. +Breccia. +Brick-earths. +Bridlington Crag. +Brittle-stars (_see_ Ophiuroidea). +_Bronteus_. +_Brontotheridoe_. +_Brontotherium ingens_. +_Brontozoum_. +_Buccinum_. +_Bucklandia_. +_Bulimus_. +Bunter Sandstein. +Butterflies. +_Byssoarca_. + +Cainozoic (_see_ Kainozoic). +Calamaries. +_Calamites; cannoeformis_. +Calcaire Grossier. +Calcareous rocks; Tufa. +Calciferous Sand-rock. +_Calveria_. +_Calymene; Blumenbachii_. +_Camarophoria globulina_. +Cambrian period; rocks of, in Britain; in Bohemia; in + North America; life of. +_Camelopardalidoe_. +Camels. +_Canis lupus; Parisiensis_. +Caradoc rocks. +Carbon, origin of. +Carboniferous Limestone. +Carboniferous period; rocks of; life of. +Carboniferous Slates of Ireland. +_Carcharias_. +_Carcharodon; productus_. +_Cardinia_. +_Cardiocarpon_. +_Cardiola; fibrosa; interrupta_. +_Cardita; planicosta_. +_Cardium; Rhoeticum_. +Caribou. +_Carnivora_, of the Eocene; of the Miocene; of the Pliocene; + of the Post-Pliocene. +_Caryocaris_. +_Caryocrinus ornatus_. +_Castor fiber_. +_Castoroides Ohioensis_. +Catastrophism, theory of. +_Catopterus_. +Cauda-Galli Grit. +_Caulopteris_. +Cave-bear. +Cave-deposits. +Cave-hyæna. +Cave-lion. +Caves, formation of; deposits in. +_Cavicornia_. +Cement-stones. +_Cephalaspis_. +_Cephalopoda_, of the Cambrian period; of the Lower Silurian; + of the Upper Silurian; of the Devonian; of the Carboniferous; + of the Permian; of the Trias; of the Jurassic; of the Cretaceous; + of the Eocene; of the Miocene. +_Ceratiocaris_. +_Ceratites; nodosus_. +_Ceratodus; altus; Fosteri; serratus_. +_Ceriopora; Hamiltonensis_. +_Cerithium; _hexagonum_. +_Cervidoe_, of the Miocene period; of the Pliocene; of the + Post-Pliocene. +_Cervus; capreolus; elaphus; megaceros; tarandus_. +_Cestracion Philippi_. +Cestracionts, of the Devonian; of the Carboniferous; of the Permian; + of the Trias; of the Jurassic; of the Cretaceous. +_Cetacea_; of the Eocene; of the Miocene. +_Cetiosaurus_. +_Choeropotamus_. +_Choetetes; tumidus_. +Chain-coral. +Chalk; structure of; Foraminifera of; origin of; with flints; + without flints. +_Chama_. +_Chamoerops; Helvetica_. +Chazy Limestone. +_Cheiroptera_, of the Eocene; of the Miocene. +_Cheirotherium_. +_Cheirurus; bimucronatus_. +_Chelichnus Duncani_. +_Chelone Benstedi; planiceps_. +_Chelonia_, of the Permian; of the Jurassic; of the Cretaceous; + of the Eocene; of the Miocene. +_Chemnitzia_. +Chemung Group. +Chert. +Chillesford Beds. +_Chonetes; Hardrensis_. +_Chonophyllum_. +_Cidaris_. +Cincinnati Group. +_Cinnamomum polymorphum_. +Cinnamon-trees. +_Cladodus_. +Claiborne Beds. +_Clathropora; intertexta_. +Clay; Red, origin of. +Clay-ironstone, nodules of. +_Cleidophorus_. +_Cleodora_. +_Climacograptus_. +Clinton Formation. +_Clisiophyllum_. +_Clupeidoe_. +_Clymenia; Sedgwickii_. +Coal; structure of; mode of formation of. +Coal-measures; mineral characters of; mode of formation of; + plants of. +Coccoliths. +_Coccosteus_. +_Cochliodus; cantortus_. +_Coleoptera_. +_Colossochelys Atlas_. +_Columnaria; alveolata_. +_Comatula_. +Conclusions to be drawn from Fossils. +Concretions, calcareous; phosphatic; of clay-ironstone; + of manganese. +Conglomerate. +_Coniferoe_; wood of; of Devonian period; of the Carboniferous; + of the Permian; of the Trias; of the Jurassic period. +Coniston Flags and Grits. +Connecticut Sandstones, footprints of. +_Conocoryphe Mathewi; Sultzeri_. +Conodonts. +_Constellaria_. +Constricting serpents of the Eocene. +Contemporaneity of strata. +Continuity, theory of. +_Conularia; ornata_. +_Conulus_. +_Conus_. +Coomhola Grits. +Coprolites. +Coralline Crag. +Corallines. +_Corallium_. +Coral-rag. +Coral-reefs. +Coral-rock. +Coral-sand. +Corals; of the Lower Silurian; of the Upper Silurian; of the + Devonian; of the Carboniferous; of the Permian; of the Trias; + of the Jurassic; of the Cretaceous; of the Eocene; of the + Miocene. +_Corbula_. +Cornbrash. +Corniferous Limestone. +_Cornulites_. +Cornus. +_Coryphodon_. +Cowries. +Crabs. +Crag, Red; White; Norwich; Antwerp; Bridlington; Coralline. +_Crania; Ignabergensis_. +_Crassatella_. +_Crepidophyllum; Archiaci_. +Cretaceous period; rocks of, in Britain; in North America; + life of. +Crinoidal Limestone. +_Crinoidea_; of the Cambrian; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous; of the + Permian; of the Triss; of the Jurassic; of the Cretaceous; + of the Eocene. +_Crioceras; cristatum_. +_Crocodilia_; of the Trias; of the Jurassic; of the Cretaceous; + of the Eocene. +Cromer Forest-bed. +_Crossozamites_. +_Crotalocrinus_. +_Crustacea_, of the Cambrian; of the Lower Silurian; of the Upper + Silurian; of the Devonian; of the Carboniferous; of the Permian; + of the Trias; of the Jurassic; of the Cretaceous. +Cryptogams. +_Ctenacanthus_. +_Ctenodonta_. +_Cupressus_. +Cursores. +Cuttle-fishes (_see_ Dibranchiate Cephalopods). +_Cyathocrinus_. +_Cyathophyllum_. +_Cycadopteris_. +Cycads; of the Carboniferous; of the Permian; of the Trias; + of the Jurassic; of the Cretaceous. +_Cyclas_. +_Cyclonema_. +_Cyclophthalmus senior_. +_Cyclostoma; Arnoudii_. +_Cynodraco_. +_Cyproea; elegans_. +Cypress. +_Cypridina_. +Cypridina Slates. +_Cyrena_. +_Cyrtina_. +_Cyrtoceras_. +_Cystiphyllum; vesiculosum_. +_Cystoidea_; of the Cambrian; of the Lower Silurian; of + the Upper Silurian. + +Dachstein Beds. +_Dadoxylon_. +_Daonella; Lommelli_. +_Dasornis Londinensis_. +Decapod Crustaceans. +Deer. +_Deinosauria_; of the Trias; of the Jurassic; of the Cretaceous. +_Deinotherium; giganteum_. +Denbighshire Flags and Grits. +_Dendrocrinus_. +_Dendrograptus_. +Desmids. +Devonian Formation; origin of name; relation to Old Red Sandstone; + of Devonshire; of North America; life of. +_Diadema_. +Diatoms; of the Devonian; of the Carboniferous; of flints; of + Richmond Earth. +Dibranchiate Cephalopods; of the Trias; of the Jurassic; of + the Cretaceous; of the Eocene; of the Miocene. +_Diceras; arietina_. +Diceras Limestone. +_Dichobune_. +_Dichograptus; octobrachiatus_. +Dicotyledonous plants. +_Dicotyles antiquus_. +_Dicranograptus_. +_Dictyonema; sociale_. +_Dicynodon; lacerticeps_. +_Didelphys; gypsorum_. +_Didus ineptus_. +_Didymograptus; divaricatus_. +_Dikellocephalus Celticus; Minnesotensis_. +_Dimorphodon_. +_Dinichthys; Hertzeri_. +_Ditoceras; mirabilis_. +_Dinocerata_. +_Dinophis_. +_Dinornis; elephantopus; giganteus_. +_Dinosauria_ (see _Deinosauria_). +_Dinotherium_ (see _Deinotherium_). +_Diphyphyllum_. +_Diplograptus; pristis_. +_Dipnoi_. +_Diprotodon; australis_. +_Diptera_. +_Discina_. +_Discoidea; cylindrica_. +_Dithyrocaris; Scouleri_. +Dodo. +Dog whelks. +Dolomite. +Dolomitic Couglomerate of Bristol. +Dolphins. +_Dorcatherium_. +Downton Sandstone. +_Draco volans_. +Dragon-flies. +Drift, Glacial. +_Dremotherium_. +_Dromatherium sylvestre_. +_Dryandra_. +_Dryopithecus_. +Dugougs. + +_Echinodermata_, of the Cambrian; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous; of the + Permian; of the Trias; of the Jurassic; of the Cretaceous; + of the Eocene. +_Echinoidea_; of the Upper Silurian; or the Devonian; of the + Carboniferous; of the Permian; of the Jurassic; of the + Cretaceous. +_Edentata_; of the Eocene; of the Miocene; of the Post-Pliocene. +_Edriocrinus_. +Eifel Limostone. +_Elasmobranchii_ (_See_ Placoid Fishes). +_Elasmosaurus_. +Elephants. +_Elphas; Americanus; antiquus; Falconeri; Melitensis; meridionalis; + planifrons; primigenius_. +Elk; Irish. +_Ellipsocephalus Hoffi_. +_Elotherium_. +_Emydidoe_. +_Emys_. +Enaliosaurians. +Encrinital warble. +_Encrinurus_. +_Encrinus liliiformis_. +Endogenous plants. +_Endophyllum_. +_Endothyra; Bailyi_. +Engis skull. +_Entomis_. +_Entomoconchus Scouleri_. +Eocene period; rocks of, in Britain; in France; in North + America; life of. +_Eocidaris_. +_Eophyton; Linneanum_. +Eophyton Sandstone. +_Eosaurus Acadianus_. +Eozoic rocks. +_Eozoön Bavaricum_. +_Eozoön Canadense_; appearance of, in mass; minute structure + of; affinities of, with _Foraminifera_. +_Ephemeridoe_. +_Equisetaceoe_. +_Equisetites_. +_Equidoe_. +_Equus; caballus; excelsus; fossilis_. +_Eridophyllum_. +_Eryon arctiformis_. +_Eschara_. +_Escharidoe_. +_Escharina; Oceani_. +_Estheria; tenella_. +_Eucalyptocrinus; polydactylus_. +_Eucladia_. +_Euomphalus; discors_. +_Euplectella_. +_Euproöps_. +European Bison. +_Eurypterida_; of the Upper Silurian; of the Devonian. +Even-toed Ungulates. +Exogenous plants. +_Exogyra; virgula_. +Extinction of species. + +_Fagus_. +Faluns. +Fan-palms. +_Favistella_. +_Favostites; Gothlandica; hemisphoerica_. +Faxöe Limestone. +_Felis angustus; leo; speloea_. +_Fenestella; cribrosa; magnifica; retiformis_. +_Fenestellidoe_. +Ferns, of the Devonian; of the Carboniferous; of the Permian; + of the Trias; of the Jurassic; of the Cretaceous. +Fig-shells. +Fishes; of the Upper Silurian; of the Devonian; of the + Carboniferous; of the Permian; of the Trias; of the + Jurassic; of the Cretaceous; of the Eocene; of the + Miocene. +Flint; structure of; origin of; organisms of; of Chalk. + Human implements associated with bones of extinct Mammals. +Flora (_see_ Plants). +Footprints of _Cheirotherium_; of the Triassic sandstones of + Connecticut. +_Foraminifera_; of the Cambrian; of the Lower Silurian; + of the Carboniferous; of the Permian; of the Trias; of the + Jurassic; of the Cretaceous; of the Eocene; of the Miocene; + of the Post-Pliocene; of Atlantic ooze; as builders of + limestone; as forming green sands. +_Forbesiocrinus_. +Forest-bed of Cromer. +Forest-bugs. +Forest-marble. +Formation, definition of; succession of. +Fossiliferous rocks; chronological succession of. +Fossilisation, processes of. +Fossils, definition of; distinctive, of rock-groups; conclusions + to be drawn from; biological relations of. +Foxes. +Fringe-finned Ganoids. +Fucoidal Sandstone. +Fucoids. +Fuller's Earth. +_Fusulina; cylindrica_. +_Fusus_. + +_Galeocerdo_. +_Galerites; albo-galerus_. +_Galestes_. +Ganoid Fishes; of the Upper Silurian; of the Devonian; of the + Carboniferous; of the Permian; of the Trias; of the Jurassic; + of the Cretaceous; of the Eocene. +Gaspé Beds. +_Gasteropoda_, of the Cambrian; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous; of the + Permian; of the Trias; of the Jurassic; of the Cretaceous; + of the Eocene. +_Gastornis Parisiensis_. +Gault. +Gavial. +Genesee Slates. +Geological record, breaks in the. +Giraffes. +Glacial period; deposits of. +_Glandulina_. +Glauconite. +_Glauconome; pulcherrima_. +Globe Crinoids (_see_ Cystoidea). +_Globigerina_. +Glutton. +_Glyptaster_. +_Glyptocrinus_. +_Glyptodon; clavipes_. +_Glyptoloemus_. +Goats. +_Goniatites; Jossoe_. +_Gorgonidoe_. +_Grallatores_. +Graphite; mode of occurrence of; origin of. +_Graptolites_; structure of; of the Lower Silurian; of the + Upper Silurian. +Great Oolite; Upper. +Greenland. Miocene plants of. +Greensand, Lower. +Green sands, origin of. +_Grevillea_. +_Griffithides_. +Grizzly Bear. +Groond Sloths. +_Gryphoea; incurva_. +Guelph Limestone. +_Gulo luscus; speloeus_. +Guttenstein Beds. +Gymnospermous Exogens. +Gypsum. +_Gyracanthus_. +_Gyroceras_. + +_Hadrosaurus_. +_Halitherium_. +Hallstadt Beds. +_Halobia_. +_Halysites; agglomerata; catenularia_. +Hamilton formation. +_Hamites; rotundus_. +_Haplophlebium Barnesi_. +Harlech Grits. +_Harpes; ungula_. +Hastings Sands. +Headon and Osborne series. +Heart-urchins. +_Heliolites_. +_Heliophyllum; exiguum_. +_Helix_. +_Helladotherium_. +_Helopora fragilis_. +_Hemicidaris crenularis_. +_Hemiptera_. +_Hemitrochiscus paradoxus_. +Hempstead Beds. +_Hesperornis; regalis_. +_Heteropoda_; of the Lower Silurian; of the Upper Silurian; + of the Devonian; of the Carboniferous. +_Hinnites_. +_Hipparion_. +_Hippopodium_. +_Hippopotamus; amphibus; major; Sivalensis_. +_Hippothoa_. +Hippurite Marble. +_Hippurites; Toucasiana_. +_Hippuritidoe_. +_Histioderma_. +Hollow-horned Ruminants. +_Holocystis elegan_. +_Holopea; Subconica_. +_Holopella; obsoleta_. +_Holoptychius; nobilissimus_. +Holostomatous Univalves. +Holothurians. +_Holtenia_. +_Homacanthus_. +_Homalonotus; armatus_. +_Homo diluvii testis_. +Honeycomb Corals. +Hoofed Quadrupeds. +Hudson River Group. +Huronian Period; rocks of. +_Hyoena crocuta; speloea; Hipparionum_. +_Hyoenictis_. +_Hyoenodon_. +_Hyalea D'Orbignyana_. +_Hybodus_. +_Hydractinia_. +Hydroid Zoophytes. +_Hymenocaris vermicauda_. +_Hymenophyllites_. +_Hymenoptera_. +_Hyopotamus_. +_Hyperodapedon_. +_Hypsiprymnopsis_. +_Hystrix primigenius_. + +_Ichthyocrinus loevis_. +_Ichthyornis; dispar_. +_Ichthyosaurus; communis_. +_Ictitherium_. +_Iguana_. +_Iguanodon; Mantelli_. +Ilfracombe Group. +_Illoenus_. +Imperfection of the palæontological record. +Inferior Oolite. +Infusorial Earth. +_Inoceramus; sulcatus_. +_Insectivora_, of the Eocene; of the Miocene. +Insects, of the Devonian; of the Carboniferous; of the Jurassic; + of the Miocene. +Irish Elk. +_Ischadites_. +Isopod Crustaceans. + +Jackson Beds. +Jurassic period; rocks of; life of. + +_Kaidacarpum_. +Kainozoic period. +Kangaroo. +Kelloway Rock. +Kent's Cavern, deposits in. +Keuper. +Kimmeridge Clay. +King-crabs. +_Koninckia_. +Kössen Beds. + +_Labyrinthodon Joegeri_. +_Labyrinthodontia_; of the Carboniferous; of the Permian; + of the Trias. +Lace-corals. +_Lacertilia_; of the Permian; of the Trias; of the Jurassic; + of the Cretaceous. +_Loelaps_. +_Lamellibranchiata_, of the Cambrian; of the Lower Silurian; + of the Upper Silurian; of the Devonian; of the Carboniferous; + of the Permian; of the Trias; of the Jurassic; of the + Cretaceous; of the Eocene. +_Lamna_. +Lamp-shells (see _Brachiopoda_). +Land-tortoises. +_Lauraceoe_. +Laurentian period; rocks of; Lower Laurentian; Upper Laurentian; + areas occupied by Laurentian rocks; limestones of; iron-ores of; + phosphate of lime of; graphite of; life of. +Leaf-beds of the Isle of Mull. +_Leda; truncata_. +_Leguminosites Marcouanus_. +Lemming. +_Lepadidoe_. +_Lepadocrinus Gebhardi_. +_Leperditia; canadensis_. +_Lepidaster_. +_Lepidechinus_. +_Lepidesthes_. +Lepidodendroids. +_Lepidodendron; Sternberg_. +_Lepidoptera_. +_Lepidosiren_. +_Lepidosteus_. +_Lepidostrobus_. +_Lepidotus_. +_Leptoena; Liassica; sericea_. +_Leptocoelia; plano-convexa_. +Lias. +Lichas. +_Licrophycus Ottawaensis_. +Lignitic Formation of North America. +Lily-encrinite. +_Lima_. +Lime, phosphate of. +Limestone; varieties of; origin of; microscopical structure of; + Crinoidal; Foraminiferal; coralline; magnesian; metamorphic; + oolitic; pisolitic; bituminous; Laurentian. +_Limnoea; pyramidalis_. +_Limulus_. +_Lingula; Credneri_. +Lingula Flags. +_Lingulella; Davisii; ferruginea_. +_Liriodendron; Meeki_. +_Lithostrotion; irregulare_. +_Lituites_. +Lizards (see _Lacertilia_). +Llama. +Llanberis Slates. +Llandeilo rocks. +Llandovery rocks; Lower; Upper. +Lobsters. +Loess. +London Clay. +Longmynd rocks. +_Lonsdaleia_. +_Lophiodon_. +_Lophophyllum_. +Lower Cambrian; Chalk; Cretaceous; Devonian; Eocene; Greensand; + Helderberg; Laurentian rocks; Ludlow rock; Miocene; Old Red + Sandstone; Oolites; Silurian period; rocks of, in Britain; in + North America; life of. +_Loxonema_. +Ludlow rock. +_Lycopodiaceoe_. +Lynton Group. +_Lyrodesma_. + +Macaques. +_Machoeracanthus major_. +_Machairodus; cultridens_. +_Maclurea; crenulata_. +_Macrocheilus_. +_Macropetalichthys; Sullivanti_. +_Macrotherium giganteum_. +_Macrurous Crustaceans_. +_Mactra_. +Maestricht Chalk. +Magnesian Limestone; nature and structure of; of the Permian + series. +Magnolia. +_Mammalia_, of the Trias; of the Jurassic; of the Eocene; of + the Miocene; of the Pliocene; of the Post-Pliocene. +Mammoth. +Man, remains of, in Post-Pliocene deposits. +Manatee. +_Mantellia; megalophylla_. +Maple. +Marble; encrinital; statuary. +Marcellus Shales. +_Mariacrinus_. +Marmots. +Marsupials; of the Trias; of the Jurassic; of the Eocene; of + the Miocene; of the Post-Pliocene. +_Marsupiocrinus_. +_Marsupites_. +_Mastodon; Americanus, angustidens; Arvenensis; longirostris; + Ohioticus; Sivalensis_. +Medina Sandstone. +_Megalichthys_. +_Megalodon_. +_Megalomus_. +_Megalonyx_. +_Megalosaurus_. +_Megatherium; Cuvieri_. +_Melania_. +_Melonites_. +Menevian Group. +_Menobranchus_. +_Meristella; cylindrica; intermedia; naviformis_. +_Mesopithecus_. +Mesozoic Period. +_Michelinia_. +_Micraster_. +_Microlestes; antiquus_. +Middle Devonian; Eocene; Oolites; Silurian. +Miliolite Limestone. +_Millepora_. +Millstone Grit. +Miocene period; rocks of, in Britain; in France; in Belgium; + in Switzerland; in Austria; in Germany; in Italy; in India; + in North America; life of. +Mitre-shells. +_Mitra_. +Moas of New Zealand. +_Modiolopsis; Solvensis_. +Molasse. +Mole. +Monkeys. +Monocotyledonous plant. +_Monograptus; priodon_. +_Monotis_. +Monte Bolca, fishes of. +_Montlivaltia_. +Mosasauroids. +_Mosasaurus; Camperi; princeps_. +Mountain Limestone. +Mud-fishes. +Mud-turtles. +Mull, Miocene strata of. +_Murchisonia; gracilis_. +_Murex. +Muschelkalk. +Musk-deer. +Musk-ox. +Musk-sheep. +_Myliobatis Edwardsii_. +_Mylodon; robustus_. +_Myophoria; lineata_. +_Myriapoda_ of the Coal. + +_Nassa_. +_Natatores_. +_Natica_. +_Nautilus; Danicus; pompilius_. +Neanderthal skull. +Neocomian series. +_Neolimulus_. +_Nerinoea; Goodhallii_. +_Nerita_. +_Neuroptera_. +_Neuropteris_. +Newer Pliocene. +New Red Sandstone. +Newts. +Niagara Limestone. +_Nipadites; ellipticus_. +_Noeggerathia_. +Norwich Crag. +_Nothosaurus; mirabilis_. +_Notidanus_. +_Numenius gypsorum_. +_Nummulina; loevigata; pristina_. +_Nummulitic Limestone_. + +Oak. +_Obolella; sagittalis_. +Odd-toed Ungulates. +_Odontaspis_. +_Odontopteris; Schlotheimi_. +_Odontopteryx; toliapicus_. +_Odontornithes_. +_Ogygia; Buchii_. +Older Pliocene. +_Oldhamia; antiqua_; slates of Ireland. +Old Red Sandstone; origin of name; of Scotland; relations of, + to Devonian. +_Olenus; micrurus_. +Oligocene. +_Oligoporus_. +Olive-shells. +_Omphyma_. +_Onchus; tenuistriatus_. +Oneida Conglomerate. +_Onychodus; sigmoides_. +Oolitic limestone, structure of; mode of formation of. +Oolitic rocks (_see_ Jurassic). +Ooze, Atlantic. +_Ophidia_; of the Eocene. +_Ophiuroidea_, of the Lower Silurian; of the Upper Silurian; + of the Carboniferous; of the Trias; of the Jurassic. +Opossum. +_Orbitoides_. +Oriskany Sandstone. +_Ormoxylon_. +_Orohippus_. +_Orthis; biforata; Davidsoni; elegantula; flabellulum; Hicksii; + lenticularis; plicatella; resupinata; subquadrala; testudinaria_. +_Orthoceras; crebriseptum_. +_Orthonota_. +_Orthoptera_. +_Osmeroides; Mantelli_. +_Osmerus_. +_Ostealepis_. +_Ostracode_ Crustaceans of the Cambrian; of the Lower Silurian; + of the Upper Silurian; of the Devonian; of the Carboniferous; + of the Permian; of the Trias; of the Jurassic; of the Cretaceous. +_Ostrea acuminata; Couloni; deltoidea; distorta; expansa, gregarea; + Marshii_. +_Otodus; obtiquus_. +_Otozamites_. +_Otozoum_. +_Oudenodon; Bainii_. +_Ovibos moschatus_. +Oxford Clay. +_Oxyrhina; xiphodon_. +Oysters. + +_Pachyphyllum_. +_Paloearca_. +_Paloeaster; Ruthveni_. +_Palasterina; primoeva_. +_Paloechinus; ellipticus_. +_Paloeocaris; typus_. +_Paloeocoma; Colvini_. +_Paloeocoryne_. +Palæolithic man, remains of. +_Paloeomanon_. +_Paloeoniscus_. +_Paloeontina Oolitica_. +Palæontological evidence as to Evolution. +Palæontological record, imperfection of the. +Palæontology, definition of. +_Paloeonyctis_. +_Paloeophis; toliapictus; typhoeus_. +_Paloeoreas_. +_Paloeosaurus; platyodon_. +_Paloeosiren Beinerti_. +_Paloeotherium; magnum_. +_Paloeoxylon_. +Palæozoic period. +Palms. +_Paludina_. +_Pandaneoe_. +_Pandanus_. +_Paradoxides; Bohemicus_. +_Parasmilia_. +_Parkeria_. +Pear Encrinite. +Pearly Nautilus. +Peccaries. +_Pecopteris_. +_Pecten Groenlandicus; Islandicus; Valoniensis_. +Penarth Beds. +_Pennatulidoe_. +_Pentacrinus; caput-medusoe; fasciculosus_. +_Pentamerus; galeatus; Knightii_. +_Pentremites_ (_see_ Blastoidea). +_Pentremites conoideus; pyriformis_. +Perching Birds. +_Percidoe_. +_Periechocrinus_. +_Perissodactyle Ungulates_. +Permian period; rocks of, in Britain; in North America; + life of. +Persistent types of life. +_Petalodus_. +_Petraster_. +Petroleum, origin of. +Pezophaps. +_Phacops; Downingioe; granulatus; loevis; latifrons; + longicaudatus; rana_. +_Phoenopora ensiformis_. +Phalangers. +Phanerogams. +_Phaneropleuron_. +_Phascolotherium_. +_Pheronema_. +_Phillipsastroea_. +_Phillipsia; seminifera_. +_Pholadomya_. +_Phormosoma_. +_Phorus_. +Phosphate of lime, concretions of; disseminated in rocks; origin of. +_Phyllograptus; typus_. +_Phyllopoda_, of the Cambrian; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous; of the + Permian; of the Trias. +_Phyllopora_. +_Physa; columnaris_. +Pigs. +Pilton Group. +_Pinites_. +_Pisces (_see_ Fishes). +_Pisolite_. +Pisolitic Limestone of France. +_Placodus; gigas_. +Placoid Fishes; of the Upper Silurian; of the Devonian; of + the Carboniferous; of the Permian; of the Trias; of the + Jurassic; of the Cretaceous; of the Eocene; of the Miocene. +_Plagiaulax_. +_Planolites; vulgaris_. +_Planorbis_. +Plants, of the Cambrian; of the Lower Silurian; of the Upper + Silurian; of the Devonian; of the Carboniferous; of the + Permian; of the Trias; of the Jurassic; of the Cretaceous; + of the Eocene; of the Miocene. +_Plasmopora_. +_Platanus; aceroides_. +_Platephemera antiqua_. +_Platyceras; dumosum; multisinuatum; ventricosum_. +_Platycrinus; tricontadactylus_. +_Platyostoma; Niagarense_. +Platyrhine Monkeys. +_Platyschisma helicites_. +_Platysomus; gibbosus_. +_Platystoma_. +Pleistocene period; climate of. +_Plesiosaurus; dolichodeirus_. +_Pleurocystites squamosus_. +_Pleurotoma_. +_Pleurotomaria_. +_Plicatula_. +Pliocene period; rocks of, in Britain; in Belgium; in + Italy; in North America; life of. +_Pliopithecus; antiquus_. +_Pliosaurus_. +_Podocarya_. +_Podozamites; lanceolatus_. +Polir-schiefer. +_Polycystina_; of Barbadoes-earth. +_Polypora; dendroides_. +_Polypterus_. +_Polystomella_. +_Polytremacis_. +_Polyzoa_, of the Cambrian; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous; of the + Permian; of the Trias; of the Cretaceous; of the Miocene. +_Populus_. +_Porcellia_. +Porcupines. +Portage Group. +Port-Jackson Shark. +Portland beds. +Post-Glacial deposits. +Post-Pliocene period. +Post-Tertiary period. +_Poteriocrinus_. +Potsdam Sandstone. +Pre-Glacial deposits. +_Prestwichia; rotundata_. +_Primitia; strangulata_. +Primordial Trilobites. +Primordial zone. +_Proboscidea_, of the Miocene; of the Pliocene; of the + Post-Pliocene. +_Producta; horrida; longispina; semireticulata_. +_Productella_. +_Productidoe_. +_Proëtus_. +Prong-buck. +_Protaster; Sedgwickii_. +_Proteaceoe_. +_Proteus_. +_Protichnites_. +_Protocystites_. +_Protornis Glarisiensis_. +_Protorosaurus; Speneri_. +_Protospongia; fenestrata_. +_Prototaxites; Logani_. +_Psammobia_. +_Psammodus_. +_Psaronius_. +_Pseudocrinus bifasciatus_. +_Psilophyton; princeps_. +_Pteranodon; longiceps_. +_Pteraspis; Banksii_. +_Pterichthys; cornutus_. +_Pterinoea; subfalcata_. +_Pteroceras_. +_Pterodactylus; crassirostris_. +_Pterophyllum; Joegeri_. +_Pteropoda_, of the Cambrian; of the Lower Silurian; of + the Upper Silurian; of the Devonian; of the Carboniferous; + of the Permian; of the Jurassic. +_Pterosauria_; of the Jurassic; of the Cretaceous. +_Pterygotus Anglicus_. +_Ptilodictya; acuta; falciformis; raripora; Schafferi_. +_Ptychoceras; Emericianum_. +_Ptychodus_. +_Pupa vetusta_. +Purbeck Beds; Mammals of. +_Puryuroidea_. +_Pycnodus_. +_Pyrula_. + +_Quadrumana_, of the Eocene; of the Miocene; of the + Pliocene; of the Post-Pliocene. +Quadrupeds (_see_ Mammalia). +Quaternary period. +Quebec Group. +_Quercus_. + +Rabbits. +_Rana_. +_Raptores_. +_Rasores_. +Recent period. +_Reptaculites_. +Red clays, origin of. +Red Coral. +Red Crag. +Red Deer. +Reindeer. +_Remopleurides_. +Reptiles; of the Permian; of the Trias; of the Jurassic; of + the Cretaceous; of the Eocene. +_Retepora; Ehrenbergi; Phillipsi_. +_Retiolites_. +_Retzia_. +_Rhætic Beds_. +_Rhamphorhynchus; Bucklandi_. +_Rhinoceridoe_. +_Rhinoceros Etruscus; leptorhinus; megarhinus; tichorhinus_. +_Rhinopora verrucosa_. +_Rhizodus_. +_Rhombus minimus_. +Rhyncholites. +_Rhynchonella; cuneata; neglecta; pleurodon; varians. +_Rhynchosaurus; articeps. +Rice-shells. +Richmond Earth. +Ringed Worms (_see_ Annelida). +River-gravels, high-level and low-level. +_Robulina_. +Rocks, definition of; divisions of; igneous; aqueous; + mechanically-formed; chemically-formed; organically-formed; + arenaceous; argillaceous; calcareous; siliceous. +_Rodentia_, of the Eocene; of the Miocene; of the + Post-Pliocene. +Roebuck. +_Rostellaria_. +_Rotalia; Boueana_. +Rugose Corals; of the Lower Silurian; of the Upper Silurian; + of the Devonian; of the Carboniferous; of the Permian; of + the Upper Greensand. +Rupelian Clay. + +_Sabal major_. +Sabre-toothed Tiger. +_Saccammina_. +_Saccosoma. +Salamanders. +Salina Group. +_Salix; Meeki_. +_Salmonidoe_. +_Sao hirsuta_. +_Sassafras cretacea_. +_Sauropterygia_. +_Scalaria; Groenlandica_. +_Scaphites; oequalis_. +_Schizodus_. +Schoharie Grit. +_Scolecoderma_. +_Scoliostoma_. +_Scolithus; Canadensis_. +Scorpions of the Coal-measures. +Scorpion-shells. +Screw-pines. +_Scutella; subrotunda_. +Sea-cows (_see_ Sirenia). +Sea-lilies (_see_ Crinoidea). +Sea-lizards (_see_ Enaliosaurians). +Seals. +Sea-mats and Sea-mosses (_see_ Polyzoa). +Sea-shrubs (_see_ Gorgonidæ). +Sea-urchins (_see_ Echinoidea). +Sea-weeds. +Secondary period. +Sedimentary rocks. +_Semnopithecus_. +Septaria. +_Sequoia; Couttsioe; gigantea; Langsdorffii_. +_Serolis_. +Serpents (_see_ Ophidia). +_Serpulites_. +Sewâlik Hills (_see_ Siwâlik Hills). +Sheep. +Shell-sands. +_Sigillaria; Groeseri_. +Sigillarioids. +Silicates, infiltration of the shells of Foraminifera by. +Siliceous rocks. +Siliceous Sponges. +Silicification. +Silurian period (_see_ Lower Silurian and Upper Silurian). +_Simosaurus; Gaillardoti_. +_Siphonia; ficus_. +Siphonostomatous Univalves. +_Siphonotreta_. +_Sirenia_; of the Eocene; of the Miocene. +_Siren lacertina_. +_Sivatherium; giganteum_. +Siwâlik Hills, Miocene strata of. +Skiddaw Slates. +Sloths. +_Smilax_. +_Smithia_. +Snakes (_see_ Ophidia). +Soft Tortoises. +_Solarium_. +Solenhofen Slates. +Solitaire. +_Spalacotherium_. +_Spatangus_. +_Sphoerospongia_. +_Sphagodus_. +_Sphenodon_. +_Sphenopteris_. +Spiders of the Coal-measures. +Spider-shells. +Spindle-shells. +_Spirifera; crispa; disjuncta; hysterica; mucronata; Niagarensis; + rostrata; sculptilis; trigonalis_. +_Spiriferidoe_. +_Spirophyton cauda-Galli_. +_Spirorbis; Arkonensis; Carbonarus; laxus; Lewisii; omphalodes; + spinulifera_. +_Spirulirostra_. +_Spondylus; spinosus_. +Sponges, of the Cambrian; of the Lower Silurian; of the Upper + Silurian; of the Devonian; of the Carboniferous; of the Permian; + of the Trias; of the Jurassic; of the Cretaceous. +_Spongilla_. +_Spongillopsis_. +_Spongophyllum_. +Spore-eases, of Cryptogams in the Ludlow rocks; in the Coal. +Squirrels. +_Stagonolepis_. +Staircase-shell. +Stalactite. +Stalagmite. +Star-corals. +Star-fishes. +St Cassian Beds. +_Stephanophyllia_. +_Stereognathus_. +_Stigmaria; ficoides_. +Stonesfield Slate; Mammals of. +Strata, contemporaneity of. +Stratified rock. +_Streptelasma_. +_Streptorhynchus_. +_Stromatopora; rugosa; tuberculata_. +_Strombodes; pentagonus_. +_Strombus_. +_Strophalosia_. +_Strophodus_. +_Strophomena; alternata; deltoidea; filitexta; rhomboidalis; + Subplana_. +Sub-Apennine Beds. +Sub-Carboniferous rocks. +Succession of life upon the globe. +_Suida_. +Sulphate of lime. +_Sus Erymanthius; scrofa_. +_Synastroea_. +_Synhelia Sharpeana_. +_Synocladia; virgulacea_. +_Syringopora; ramulosa_. + +Tabulate Corals; of the Lower Silurian; of the Upper Silurian; + of the Devonian; of the Carboniferous; of the Permian. +_Talpa Europoea_. +_Tapiridoe_. +Tapirs. +_Tapirus Arvernensis_. +_Taxocrinus tuberculatus_. +_Taxodium_. +_Teleosaurus_. +Teleostean Fishes; of the Cretaceous. +_Telerpeton Elginense_. +_Tellina proxima_. +_Tentaculites; ornatus_. +_Terebra_. +_Terebratella; Astleriana_. +_Terebratula; digona; elongata; hastata; quadrifida; + sphoeroidalis_. +_Terebratulina; caput-serpentis; striata_. +Termites. +Terrapins. +Tertiary period. +Tertiary rocks, classification of. +_Testudinidoe_. +Tetrabranchiate Cephalopods; of the Cambrian; of the Lower + Silurian; of the Upper Silurian; of the Devonian; of the + Carboniferous; of the Permian; of the Trias; of the Jurassic; + of the Cretaceous; of the Eocene; of the Miocene. +_Textularia; Meyeriana_. +Thanet Sands. +_Theca_. +_Theca Davidii_. +_Thecidium_. +Thecodont Reptiles. +_Thecodontosaurus; antiquus_. +_Thecosmilia annularis_. +_Thelodus_. +Theriodont Reptiles. +_Thylacoleo_. +Tile-stones. +_Titanotherium_. +Toothed Birds. +Tortoises. +_Tragoceras_. +Travertine. +Tree-Ferns, of the Devonian; of the Coal-measures. +Tremadoc Slates. +_Trematis_. +Trenton Limestone. +_Trianthrus Beckii_. +Triassic period; rocks of, in Britain; in Germany; in the + Austrian Alps; in North America; life of. +_Triconodon_. +_Trigonia_. +_Trigoniadoe_. +_Trigonocarpum; ovatum_. +Trilobites; of the Cambrian; of the Lower Silurian; of the + Upper Silurian; of the Devonian; of the Carboniferous. +_Trimerellidoe_. +_Trinucleus; concentricus_. +_Trionycidoe_. +_Triton_. +_Trochocyathus_. +_Trochonema_. +_Trogontherium; Cuvieri_. +Trumpet-shells. +Tulip-tree. +_Turbinolia sulcata_. +_Turbinolidoe_. +_Turrilites; catenulatus_. +_Turritella_. +Turtles. +_Typhis tubifer_. + +_Ullmania selaginoides_. +Unconformability of strata. +Under-clay of coal. +_Ungulata_, of the Eocene; of the Miocene; of the + Pliocene; of the Post-Pliocene. +Uniformity, doctrine of. +_Unio_. +Univalves (_see_ Gasteropoda). +Upper Cambrian; Chalk; Cretaceous; Devonian; Eocene; Greensand; + Helderberg; Laurentian; Llandovery; Ludlow rock; Miocene; + Oolites; Silurian period; rocks of, in Britain; in North + America; life of. +_Ursus arctos; Arvernensis; ferox; speloea_. +_Ursus_. + +Valley-gravels, high-level and low-level. +_Vanessa Pluto_. +_Varanidoe_. +Vegetation (_see_ Plants). +_Ventriculites; simplex_. +Venus's Flower-basket. +_Vermilia_. +_Vespertilio Parisiensis_. +Vicksburg Beds. +Vines. +Vitreous Sponges. +_Voltzia; heterophylla_. +_Voluta; elongata_. +Volutes. + +_Walchia; piniformis_. +Walrus. +Wealden Beds. +_Wellingtonia_. +Wenlock Beds; Limestone; Shale. +Wentle-traps. +Werfen Beds. +Whalebone Whales. +Whales. +Whelks. +White Chalk; structure of; origin of. +White Crag. +White River Beds. +Wild Boar. +_Williamsonia_. +Winged Lizards (_see_ Pterosauria). +Winged Snails (_see_ Pteropods). +Wing-shells. +Wolf. +Wolverine. +Wombats. +Woolhope Limestone. +Woolly Rhinoceros. +Woolwich and Reading Beds. +Worm-burrows. + +_Xanthidia_. +_Xenoneura antiquorum_. +_Xiphodon_. +_Xylobius; Sigillarioe_. + +_Zamia spiralis_. +_Zamites_. +_Zaphrentis; cornicula; Stokesi; vermicularis_. +_Zeacrinus_. +Zechstein. +_Zeuglodon; cetoides_. + + + + +*** END OF THE PROJECT GUTENBERG EBOOK THE ANCIENT LIFE-HISTORY OF THE EARTH *** + +Updated editions will replace the previous one--the old editions will +be renamed. + +Creating the works from print editions not protected by U.S. copyright +law means that no one owns a United States copyright in these works, +so the Foundation (and you!) can copy and distribute it in the +United States without permission and without paying copyright +royalties. 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