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 (> E O L O G Y 
 
 ] FOPv SCHOOLS x\ND COLLEGES. 
 
 BY 
 
 H. ALLEVNE NICHOLSON, 
 
 M.D., D.Sc, M.A., Ph.D., F.R.S.E., F G.8., Etc., 
 
 PROFESSOR OK N\rCR.\I, HISTOHY AND BOTANY IN rNlVEKSITY rOM.lME TORONTO I 
 
 FUKMKKI.Y I.KCirUKK ON NATI'RAL HISTORY IN THE MKDirAl, sniiioi, OF K1>IN- 
 
 Ul'KOli: AlTlloR OK "MANr.vr, of zoology for THE rSE OF STI'IIF.NTS," 
 
 '•TEXr-UOOK OK onoLOGV KOR 80IIOOL8 AND COLLEGES." •'GEOLOUY 
 
 OK flMBBKLAND ANU WESTMORELAND," ETC., ETC. 
 
 TORONTO: 
 ADAM, STEVENSON ^ CO. 
 Xi:W YOi:K: U AITLETON & CO., &4i) ii Ml UKOADWAY. 
 
 1S72. 
 
H5 
 
 T^-^^ 
 
 Gntereu, accordinf^ to Act of ConcreKs, in the year 1871. by D. APPLETON & CO , 
 In the Office of the Librarian of Congrenn, »t M'asliiugion. 
 
 Entered, aocordiiip to tlie act of tlic Parliament of Canada, in tin- year one tliousnnd 
 eisrlit hundred and 8<;vcnty-one, by H. ALLEYNE NiC'lloLiSON. in tlie < Hiit- of the 
 Minister of Afrrioiiiture. 
 
PRE FAC E. 
 
 The object of the present work is to present to the learner 
 
 the leading principles and facts of geological science in as 
 
 brief a compass as is compatible with clearness and accuracy. 
 
 No science stands less alone, or is less independent of the 
 
 other sciences, than jreology. Its foundation, as a science, is 
 
 upon Physical Geography, and this subject has, therefore, been 
 
 treated in the earlier portion of this work as fully as space 
 
 would allow. No adequate knowledge, again, of the facts 
 
 and generalizations oi Pal.neontology can be acquired without 
 
 some previous acquaintance with Zoology and Botany, the 
 
 former more especially. A brief outline of the classification 
 
 of the animal kingdom has, therefore, been here introduced ; 
 
 but the progress of the learner would be much facilitated by a 
 
 more extensive study of Natural History than can possibly be 
 
 presented in a work primarily devoted to Geology. 
 
 Piila3ontology, however, is to such an extent an indepen- 
 dent science, and embraces such an extended area, that it can 
 only be properly handled in a special treatise; and such a 
 work is now in course of preparation by the autlior. 
 
 As to the plan of the work, it is sufficient to state that it 
 is not based primarily upon American geology. Many im{)or- 
 tant formations are not represented at all, or only in a very 
 incomplete form, in America; while the t^pes of the great 
 geological formations are at present to be sought for in 
 
(I 
 
 IV 
 
 PREFACE. 
 
 Europe. The author is far from saying that there is any 
 reason in Nature why this should be so ; but the vast Ameri- 
 can CJontinent has as yet been very imperfectly explored ; 
 and there can be no question but that for many years to come 
 European names and European types will hold their ground 
 in geological literature. At the same time, the leading 
 facts of American geology are in all cases stated, and in 
 this connection the author feels bound to acknowledge the 
 obligations which he is under to the works of Profs. Hall and 
 Dana. 
 
 Most of the illustrations of the work have been supplied 
 by the publishers from Sir Charles LyelPs classical treatise, 
 the "Elements of Geology." The remainder have been 
 drawn upon the wood by the author, and their source, where 
 not original, is acknowledged in the text. 
 
 -," * ' 
 Toronto, Ontakio, ^tt^TMs/ 12, 1871. 
 
TABLE OF CONTENTS. 
 
 PART L 
 
 PnrSICAL GEOORAPnY. 
 
 CHAPTER I. 
 
 General Scope of Geology — Modern Geology founded upon Phjrgical Geography— Scope of 
 Physical Gfonrraphy — Planetary Kclations of the Earth — Figure and Dimensions of the 
 Earth — Primitive Condition of the Earth — Internal Temperature of the Earth — Question 
 as to the Fluidity of the Interior of the Earth— Surfiice of the Earth — Origin of Dry 
 Land— Distribution of the Dry Land, Pages 1-9 
 
 CHAPTER II. 
 
 Iklountalns— Mountains of Clrcumdenndation — of Uptlltlng^— of Ejection — Volcanoes — 
 General Phenomena of Volcanic Eruptions— Geographical Distribution of Volcanoes — 
 General Structure of a Volcanic Cone— Exciting Causes of Volcanic Eruptions — Fiirth- 
 quakcs— Their Connection with Volcanic Action, and their General Phenomena, p. 10-22 
 
 CHAPTER III. 
 
 Origin of Valleys— Denudation defined — Action of Rain as a Denuding Agent— Elvers— The 
 Sea aa a Dcnudhig Agent, p. 28-80 
 
 CHAPTER IV. 
 
 Ice as a Denuding Agent — Line of Perpetual Snow— Ghclcrs— Formation of Glaciers — Mo- 
 raines—Polished and Striated Blocks — Striation of the Fundamental Rocks — Koclies 
 Moutonnt'cs — Perched Blocks — Erratics — Continental Ice — Icebergs — Transportation 
 of Erratic Blocks by Icebergs— Frost, p. 31-41 
 
 CHAPTER V. 
 
 Action of the Atmosphere upon the Earth's Surface— Weathering— Sand-dnnes— Organic 
 Agencies— Accumulations of Vegetable Matter— Peat — Shell-beds— Atlantic Ooze — 
 Coral-rueb— Bearing of the Facta of Physical Geography on Geok>gical Doctrine, p. 42-47 
 
VI 
 
 TABLE OF CONTENTS. 
 
 PAPwT II. 
 Q E L O a Y. 
 
 CHAPTER VI. 
 
 Dcflnitlon of Oeologj'— Successive Foriimtion of the Crust of tho Earth — Doflnitlon of tho 
 term "Hock" — ClassUlcatlou of Kocks— Aqueous Kocks — Stratiticutlon — Fossils — Char- 
 acters aud Origin of thu Volcunio Uocks — Granitic Uocks — Metuuiorphic Uocks, p. 46-^9 
 
 CIIAPTEK VII. 
 
 Aqueous Hocks— Mechanically-forincd Rocks— Arenaceous Kocks — Sands, Sandstones, 
 Grits, and (Jonslornurates— Argillaceous Rocks— Clays, Mari, Loam— Clieinicully and 
 Orwnically formed Rocks— Chalk— Limestone — Gypsum — Rock-salt— l,."oal— Gradations 
 between the Groups of Aqueous Rocks, p- CO-08 
 
 CHAPTER VIII. 
 
 Volcanic Rocks— Lova-flows nnd Traps — Dikes— Ashes and Scoria; — Mineral Composition 
 of tho Volcanic and Trappean Rotks — Felspathic and Aupltic Lavas and their Moahani- 
 cai Accompaniments — Fulspatliiu- and llornblondic Traps and thehr Mechanical Accom- 
 paniments — Porphyry and Amygdaloid, p. 69-74 
 
 CHAPTER IX. 
 
 riuconic Rocks— Composition, Characters, and Mode of Formation of Granite- Syenito— 
 Protoghic—Eurito— Passage of tlic Granitic Rocks into Trap, . . . p. 75-77 
 
 CHAPTER X. 
 
 Metamorphlc Rocki«— Gneiss — Hornblende-schist— Mica-schist — Clay-slate — Qnartzite— 
 Mctomorphic Limestone, p. 78-80 
 
 CHAPTER XL 
 
 Divisional Planes of Rocks— Planes of Stratification and Lamination— Planes of Jointing- 
 Columnar Traps and Lavas— Cleavage— Orlghi of Cleavage— Foliation, . . p. 81-33 
 
 CHAPTER XIL 
 
 Lateral Extent of Beds— Original Ilorizontality of Strata— Diagonal Stratification— Ripplo- 
 marks, Desiccation-cracks, Rain-prints — Inclined Strata — Dip — Strike — Contortions of 
 Stratflr— Anticlinal and Synclinal Curves— Causes of Contortions and Curves, p. 89-98 
 
 CHAPTER XIII. 
 
 Unconformability— Overlap— Faults — Denudation of Faulta — Lateral Shift produced hy 
 Faults— Repetition of Strata by FaulU, p. 99-108 
 
 CHAPTER XIV. 
 Tho Relative Ages of the Aqueous Rocks— Test of Age by Superposition— Test by Mineral 
 Characters— Test by included Organic Remains— Outlines of Zoological and Botanical 
 Classifications— Chronological Succession of the Aqueous Rocks, . . p. 109-123 
 
TABLE OF CONTENTS. yii 
 
 CHAPTER XV. 
 
 I^urontlan Series— Life of the Laurentlan Series— lluronian Formation— Cambrian Series— 
 Life of the Cumbrian Kocks, !«»«« l..'4-iao 
 
 CHAPTER XVI. 
 
 Silurian Formation— Origin of tho name Silurian— Silurian Rocks of Britain— Silurian Roeks 
 of Nortli .Vuicrica— Lile of tho Silurian Period, p. 131-141 
 
 CHAPTER XVII. 
 
 Old Red Sandstone— Name Devonian— Old Red Sand.stone and Devonian Rocks of Britain — 
 Devonian iiocka of North America— Life of tho Devonian Period . . p. 142-149 
 
 * 
 
 CHAPTER XVIII. 
 
 Carboniferous Rocks — Carboniferous Slates and Llmestono — Mlllstono Orlt— Coal-moasnres 
 — Plants of the Coal — Other Fossils of tho Coal-measures — Origin of Coal — Life of iho 
 Carbouiferous Period, p. 150-162 
 
 CHAPTER XIX. 
 
 Permian Rocks— Development In Russia and Germany — Pcrmians of Britain — Permian 
 RocksofNorth America— Life of the Permhin Period, .... p. 103-1(56 
 
 CHAPTER XX, 
 TriassicRocks— Orlghi of Rock-salt— Life of tho Trlasslc Period, . . . p. 167-173 
 
 CHAPTER XXI. 
 
 Jurassic Rocks— Lias— Lower Oolites— Middle Oolites— Upper Oolites— Jurassic Roeks of 
 North America— Life of the Jurassic Period, p. 174-1^ 
 
 CHAPTER XXII. 
 
 Cretaceous Series— Wealdcn— Lower Greensand—Gault— Upper Greensand-Chalk-Maes- 
 trleht and FaxOe Beds— Chalk of the South of Europe— Cretaceous Rocks of North 
 America— Origin ofChalk— Origin of Flints— Life of tho Cretaceous Period, p. lSo-196 
 
 CHAPTER XXIIL 
 
 Relations of the Kalnozolc to tho Mesozoic Rocks— Classification of the Kalnozoic Rocks- 
 Eocene Rocks— Life of the Eocene Period, p. 197-204 
 
 CHAPTER XXIV. 
 
 Miocene Rocks— Miocene Deposits of Europe— American Miocene— Life of the Miocene 
 Period— Vegetation of the Miocene Period, p. 205-210 
 
 CHAPTER XXV. 
 
 Pliocene Rocks— Coralline Crag— Red Crag— Pliocene Deposits of Europe and America- 
 Life of the Pliocene Period, p. 211-215 
 
: I 
 
 Viil TABLE OF CONTENTS. 
 
 CHAPTER XXVI. 
 
 Post-Tertiary Fonnatioii*— Cromer Forest-bod— Glacial Period, . . . page 216-221 
 
 CHAPTKR XXVII. 
 
 McaninfT of the Term AiluTlum—Drick-eorths— Loess — IIlgli-loTcl and Low-lcrol Valley 
 Urovtils — (Javera-deposita, p. 222-220 
 
 CHAPTER XXVIII. 
 
 Bccent Period— Age of Stone— Age of Bronze— Ago of Iron— Kttchcn-intddonB— Danish 
 Peat— Swiss Lake-dwelliDga — General Scarcity of Human Remains — TyiH's of 
 Bkiill, p. 2S0-288 
 
 CHAPTER XXIX. 
 
 Volcanic and Trappean Rocks, their Modes of Occurrence — Tests of Age— Contcmpomncous 
 and Intrusive Traps— Trap-dikes, p. 284-289 
 
 CHAPTER XXX. 
 
 Granitic Rocks — Agea of the Granitic Rocks— Granite Vtins— Metamorphlsm produced by 
 Granite — Metamorphio Rocks— Ago of the Mctamorphic Rocks, ... p. 240-248 
 
 CHAPTER XXXI. 
 
 Mineral Veins— Mode of Oocurrence of Metallic Ores— Connection of Veins with Faults — 
 Mode of Deposition of Metals in Veins- Ages of Veins, .... p. 244-240 
 
LIST OF ILLUSTRATIONS. 
 
 no. 
 
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 Monntn'ins of C'lrcumdenudation, 
 
 MountiiiiiH of Uptiltiiii,', 
 
 Vesuvius from tho West, 
 
 Diajjrara of a QuicHcent Volcano, 
 
 Section of tho Irtlaiid of Palina . 
 
 Section of a Voleunic Cone, . 
 
 Section of Niatfura Fulls, 
 
 Section of a River Valley (Schoharie), 
 
 Mer du (ilace, .... 
 
 Dia^i^rum of tho Moraines of a Glacier, 
 
 PoTMhed M\d Striated Linieatone, 
 
 Koche Moutonnee, .... 
 
 Erratic Bloci< oi\ the Jura, 
 
 Structure of Coral-reefs, 
 
 Section of Stratitted Deposits, . 
 
 Volcanic Dike in Madeira, 
 
 Joints in Limestone, . . 
 
 Isle of Cyclops, .... 
 
 Diagram of Columnar Trap, 
 
 Diagram to illustrate Slaty Cleavage, 
 
 Striped and Faulted Slate, 
 
 Dia<^ram to illustrate tho Thinning out of Bods 
 
 False-bedding, . . . . 
 
 Dia.frain to illustrate the Formation of Ripple -mark. 
 
 Ripple-marked Sandstone. 
 
 Diagram to illustrate the Dip of Inclined Strat 
 
 Inchned Strata, .... 
 
 Contorted Strata, .... 
 
 Diagram of an Anticlinal Curve, . 
 
 Diagram of a Synclinal Curve. 
 
 Diagram to illustrate the Production of Contortions 
 
 Section of Unconformable Strata, 
 
 Ground-plan and Section of Unconformable Strata, 
 
 Diagram of Overlap, .... 
 
 Diagram to illustrate the Production of Faults, 
 
 Section of Faulted and Shifted Strata, 
 
 Diagram of a Fault, .... 
 
 Denudation of Faults, 
 
 Diagram to illustrate tho Lateral Shift of Beds, 
 
 R "petition of Beds by Faults, 
 
 Foraminifera, . . . . , 
 
 Recent Corals, .... 
 
 Rhizocrinu8 Lofotengity . . . , 
 
 Sea-urchin ( Cidaris), 
 
 PAflB 
 
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 LIST OF ILLUSTRATIONS. 
 
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 Pterygotus AnglicuK^ .... 
 
 Lingula O'ltiiia^ ..... 
 
 SIjcUs of Univalve Mollusks; 
 
 I'eurly Nautilus, ..... 
 
 Skeleton ol" lieavcr, .... 
 
 Ideal Section of thy Earth'a Crust, . 
 
 Section of the rre-Canibrian Kocks of Scotland, 
 
 Section of the (Jamhrian liock.s of the Longmynd, 
 
 J'ttradnxidts Jiohcmicufs, .... 
 
 iJikelocephalua Mmnesottnsis, , 
 
 Oltlhamia atitiqua, . 
 
 Jli/menocaris vermica uda, 
 
 Lingula Davuii, 
 
 Olenus micrvrvSy 
 
 Tetragrapaus bryonoides, 
 
 Generalized Section of the Silurian Rocks of Britain, 
 
 Vlilymograpstis patulus^ . . . . . 
 
 Asaphus tyrannus, j 
 
 Ogi/gia Jiuc/iii, ) 
 
 Orlkis tricenaria^ 
 
 Ovthis vespertilio, 
 
 tStrophomena arandis, 
 
 Priitamerua oolongus, 
 
 Hal y sites catenularhts, 
 
 Favosites G(4hlan<li( 
 
 Omphyma turbinatum^ 
 
 Orthis ehgaittvla. 
 
 I 
 
 ira, [• 
 tm, ) 
 Ort/iis e/,gnit(u/a, i 
 
 lihynchniidUi naricnlti. V 
 Rliyaclioiulla WUtoni^ ) 
 
 Pttraxpif Jkiiikioi, . , » . 
 
 Oiic/ius hniiidfiatus. ) 
 
 Shagreen -scales of 27ielndtis, ^ . . . 
 
 Generalized Section of the Silurians of North Anaerica, 
 LckiiiofipJutrit(S BaHicus^ .... 
 
 Tr! II udeus concent Hcuf^ ..... 
 
 Troc/ioceraa qigaideus^ \ 
 
 Vrtlinaras Lulensc^ j- . . . . 
 
 Ci'/Jiafa-^pis ZytUii, ..... 
 
 Aaianfitcs {Vycloptrris) I/ibtn'tiicvs, 
 
 /loloptyrJiitis^ restored, ..... 
 
 Sjnri.fir diy'iinctus, ...... 
 
 Calceola sandalina, ..... 
 
 Phacops laUfrnni>y ...... 
 
 Section of tlie Devonian Kocks of North America, 
 SJqillarla Chfmnngensis, . . . . . 
 
 Megalodon cucullaius^ . . , . , 
 
 CJymenia li'/itaris, ..... 
 
 General Section of the Carboniferous Rocks, . 
 
 Litliostrotion bamltiforme^ \ 
 
 Lnusdaldafiorifovmu^ \ . . . . 
 
 Cyatlwcrinut; planvs^ . . . ... 
 
 Product a sent ircficvlata, . . . . , 
 
 Goniatite^ erenidria^ ..... 
 
 Teeth of CochUodits contortus, . . . , 
 
 Stem of Lepidodendron, \ 
 
 Fi'ui^mont of LfpidoUendron Stcrnbergii, ) 
 
 Calamites canna'fcnnis, 
 
 Cahtmites Sucoi' " 
 
 Root termiiintit 
 
 Sigillaria Icuvigata, 
 
 AifpKioaenaron i^iuri 
 'tna'fcnnis, ^ 
 
 cowi), > 
 
 ition of Calamite, J 
 
 PACK 
 
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LIST OF ILLUSTRATIONS. 
 
 no. 
 
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 'cum, 1 
 sis, > 
 1, ) 
 
 Stigmaria ficoidcs^ .... 
 Erect Fos.iil Trees, Coal-mcaaures, 
 Archegosaurus minor^ 
 Litiiutus rotundatuSy 
 
 Cjjtherii injlata, .... 
 
 Spirifer trigonalis, \ 
 iipirifer ylaber, ) ' 
 
 Generulized Scctio i of the Permian Kocks, 
 Watchia piniformiii, 
 Froduda horrida^ \ 
 
 Lingula Crediierii, > ... 
 
 Spii'iftr undulatua, ) 
 ()[it\\no o{ IWizoiiiscus, . 
 Generalized Section ot the Triassic Rocks, 
 Footprints of Ch' irotherium^ , 
 Voltzla hderophi/Ua^ 
 C\ rat 'tea nodosus, . . 
 
 Encrinus liliiformis, 
 C'lrdium Rhcetuum, 
 Piictea Valoiiiiusis. 
 Avicula coiitorta 
 
 Teeth of IL/botluit pfii-atilis, ) 
 Tooth o{ Sduric/it/ii/fi apiiutUs, > . 
 Sciilo of O'/i'olfpJ'^ tenuistriatus, ) 
 Molar tootli of Mierolrstes aatlfjuus, 
 Footprint.s in Triassic Sandstones of the Connecticut Valley 
 Generalized Section of the Jurassic Rocks, 
 Gruphea incnrva, .... 
 Jietemnltes clongatm, 
 Ammonites Bucklandi, | 
 Ammoiiitts plnnorbis, j ' 
 H.rtracriii'is Briareus, . . . , 
 
 Hi/hodus reticulattts, .... 
 PUrophyllam, comptiim, . . . 
 
 Ammonites Tfumphri'siitnus, , 
 
 Apiocrinus rotund us, 
 I'lmscolothcrium Bucklandi, 
 B'lemnites hastntus, . . . , 
 
 Tli'cosmilia annularis, . , • . 
 
 Odrea distorta, .... 
 Pterodadylus crassirostris, 
 Plagiaulax minor, . . . 
 
 Ci/cadeoidea megnlophylla, ) 
 Znmites spiralis. j * • 
 
 Ic/itki/osaurus communis, \ 
 PUjiiosaurusdolichodeirus, j 
 Architopterux macrura. 
 
 Generalized Section ot the Cretaceous Rocks, 
 Teeth of /guanodon Mantelli, 
 Aneyloceras ciigas, \ 
 
 Nautilus pllcatus, ( ' * * 
 
 Ancf/loreras spini^jcrum, 
 Ventriculites radiatus 
 Inoceramus Lamarckii, 
 
 Bteulites Faujasii, j 
 Jiarulites anceps, ) 
 Turrilites costal us, \ 
 Scnphites cequalis, j " 
 Mlcrister cor.-anffuinum, 
 Galerites alhogalerus, 
 
 PAoa 
 157 
 
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 iro 
 
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\i 
 
 xu 
 
 na. 
 
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 21 r 
 
 21;. 
 
 218. 
 
 219. 
 
 220. 
 
 LIST OF ILLUSTRATIONS. 
 
 Motamurtu Camperi, 
 HippuriteH organisans, . 
 
 170. Orcunic Bodies in the Atlantic Ooze, 
 Generalized Section of the Eocene Bocks, 
 Valuta nodosa^ .... 
 Calcarina rarispina, ) 
 Spirolina stenoaioma^ ) * ' 
 
 AumiiiUlUea Puschi, . , 
 
 Carcharodon heterodon, \ 
 (Modus obiiquusy J 
 
 Teeth of Zevglodon eetoidei, ) 
 Vertebra of the same, J * 
 
 I'aicEotherium magnum^ 
 Deirwiherium giyanteum^ 
 Voluta Lamherti, . , , 
 
 Fulgur caiialicuiatua, \ 
 Fusus guadricostatuB, ) ' 
 Vanessa Pluto^ 
 Chamarops Helvetica, ) , 
 Sabal major, j 
 
 Flatanus aceroides, ) 
 
 Cinnamomum polymorp7turn, J 
 Section of the Suffolk Crag, 
 Voluta Lamherti, 
 Jhrrula reticulata, 
 Temnechinus excavaffti, 
 Fusus contrarius. 
 Purpura tetragona, 
 Nassa granulata, 
 Cyprcea Europota, 
 Molar of Mastodon Arvemensts, 
 Molar of Elephns meridionalis, . 
 205. Shells of the Drift of Scotland, 
 Eecent and Post-Pliocene Alluvial Deposits, 
 ^lo]ar of Flfplias antiguu^, . 
 Section of Cavern and River-valley, 
 Molai of Mammoth, .... 
 Lower Jaw of Cave-Hytena, 
 Short-headed Skull, ) 
 
 .} 
 
 Long-headed Skull 
 
 Trap overlying Sandstone. 
 
 Diagram of the Granitic, Aqueous 
 
 Step-like appearance of Traps, . 
 
 Diagram of Trap-dike, 
 
 Section of an Intrusive Trap, 
 
 Trap intruded in Limestone and Shale, 
 
 Granitic Veins, . . . . 
 
 Section of Mineral Veins, . 
 
 and Volcanic Formations 
 
 PAOB 
 
 192 
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 (lU 
 
 hi; 
 
 \\\ 
 
 S 
 
GEOLOGY. 
 
 PART I. 
 
 PHYSICAL GEOGRAPnr. 
 
 CHAPTER I. 
 
 Geology (Gr. ge^ th(^ earth ; logos, discourse) is the science 
 which IS concerned with the investij^ation of the materials 
 which compose the earth, the manner in which these materials 
 have been arranged, and the causes and mode of origin of 
 these arrangements. The forms, properties, chemical compo- 
 sition, and local distribution of the materials which compose 
 the crust of the earth, constitute the separate science of Mm- 
 eralogy, whicli is, indeed, closely related to Geology, but 
 which, nevertheless, is not essential to the study of the latter 
 science. A limited knowledge, however, of Mineralogy is es- 
 sential to a due comprehension of the phenomena of Geology, 
 and such details as are thus requisite will be introduced in 
 their proper place. Palceontology (Gr. palaios^ ancient ; onta^ 
 beings ; logos, discourse) is a branch of Geology which treats 
 of the past life of the g obe and is concerned with those ani- 
 mals and plants which — as will be seen 1 areafter — have peo- 
 pled the earth at successive periods, and have died out, to be 
 replaced by others different in their character and structure. 
 Here, therefor. , Geology comes closely in contact with the 
 sciences of Zoology and Botany, the sciences which treat of 
 the various animals and plants vrhich inhabit the earth at the 
 present dsiy. Palaeontology, in fact, is nothing more or less 
 than the Zoology and Botany of the past, and it is only espe- 
 cially connected with Geology in so far that by its study the 
 observer is enabled to determine the historical succession of 
 the materials which compose the globe. For the study of 
 
I 
 
 ■ 
 
 t ' 
 
 :(|i 
 
 
 8 
 
 PHYSICAL GEOGRArUY. 
 
 Palacontolocry, some knowledge of the fundamental facts of 
 Zoology and Jiolany is requisite, and an outline of some of 
 these necessary facts will be subsequently given. Physical 
 Geo(/raphy^ finally, comprises a knowledge of the figure and 
 motion of the earth, of the composition, form, and distribution 
 of the dry land, and oi the forces wliicli tend to modify its 
 surface, of the character and distribution of the rivers and 
 lakes which are placed on the land-masses, of the sea and at- 
 mosphere, and lastly, of the animal and vegetable life of dif- 
 ferent portions of the surface of the earth. Modern Geology 
 rests, as a science, upon Ph^'sical Geogra])hy; and it is abso- 
 lutely necessary that tlie student sliould acquire some knowl- 
 edge of the fundamental facts of the latter science, as a pre- 
 liminary to his commencing the study of the former. It is 
 hardly necessary, however, to say that only the leading facts 
 of Physical Geography can be touched upon here, in tlie very 
 briefest manner, and only so far as tiiey have a direct bearing 
 upon the study of Geology. Tlie points which require to be 
 alluded to in this connection are, the form and phuietary rela- 
 tions of the earth, the distribution of the dry land, and the 
 agencies wiiich tend to alter the characters of the earth's 
 surface, especially the effects produced by rivers, ice, the at- 
 mosphere, and volcanoes. 
 
 Planetatiy Relations of the EaPwTii. — The earth is one 
 of the smaller of the planets which compose our system. It 
 performs an annual revohition round the sun, in an elliptical 
 orbit, at a mean distance of 95,000,000 miles. It also rotates 
 in twenty-four hours about its own axis, this axis being in- 
 clined a little more tiian twenty-three degrees to the plane of 
 its orbit. The moon is a satellite of the earth, revolving 
 round it at a mean distance of 240,000 miles, and causing by 
 its attraction certain terrestrial phenomena, of which the most 
 important are the tides. 
 
 Figure axd DijrExsioxs of the Earth. — Astronomy 
 teaches us that the earth has the form of what is technically 
 called an " oblate si)heroid," That is to say, it is not a per- 
 fect sphere or globe, all the diameters of which are equal ; 
 but it is flattened at the poles, like an orange, one diameter 
 being longer than the other. The earth revolves about an 
 imaginary axis, the two extremities of which constitute the 
 poles — the North pole and the JSouth pole. This, the polar 
 axis of the earth, is, roughly speaking, 7,900 miles in length ; 
 while the equatorial or greatest diameter of the earth is 7,93(3 
 miles in length, exceeding the polar diameter by J36 mil >. 
 
 I- 
 
rRIMlTlVE CONDITION OF THE EARTH. 
 
 8 
 
 facts of 
 5omc of 
 Physical 
 are and 
 tribution 
 odify its 
 ,ers and 
 I and at- 
 e of dif' 
 Geology 
 
 is abso- 
 le knowl- 
 is a prc- 
 r. It is 
 ing facts 
 tiic very 
 , bearing 
 re to be 
 tary rela- 
 
 and the 
 e earth's 
 e, the at- 
 
 th is one 
 tern. It 
 lliptical 
 D rotates 
 
 jeinp;' in- 
 plane of 
 evolving 
 ising by 
 the most 
 
 tronomy 
 thnically 
 [)t a per- 
 equal ; 
 liameter 
 )out an 
 Lute the 
 he polar 
 llen<j:th; 
 lis 7,92G 
 mil s. 
 
 The earth, therefore, is flattened at the poles, and bulges out 
 at the equator. 
 
 That llio earth, bcinf:^ such an ohlato spheroid, with unequal axes, should 
 revolve alioiit its t^hortcst axi.s i8 in obedience to well-known mechanical 
 laws. Wliotlier the eartii has ever revolved about an axis dillerent to its 
 I(re^ent one, or ever will do so, we do not know. As things stand, however, 
 the earth's eircuinf'ereiice at the etjuator is greater by some eighty-threo 
 iiiiles than its circumference at the poles, and it is, therefore, practically in 
 the condition of a sphere revolving on its shortest axis, and having a thick 
 belt surrounding it in a plane perpendicular to the axis of rotation. Any 
 disturbing force applied to the earth, with a tendency to alter its present 
 axis of rotation, would have to overcome the excess of centrifugal force re- 
 siding in the nuitter of this e(|ualorial belt. This excess of centrifugal 
 force is so enormous in amount that we may safely say we know of no force 
 cajiablc at the present day of effecting this change. 
 
 It is worthy of notice that the present form of the earth 
 — the form, namely, of an oblate splioroid — is precisely the 
 form whi(;li any body composed of lluid or semi-fluid sub- 
 stances would tend to assume, if it were set free in space 
 after a pn^iiminary movement of revolution had been impart- 
 ed to it. In other words, the centrifugal force developed by 
 tlie rotjition would tend to accumulate the component parti- 
 cles of such a body along a zone lying at right angles to its 
 axis of revolution. Any revolving body, of whatever origi- 
 nal form, the particles of which are free to move, would ulti- 
 mately assume tlie form of an oblate spheroid, revolving upon 
 its shortest axi.s, and having its longest diameter at right 
 angles to its axis of revolution. The present figure of the 
 earth is, therefore, a strong argument in favor of the belief 
 that the whole earth w:js at one time con>posfHl of melted ma- 
 terials, the })articles of which were free to move in any direc- 
 tion toward which they might be impelled. 
 
 Pkimitive Condition of the Eaktii. — With regard to 
 the original and primitive state of the earth, it is suflicient to 
 state that all known facts support the theory that the earth 
 has been, and is still, a gradually-cooling body. Upon this 
 theory, the materials composing tlie earth were at one time in 
 a state of vapor or gas, in which condition, of course, they 
 would occujiy enormously more space than they do at present. 
 As the loss of temperature went on, the gaseous matters of 
 the primitive earth would radial(^ their heat from the periph- 
 ery, and would contract and ultimately become fluid. Fi- 
 nally, as the cooling process ])roceeded further and further, 
 solidilication wotdd at la.st commence, either at the surfiice, or 
 at the centre, or at botli simultaneouslv. This is certainly to 
 
I I 
 
 I , 
 
 4 PHYSICAL GEOGRAPHY. 
 
 a great extent a mere theory, but it is supported by two facts : 
 One of these is the fact that the present form of the earth is 
 exactly that which it would have assumed supposing it to have 
 been formerly fluid or semi-fluid, and to have been revolving 
 at its present velocity. The second of these is the undoubted 
 high temperature of parts, at any rate, of the interior of the 
 earth at the present day ; and here we get upon tolerably firm 
 ground. 
 
 Internal Temperature op the Earth. — As to the 
 present temperature of the interior of the globe, the following 
 facts enable us to come to some definite conclusion : 
 
 1. The phenomena exhibited at the present day — to be 
 spoken of more particularly hereafter — prove beyond a doubt 
 that large portions, at any rate, of the interior of the earth 
 are in a state of complete fluidity, the fusion being the result 
 of heat. At present the traces of direct volcanic action are 
 only partially distributed over the globe ; but we have ample 
 and abundant {)roofs that volcanic action has taken place 
 everywhere over the earth's surface at some 'ime or other. 
 Further, the universal presence at the surface ' .' rocks which 
 can be shown to have been originally melted and fluid, is quite 
 sufficient proof that there has always existed — as there still 
 exists —in the interior of the earth some powerful and general 
 source of heat. 
 
 2. It is well known that the heating eflfect of the sun's 
 rays upon the soil extends to but a very limited depth below 
 the surface, and that a point is soon reached at which no per- 
 ceptible effbct is produced by any external source of heat. 
 Nevertheless, it has been shown, as the result of direct experi- 
 ment and observation, tliat there is a gradual and tolerably 
 regular increase of heat as we recede from the surface of the 
 earth and approach its centre. The exact ratio of this increase 
 of temperature does not appear to be absolutely constant, but 
 some increase there always is. In the case of mines, the or- 
 dinary rise of temperature, as we descend, is usually stated to 
 be 1° Fahrenheit for every fifty or sixty feet of descont, after 
 the first hundred. It is probable, however, that thi increase 
 would be found to be much more rapid than this at great 
 depths. The same fact, and pretty nearly the same rate of 
 increase, is shown by the phenomena of artesian wells, in 
 which the water always comes from great depths, and always 
 has a temperature considerably higher than the air. In the 
 same way, such natural hot springs as are known to us, are 
 either in the neighborhood of volcanoes, or can generally be 
 
 illi: 
 
FLUIDITY OF THE INTERIOR OF THE EARTH. 5 
 
 shovm to be situated on lines of " fault," i. e., on the line of 
 great cracks or fissures which penetrate through the crust of 
 the earth to a greater or less depth. 
 
 3. Whenever we can study at the surface rocks wliich can 
 be shown by geological evidence to have been formerly buried 
 at great depths in the earth, these- show unmistakable marks 
 of having been subjected to the action of heat. 
 
 The above are the chief direct proofs of the internal heat of the globe, 
 but there i.-s other equally forcible evidence to be drawn indirectly from the 
 niKin tlensifif or weight of the earth. By numerous experiments it has been 
 bIiowu that the entire earth has a mean density or specific gravity of between 
 Jive and six. That is to say, the earth is in the same condition as regards 
 its density, as an imaginary globe would be of the same size, and composed 
 throughout of a simple homogeneous substance weighing between five and 
 six times as much as water. The earth, however, is not homogeneous, com- 
 posetl of one uniform substance, but heterogeneous, composed of different 
 materials having different densities. Talving the average of the rocks which 
 compose the crust of the earth, we find their average density to be only 2.6 
 to 3.0. The mean dcui^ity, therefore, of the earth, is at least twice what it 
 ought to be if it were made of any known rock, as that rock appears at the 
 surface. At first sight, it might be thought that this would prove the pres- 
 ence in the interior of the earth of some materials much heavier than ordi- 
 nary rocks, such as the metals. And this would be so, if the effect of 
 gravity were left out of consideration. The earth is truly twice as heavy as 
 it would be if it were entirely composed of any known rock, as that rock 
 appmrs at the surface. Say the earth were composed of granite, which 
 weighs about 2.5, and which represents, therefore, the average weight of 
 rocks. Granite weighs about two and a half times as much as water ut the 
 surface of the earth, but by the effects of gravity, as we recede from the 
 surface, its density would gradually go on increasing, till at the centre of the 
 earth its <lensity would be about eight times greater than at the surface, or 
 at least twenty times as heavy as water, supposing the ratio of compression 
 produced by gravity to be uniformly the same from the surface to the centre 
 of the earth. If, therefore, the earth were conceived to be a homogeneous 
 globe of granite, it would have a much higher mean density than only five or 
 six. It would have a mean density of at least ten or twelve. 
 
 Seeing, then, that as a matter of fact the mean density of the earth is no 
 more than about Jive (accurately 5.675), we have to look for some force 
 •which could counteract this compressing effect of gravity, and could prevent 
 this regular increase of density in passing from the surface to the centre. 
 We know of no other force capable of effecting this except the expansive 
 power of heat, so that what is learned in this Way fully corroborates what 
 we are taught by direct observation. 
 
 QuESTIOl^ AS TO THE FLUIDITY OF THE INTERIOR OP THE 
 
 Earth. — Tlie general belief as to the condition of the globe 
 at present is that it consists of a cool, non-conducting cniHt or 
 external envelope surrounding a highly-heated interior, and 
 now the question arises, In what condition is that interior ? 
 If we take 1° Fahrenheit for every 90 feet of descent as 
 
I' I 
 
 '» 
 
 :l|! 
 
 ijii 
 
 ill 
 
 I i 
 ) t 
 
 a 
 
 
 
 PHYSICAL GEOGRAPHY. 
 
 m I 
 
 the average increase of temperature, as we recede from tJio 
 surface of the eartli and aj)pr()ach its centre, then, at a d(>pth 
 of 00 miles below the surface, we should everywhere come 
 down to a region in which the temperature would be about 
 5,000° Fahr. Now, all known rocks melt at al)out 2,000°, 
 and platinum, one of the most refractory of metals, fuses at a 
 little over 3,000°. At a depth, therefore, of about fifty miles 
 below the surface, we should have all the materials which 
 compose the crust of the earth in a state of fusion. At a still 
 greater depth, supposing the law of increased temperature to 
 hold gootl, all these melted substances would be further 
 reduced to a state of vapor or gas. The condition, therefore, 
 of the earth M'ould be that of a hollow s])here, gaseous at its 
 centre, with intermediate zones of fluid or pasty matter, and 
 with a solid outer envelope or crust. This supposition, how- 
 ever, overlooks the efl'ect of gravity, and could only be exactly 
 correct supposing gravity to be wanting. 
 
 It is well known that, as a general rule, the cflfect of press- 
 ure is to raise the fusing-point of any material. If a given 
 body would melt at the surface of the earth at a given tem- 
 perature, it would require a much higher temperature to melt 
 it if it were exposed to pressure; as it would be if removed 
 neaicr to the centre of the earth. Consequently, though the 
 condition of the interior of the earth may well be as described 
 above, the actual depth at whicb these changes occur will cer- 
 tainly be greater than is indicated by the mere law of the 
 increase of temperature in descending below the surface. 
 
 In what exact ratio, and to what exact extent, the pressure 
 of gravity interferes with the fusion of the interior of the 
 earth, we do not know ; but that it must so interfere is certain. 
 The phenomena of volcanoes, however, prove that, in certain 
 localities and at certain times, at any rate, melted matter is to 
 be found at no great depth below the surface of the earth. 
 
 Upon the whole, then, it would appear safe to conclude 
 that the earth consists of a, comparatively speaking, thin skin 
 or solid crust surrounding a more or less completely fluid in- 
 terior. 
 
 Surface of the Eaetit. — When we come to consider the 
 surfiice of the earth, the first and most obvious fact which 
 strikes us is, that it consists partially of dry land and partially 
 of water. This ftict is so obvious that we never ask ourselves 
 why this should be so, but in reality it is a circumstance re- 
 quiring explanation. It is quite conceivable that the surface 
 of the earth might have been perfectly level, completely cov- 
 
SURFACE OF THE EARTH. 
 
 ercd by water, and exhibitinf]^ no dry land. As it is, we not 
 oiilv have dry land, ns'iwr in some instances to over 29,000 
 fe<'t above the sea-level, but we know that depressions fully as 
 deep, and probably much deeper, exist below tiie level of the 
 sea. If the crust of the earth had been always al)solutely 
 innnovable, and were so now, no such state of allairs wouUl 
 b(; founil, since, as we shall see later on, every thiii^-:il)ov(' tiie 
 sea would l)y this time have been reduced to below the level 
 of the lowest tides. 
 
 Tiie orii^in and existence, then, of dry land is only to bo 
 explained upon the supposition that the crust of the earth is 
 not immovable, but that it is liable to partial elevations and 
 depressions, one portion being- raised, while another is station- 
 ary or is depressed. If the conception of the ^lobe as a fluid 
 mass surroundt.'d by a thin solid crust be the correct one, it is 
 easy to see how such movements might take place ; though 
 it is ditlicult to point to the exact cause of any particular 
 movement, or, indeed, of these movements in general. In 
 some cases, perhaps, the elevating force may be steam gener- 
 ated by the access of water through fissures in the crust of the 
 earth to the highly-heated interior. A more general cause, 
 however, for these movements may be found simply in the 
 irregular contraction of a highly-heated and heterogeneous 
 glob(\ surrounded by a comparatively rigid crust, and slowly 
 parting with its heat. 
 
 When, therefore, we meet with dry land, we believe that 
 its existence is to be ascribed to a partial elevation of the 
 crust of the earth at this particular point ; and the chief rea- 
 sons for this belief are as follows : 
 
 We find everywhere in the dry land the remains of sea- 
 animals embedded in the rocks ; this proving plainly that tliese 
 rocks were originally covered by the ocean, and that, in fact, 
 they were actually formed at the bottom of the sea. The 
 rocks containing these marine animals occur now at various 
 elevations above the present sea-level, having been detected 
 as high as human observations can be made. (Fossil shells, 
 for instance, have been found in the Himalayas at a height of 
 over 18,000 feet.) Now, there are only two means of account- 
 ing for this fact: either the sea must have retired and left 
 these rocks dry ; or, the rocks must have been raised above 
 the level of the sea by some agency. At first sight it would 
 seem more likely that the sea should have altered than tlic 
 solid land ; but no fact is better established than that it is 
 really the land which has changed its position. 
 
^'1 
 
 ! 
 
 
 iiii 
 
 
 '■ • 
 
 jl 
 
 !!! ^ 
 
 ;»! 
 
 ill' 
 
 8 
 
 PHYSICAL GEOGRAPHY. 
 
 Tlie sea cannot sink permanently at any one point without 
 sinking to the same amount over tlie entire globe. Nor, 
 again, can the sea-level be permanently raised at one point, 
 unless it is raised universally and equally. This single consid- 
 eration is sufficient to destroy any theory that the sea either 
 permanently retires from the land, or permanently gains upon 
 it at any particular point simply by overflowing it. 
 
 Ou the other hand, passing over at present the numerous 
 proofs afforded by geology of the movements in the earth's 
 crust, we can actually observe the process going on in certuin 
 regions of the world. Thus, it has been established that the 
 west coast of Greenland is gradually sinking over a space of 
 about six hundred miles from north to south. In the same 
 way it has been shown that a great portion of Sweden and 
 Norway is gradually being elevated at a rate of about three 
 feet in a century. In South America, the plains of Patagonia 
 and the pampas of Buenos Ayres have been elevated within 
 comparatively modern times, as shown by the existence on 
 their surface of numerous marine shells of living species. 
 Scotland is believed to have undergone an upheaval of about 
 forty-five feet since the time of its occupation by the Romans. 
 Lastly, many instances are known, in which extensive tracts 
 of land, sometimes covering hundreds or even thousands of 
 square miles, have been suddenly elevated or depressed con- 
 temporaneously with the occurrence of earthquakes. 
 
 We must, then, altogether give up the old belief that " the 
 ocean was formerly universal, and that it has gradually sunk 
 down to its actual level, so that the present continents and 
 islands were left dry " (Lyell). On the contrary, we must be- 
 lieve that every portion of dry land at present above the sea- 
 level is there in consequence of a local elevation of the crust 
 of the earth at that point. And, not only is this the case, but 
 geology shows us by unmistakable evidence that alternate 
 elevation and depression of portions of the dry land has been 
 part of the order of Nature and has been going on throughout 
 the whole of geological time. What is now dry land has 
 been beneath the sea, not once, but many times, and may and 
 will be again submerged. Our present seas, in the same way, 
 roll over what has been many times, and will again be, dry 
 land. Thus, in the words of Sir John Herschel, " we come to 
 perceive that the actual configuration of our continents and 
 islands, the coast-lines of our maps, the direction and eleva- 
 tion of our mountain-chains, the courses of our rivers, and the 
 soundings of our oceans, are not things primordially arranged 
 
DISTRIBUTION OF THE LAND. 
 
 b without 
 »c. Nor, 
 nc point, 
 le consid- 
 jea either 
 ains upon 
 
 numerous 
 le earth's 
 in certain 
 I tliat the 
 space of 
 the same 
 k^eden and 
 Dout three 
 Pata<ifonia 
 ted within 
 stence on 
 T species. 
 i\ of about 
 e Romans, 
 sive tracts 
 usands of 
 essed con- 
 that " the 
 lally sunk 
 inents and 
 must be- 
 e the sca- 
 the crust 
 case, but 
 alternate 
 has been 
 iroughout 
 land has 
 may and 
 lame way, 
 bn be, dry 
 le come to 
 [lents and 
 Ind eleva- 
 and the 
 arranged 
 
 y^-^ 
 
 M 
 
 in the ponstmction of our plobo, but results of successive and 
 complex actions on a former state of thing's ; t/utt, aji^ain, of 
 similar actions on another still more remote; and so on, till 
 the ()ri<>:inal and really jiermanent state is pushed altogether 
 out of sight and beyond the reach even of imagination ; while, 
 on tin; other hand, a similar and, as far as we can see, inter- 
 minable vista is opened out for the future, by which the habi- 
 tability of our planet is secured amid the total abolition on it 
 of the present theatres of ♦errestrial life." 
 
 DisTRiKiTiox OP TiiE L.>xn. — As regards the distribution 
 of th(^ dry land, the most ol.vious and geologically important 
 fju't is the preponderance ol the great continental masses in 
 the noithern hemisphere as compared with the southern. 
 Thus, Europe and Asia wholly, two-thirds of Africa, and fully 
 one-half of the American Continent, are situated north of the 
 (•({uator. In the southern hemisphere we find only about one- 
 third of Africa, the greater portion of South America, and the 
 continental island of Australia, with New Guinea, and part of 
 Sumatra and Borneo. . - , , 
 
 Calculating the entire superficial area of the globe at about 197,000,000 
 of square miles, the dry land only occupies about 52,000,(»O0 square miles, 
 and the ocean covers the remaining 115,000,000 square miles. Of the dry 
 land, about 89,000,000 of square miles lie in the northern hemisphere, and 
 only about 13,000,000 in the southern hemisphere, or no more than one- 
 fourth of the entire land-surface. On the other hand, while the ocean covers 
 nearly three- fourths of the entire surface of the globe, more than seven- 
 twelfths of this is found in the southern hemisphere. 
 
 The general fact indicated by the preponderance of land in 
 the northern hemisphere is that the centre of gravity of the 
 earth must be eccentric as regards the centre of figure of the 
 earth ; and that the eccentricity must be in the direction of the 
 southern hemisphere, since here the greatest mass of the 
 ocean is accumulated. This further indicates, as pointed out 
 by Huxley, that the force which sustains our continents must 
 be one of " tumefaction." 
 
 The relative distribution of land and water has many other 
 important bearings, especially as concerns climate, and some 
 of these will be noticed hereafter. - 
 
f i 
 
 PHYSICAL OEOORAPHT. 
 
 CHAPTER II. 
 
 Mountains. — When we come to consider the general feat- 
 ures of the land, the first and most striking feature of all is 
 found in the great mountain-cliains which diversify tlie surface 
 of the great continents. Mountains are those portions of the 
 surface of the earth which are elevated for more than a tliou- 
 siind feet above the level of the sea ; tliis limit being, of course, 
 an entirely arbitrary one. Mountains niay occur in groups, 
 ranges, or chains, and little need be said here as to their dis- 
 tribution over the surface of the earth. It is curious, how- 
 ever, to notice the difference in this respect between the New 
 and Old Worlds. In the New World, the great mountain- 
 cliains have a general direction approximating to a meridional 
 one, tiiat is to say, more or less nearly running from nortli to 
 south. They not only coincide with the general axis of the 
 continent (which, indr'ed, they themselves cause), but they 
 more or less (dosely follow the coast-line, for a distance of over 
 eight thousand miles. In the Old World, on the other hand, 
 there is no single well-defined mountain-chain following the 
 general coast-line ; but there is a broad, mountainous zone, ex- 
 tending across Europe and Asia in a direction more or less at 
 right angles to the meridian, or from east to west. 
 
 Kinds of Mountains. — All mountains may be looked upon 
 as belonging to one of three kinds : mountains of circumdenu- 
 dation, mountains of uptilting, mountains of ejection (Jukes). 
 
 1. Mountains of circumdenudation are those mountains 
 which have been formed by a removal of surrounding matter. 
 It is quite clear that, if the whole, or any portion of a mass 
 of land were raised to a certain elevation above the level of the 
 sea, and were then subjected to any forces which could remove 
 
MOUNTAINS. 
 
 11 
 
 from the elevated portion all the external materials, we should 
 liiivc a group or range of mountains left standing in the cen- 
 tra, as a kind of backbone. Hills, then, of circumdenudation 
 ^Fig. 1) are simply musses of land left untouched out of a gen- 
 erally elevated region, the outer portions of which have been 
 n:iiioved. What the forces are which produce mountains of 
 thi.s kind, we shall afterward see. In most mountains of cir- 
 cumdenudation the base of the hill is formed of the same 
 materials or rocks as those which occur in the adjacent hivv 
 ground; wliile the upper part of the hill is formed of rocks 
 
 :i. • -i r-V°n?ni ' II ' k " H ^1 " r" II 11 ^' iP ir H "^ I I " I I " H ' B - 
 
 Fid. 1.- lju(,'r;iiii to lllustniti' inomitiiliis of ciroMiiKlt'iuiilation. The dotted lines rc'iiri'Sent 
 tbu uiass ol'uiuturiul which lias been removed by deoudation. 
 
 which do not occur in the low ground immediately adjacent, 
 
 since they have been removed by denudation. Most of the 
 
 individual iiilla, even in ranges of tiie following class, are 
 
 , mountains of circumdenudation. That is to say, the whole 
 
 '<> rcirion has been elevated as a single mass, and then tlie moun- 
 tains have been carved out of it by various " denuding " agents, 
 
 . , w iiich will be subsequently spoken of. 
 
 2. Mountains of iiptiltlng arc those mountains which 
 have been formed by the direct elevation of a given region 
 along a given line. As a rule (Fig. 2), the rang(js formed in 
 this way are due to the crumpling and folding up of an exten- 
 sive region. Sometimes, however, the ehn'ating forces have 
 produced a long fissure or crack in the crust of the earth, and 
 
 I Fio. 2.— Mountains of uptiltinff. Section of the Appalaohinn ohain, sliowin-r how a succoa- 
 • Biou of parallel ridges hjis been formed by powerful folds in the rocks. 
 
 have then simply raised the portion of land on one side of the 
 fissure, while the other side has remained stationary or sunk 
 
12 
 
 PHYSICAL GEOGRAPHY. 
 
 ' M 
 
 : , 
 
 I I 
 
 I 
 
 I 
 
 down. In all cases, the mountain-ranjifes of this class exist, 
 not in consequence of " denuding " forces carving them out 
 of the general surface of the ground, but in spite of these 
 agencies. At the same time, the individual hills of any range 
 produced by uptilting are generally, if not universally, pro- 
 duced by circumdenudation. In most mountains of uptilting 
 (Fig. 2), the central and most elevated portions of the moim- 
 tain-range are found to consist of older rocks ; and the low- 
 grounds consist of beds which are higher in the series, and 
 which originally covered the entire mountain-mass, but have 
 been subsequently removed by denudation. 
 
 3. Mountains of (Jection are those hills formed by mate- 
 rials derived from the interior of the earth and raised above 
 the surface by the action of subterranean forces through an 
 orifice or opening in the crust of the earth. In these cases 
 (Fig. 3), the ejected materials, of course, get piled up round 
 tlie orilice through which they are expelled, so as ultimately 
 to form a hill of a more or less accurately conical form, all the 
 beds of which have i general inclination or "dip" away from 
 the central opening. Of this nature are no other hills save 
 only " volcanoes," and they are, therefore, of comparatively 
 rare occurrence. They sometimes, however, attain a great 
 size, Etna, in Sicily, being about ten thousand feet in height, 
 and ninety miles in circumlerence at the base ; while some 
 of the volcanoes of the New World have a height nearly twice 
 as great. 
 
 VOLCANOES. 
 
 Before going on to spe.ik of valleys and of denuding agents 
 in general, it may be as well to introduce here all that need 
 be said on the subject of volcanoes. 
 
 What is understood by a "volcano" is an aperture in the 
 crust of the earth from which are discharged greater or less 
 quantities of the molten materials which form the interior of 
 the earth, if not universally, at any rate in the locality in 
 which the volcano occurs. Volcanoes may be either active or 
 extinct, and they may be either suha'erial or submarine. Active 
 volcanoes are those which are now ejecting materials, or have 
 done so in the historical period ; extinct volcanoes are those 
 which have all the characters of volcanic cones, but have not 
 ejected materials during the historical period. In submarine 
 volcanoes the aperture from which the molten matter is ejected 
 — in all cases called the crater — is below the level of the sea ; 
 and thus the ejection of melted material is hidden from our 
 
VOLCANOES. 
 
 13 
 
 class exist, 
 T them out 
 te of these 
 f any range 
 3rsally, pro- 
 3f uptilting 
 f the moun- 
 nd the low 
 series, and 
 
 ed by mate- 
 
 dsed above 
 
 through an 
 
 these cases 
 
 3d up round 
 
 IS ultimately 
 
 form, all the 
 
 ' away from 
 
 3r hills save 
 
 jmparptively 
 
 tain a great 
 
 et in height, 
 
 while some 
 
 nearly twice 
 
 iding agents 
 11 that need 
 
 ;rture in the 
 eater or less 
 
 interior of 
 
 locality in 
 
 ler active or 
 
 Hue. Active 
 
 (ials, or have 
 
 «s are those 
 
 it have not 
 
 submarine 
 
 ler is ejected 
 
 of the sea ; 
 
 ;n from our 
 
 eves, unless it should go on for a suflioiont length of time, or 
 for a sufficient extent, to be visible above the surface of the 
 se.a. Subatirial volcanoes aro those which have the crater or 
 aperture of ejection upon the land, and it is these with which, 
 of course, we are best acquainted. Most of the points which 
 should be known about volcanoes may be illustrated by Vesu- 
 vius, whi(;h has recently formed the subject of a most valuable 
 and interesting work by Pro£ Phillips, of Oxford. 
 
 
 i^:-^^^=^--=^-^^-^^.gnisirin;jihi]ffria(ilB%^ 
 
 Fio. 3. — Vesuvius from Uic west (after Phillips). 
 
 In the first place the activity of an " active" volcano is 
 not constant, but is intermittent. Tliat is to say, no volcano 
 constantly emits melted matter, or even smoke or flame, ex- 
 cept in a few exceptional cases. In the cac" of Vesuvius, the 
 earliest recorded paroxysm of activity, or *' eruption," took 
 place in the year 79 A. d. Traditions existed of former erup- 
 tions, and such, no doubt, had taken place, but for n)any cen- 
 turies the mountain had been quiescent, and exhibited to the 
 non-geological observer no peculiarities to separate it from 
 other mountains. 
 
 Examined in its quiescent state, Vesuvius, like any other 
 volcano, would exhibit the following appearances : The hill 
 Wfmld be more or less nearly conical in shape, probably con- 
 siderably and often irregularly truncated at its suuunit. At 
 the top, however, would be found a deep d(>pression or pit, 
 the remains of the old crater, the bottom of which, in the quiet 
 
'U'li 
 
 
 14 
 
 PHYSICAL GEOGBAPHY. 
 
 state of the mountain, would have completely solidified. To 
 imagine a quiescent volcano, therefore, we have only to con- 
 ceive of a gigantic cone, the summit of which is broken off, 
 and which is furnished with a deep depression. This depres- 
 
 Fio. 4. — Diagram to illustrate the condition of a quiescent volcano. 
 
 sion has its floor formed by the solidified molten matter which 
 formerly filled the vent, and its size is sometimes exceedingly 
 groat. Thus the old crater of Bromo, in Java, is between 
 four and five miles wide, and is formed by a central floor sur- 
 rounded by a ring of precipices varying from two to twelve hun- 
 dred feet in height (Jukes) ; and these dimensions are nothing 
 extraordinary. 
 
 When the volcano has a paroxysm of activity, far other 
 phenomena are observable ; and they are essentially the same 
 wlien the volcano is a new one, or whether it has been for- 
 merly in activity. Supposing, however, the volcanic focus to 
 have been previously active, and to have enjoyed a longer or 
 shorter period of quiescence, the conditions of the case are 
 these : I3eneath the volcano — at no very great depth — is a 
 vast accumulation of molten rock, which is being impelled 
 toward the surface. We need not stop now to inquire into 
 the nature of the forces which drive the melted matter up- 
 ward, but they are almost universally admitted to be of the 
 nature of some elastic gas, probably steam. Be this as it may, 
 in this effort toward ejection, the impelHng and elevatory 
 forces are resisted by the weight of the volcano itself, and by 
 the cohesion of the solidified matter which fills the ancient 
 vent. This resistance generally giver rise to more or less 
 violent vibrations of the ground, or earthquakes, usually at- 
 tended by subterranean noises, often compared to the noise 
 of many carta on a stony road, or to underground thunder ; 
 and not uncommonly attended with more or less elevation of 
 the ground surrounding the volcano, this, in turn, often caus- 
 ing the sea to advance and retire with great rapidity, and in 
 gigantic waves, IJltiiQately the contest is ended by the vie- 
 
VOLCANOES. 
 
 16 
 
 idified. To 
 )nly to con- 
 broken otf, 
 ?his depres- 
 
 Icano. 
 
 natter which 
 exceedinp:ly 
 , is between 
 ral floor sur- 
 otwelvehun- 
 s are nothing 
 
 [ty, far other 
 ,lly the same 
 as been for- 
 nic focus to 
 a longer or 
 the case are 
 depth — is a 
 ing impelled 
 inquire into 
 . matter up- • 
 to be of the 
 [lis as it may, 
 id elevatory 
 tself, and by 
 the ancient 
 ore or less 
 L usually at- 
 to the noise 
 nd thunder; 
 elevation of 
 L often c.'ius- 
 jidity, and in 
 by the vic- 
 
 tory of the elevating forces ; the solidified matter which chokes 
 the old crater is blown out ; or an easier solution is found in 
 the formation of a fresh opening somewhere in the sides of the 
 mountain. 
 
 Now the eruption proper is fairly begun, and perhaps the 
 commonest phenomenon which indicates that the crater is 
 opcHj is the jiresence of a vast column of vapor over the vol- 
 canic vent. This column of expanded vapors and gases is well 
 known by the simile of Pliny, who compared it to a gigantic 
 pine-tree, narrow below, like a great trunk, but widening out 
 above into an enormous mass of foliage. It may remain over 
 the mouth of the volcano for many days before any further 
 sign is shown ; and it is not at all uncommon for tl e clouds 
 accumulated in this way to part with their condensed moist- 
 ure, giving rise to abundant and heavy showers of rain. 
 
 The next phenomenon is generally the ejection from the 
 crater of vast columns of what are known as volciinic ashes, 
 ■ ecorijp, and volcanic bombs. The "ashes" are simply the 
 melted rock shot up by the imprisoned gases beneatli to a 
 great height in tlie air, and thus granulated or reduced to im- 
 palpable dust. They may be carried by the wind for great 
 distances, even hundreds of miles ; and it was by immense 
 showers of ashes that Pompeii w as buried at the great Plinian 
 eruption of Vesuvius in the year 79 a. d. " Scoria^," again, is 
 the name given to portions of the melted rock or " lava," shot 
 jup above tlie crater in the same way as the ashes, but not re- 
 jduced to powder. When thus ejected, the melted rock con- 
 tains much gas or vapor enclosed in its interior, and by the ex- 
 [pansion of these gases it is rendered cindery or spongy, with nu- 
 [merous irregular cells or cavities. Still larger m.asses of lava, 
 i thrown up in the same way, and cooling rapidly during their 
 [flight, constitute the so-called " volcanic bombs." Both the 
 ejected scoriie and stones are thro^vn up violently to a height 
 of one to two thousand feet. If they are thrown up vertically, 
 they simply fall back again into the crater; but if the angle 
 [of ejection be inclined to the vertical, they describe parabolic 
 jcurves, and may fall at distances of from five to eight miles 
 [from the centre of eruption. 
 
 Along with the ashes, and scoriae, and vapors of different 
 finds, great bursts of steam are usually emitted from the cra- 
 ter from time to time. The rapid evaporation of the watery 
 |vapor in these jets of steam produces a high degree of elec- 
 trical tension, and consequently discharges of electricity in the 
 form of lightning occur with great frequency and brilliancy. 
 

 I 
 
 ll 'I 
 
 mi 
 
 11 
 
 lili 
 
 16 
 
 PHYSICAL GEOGRAPHY. 
 
 Tlie last and most familiar phenomenon of an eruption is 
 the appearance of a true current of molten rock, constituting 
 what is known as " lava." When the internal pressure has 
 reached a sufficient intensity, the melted rock which fills the 
 interior of the volcanic cone is raised ultimately to the lip of 
 the crater ; or, if the sides of the cone are weak, a fresh fissure 
 may be made somewhere below the actual crater. In either 
 case, the molten lava now flows down the side of the moun- 
 tain, as a river of red-hot, viscous, slowly-moving fluid. Its 
 rate of progress is not very rapid, the consistency of melted 
 lava being something like that of thick honey or pitch. Even 
 on slopes of thirty degrees it does not move more than a few 
 miles an hour, and on ordinary declivities its rate of motion is 
 iK)t more than from a mile, or half a mile, down to thirty or 
 forty feet in an hour. As the lava-current makes its way down 
 the sides of the mountain, it parts, of course, with some of its 
 heat, anu, tlierefore, gradually solidities. Tlie sides and sur- 
 face of the current, however, generally solidify before the cen- 
 tre ; so that one may walk across a current that is externally 
 converted into solid rock, but is red-hot and fluid in its centre. 
 Very often, indeed as a rule, more than one current of lava is 
 ejected during the course of an eruption, and generally from 
 more than one point. In many cases, too, the current con- 
 tinues to flow for many days, and extends ultimately for many 
 miles from the centre of eruption. Whenever the elevating 
 forces have their tension relieved by the escape of tlie ashes, 
 scoriae, and lava, the phenomena of the eruption cease ; and 
 they may either return after a tolerably short interval, or the 
 volcano may remain quiescent for many years or many centu- 
 ries. Very often, however, quiescent volcanoes emit various 
 gases and vapors, either themselves, or from minor vents 
 (" fumaroles") in their immediate neigliborhood. 
 
 These, then, are the general phenomena of an ordinary 
 eruption of such an intermittent volcano as Vesuvius, and the 
 subject may perhaps be rendered a little clearer by giving an 
 account of a single eruption of this celebrated volcano. The 
 account here chosen is the one given by Sir William Hamilton, 
 the British ambassador at Naples, describing the great erup- 
 tion of 1766, and is quoted from Prof. Phillips's work on 
 Vesuvius : 
 
 " In September, 1765, the vapors evolved from Vesuvius 
 grew to be considerable ; in October, black smoke with clouds 
 of steam; and at last red tints appeared in these smoky 
 wreaths. In November, the mountain being covered with 
 
 x-m 
 
VOLCANOES. 
 
 17 
 
 eruption is 
 constituting 
 iressure has 
 ich fills the 
 o the lip of 
 fresh fissure 
 . In either 
 if the moun- 
 r fluid. Its 
 ;y of melted 
 ►itch. Even 
 J than a few 
 of motion is 
 to thirty or 
 ts way down 
 fi some of its 
 les and sur- 
 tbre the cen- 
 is externally 
 in its centre. 
 3nt of lava is 
 3nerally from 
 current con- 
 ely for many 
 he elevating 
 of the ashes, 
 cease ; and 
 Iterval, or the 
 many centu- 
 emit various 
 minor vents 
 
 an ordinary 
 Ivius, and the 
 ]by giving an 
 [olcano. The 
 
 im Hamilton, 
 great crup- 
 
 )s's work on 
 
 |-om Vesuvius 
 
 with clouds 
 
 [these smoky 
 
 covered with 
 
 snow, a 'hillock of sulphur' about six feet high, which had 
 been recently thrown I'.p, gave fortli a light-blue flame from 
 the top. . . . Tlie eruptions, to which these smoke-ejections 
 were prophetic or preparatory, began on Good Friday, the 
 /38th March, 18G6. A lew days previously, the great and fatal 
 iina'^-e of the pine-tree appeared above the crater, and at night 
 the smoke a})peared like flame. On the day named, a violent 
 explosion and shower of red-hot cinders occurred. At seven 
 o'clock in the evening, the lava began to boil over the mouth 
 of tlie volcano, at first in one stream," but afterward dividing 
 into two. " The lava ran nearly a mile in an hour's time, 
 when the two branches joined in a hollow on the side of the 
 mountain without proceeding farther. The lava had the ap- 
 pearance of a river of red-hot and liciuid metal, such as we see 
 in the glass-houses — on which were large, floating cind'^rs, 
 haU-nghted, and rolling over one another with great precipi- 
 tation down the side of the mountain, forming a most beauti- 
 ful and uncommon cascade. As the eruption proceeded, the 
 lava, which at first was pale and bright, became of a deep red. 
 In daylight it scarcely seemed fier}', but a thick, white smoke 
 marked its course. . . . On the 10th of April, at night, the 
 lava disappeared from the side of the mountain toward Naples, 
 but broke out with more violence (toward Torre delP Annun- 
 ziata) on the other side. ... Its source was a clear outburst 
 from the side of the cone about half a mile from the mouth of 
 the volcano. It flowed like a torrent, with violent explosions 
 and earth-shakings. The heat was such as to forbid a nearer 
 approach then about ten feet. The consistency of the lava 
 was such that a stick made no impression, and stones thrown 
 forcibly on tlie current did not sink in it. It ran with amazing 
 velocity, in the first mile with a rapidity equal to that of the Sev- 
 ern at Bristol. The stream at its source was about ten feet 
 wide, but soon expanded itself ... so that at night it had the 
 appearance of a continued sheet of fire, four miles in length, 
 and in parts near tw^o in breadth. . . . The \'ineyards and 
 cottages were injured or destroyed, in spite of the opposition 
 of many images of St. Januarius which were placed upon the 
 cottages or vines. The lower part of the current was covered 
 with red-hot stones — a kind of w.dl, ten or twelve feet high — 
 which rolled on irregularly and slowly about thirty feet in an 
 hour. The lava continued to flow at intervals, with ejections 
 of stones and ashes, till the early part of June, or even till the 
 10th of December, 17GG." 
 
 Geographical Distbibution op Volcanoes. — Tlie esti- 
 
 , i- 
 
[ ( 
 
 i 
 
 J r 
 
 ' 
 
 
 
 
 ^ 
 
 
 ■ 
 
 
 
 
 
 s- 'i 
 
 ; 'Si 
 
 i ! 
 
 ? i 
 
 
 ,k 
 
 m 
 
 18 
 
 PHYSICAL GEOGRAPHY. 
 
 mated number of volcanoes which have been active within the 
 last century and a half is about three hundred, but this num- 
 ber might probably be at least trebled without going beyond 
 the facts. Little consideration can be given here to the locali- 
 ties in which volcanoes are found at the present day, but some 
 of the best-known foci of volcanic action may be mentioned. 
 In Europe are the well-known volcanic cones of Vesuvius, near 
 Naples, and Etna in Sicily, with the cone of Stromboli in the 
 Lipari Islands. Iceland is another ancient and equally well- 
 known seat of volcanic energy, Hecla being the most famoue 
 of its vents. The island of Teneriflfe is an enormous volcanic 
 peak, having a height of seventeen thousand feet. On the 
 American Continent a group of volcanoes occurs in the Chilian 
 Andes, containing as least sixteen active vents. In Bolivia ip 
 a second group of six or eight cones occupying the elevated 
 plateau of Titicaca. Still farther northward, on the table-land 
 of Quito, are eighteen active volcanoes. In Central America 
 and Mexico there is another well-known group of volcanoes. 
 On the west coast of North America occur only tMO isolated 
 cones, Mount St. Helens, at the mouth of the Columbia River, 
 and Mount Edgecombe in Alaska. The most volcanic region 
 of the globe is situated at the northern extremity of the Pa- 
 cific, extending between America and Asia, and comprising 
 the peninsulas of Aliaska and Kamschatka, and the Aleutian, 
 Kurile, and Japanese islands. In this region at least fifty-one 
 active volcanic vents are known. In the Philippines and 
 Moluccas are other groups of volcanoes. In the Sandwich 
 Islands are two gigantic cones (Mounts Loa and Kea), which 
 attain a height of fourteen thousand feet. In Java are forty- 
 six cones, varying from four thousand to nearly twelve thou- 
 sand feet in height, and in Sumatra are nineteen. In New 
 Zealand are three active volcanoes, but the volcano which 
 in either hemisphere approaches most nearly to the Pole is 
 Mount Erebus, discovered by Captain Ross, in the Antarctic 
 Continent (Herschel). 
 
 From the general phenomena of the geographical distribu- 
 tion of volcanoes, two principal laws are deducible : 
 
 1. When situated on islands, volcanoes are generally ar- 
 ranged along straight lines. Thus, in the Aleutian Islands 
 there are twenty-three active volcanoes, occupying a straight 
 line of nine hundred miles in length. In the Kurile Islands, 
 eleven active volcanoes with many extinct vents form a nearly 
 straight line, six hundred miles in length. In Java, Sr.mbava, 
 and Floris, a line of active volcanoes exists nearly eleven hun- 
 
STRUCTURE OF VOLCANIC CONE. 
 
 19 
 
 e within the 
 jt this nura- 
 )ing beyond 
 to the locali- 
 ty, but some 
 mentioned, 
 jsuvius, near 
 imboli in the 
 equally well- 
 most famouB 
 lous volcanic 
 let. On the 
 1 the Chilian 
 In Bolivia If 
 the elevated 
 lie table-land 
 tral America 
 of volcanoes, 
 two isolated 
 umbia River, 
 Icanic region 
 y of the Pa- 
 i comprising 
 he Aleutian, 
 east fifty-one 
 ppines and 
 e Sandwich 
 s^ea), which 
 Lva are forty- 
 twelve thou- 
 n. In New 
 cano which 
 the Pole is 
 he Antarctic 
 
 ical distribu- 
 e : 
 
 generally ar- 
 tian Islands 
 g a straight 
 rile Islands, 
 )rm a nearl}^ 
 a, Si:nibava, 
 eleven hun- 
 
 dred miles in length. Tliis linear arrangement of volcanoes 
 points to their being situated along continuous lines of fissure 
 ill the crust of the earth. 
 
 2. When placed oti continents, volcanoes are almost always 
 in the immediate neighborhood of the sea or coast-line. Tims, 
 all the American volcanoes are situated on the western or Pa- 
 cific seaboard, especially those of the great chain of the Andes. 
 Ill fact, there are only two instances of volcanoes habitually 
 active placed more than three hundred miles from the sea, and 
 these two are in countries hitherto almost wholly unknown 
 (in the Thian Shan Mountains of Central Asia). This law sup- 
 ports the theory that one of the main agents in the production 
 of volcanoes is the access of the sea-water to the heated inte- 
 rior of the earth through fissures in the crust. 
 
 Gexeral Structure of a Volcanic Cone. — It is not dif- 
 ficult, on a consideration of the general course of a volcanic 
 eruption, to understand now the ordinary structure of a volcanic 
 cone. In the first place, we have a chasm or fissure in the 
 crust of the earth from wliich great quantities of gases and 
 steam are emitted, and hurled uj) with these are vast clouds 
 of ashes, with fragments of cinder}' scorije, and larger masses 
 of melted lava. Tliese mostly describe parabolic curves, and 
 fall at greater or less distances from the volcanic vent, the 
 lightest usually falling farthest from the crater, the heaviest 
 nearest to it. The ashes float suspended in the atmosphere, 
 l)ut ultimately sink to the ground, often at very great distances 
 from their point of ejection. As this goes on, by mechanical 
 laws a cone will be gradually accumulated round the crater ; 
 and this cone will consist of beds of ashes, scoriae, and stones, 
 more or less intermixed with one another, or distinct. All the 
 beds of the cone will be found to be directed away from (or 
 to " dip " away from) the crater, at first at a tolerably steep 
 inclination, but gradually getting more and more nearly hori- 
 zontal as we recede from the crater (Fig. 5). The crater, in 
 
 Fio. 5.— Section of the island of Paimn (aftor LvpI!).— a h. The old crater; c, Commence- 
 ment of the steeper Inclination ol'the beds; «, Lateral cone. 
 
 the mean while, has been kept open by the constant passage 
 upward of steam and other vapors. ITie intermittent flows 
 of melted rock or lava are found alternating with (or " inter- 
 
ir^ 
 
 Mill 
 
 > ! 
 
 20 
 
 PHYSICAL GEOGRAPHY. 
 
 stratified" with) the ashy and scoriacoous bods at diifcrent lev- 
 els (Firr. G). As, however, the flows of hiva are f^enerally 
 irregular in strengtli and vokiine, and only last for a compara- 
 tively short time, they usually give rise to beds of irrei^ular 
 thickness, and mostly in the form of discontinuous masses 
 intermixed with the ashes. From the crater, too, there pro- 
 ceed in all directions throuoh the mass of the cone various fis- 
 sures or cracks, more or less vertical, formed by the constant 
 shakinf:^ to which the cone is subjected. As the fluid lava Alls 
 the crater in its endeavor to overflow, it is forced by tlie enor- 
 mous pressure to fill all these cracks and fissures. When the 
 lava in these fissures cools and solidifies, each fissure is con- 
 verted into a dike^ as it is called. Often these fissures extend 
 for considerable distances, and they may all be filled with lava 
 in this way, constituting so many " dikes," or nearly vertical 
 walls of solidified lava, binding the whole cone into a solid 
 mass, and perhaps extending for many miles away from the 
 original vent. 
 
 Fio. 6. — Sopfion of a volranic cone. — a, Beds of ash, dipping awny from the crater; 
 f>. l'.e<ls of lava intcrstratiflod with the ashi's; c. Dikes of lava cutting across all the 
 bt'ds of the cono. The crater is filled by a plug of solid lava. 
 
 Exciting Causes op Volcaxic ERFPnoire. — As regards 
 the immediate causes of volcanic excitement, there are only 
 two tlieories which need be noticed. In the first of these, it 
 is supposed that volcanic eruptions might be caused by the 
 presence in the interior of the earth of great reservoirs of the 
 metallic bases of the earths and alkalies in an U7ibte7vit or un- 
 oxidized condition. The action of water upon such masses 
 might no doubt produce all the phenomena of a volcanic erup- 
 tion; but there is no ground fi^r assuming their existence. 
 The second and most generally accepted theory is, that vol- 
 canic eruptions are due to the access of water from the surface 
 to the highly heated interior of the globe, thus causing the 
 generation of an enormous quantity of explosive and expan 
 sive steam. Tliis theory meets all the requirements of the 
 case, and specially agrees with the two great facts as to the 
 geographical distribution of volcanoes — that insular volcanoes 
 are generally linear, as if placed along fissures, and that cou- 
 
EARTHQUAKES. 
 
 21 
 
 tincntal volcanoos are almost universally in the immodiat*' 
 neighborhood of the sea. The prcduction of the fissures hy 
 ^vhi^•h tlic sea gains access to the heated interior, as already 
 said, is most probably to be ascribed to the irregular contrac- 
 tion of a slowly-cooling globe, fluid toward its centre, but sur- 
 rounded by a crust of various materials and of unequal strength. 
 
 EARTHQUAKES. 
 
 Closely connected with volcanoes are those vibnitions of 
 the solid crust of the earth and those undulations in its waters 
 which are know^n as earthquakes. Earthquakes consist in a 
 scries of vibrations or undulations of the crust of the earth, 
 generally propagated from a central point or focus. The ex- 
 act cause of earthquakes is more or less obscure, but it is cer- 
 tain that they are so far connected with volcanic action as to 
 be always more frequent and more violent in those countries 
 which are the present theatres of volcanic energy ; while an 
 eruption or paroxysm of volcanic activity is almost alwjiys [)re- 
 ceded by earthquake-shocks : and the volcanic vents of a region 
 are usually quiescent, as if relieved, during the actual continu- 
 ance of an earthquake in the same district. The subject of 
 earthquakes is so extensive that no more than a few of the 
 leading facts concerning them can be here mentioned. 
 
 As just remarked, earthquakes occur most commonly in 
 volcanic regions. They occur, therefore, with the greatest 
 frequency and violence in South America, the islands of the 
 Pacific Archipelago, Japan, Upper and Western India, South- 
 em Europe, and parts of North America. An earthquake is 
 generally ushered in by profound atmospheric tranquillity, and 
 more or less disturbance in the waters of the fated region. 
 The sea advances and retires, springs and wells dry up, or be- 
 come muddy and impure ; and often there are r jbterranean 
 noises like the rumbling of carriages, or the thunder of artil- 
 lery. The actual vibration or undulation of the ground which 
 constitutes the shock rarely lasts more than a few seconds, or 
 perhaps one or two minutes, but, if severe, this space of time 
 will suffice for the overthrow of every elevated structure upon 
 the surface of the affected district. Chasms and fissures open 
 in the ground, often with the emission of smoke, flame, or tor- 
 rents of water ; and these fissures may close again instanta- 
 neously, or may remain permanently open ; while they are 
 sometimes sufficiently extensive to swallow up whole cities. 
 
 Very often great tracts of land, sometimes occupying many 
 hundreds of square miles, may be suddenly uplifted or de- 
 
22 
 
 PHYSICAL GEOGRAPHY. 
 
 f m 
 
 pressed. When the area thus affected is part of the bod of 
 the ocean, the result is the production of a pi^aiitic wave, 
 which runs out in all directions from the point of ffieutest ele- 
 vation or depression. Tliese " earthquake-waves, as they are 
 called, are often of gigantic dimensions, and they are some- 
 times propagated for a distance of many thousand miles. Thus, 
 in the celebrated earthquake of Lisbon, in 1755, "a portion 
 of the coast-line sank suddenly to a depth of six hundred feet, 
 and the result was a wave of sixty feet in height, which swept 
 over the land, ravaged the whole coast of Portugfil, and was 
 propagated seaward quite across the Atlantic to the West In- 
 dies" (Herschel). Again, in the terrible earthquake of 1854, 
 in Japan, a number of these colossal earthquake-waves were 
 generated, and were propagated across the Pacific to California. 
 These earthquake-waves, from their mode of origin, are 
 obviously "forced" waves, and they are commonly spoken of 
 as "waves of translation." Various geological phenomena 
 have been ascribed to the action of such waves sweeping 
 across the land, but in most cases this explanation has been 
 an erroneous one. ^ . 
 
CHAPTER III. 
 
 DENUDATION. 
 
 Havtnq now briefly considered the phenomena of moun- 
 tains, we come next to consider the otlier features of the land, 
 and there are none specially requiring consideration from a 
 geological point of view except valleys. As has been shown, 
 mountains are of various kinds, but this cannot be said to be 
 the case with valleys. It is true that the primitive cause de- 
 termining tiie formation of a valley is not always the same. 
 It may be a fold or flexure in the rocks, or a crack or fissure, 
 or a great displacement of contiguous regions, bringing into 
 immediate contact rocks of different hardness. The cause 
 which determines the formation of a valley may differ in dif- 
 ferent cases, but the actual work of formation is the result of 
 the removal or " erosion " of the solid rock by means of what 
 are known as the " denuding agents ; " and this leads us to 
 Bpeak of the subject of " denudation." 
 
 Denudation is the general term applied by geologists to 
 the removal of any portion of the crust of the globe so as to 
 lay hare an inferior or fresh surface, Man, for instance, 
 when he removes the soil from a rock-surface, in order to form 
 a quarry, is a denuding agent. In the ordinary course of 
 Nature, however, and with but a few insignificant exceptions, 
 the denuding agents by which solid particles of matter are re- 
 moved, are rain, rivers, the sea, and ice ; water, in fact, in 
 some form or other. At the same time the efficiency of those 
 agents may be much increased, and the work of denudation 
 hastened, by certain subsidiary agencies, which will, where 
 necessary, be alluded to. 
 
 Rain. — Rain is chiefly of importance as a denuding agent, 
 from the fact of rivers owing their production to this cause, 
 and also to the greatly increased power of rivers in heavy floods. 
 
24 
 
 PHYSICAL GEOGRArilY. 
 
 i:i 
 
 ■ ■ 4 
 
 Riiiii, however, itself 1ms a percept il)]o tliouj^li seldom exten- 
 sive action as a denudinn^ a;j^(Uit. Every shower tliat falls ex- 
 erts a C(!rtain amount of wearing- and wasting infhicncf? njjon 
 the cartii's surface; its efl'ects bein/if, of course, chiefly visible 
 upon porous soils and incoherent materials, such as sands and 
 clays. The action of the rain upon such materials may be 
 studied in any ploughed field that is not absolutely level. It 
 is unnecessary to add that the action of rain is most marked 
 in those countries which are subject to heavy and sudden 
 showers. 
 
 Rain also exerts a marked chemical effect upon certain 
 rocks, especially upon limestones. Tills it efl'ects by its power 
 of dissolving carbonate of lime, a power which is much in- 
 creased when it contains in solution a certain amount of car- 
 bonic acid. In this way, no limestone can be exposed for any 
 length of time to the action of rain, without exhibiting a verv 
 marked loss of substance ; and limestone may usually be rec- 
 ognized in the field by the worn and " weathered " appear- 
 ance of its surface where exposed. 
 
 RiVEKR. — Rivers are most important agents in modifjnng 
 the surface of the ground, and it is impossible to over-estimate 
 the effects produced in this way by rivers a(;ting through 
 countless ages. The moment any portion of the earth's sur- 
 face is raised above the level of tlu; sea, so as to constitute 
 dry land, rivers begin to be formed, and instantly commence 
 the work of denudation, which they never cease till the whole 
 is again reduced to the level of the sea. 
 
 AH rivers owe their origin to atmospheric precipitation in 
 the higher regions of the land. They owe their existence to 
 the precipitation on high grounds, in the form of rain, of the 
 watery vapor raised into the atmosphere by the heat of the 
 sun's rays. Every little cVi and rivulet, produced in this way 
 in the higher regions of n district, tends on its way to a lower 
 level to carry with it a. portion of the solid materials which 
 compose its bed or channel. The larger streams produced by 
 the union of these act in the same way, and the mere exist- 
 ence of a bed or channel is the best proof of the existence of 
 the action in question. The action of rivers as denuding 
 agents, from the nature of the case, is chiefly exercised in a 
 vertical direction, is confined to the actual channel for the time 
 being, and is almost wholly mechanical, depending upon the 
 wearing power of water in motion. The work done by rivers 
 depends, therefore, upon the amount of declivity or fall in their 
 beds, and the consequent rapidity of their currents, and also 
 
 
DENUDATION. 
 
 25 
 
 partly upon the volume of water carried by carli. Tliis last 
 I'lctnrnt, however, has not so inueh elVect as ini<^lit be ima- 
 ^riiu'd, since t])e (leiiiKliii^ powi-r of even a small torrent may Ix; 
 as ^r(»at as, or greater than, that of a large; river, snpposiiig 
 its enrrent to be proportionately more rapid. The denuding 
 work of rivers d -| ends, also, to a gri^at extent, upon the 
 nature of the rocks which form the bed ; being greatly favored 
 by the existence of soft and incoherent b<'ds, by the presence 
 of numerous fissures, or by the existence of great disturbance 
 in the rocks. Thus, the trills of Niagara owe their existem^c 
 to tin; wearing action of the river upon a bed of soft shale 
 which forms tiie base of the fall, and is capped by a hard bed 
 of limestone (Fig. 7). The river gradually wears away and 
 
 ' iTio. 7.— Skotch-sectlon of tho Falls of Nlajrira.— </. Nlfipara UmeBtono; 6, Niagara shales; 
 
 c, Medina aandsloucs. 
 
 eats out the yielding shale, and lea es the harder limestone 
 unsupported below. Tlie result of this is the breaking off of 
 great masses of the limestone left thus without support, and 
 the fall is in this way being gradually removed farther and 
 farther up the river. Like rain, rivers also exercise a decided 
 chemical action upon limestones, dissolving them and wearing 
 them away by tlusir solvent power upon carbonate of lime. 
 
 All rivers, then, alike, in their course from the mountains 
 in which they rise to the sea in which they end, tend to carry 
 down portions of the land to a lower level, never wholly rest- 
 ing in this tendtmcy till the materials which they carry down 
 are delivered into the ocean. 
 
 The amount of matter carried down in this way varies 
 with the nature of the rocks over which the river flows, with 
 the rapidity of its descent from the high lands to the low 
 lands, with the amount of water which it habitually conveys, 
 and with its liability to sudden floods. The proofs of the de- 
 nuding powers of rivers are partly what we see rivers doing 
 7i0Wy and partly what we see they hav- done in past time. 
 
 When we see a river turbid and muddy, as in high floods, 
 the slightest reflection assures us that this can only be from 
 the suspen.^Ion in its water of solid particles of sand or mud, 
 
w 
 
 m 
 
 iw 
 
 ill 
 
 26 
 
 PHYSICAL GEOGRAPHY. 
 
 which it has gathered on its course, and is carrying down with 
 it to a lower level. Many rivers palpably bring down sus- 
 pended solid matter, whether they are in flood or not, and all 
 rivers do so really, at all times, though the amount of solid 
 matter may not be sufficient to discolor the water. To gain 
 some idea of the amount of matter thus transported, we must 
 look chiefly to the eflFects which existing rivers have accom- 
 plished in past time. These efibcts are twofold, and are 
 found in the marks left by the rivers in their passage over the 
 land, and in the accumulation of the materials which they 
 bring down in certain localities, and especially at their point 
 of entrance into the ocean. 
 
 Every river (Fig. 8) flows in a certain definite channel or 
 bed, enclosed by banks of varying height, and often occupy- 
 ing a valley which is bounded by other banks or bluff's, also 
 of varying height. It cannot always be asserted positively 
 that these more distant banks are the work of the stream, 
 though this is mostly the case, since it can often be shown 
 
 ,i-i-i„ 
 
 £ 
 
 M ,,,!! lJ_ 
 
 • i i '' if .1 ,1 l i' ' li ' II i','' iL.riTi'^lliJJ^'tc^ii^i^lii. u_j i_ 1 1 1 — ii— ..i--^ 
 
 Fig. 8. — Sketch-section of the valley of the Schoharie River at Schoharie, N. T., showing 
 the actual bed of the river hollowed out of an alluvial plain, and bounded by precipi- 
 tous, rocky bluffs. 
 
 
 1; 
 
 i 
 
 that the rocks in these bluff's were at one time continuous, 
 while the plain which they enclose is generally under water in 
 high floods. In all cases, however, the actual bed of the river 
 (Fig. 8, a) is the work of the river itself, and is the result of the 
 wearing action of the river-current. Not only is this the 
 case, but there is a constant tendency to scour out and deepen 
 the channel by the carrying away of detritiis to a lower level. 
 The exact amount of work done in this way by any river 
 varies with the set of the current in any particular portion of 
 its course, and according to many little peculiarities of merely 
 local origin. Thus, nothing is commoner than to find a stream 
 
DENUDATIOJT. 
 
 27 
 
 down with 
 down sus- 
 lot, and all 
 mt of solid 
 •. To gain 
 jd, we must 
 ave accom- 
 d, and are 
 ge over the 
 which they 
 their point 
 
 I channel or 
 ten occupy- 
 r bluffs, also 
 d positively 
 the stream, 
 n be shown 
 
 N. Y., showing 
 mdcd by precipi- 
 
 continuous, 
 der water in 
 of the river 
 result of the 
 is this the 
 and deepen 
 ower level. 
 y any river 
 r portion of 
 3s of merely 
 nd a stream 
 
 •yf 
 
 rapidly silting up and filling one portion of its bed, while it is 
 with equal rapidity deepening its channel in another place. 
 The wearing, or " erosive " action of a stream in forming its 
 own channel, and in deepening it when once formed, is seen 
 most plainly and markedly — as a matter of course — in the case 
 of mountain-torreats. I.i any such, the bottom of the stream 
 invariably shows laost plainly the marks of wearing down by 
 water, even when it passes over the hardest rocks. Often dec]> 
 circular holes or caldrons — pot-holes — are formed by the whirl- 
 ing action of the water keeping in constant lotation a few 
 pebbles. In all cases, water-falls scoop out deep holfs, and 
 often they undermine the ledges over which they are precipi- 
 tated, and then break them off in large masses. 
 
 Another mark of the "degrading power of water in mo- 
 tion is seen in almost all streams, but preeminently in moun- 
 tain-streams, and that is the number of rounded stones and 
 bowlders which they always contain. These are generally 
 blocks of rock, which have fallen into the stream, and have 
 become gr^ually rounded by the wearing action of the run- 
 ning water, and by friction against other blocks. By a con- 
 tinuance of this process, the blocks are finally converted into a 
 number of rounded, water-worn pebbles. These, in turn, are 
 gradually rubbed down into sand or mud, till the whole may 
 be ground down into minute particles, and thus rendered 
 available for transport to the ocean. The amount of solid ma- 
 terial thus transported by rivers has been often estimated, and 
 reaches an enormous total in the case of great rivers. Thus, 
 the Ganges annually carries down to the sea 6,368,000,000 
 cubic feet of solid matter. The Mississippi brings down 
 3,000,000,000 cubic feet annually, and the Hoang-ho is said to 
 bring down no less than 48,000,000 cubic feet of solid matter 
 per day, or about 18,000,000,000 cubic feet per annum. 
 
 The work done by a river may be further estimated by the 
 amount of solid material which it deposits at its mouth. All 
 the solid matter conveyed by a river is not deposited in this 
 way. Much is deposited at various points in the course of 
 the river itself, and much more is carried off into the sea, or 
 swept away by oceanic currents. Such materials, however, 
 as are deposited, constitute an area of flat land at the mouth 
 of the river, this being what is known as a delta. All rivers 
 of any size form a delta at their entrance into the sea, and 
 many do so where they open into a lake. In so doing, the 
 river divides and subdivides into more or less numerous 
 branches, and deposits the solid sediment which it holds in 
 
¥ 
 
 4 
 
 Ml 
 
 m\ 
 
 28 
 
 PHYSICAL GEOGRAPHY. 
 
 suspension. In fact, the river, when its course becomes suffi- 
 ciently level and its current sufficiently slow, at once begins 
 to deposit all suspended matter; till it finally succeeds in 
 chokinf^ up its mouth with a larger or smaller area of mud and 
 sand, vvhicli it has itself brought down, and through which it 
 has painfully to fight its way to the open ocean by many and 
 tortuous channels. Most rivers form deltas of more or less 
 size ; the deltas of some are especially noteworthy for their 
 size. The delta, for instance, which is formed by the com- 
 bined efforts of the Ganges and Brahmapootra covers an area 
 of nearly 60,000 square miles, or an area larger than that of 
 England and Wales. In like manner, the whole, or almost 
 the whole, of Holland has been deposited by the Rhine ; 
 Egypt, as remarked by Herodotus, is " the gift of the Nile," 
 and the delta of the Mississippi is as large as the whole of 
 England. We have in such deltas a measure of part, at any 
 rate, of the denudation effected by these rivers, since every 
 solid particle in the delta has been brought down by the river 
 from the interior of the country. For every foot, therefore, 
 of solid matter that is added to the delta, a foot has been re- 
 moved from somewhere inland. 
 
 There are many great rivers, however, which do not form 
 deltas, or which cannot extend them beyond certain limits. 
 In the case of the Nile, the farther extension of the delta is 
 prevented by a powerful marine current which sweeps its sea- 
 ward edge. The Amazons, the largest river in the world, forms 
 no delta, the volume and force of its waters being sufficient to 
 carry out far to sea all the solid matters held in suspension, 
 where they are tranquilly deposited at the bottom. The St. 
 Lawrence also forms no delta, but for a difierent reason. Be- 
 fore reaching the ocean, the St. Lawrence has to pass through 
 the chain of the great American lakes, and the greater part 
 of its sediment is deposited in these. Other things remaining 
 the same, the St. Lawrence will ultimately succeed in filling 
 these lakes, and it will then begin to form a delta. 
 
 The Sea. — Among the most powerful of the agents which 
 tend to wear away the land and to reduce it to the sea-level, 
 is the sea itself. The rivers, running over the land, act chiefly 
 vertically, cutting for themselves shallower or deeper channels 
 to form their beds. The sea, on the other hand, acts upon the 
 margins of the land in a horizontal manner chiefly, tending 
 gradually to cut down the land exposed to its action to a uni- 
 form level. Every portion of the land which is elevated 
 above the sea is exposed twice in the twenty-four hours to the 
 
DENUDATION. 
 
 20 
 
 comes suffi- 
 )nce begins 
 succeeds in 
 of mud and 
 gh which it 
 y many and 
 tore or less 
 by for their 
 3y the com- 
 v^ers an area 
 :han that of 
 3, or almost 
 the Rhine; 
 ,f the Nile," 
 he whole of 
 part, at any 
 since every 
 by the river 
 )t, therefore, 
 has been re- 
 do not form 
 rtain limits, 
 the delta is 
 eeps its sea- 
 world, forms 
 sufficient to 
 suspension, 
 m. The St. 
 eason. Be- 
 )ass through 
 greater part 
 s remaining 
 ed in filling 
 
 gents which 
 he sea-level, 
 i, act chiefly 
 ler channels 
 its upon the 
 fly, tending 
 on to a uni- 
 is elevated 
 hours to the 
 
 abrading action of the tides all along its coasts ; and the re- . 
 suits ot"this are exhibited in the plainest manner along every 
 const-line, being, of course, more evident in those seas in 
 which the tide rises highest, and the waves attain their great- 
 est height and strenglh. Tlie shingle and gravel-banks, and 
 even the sand itself of the sea-shore, are almost all derived 
 from the waste material which the sea has produced by slowly 
 eating away the land. The pebbles in every shingle-bed on 
 all sea-coasts are thoroughly rounded and smooth, showing 
 that they have been gradually worn down to their present 
 shape by Ixnng constantly rubbed against one another by 
 every tide in its advance and recession. The finer particles 
 produced by the further attrition of the pebbles constitute the 
 sand and mud of the shore. 
 
 In like manner, the sea, especially during high tides, grad- 
 ually undermines the land, acting most powerfully upon a 
 horizontal plane at the foot of the clilfs which usually form 
 the margins of the beach. tTlie upper portions of the cliff are 
 thus deprived of support, and slip down, forming broken 
 masses which are easily acted upon by the waves, are gradual- 
 ,' ly ground down into sand or mud, and are carried off else- 
 iV -where to form sand-banks or marine accumulations of different 
 kinds. By this process, the land is gradually eaten away, 
 I and there are many cases in which this can be rendered palpa- 
 4 bly evident to us by authentic records, showing that centuries, 
 % or perhaps only years, ago the sea extended for many acres or 
 ' even miles over what is now covered by the waves. 
 
 All the cliffs, then, which border the sea-coast have been 
 formed by the sea itself, gradually eatnig back into the land. 
 In like manner, we are forced to come to tiie conclusion that 
 many cliffs and precipices now far inland have been formed at 
 ^ some former period by the sea, at a time when it extended 
 iimch farther inland than it does now ; or, to speak more cor- 
 rectly, at a time when the land was very much less elevated 
 than it is at present. 
 
 If wo imagine any portion of the land being slowly ele- 
 vatcMl above the sea, at the rate of a few inches or a few feet 
 a year, it is clear that every portion of its surface will in turn 
 foim a coast-line, and will be exposed to the denuding power 
 of the sea. We have every reason to believe that this is 
 what really occurs. Every portion and fragment of our exist- 
 ing dry land has been raised from the deep, and, in the course 
 of this process, every portion of its surface h.is constituted a 
 coast-line for a longer or shorter period, according to tho 
 
so 
 
 PHYSICAL GEOGRAPHY. 
 
 ll! il 
 
 Ml 
 
 rapidity with which the elevation has been accomplished. In 
 this way, many inland clifls, scars, precipices, valleys, and 
 mountain-passes, have undoubtedly been formed by marine ac- 
 tion ; though in other cases we cannot suppose that the sea 
 has been the agent employed. 
 
 By the constant repetition of these denuding actions 
 throughout long periods, we are readily able to believe that 
 the sea has removed from the land vast masses of rock, and 
 has, therefore, cooperated most extensively and powerfully 
 with the other denuding agents in producing the present con- 
 figuration of the land. The action of the sea, too, does not 
 cease altogether with its erosive influence upon the coast-lines 
 exposed to the daily rise and fall of the tides. 
 
 There is good reason to believe that some oceanic currents 
 have sufficient power and velocity to scoop out submarine 
 valleys in the softer and more incoherent materials of the sea- 
 bottom, though they can only act in shallow seas, and are not 
 likely to affect the harder rocks. ^ 
 
 It must be carefully borne in mind that the sea, like the 
 rivers, destroys nothing of the land, but simply rearranges it. 
 Every particle of solid matter which is carried off by the sea 
 from the land is deposited somewhere else, forming part of 
 sedimentary accumulations, which will at some future period 
 form dry land. In many cases, by the action of oceanic cur- 
 rents, the materials derived from the land are conveyed to 
 great distances, and we cannot point to their resting-place. 
 They must, however, ultimately be deposited somewhere^ and, 
 in many cases, we have direct instances of this fact, in the 
 existence of sand-banks and bars, or even in the silting up of 
 bays and estuaries. 
 
 f«t.». 
 
 
CHAPTER IV. 
 
 ICE AS A DENUDING AGENT. 
 
 We have now to consider an exceedingly interesting and 
 important subject, namely, the effect of water upon the land 
 in the form of ice. In ascending from the sea-level, as i8 
 known to all, there is a gradual and regular diminution of the 
 temperature, till in every country a line may be ultimately 
 reached, where the temperature is so greatly and permanently 
 reduced that the snow which falls will not melt. This line is 
 called the " line of perpetual snow," and its position varies 
 in different countries and in different climates, being, of couree, 
 much sooner reached in cold than in hot regions. In Britain 
 the line of perpetual snow is about five thousand feet above 
 the sea-level ; and, as there are no mountains of this height, 
 there is no perpetual snow. In Iceland, and at the North 
 Cape, the line of perpetual snow is about two thousand feet 
 above the level of the sea ; in Norway about four thousand 
 feet ; in the Alps about eight thousand feet ; in the Equato- 
 rial Andes about sixteen thousand feet; in the Himalayas, 
 from thirteen to twenty thousand feet ; and in the Antarctic, 
 and part of the Arctic regions, the line of perpetual snow 
 agrees with the sea-level. 
 
 Glaciers. — It follows from the above, that all those por- 
 tions of a mountain-range which lie above the level of the line 
 of perpetual snow are constantly receiving fresh accessions of 
 snow ; and, as the snow does not melt, these annual additions 
 would indefinitely increase the height of mountains, if it were 
 not that a portion of the snow is constantly descending the 
 mountains by gravitation. The pressure from behind, pro- 
 duced by the constant accumulation of snow above the snow- 
 line, constantly thrusts portions of the snow down the moun- 
 tain into precipitous valleys. In this process of descent from 
 
32 
 
 PHYSICAL GEOGRAPHY. 
 
 if' 
 
 II 
 it 
 
 
 I i 
 
 i4h! 
 
 1 :i 
 
 1 ' '^ 
 
 1 ^ 
 
 the constantly roplcnisliod upper snovv-fiekls, partly by press- 
 ure, and partly by tlia\vin<»' and freezing over again, the snow 
 becomes gradually converted into solid ice. The result of this 
 is that, if we take such a mountain-range as the Alps, we find 
 the upper portion of the chain covered by a constant and per- 
 manent coating of snow; while from all the principal valleys 
 which flank the highest hills there proceed rivers of solid ice, 
 constituting what are called fflccierSj and formed in the way 
 just described (Fig. 9). 
 
 Fig. 9.— The Glacier of the Mer de Glace (from a photograpb). 
 
 The general phenomena of a glacier, which are of geologi- 
 cal importance, are these : The entire mass of ice forming the 
 glacier is not stationary, but is constantly moving down the 
 mountain to a lower level, exactly as a river or as any viscous 
 fluid would do, only at a much slower rate of movement. The 
 weight of the glacier is the cause of the movement, and its 
 motion is rendered possible chiefly by the great facility with 
 
ICE AS A DENUDING AGENT. 
 
 83 
 
 'tly by pross- 
 liii, the snow 
 result of this 
 Alps, we find 
 itcint and per- 
 icijial valleys 
 3 of solid ice, 
 [ in the way 
 
 -M: 
 
 i-ti^'': 
 
 
 i'i«l3 
 
 ^^ 
 
 -which ice will break and instantly unite a<rain by the freczinnr 
 to»r('thcr(jf the freshly-fractured surfaces (a i)henc>nienon known 
 1)V the technical name of " rep-elation "). The rate of niove- 
 iiHMit of glaciers varies from a few inches to ])('rha])S a couiile 
 of feet in the twenty-four hours, and is uiiferent at diilerent 
 seasons. 
 
 As the glacier pushes itself out in the lower and conse- 
 quently warmer portions of the mountain-region, its rate of 
 advance is not sufficiently rapid to counteract the loss which 
 it suffers by melting ; so that a point is always reached at last 
 beyond which the foot of the glacier cannot proceed. The 
 melting which goes on at this point, as well as over the whole 
 surface of the glacier, generally gives rise to a permanent and 
 often very large stream, which is entirely fed by the glacier. 
 (Tims, the source of the Ganges is from one of the great gla- 
 ciers of the Himalayas, from the foot of which it issues as a 
 nuiddy stream more than forty yards in width.) It is to be 
 remembered, however, that the thickness of a glacier is so 
 great (from two to eight hundred feet) that the ice-stream can 
 descend far below the line of perpetual snow, before the melt- 
 ing is so rapid that the daily advance is neutralized. Thus 
 the snow-line in the Alps is about eight thousand feet above 
 the sea-level, but the glaciers descend from three to four thou- 
 sand feet below this line. 
 
 Another phenomenon of glaciers of great geological im- 
 portance is what is known as the "moraines." As the glacier 
 moves slowly down its enclosing valley, innumerable masses 
 of rock and earthy matter are detached by frost, avalanches, 
 2j and other agents, and fall down upon the surface of the mov- 
 o ing ice. In this way, the glacier becomes fringed on each 
 . siile with a long line of masses of rock and soil, all along its 
 ^ margins, which it carries down with it to lower levels. These 
 constitute the " lateral moraines " of a glacier (Fig. 10). If, 
 as often happens, two glaciers coming out of separate valleys, 
 unite into a single stream, then the right lateral moraine of 
 the one and the left lateral moraine of the other combine to 
 I form a long line of blocks and earth which occupies the centre 
 I of the new ice-stream formed by the union of the two tril)uta- 
 [ries. This constitutes what is called the " median moraine " 
 [of a glacier (Fig. 10). Often there are several median mo- 
 raines, and the number and position of these depend wholly 
 [upon the number and size of the tributary glaci(?rs which coa- 
 ilesce to form the main ice-stream. Lastly, when the glacier 
 [reaches the point at which the rate of melting is so great as to 
 
34 
 
 PHYSICAL GEOGRAPHY. 
 
 
 overcome 
 which it carries 
 
 its downward movement, all the solid materials 
 in the form of lateral and median moraines 
 
 MM 
 
 Fio. 10. — Diapram to show tl ipte 
 ral and median moraines of u gJa 
 cier. 
 
 are, of course, left by the melting of the ice, constituting what 
 
 is called the " terminal moraine." 
 The terminal moraine, then, of a 
 glacier is a long mound, or series of 
 jcfi mounds, of earth and stones con- 
 )^ fusedly intermixed) running at right 
 sVw/ angles to the valley, and occupying 
 ^j the whole front of the glacier. It 
 '^ is, however, seldom so perfect as 
 this, being usually breached in vari- 
 ous places by the stream or streams 
 which proceed from the extremity of 
 the glacier, and a portion of its solid 
 materials being thus carried off into 
 lower regions. 
 
 A terminal moraine may be easily 
 recognized by the following points, 
 even in places from which the gla- 
 ciers have now completely disap- 
 peared: In the first place, all the 
 materials composing any such termi- 
 nal moraine would be " unstrati- 
 fied ; '* that is, they would be confusedly thrown together, 
 the heavier blocks being mixed up with the finer earthy ma- 
 terials, without any arrangement into distinct beds, or, in fact, 
 any arrangement at all. If, on the other hand, the ridge had 
 been deposited by running water — if, for instance, it were the 
 delta of an old torrent — this would not be the case. In this 
 case, we should find the ridge " stratified ; " composed, that 
 is, of alternating layers of coarser or finer materials, according 
 as the stream had power to bring down pebbles or large blocks 
 at one time or only mud and sand at another time. Secondly^ 
 all the blocks in a moraine-ridge are more or less angular^ and 
 never completely rounded and water-worn. Having simply 
 been carried down as they fell upon the surface of the glacier, 
 and having mostly been subjected to no attrition or wearing 
 down, their edges generally remain sharp and unworn, just as 
 thoy were when originally broken off from the parent-rock. 
 If the ridge had been deposited by running water, all its con- 
 tained blocks wGi:ld be "educed to the condition of rounded 
 pebbles and gravel of uilferent sizes, with water-worn bowlders. 
 Thirdly^ one might always detect in the blocks of a moraine 
 
ICE AS A DENUDING AGENT. 
 
 \i5 
 
 id materials 
 an moraines 
 -ituting wliat 
 il moraine." 
 
 then, of a 
 , or series of 
 
 stones e()n- 
 ling at right 
 d occupyin}:^ 
 1 glacier. It 
 ) perfect as 
 ched in vari- 
 n or streams 
 extremity of 
 )n of its solid 
 tried off into 
 
 nay be easily 
 
 wing points, 
 
 hich the gla- 
 
 letely disap- 
 
 lace, all the 
 
 y such termi- 
 
 *' unstrati- 
 
 vn together, 
 
 earthy ma- 
 
 1, or, in fact, 
 
 le ridge had 
 
 it were the 
 
 ise. In this 
 
 Tiposed, that 
 
 s, according 
 
 arge blocks 
 
 Secondly^ 
 
 ngular, and 
 
 ving simply 
 
 the glacier, 
 
 or wearing 
 
 ['orn, just as 
 
 parent-rock. 
 
 , all its con- 
 
 of rounded 
 
 n bowlders. 
 
 : a moraine 
 
 some which would be flattened upon one or more sides, the 
 lattened side being at the same time more or less polished, 
 ind covered with more or less numerous scratches, grooves, or 
 I'* stria?," usually pretty straight and similar in their direction. 
 I These polished and striated blocks are produced in this way : 
 IAs tlie glacier moves down the valley, it meets here and there 
 l"witli uneven, rocky ground, which it has to surmount. Wlien 
 lihis occurs, the glacier becomes fissured with broad and deep 
 ! rents, or cracks, which are called " crevasses," and which run 
 traiisverscly to the axis of the glacier, generally pointing upward. 
 iiilnto these broad and deep fissiu-es, rocks, sand, and eartli, may 
 be precij)itated, either from the rocky banks of the glacier, or 
 by the liquefaction of the ice surrounding parts of the mo- 
 raines. The rocks thus conveyed to the bottom of the crevasse 
 got froz(m into the lower surface of the glacier, and are carried 
 down with it in its downward course. In this course, partly 
 by the weight of the superincumbent ice, and partly in conse- 
 quence of the enormous pressure under which the glacier 
 moves, these blocks get liattened, polished, and deeply grooved, 
 on the face which is opposed to the rocks over which the gla- 
 cier makes its way. 
 
 Reciprocally, the rocks which form the bed of the glacier 
 are worn down, polished, and grooved, with long rectilinear 
 *. .furrows, by having these blocks dragged over them under such 
 an enormous pressure. Should the stones which are fixed into 
 the bottom of the glacier change their position from any cause, 
 xisuch as the melting of a portion of the ice, they will be liable 
 ^ ^^,to be flattened, polished, and striated upon more sides than 
 ^one, and the striae may run in different directions. In any 
 %case, however, in all the moraines of our modern glaciers, the 
 %numbe" of striated and polished blocks is very small as com- 
 pared ivith the total number of blocks in the moraine. On the 
 other hand, in many ancient moraines the number of striated 
 blocks is proportionately very large. 
 
 Let us now consider what would be the condition of a val- 
 ley down which a glacier had made its way ; supposing the 
 glacier to have altogether disappeared, or to have partially 
 Tc tired, both cases being of common occurrence. As before 
 said, a glacier, though moving slowly, exercises an enormous 
 pressure, and moves with a perfectly irresistible force. As a 
 result of this, the rocks which underlie a glacier are every- 
 where and in all cases more or less completely smoothed and 
 ^ rounded, and their salient projections worn down. Not only 
 Iocs this occur, but every stone and grain of sand which is 
 
30 
 
 PHYSICAL GEOGRAniY. 
 
 i 
 
 hi 
 
 li' 
 
 m 
 
 
 iin^u; 
 
 H 
 
 frozen into the lower surface of the ghicicr acts as a gravirifr- 
 tool, leaving its mark upon the bed of the glacier in the form 
 of a rectilinear groove or fuirow, pointing in the san)e fVnvc- 
 tion as the course taken by the glacier itself (Fig. 11). 
 
 Fio. 11. — Limestone polished, furrowed, and scratched, by the glacier of Roscnlnnl. In Swit- 
 zerland (Agassiz). — (I </, White streaks or scratches, formed by small grains of flint 
 frozen into the ice ; b b, Furrows. 
 
 Whenever, then, we find the rocks exliibiting this snioothod 
 and rounded outline, with their surfaces polished and scored 
 with long, straight furrows, we may be certain that a glacier 
 has been at work. TJiese are the phenomena which we see at 
 the present day wherever a glacier has retired and left any 
 portion of its bed exposed to view ; and we find similar phe- 
 nomena in places where there are now no glaciers. Thus, the 
 fundamental rocks in the mountainous parts of Great Britain, 
 and almost the whole of Europe, and over a great part of 
 North America, are everywhere polished, smoothed, and stri- 
 ated. From this we know, in conjunction with many other 
 proofs of the same fact, that all these districts, at a compara- 
 tively recent period, have been covered by great glaciers. 
 
 Another common phenomenon produced at the present day 
 by glaciers, and found in many localities where there are now 
 no glaciers, are what are known as " roches moutonn^es " (or 
 sheep-like rocks). These are dome-shaped masses of rock 
 
ICE AS A DENUDING AGENT. 
 
 07 
 
 as <a graving'- 
 r in the form 
 
 ,1;. 
 
 e same nircc- 
 . 11). 
 
 Ro?onlaul in Swit- 
 ill gniiud of Hint 
 
 ^ (Fi<^. 12), which are flattened and rounded on the surface look- 
 
 || in^ up the valley, in conseciuonco of the passage of a ghicier 
 
 :i over tlicni, but which p'cnerally present a more or less abrupt 
 
 i and rugged face on the side looking down the valley, since 
 
 Fio. 12.— Boches moutonnies. In the Lake-district of the north of England. 
 
 this side was not exposed so much to the pressure of the gla- 
 cier. Equally common in glaciated countries are what are 
 known as " perched blocks." If, it should happen that any 
 conical peak or sharp ridge should project through the glacier, 
 and that the surface of the ice should be much lowered by 
 melting, rings of blocks from the moraines may be left round 
 such a peak, or a single block may be left upon such a ridge ; 
 and these are then known as " perched blocks." 
 
 What are called " erratic blocks," or simply " erratics," 
 (Fig. 13), are of another nature, and are not so commonly pro- 
 
 uhis smoothofl 
 (d and scored 
 [hat a glacier 
 ich we see at 
 |and left any 
 
 similar phe- 
 IS. Thus, the 
 
 reat Britain, 
 [reat part of 
 
 led, and stri- 
 many other 
 
 [t a eompara- 
 
 ;laciers. 
 present day 
 
 here are now 
 
 [onuses" (or 
 
 Bses of rock 
 
 to. 18.— The Pierre & Bot, an erratic granit« block, derived from the Alps, and now situated 
 
 on the Jura. 
 
 luced by glaciers as by icebergs. From the mode in which 
 noraines are formed and transported, it follows that the blocks 
 rhich are found ;n a tenninal moraine are often quite different 
 In composition to the rocks in the immediate neighborhood of 
 the moraine. If we suppose, for instance, that a glacier de- 
 scends a valley the upper part of which is occupied by gianite, 
 
1 
 
 I* i 
 
 *: 
 
 M 
 
 liil! 
 
 liii 
 
 ill. ' .>i 
 ill' ''* 
 
 K 
 
 m' 
 
 1 i! 
 Ill 
 
 88 
 
 PHYSICAL GEOGRAPUY. 
 
 while tho lower portion is entirely composed of limoatono, 
 we should fmd in tlie terminal moraine of such a glacier 
 numerous blocks of granite which have traveUed, it might 
 be, many miles from their source, and which now repose 
 upon limestone, there being no granite nearer than the nead 
 of the valley. In all ordinary cases of glaciers it is quite 
 obvious that these " erratic blocks," though they nmv dilVcr 
 frotn the rocks immediately adjacent, must nuverthelcs > ng 
 to the valley down which the glacier moves ; or, in tccimical 
 language, the erratics of a glacier belong to the same " hydro- 
 graphical basin." In some instances, however, as in the enor- 
 mous extinct glaciers which formerly occupied the Alps, this 
 ceases to be the case. In these eases, the size of the glacier 
 was so enormous that it was able to ignore altogether tlio 
 ordinary lines of drainage ; and in these cases erratics may be 
 found many leagues from the parent-rock, and in altogether 
 different hydrographical basins. Thus, lunnerous and very 
 large erratic blocks of granite and other crystalline rocks, origi- 
 nally derived from Mont Blanc, arc now found lodged on the 
 limestone ridge of the Jura, at a distance of more than fifty 
 miles from the parent rock, and after having crossed tin n^reat 
 valley in which the Lake of Geneva is situated. In f par- 
 ticular case, there is good evidence that these blocks h oen 
 transported by a glacier enormously larger than any at pres- 
 ent found among the Alps.* As a general rule, however, 
 " erratic blocks," that is, blocks of rock which are now found 
 far removed from their parent-rock, have been carried, not by 
 glaciers, but by icebergs^ us we shall shortly see. And, when 
 transported in this way, erratics may be carried many hun- 
 dreds of miles from their original source — very much farther 
 than could be effected by any glacier. 
 
 Before passing on to consider continental ice and icebergs, 
 one or two other common phenomena of glaciers may be men- 
 tioned. Among these are certain caldron-like (excavations in 
 the solid rock, which are called " moulins." It often happens 
 that a stream flows over the surface of the glacier, produced 
 by the melting of portions of the snow above. If such a stream 
 happen to meet with one of the great fissures or crevasses 
 which intersect every glacier, it is engulfed, and has to make 
 its way out below the glacier. In these cases the stream 
 forms a cascade at the point where it is swallowed up, and, 
 
 * The present placiers of the Alps have a length of from five to twenty miles, and a thick- 
 ness of from two or three hundred up to eight hundred feet Tho extinct glaciers of the 
 Alps must have been from fifty to one buudred and My miles Lu ieng^, and from one to 
 three thousand feet in thickness. 
 
ICE AS A DENUDING AGENT. 
 
 r limostono, 
 h a glatiit-r 
 (1, it might 
 now repose 
 lan the nead 
 1 it is quite 
 y uiav dilVer 
 eles nng 
 
 in tecnnical 
 line " hydro- 
 
 in the enor- 
 u; Alps, this 
 
 the ghicier 
 
 toirether tlio 
 
 P I 
 
 utics may be 
 
 n altogether 
 
 is and very 
 
 ! rocks, origi- 
 
 adged on the 
 
 )re than fifty 
 
 3ed till o;reat 
 
 [ In t' par- 
 
 iksh oen 
 
 any at pres- 
 
 , however, 
 
 now found 
 
 rricd, not by 
 
 And, when 
 
 many hun- 
 
 much farther 
 
 md icebergs, 
 nay be men- 
 cavations in 
 'ten happens 
 er, produced 
 ch a stream 
 or crevasses 
 has to make 
 the stream 
 v^ed up, and, 
 
 .jiles. and a thick- 
 ict f?lacier9 of the 
 1, oud from one to 
 
 le 
 
 iR: 
 
 ,#s 
 
 bv the constant action of the fallinj^- stream, a deop, rircnlur 
 cavity or kettle is formed in the rock below. Tartly by fheso 
 surface-st reams of a glacier, and partly by the melting of its 
 lower end, there almost always proee<'ds from the extremity 
 of every glacier a larger or smaller stream. The water of this 
 stream is icy cold, and ischarged with fine mud, derived from 
 the glaciier itself, partly from the moramie matter, and partly 
 from the attrition of the glacier on the rocks which form its 
 bed. \iy these glacier-streams large quantities of line mud 
 and loam are being contimially carried down and dei)osited 
 in the lower regions. As in the case, therefore, of rivers and 
 ')f the sea, the work of destruction is constantly accompanied 
 by an exactly equivalent amount of deposition, but the two 
 j)r(»cesses, though simultaneous and equal, go on in dillerent 
 Incalities. Every particle of matter worn down by a glacier, 
 from the rocks over which it moves, or carried down in its 
 moraines, is preserved and aceunmlated somewhere else; an<l 
 in many instances these "glacial" formations attain a gicat 
 thickness, and are a very marked feature in the geology of a 
 ( ountry. 
 
 Continental Ice and Icebergs. — We have now to con- 
 sider the phenomena presented by glaciers and continental ice 
 ill extremely cold districts, as in the Arctic and Antarctic re- 
 gions. In Switzerland the pres* iit glaciers do not descend 
 farther than to a line about thirty-five hundred feet above the 
 sea-level, or about four thousand feet below the line of per- 
 ])etual snow. When they reach this point, they melt so rap- 
 idly that their downward progress is completely stopped. In 
 colder countries, however, where the line of perpetual snow 
 is much lower, we have a fresh set of phenomena. If we take 
 such a country as Greenland, in which the snow-line is only 
 fiom one to irwo thousand feet above the level of the sea, the 
 cold is so great that the glaciers have not time to melt before 
 they reach the sea-level ; and they, therefore, push off now 
 from the land into the sea. For a certain distance, they 
 simply grate along the bottom of the sea ; but ultimately 
 , the water becomes too deep to allow of this, and the end 
 I of the glacier breaks off in great masses, which float away, 
 and are then known as " icebergs." Not only is this the case, 
 [but the cold is so intense, and the annual snow-fall so great, 
 [that, in place of any single glacier or glaciers, the entire coun- 
 itry becomes covered with a single sheet of ice, constantly 
 jinoving from the interior to the sea, and cor(stituting what is 
 [known as " continental ice." As described by Dr. Rink, the 
 
40 
 
 PHYSICAL GEOGRAPHY. 
 
 
 ' if 
 
 whole of the interior of Greenland is covered by a gigantic 
 sheet of ice, which entirely conceals all the features of th( land 
 beneath an icy mask, and the whole of which is constantly 
 moving toward the sea. The main outlets by which the ice is 
 discharged are several large friths which would be the outlets 
 of so many rivers, if the climate were milder. Down these 
 friths the ice makes its way in colossal masses several miles 
 wide, and hundreds of feet in thickness. These masses con- 
 tinue to push off into the sea, till the depth of several hundred 
 or a thousand feet is reached, grinding along the sea-bottom 
 as they go. Finally, when the water gets sufficiently deep to 
 iloat them, enormous masses break off from the ends of these 
 glaciers, and float awaj'' as icebergs. 
 
 It 18 highly probable that the condition of Scotland and Scandinavia was 
 at one time the same as we now see in Greenland. If we could get at the 
 land-surface in Greenland, we should doubtless see what we now observe in 
 Scotland, namely, that all the higher regions of the country are everywhere 
 scored and polished like the rocks which underlie a glacier. 
 
 Icebergs, then, are produced by glaciers or by continental 
 ice, when the sea-coast is reached, and the more important 
 phenomena which they present are these : Being detached by 
 fracture from great glaciers, icebergs frequently carry with 
 them enormous quantities of earth and great masses of rock, 
 derived from the moraines. In some cases individual icebergs 
 have been calculated to have carried from fifty thousand to 
 one hundred thousand tons of soil and rode. When these 
 rock-laden bergs have drifted to a latitude so low that they 
 melt, this burden of rock and soil is, of course, deposited upon 
 the floor of the ocean. In this way, an incalculable quantity 
 of solid matter is annually removed from the neighborhood of 
 the poles, and deposited at some point nearer the equator ; 
 and in this way numbers of large angular " erratic blocks " are 
 at the present day deposited on the bed of the sea, many hun- 
 dreds of miles, it mav be, from their original source. 
 
 This action of bergs explains the constant occurrence 
 of erratic blocks i arious parts of Europe and America, in 
 regions where theic are now no glaciers, and at distances from 
 the parent-rock too great to allow us to suppose that they 
 could have been transported by glaciers. By the putting to- 
 gether of a number of facts of this kind, it has been demon- 
 strated that a large portion of Europe and America has at a 
 recent geological period been submerged beneath the waters 
 of an icy sea, carrying numerous icebergs laden with rock and 
 earth. 
 
 Lli 
 
 iWI 
 
ICE AS A DENUDING AGENT. 
 
 41 
 
 >y 9- gigfintic 
 es of th< land 
 is constantly 
 lich the ice is 
 3e the outlets 
 
 Down these 
 several miles 
 
 masses con- 
 veral hundred 
 le sea-bottom 
 ently deep to 
 ends of these 
 
 Scandinavia was 
 could get at the 
 B now observe in 
 ' are everywhere 
 
 )y continental 
 
 'e important 
 
 r detached by 
 
 [y carry with 
 
 isses of rock, 
 
 dual icebergs 
 
 thousand to 
 
 When these 
 
 ow that they 
 
 posited upon 
 
 ible quantity 
 
 hborhood of 
 
 ;he equator; 
 
 c blocks " arc 
 
 a, many hun- 
 
 rce. 
 
 it occurrence 
 America, in 
 istances from 
 se that they 
 e putting to- 
 seen demon- 
 rica has at a 
 the waters 
 nth rock and 
 
 In many cases, owing to the set of oceanic currents, or the 
 prevalence of particular winds, the great majority of tlie ice- 
 bergs derived from any special region may be drifted in one 
 given direction. In tliis way, trains of erratic blocks and 
 musses of unstratified matter may be produced or accumulated 
 along particular lines. 
 
 It only remains to add, that the size of many icebergs is 
 most enormous. Many have been carefully measured, which 
 were from one to two hundred feet above water, and from two 
 to five miles in length. As the specific gravity of ice is such 
 that only one-tenth of a mass of it can appear above water, 
 the real height of these stupendous bergs must have been 
 from one to two thousand feet. It need not be said that the 
 momentum of such a floating mass must be exceedingly great. 
 
 Frost. — Before leaving this subject, it may be mentioned 
 that considerable denuding power is exercised on a small scale 
 by frost alone. Tlie freezing of the water which penetrates 
 the interstices and fissures of rocks is accompanied with an 
 irresistible expansion, by which almost all rock-masses sutler 
 more or less waste during the course of every winter. The 
 result of this action is to detach larger or smaller fragments 
 bodily, and to render the whole mass more liable to the attacks 
 of other denuding agencies. 
 
 i 
 

 m 
 
 te 
 
 fii 
 
 ;d 
 
 hf 
 
 1 ^ 
 
 1' 
 i'j 
 
 I !■'■ 
 
 Hi 
 
 1 r^^^lf!! 
 
 
 1 ^1 
 
 '■|i 
 
 it' ; 
 
 1. 1 
 
 CHAPTER V. 
 
 ACTION OP THE ATltfOSPHERE AND OP LIVINC 
 
 THE EARTH. 
 
 ,EINGS UPON 
 
 Weathering. — The last denuding agent which requires 
 notice is the atmosphere, with its contained gases and moist- 
 ure ; and the effects of this may be either chemical or mechani- 
 cal. The chemical actions of the atmosphere upon rocks may 
 all be considered under the head of " weathering." It is well 
 known that no rock-surface can be exposed for a sufficient 
 length of time to the action of the atmosphere without under- 
 going a certain amount either of actual disintegration or of 
 chemical change. The effects produced vary with the ingre- 
 dients contained in the atmosphere, and also with the nature 
 of tlie rock itself. Many rocks yield much more rapidly than 
 others, those yielding most quickly which contain any ele- 
 ment which is soluble in carbonic acid dissolved in water. 
 Tims, limestone may be almost invariably lecognized in tlie 
 field by the fact that its exposed surface is generally fretted 
 and worn into cavities and hollows ; this being due partly to 
 the action of rain-water holding carbonic acid in solution, and 
 partly to tlie atmosphere alone when sufficiently moist. Again, 
 all rocks wliich contain soluble silicates, such as granitic and 
 trappeau rocks, yield more or less to the action of the air. In 
 these cases the carbonic acid of the atmosphere, though a 
 weak acid, replaces part of the silicic acid of the silicate, and 
 converts it into a soluble carbonate. Hence, in almost all 
 basalts and trap-rocks the weathered surface will effervesce 
 upon the addition of a mineral acid. Rocks, composed of pure 
 silica, such as sandstones, are almost indestructible by the 
 atmosphere, if they are sufficiently coherent and compact. In 
 all cases, however, the chief chemical effect of the atmosphere 
 is to render the surface of rocks, where exposed, more porous, 
 
 Vi 
 
 "I 
 
SUB-AERIAL DEPOSITS. 
 
 43 
 
 EINGS UPON 
 
 and thus to pave the way for the more effective attacks of 
 water in all its forms. 
 
 Mechanical Action of the Atmosphere. — Winds in 
 some cases cause considerable modifications of the earth's sur- 
 face, by transportiufr loose and ini;oherent sands from one 
 place and accumulating them in another. Such " sul)-aerial " 
 deposits are the sand-dunes of parts of the coasts of Britain, 
 France, and North America. They are wholly the result of 
 tlie action of the wind upon the loose sand of the sea-shore, 
 and they have the form of low mounds of sand generally ar- 
 ranged in irregular layers. In some cases, they gain consider- 
 ably upon the land and do much damage. In all extensive 
 deserts, also, similar hills are formed by the drifting together 
 of the sands by the wind, and the surface is constantly under- 
 going modification from this cause. 
 
 Organic Agexcies. — The denuding or destructive effects 
 of living beings uj)()n the earth's surface are comparatively so 
 insignificant that they may be passed over altogether; but 
 much material may be added to the earth's crust by the agency 
 of living beings, and this subject requires a brief notice. 
 
 Accumulations of Vef/etable Matter. — The incessant growth 
 and decay of vegetables are constantly adding to the surface 
 fresh matter in the form of vegetable soil or " humus." The 
 thickness of this varies with the luxuriance of the vegetation 
 in any particular locality, being greatest in tropical regions, 
 and smallest in rainless districts. Vast accumulations of drift- 
 wood are formed in various rivers, the upper waters of which 
 pass through heavily-timbered regions; and vast masses of 
 decaying vegetable matter are often accumulated in extensive 
 swamps. In temperate zones, these last chiefly assume the 
 form of "peat," which is mainly formed by the growth of 
 mosses of the genus i^jyhafpnim. Peat may accunndate to a 
 great thickness, and it sometimes becomes an imperfect coal. 
 We shall aft(;rward see that " coal " owes its origin to the ac- 
 cumulation of vegetable matter in immense swamps. 
 
 Action of Animals. — As regards the action of animals, 
 there are only three points which reciuire notice: 1. Shell- 
 beds may be formed by the growth and accumulation of such 
 shells as oysters and mussels. Such beds attain a consider- 
 able thickness in somecrses, and it can be shown that various 
 shelly beds have been fr;'med in a similar manner at various 
 periods of the earth's lustory. 2. It has been shown that at 
 the bottom of the deep Atlantic there is now forming a deposit 
 of a white mud which is known as ooze, and which is composed 
 
-i' 
 
 ■5 
 
 ' 
 
 44 
 
 PHYSICAL GEOGRAPHY. 
 
 i k\ 
 
 almost entirely of the minute calcareous shells of certain mi- 
 nute animalcules, known as Foraminifera. We shall after- 
 ward see that chalk has had a very similar origin, and that 
 the shells of these same animals also enter largely into the 
 composition of other less important rocks. 3. The structures 
 known as "corals" are the skeletons of certain "zoophytes" 
 allied to the sea-anemones, so common on every coast. Corals 
 are composed of carbonate of lime, and, like the animal which 
 produces them, they may be simple or compound ; in other 
 words, a coral may be the work of a single " polype," or it 
 may be composed of the common skeleton secreted by a num- 
 ber of polypes united together, and forming a colony. The 
 *' simple " corals, though sometimes of large size, do not form 
 accumulations of any note. The "compound" corals, how- 
 ever, form, under favorable conditions, enormous masses which 
 are known as " coral-reefs," and which are a marked feature 
 in many oceans, such as the Pacific and Indian Oceans. It 
 will afterward be shown that many of the limestones which 
 have been formed at various periods in the earth's history, 
 owe their origin to the action of coral-polypes. They are 
 either actually old coral-reefs, or they are conjposed of accu- 
 mulations of fragments of coral, broken down into sand, and 
 afterward compacted together by the action of water holding 
 carbonic acid in solution. 
 
 When it is understood that compound corals, such as we have been 
 speaking of, are produced by the combined eflorts of a number of polj'pes, 
 essentially the same in structure as our ordinary sea-anemones, it is readily 
 intelligible that under favorable circumstances large masses of coral may be 
 produced in this way. When these masses attain such a size as to be of 
 geographical importance, they are spoken of as " coral-reefs," and the phe- 
 nomena exhibited by these are of such interest as to demand some notice. 
 The coral-producing polypes require for their existence that the average tem- 
 perature of the sea shall not be less during winter than 66 degrees; and, as 
 our seas are considerably colder than this, we have no coral-reefs. Reefs, 
 liowever, abound in all the seas not far removed from the equator, being 
 found chiefly on the cast coast of Africa and the shores of Madagascar, in the 
 Red Sea and Persian Gulf, throughout the Indian Ocean and the whole of the 
 Pacific Archipelago, around the West-Indian Islands, and on the coast of 
 Florida. The headquarters, however, of the reef-building corals may be said 
 to be around the islands and continents of the Pacific Ocean, where they often 
 form masses of coral many hundreds of miles in length. According to Darwin, 
 coral-reefs may be divided into three principal forms, viz., Fringing-reefs, 
 Barrier-reefs, and Atolls, distinguished by the following characters : 
 
 1. Friuffinff-rrcfx (Fig. 14, 1). — These are reefs, usually of a moderate 
 size, which may either surround islands or skirt the shores of continents. 
 These shore-reefs are not separated from the land by any very deep channel, 
 aud the sea ou their outward oiargius is not of any great depth. 
 
CORAL-REEFS. 
 
 45 
 
 2. Barrier-reefs {F\g. 14, 2).— These, like the preceding, may either encir- 
 cle islands or skirt continents. They are distinguished from fringing-reefs by 
 the fact that they usually occur at much greater distances from the land, that 
 there intervenes a channel of deep water between them and the shore, «ind 
 soundings taken close to their seaward margin indicate great depths. 
 
 [Fia. 14.— StniPtnre ofCorol-rcofh.— 1, Frinjdnp-rpof; 2, nnrrior-reef ; 8, Atoll; fr, Sca-levol ; 
 b, ('oral-reef i o, Primitive laad; (/, rortion of sea wiiiuu tl ; rect^ forming a chamiel or 
 lagoot. 
 
 As an example of this class of reefs may be taken the great barrier-reef 
 [on the north-east coast of Australia, the structure of which is on a gigantic 
 scale. This reef runs, with a few trifling interruptions, for a distance of 
 I more than a thousand miles, with an average breadth of thirty miles, and an 
 [area of thirty-three thousand square miles. Its average distance from the 
 j shore is between twenty and thirty miles, the depth of the inner channel ia 
 [from ten to sixty fathoms, and the sea outside is " profoundly deep " (in 
 [some places over eighteen hundred feet). 
 
 3. Atolls (Fig. 14, 3). — These are oval or circular reefs of coral enclosing 
 [a central expanse of water or lagoon. They seldom form complete rings, the 
 jrecf being usually breached by one or more openings. They agree in all par- 
 (ticulars with those barrier-roefs which surround islands, except that there is 
 1 110 central island in the lagoon which they enclose. 
 
 Beyond a depth of one hundred feet below the level of the lowest tides, 
 [no portion of a coral-reef is formed of growing and living corals, but is en- 
 Itirely composed of dead coral or "coral-reef-rock," which is a white lime- 
 Istone composed of corals and shells. According to Dana, the chief kinds 
 lof coral-rock are, 1. A fine-grained, compact limestone, with hardly a trace 
 lof a coral or shell; 2. A rock equally hard and compact, but with embedded 
 Icorals and shells ; 3. A conglomerate of broken corals and shells ; 4. A rock 
 
46 
 
 PHYSICAL GEOGRAPUY. 
 
 1.. 'iii 
 
 w 
 
 »1. 
 
 composed of corals standing as they grew, the interspaces between them 
 tilled up with pounded coral, shells, and fragments. 
 
 Bearing op the Facts op Physical Geography on 
 Geological Doctrine. — Having now considered the chief 
 agencies which we see at work upon the globe at the present 
 day, a few words may be said as to the bearing of these facts 
 ujwn geological doctrine. There were formerly, and are still, 
 two great schools of geological thought, the members of which 
 are known as " Catastrophists " and " Uniformitarians." The 
 Catastrophists explained all geological phenomena upon the 
 belief that the forces which Ave see at present at work upon 
 the globe formerly acted with much greater intensity than 
 they do now, and produced, therefore, much more striking 
 effects within the same period of time. They believed that 
 great catastrophes and convulsions were part of the order of 
 Nature. To explain geological phenomena, they called in the 
 agency of intense volcanic activity, gigantic rivers rushing 
 over the land, terrific convulsions of the crust of the earth 
 causing deration or depression of the land to the extent of 
 hundreds or thousands of feet, enormous earthquake-waves 
 ravaging whole continents, and other exaggerated physical 
 agencies. 
 
 The Uniformitarians^ headed by Sir Charles Lyell — the 
 most thoughtful and philosophical of living geologists — sup- 
 port, on the other hand, the belief that at no period in the 
 earth's history were the physical forces of tlie globe more ac- 
 tive than we see them at present. They hold that all geologi- 
 cal phenomena — on however gigantic a scale — can be explained 
 by the action of the same forces which now affect the globe, 
 working with just the same force as we see now, but acting 
 through longer periods of time. The Uniformitarians, in fact, 
 hold as their fundamental doctrine " the adequacy of existing 
 causes," as it has been called. They believe that at no period 
 of which we have geological evidence were any physical forces 
 in existence different either in kind or in amount to those of 
 which we have now cognizance. As a matter of course, if we 
 assume " the adequacy of existing causes" in tiie production 
 of all known geological phenomena, we must at the same time 
 demand a vastly-extcmded period of geological time. A small 
 force may produce the same effect as a great force, but it will 
 require a much longer time proportionately to do it in. 
 
 Uiiiformitarianism is the basis of modern geology, and 
 hence the importance of comprehending the leading facts of 
 
 Pl>-.- 
 
GEOLOGICAL DOCTRINES. 
 
 47 
 
 between them 
 
 physical geography before grappling with the problems of 
 geology. It must be remembered, Iiowever, that, as in so 
 many other cases of conflicting doctrines, there is some truth 
 on both sides. In the main, doubtless, Uniformitarianism is 
 tlie true key to the explanation of geological phenomena. 
 Still, Catastrophism is not wholly false ; since unquestionably 
 there must have been times, in the earth's history, in which 
 known forces acted with greater intensity than at present, and 
 possibly there were even forces at work which we do not 
 recognize now. Thus, the hypothesis that the earth is a slowly- 
 cooling globe certainly implies that the forces of fire were at 
 one time much more active and energetic than they are now. 
 Whether this has been the case to any marked extent within 
 the time of which we have geological record, is a matter for 
 argument j but, that it has been so once, is almost certain. 
 
 m 
 
I 
 
 PART II. 
 
 G E L T. 
 
 ll 
 
 CHAPTER VI. 
 
 DEPrNTTiON OP Geology. — Geology, in a limited sense, 
 is concerned with the investigation of the materials which 
 compose the earth, and the manner in which these are arranged. 
 Strictly speaking, this would lead us into an investigation of 
 the earth's interior ; and there are many geological phenomena 
 which can only be explained by some theory as to the con- 
 dition of the interior of the globe. Grounds, however, have 
 already been given for the general belief that the earth con- 
 sists of a cool envelope or " crust," surrounding a highly- 
 heated interior. 
 
 Successive Formation op the Crfst op the Earth. — 
 At present we have only to do with the crust of the earth y 
 that is to say, with that comparatively " small portion of the ex- 
 terior of our planet which is accessible to human observation, 
 or on which we are enabled to reason by observations made at 
 or near the surface " (Lyell). In various ways we are enabled 
 to form some judgment of the composition of an external shell 
 of the earth, to the depth of, perhaps, ten miles, or ^^ of the 
 distance from the earth's surface to its centre ; and this is all 
 that is meant by the " crust of the earth." It is quite con- 
 ceivable that the whole crust of the earth might be composed 
 of a single substance, say sandstone ; but every one knows 
 that this is not the case, and that, really, different materials 
 occur in different places ; here sandstone, there granite, here 
 chalk, there coal, and so on. It is also conceivable that these 
 different materials should all have been created exactly in the 
 
CLASSIFICATION OF ROCKS. 
 
 49 
 
 same place and exactly in the same condition as we now find 
 them. Tills, however, also is far from being the case. A 
 very limited knowledge of geology shows us that the mate- 
 rials which now compose the crust of the earth have acquired 
 their present position and condition slowly and under differing 
 circumstances, and that they weve formed at successive periods. 
 During each of these successive periods, successive races of 
 animals and plants inhabited the earth, and remains of these, 
 in greater or less plenty, are preserved in the rocks of each 
 period, constituting what are known as "fossils." 
 
 Definition op the Term " Rock." — The crust of the 
 earth, then, consists of various different materials, produced 
 at different successive periods, occupying certain definite 
 spaces, and not confusedly mixed together, but exhibiting, on 
 the "ontrary, a definite order of arrangement. All these ma- 
 terials, however different in appearance, texture, or compo- 
 sition, are called " rocks " by the geologist. Technically, 
 therefore, the term " rock " is to be understood as applying 
 to all the materials composing the crust of the earth. In the 
 language of geology, the finest mud, or the loosest sand or 
 gravel, is just as much rock^ as is the hardest and most com- 
 pact granite. 
 
 Classification of Rocks. — All the rocks which compose 
 the crust of the earth may be classed under one or other of 
 four great divisions, known as the Aqiceotis, Volcanic^ Plu- 
 tonic^ and Metamorphic Rocks / and each of these requires 
 special consideration. 
 
 I. Aqueous Rocks. — These are often spoken of as the 
 Sedimentary or Fossiliferous rocks, and they constitute by 
 far the greater part of the crust of the earth. They are dis- 
 tinguished from the other rocks by two facts : Firstly, all aque- 
 ous rocks are stratified ; that is to say, they are composed of 
 a number of different layers or strata (Fig. 15). These layers 
 may consist of a single material, as of sandstone, limestone, 
 I or the like, or they may consist of diffierent materials. In all 
 cases, if we extend our examination of the aqueous rocks 
 sufficiently far, we find that they are not only composed of 
 [successive layers, but that one set of beds or strata of one kind 
 I follows another set of beds of another kind. Beds of sand- 
 stone alternate with beds of limestone, succeeded by beds of 
 shale, and so on. There is, therefore, a succession of the beds 
 of aqueous rock, but the succession is not a uniform and con- 
 stant one; nor are the beds of one kind referable to one pe- 
 [riod of the earth's history, and the beds of another kind to 
 
1 1 
 
 60 
 
 GEOLOGY. 
 
 another. On the contmry, beds of all the known kinds of 
 aqueous rocks have been formed during each great geological 
 period. 
 
 Whether composed of a single substance, or of many such 
 alternating with one another, a stratified rock may be com- 
 posed of layers of different degrees of thickness, varying from 
 the thickness of writing-paper up to many feet. In some 
 cases, especially in some sandstones and conglomerates, the 
 strata are of such thickness that when a small piece alone is 
 examined, it is impossible to make out the nature of the rock, 
 and the stratification is only visible on a large scale. In most 
 stratified rocks there is a double composition out of distinct 
 layers. In the first place, the rock is divided into a series of 
 tolerably thick layers, which separate readily from one another, 
 since, in fact, their surfuc(;s are not actually continuous. These 
 layers are the true strata. In the second place, each stratum 
 is generally composed of a greater or less number of minor 
 layers, of different grain or color, and which do not readily 
 separate from one another. At the same time, if force be ap- 
 plied to the rock, it will split more readily along the line of 
 these layers than along any other line. Tliese layers are 
 usually spoken of as the laminoe of deposition^ or simply as 
 the laminm of an aqueous rock. 
 
 As regards the origin of the stratified rocks, we are al)le 
 to infer that the materials which compose them have formerly 
 been streioed out by the action of water, from what we see on 
 a smaller or larger scale wherever there is water in motion. As 
 we have seen, every stream, where it runs into a lake or into the 
 sea, carries with it a burden of mud, sand, or 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 heavi- 
 est pebbles, of course, first, the sand and finer pebbles next, 
 and the finest mud last. Ultimately, therefore, there is formed 
 in every lake a series of stratified rocks, produced by the 
 streams which flow into the lake. We might have inferred 
 that this would be so, without actually knowing it to be the 
 case ; but, when a lake is drained, and we can examine its floor, 
 we actually find such a succession of stratified deposits. These 
 may vary in different parts of the lake according as one stream 
 brought down one kind of material, and another stream con- 
 tributed a different kind ; but in all cases the materials will 
 bear ample evidence that they were produced and deposited 
 by running water. The finer beds, of clay or sand, will all be 
 
 -■•^ 
 
 '■■§ 
 
AQUEOUS ROCKS. 
 
 61 
 
 ' many such 
 ay be coin- 
 iirying from 
 . In some 
 leratcs, the 
 ;ce alone is 
 of the rock, 
 e. In most 
 b of distinct 
 3 a series of 
 one another, 
 ious. These 
 acli stratum 
 )er of minor 
 not readily 
 force be ap- 
 1 the line of 
 B layers are 
 or simply as 
 
 we are able 
 
 ive formerly 
 
 it we see on 
 
 motion. As 
 
 e or into the 
 
 ed pebbles, 
 
 ;s bed and 
 
 lied by tlie 
 
 , the heavi- 
 
 ibles next, 
 
 e is formed 
 
 ced by the 
 
 five inferred 
 
 it to be tlie 
 
 ine its floor, 
 
 sits. These 
 
 one stream 
 
 stream con- 
 
 iterials will 
 
 deposited 
 
 will all be 
 
 
 nrranfjod in thicker or thinner layers, or " laminjr," and will 
 be more or less regularly " stratitied." If there are beds of 
 gravel, the pebbles of these will be rounded and smooth, as 
 are the pel)bl(?s in any brook-course. And, in all probability, 
 Ave should find in some of the beds the remains of fresh-water 
 shells or })lants, or of other organisms which inhabited the 
 lake or its banks, at the time when these beds were in pro- 
 cess of formation. 
 
 As we have seen, also, most large rivers deposit much of 
 the materials which they bringdown, at their mouths, forming 
 " deltas." When such a delta is cut through, cither naturally 
 or artificially, we find that it is composed of a succession of 
 horizontal layers of sand or mud, varying in mineral comjio- 
 sition, in color, or in grain, according to the nature of the ma- 
 terials brought down by the river at different periods. In 
 other cases, no delta is formed, but all the materials carried 
 down by the river are hurried out to sea, to be finally depos- 
 ited in alternating beds in some distant and tranquil portion 
 of the ocean. Lastly, the sea itself is constantly preparing 
 fresh stratified deposits by its own action, irrespective of the 
 materials incessantly delivered over to it by rivers. As already 
 explained, the sea upon every coast is constantly wearing back 
 into the land, and breaking up its component rocks to form the 
 shingle and sand which we meet with on every shore. The 
 materials thus obtained are not lost, but are finally laid down 
 somewhere in the form of fresh accumulations of rock. 
 
 Fia. 15. — Section of stratified roclis (after Sir Henry Do la Beche). 
 
 WTienever, then, we find anywhere inland any series of 
 rocks having these characters — composed, that is, of distinct 
 layers, the particles of which, whether large or small, show 
 distinct traces of the wearing action of water — we are justified 
 in assuming that they have been laid down by water at some 
 
1 
 
 I 
 
 'I? 
 
 u 
 
 68 
 
 GEOLOGY. 
 
 H:' 
 
 ^iili 
 
 former period in the way described. Eitlior tho.y were laid 
 down in some ancient lake, by the combined action of the riv- 
 ers which flowed into it, or they were deposited at the mouth 
 of some ancient river, forming its delta, or th(;y were accumu- 
 lated at the bottom of the ocean. In the first two cases, any 
 remains of animals or plants which the beds might contain 
 would be the remains of such as inhabit fresh water, or live 
 upon the land. In the third case, any organic remains present 
 would be in great part or entirely those of marine animals. 
 
 The fundamental and essential character of all aqueous 
 rocks, then, is that they must be stratijiedy or arranged in dis- 
 tinct layers (Fig. 15). In the second place, however, the great 
 majority of aqueous rocks show their origin quite as conclu- 
 sively by the fact that they contain fossils. By the term 
 " fossil " is understood " any body, or the traces of the exist- 
 ence of any body, whether animal or vegetable, which has been 
 buried in the earth by natural causes " (Lyell). Jt is true 
 that there are many individual beds in any stratiHed formation, 
 or in some cases a whole series of beds, perhaps to the thick- 
 ness of thousiinds of feet, in which no fossils of any kind can 
 be detected. In these cases, however, evidence can always be 
 obtained otherwise that these " unfossiliferous " beds were 
 formed by aqueous agency, and they can almost always be 
 shown to be harmoniously related to other beds which are 
 " fossiliferous," or contain fossils. The nature and character 
 of the fossils in any given stratum or group of strata will 
 always afford accurate evidence as to the mode of its deposi- 
 tion. If the beds contain the remains of animals similar to 
 those which now live in the ocean, we know that they wen; 
 deposited at the bottom of the sea. If the fossils are those of 
 animals and plants such as now inhabit fresh water, we know 
 that the beds are " fluviatile " or " lacustrine ; " that they were 
 laid down in some river or in a lake. 
 
 The term " formation " is employed by geologists to des- 
 ignate groups of rocks which have been laid down during one 
 period, which have a common origin, or which hav so 
 common character as regards their composition " ius we 
 may speak of stratified and unstratified form , aqueous 
 
 and igneous formations, fresh-water and mar Ibrmations, 
 fossiliferous and unfossiliferous formations, secoiiu.jry and ter- 
 tiary formations, and so on. 
 
 The two tests, then, of any given rock having an aqueous 
 origin, are firstly^ that it must be stratified or disposed in dis- 
 tinct layers j and, secondly y that it may contain fossils, or, if it 
 
 ■'('% 
 
 
VOLCANIC ROCKS. 
 
 53 
 
 were laid 
 of the riv- 
 the mouth 
 •e accumu- 
 cases, any 
 rht contain 
 lor, or livo 
 ius present 
 nimals. 
 11 aqueous 
 ged in dis- 
 •, the great 
 } as conolu- 
 T the term 
 
 the exist- 
 ih has been 
 
 Jt is true 
 . formation, 
 5 the thick- 
 ly kind can 
 I always be 
 beds were 
 always be 
 
 whicli are 
 i character 
 strata will 
 its deposi- 
 
 similar to 
 
 they wen; 
 
 e those of 
 we know 
 
 they were 
 
 tsts to des- 
 luring one 
 lav" soi 
 us we 
 , acjueous 
 lormations, 
 Iv and ter- 
 
 [n aqueous 
 ked in dis- 
 tls, or, if it 
 
 'm 
 
 does not, that it will be harmoniously related to bods that 
 do contain fossils. There are two cases, however, in which 
 lM)tli thcs(! nMiuireinents are fulfilled, and the nx-k is neverthe- 
 less not aqueous in its origin, nor in its rnochj of formation. 
 In one casii we may have stratified deposits formed by the 
 ashes omitted from a volcanic vent, and simply falling on the 
 surface of the land ; and these may contain the remains of 
 anitnuls or ])lants, imbedded in them as they fell. Or, these 
 ashes may fall into a lake or into the sea, and may become very 
 regularly laminated; but in this case the beds become aque- 
 ous as to their actual mode of deposition, though as to their 
 origin they are volcanic. Secondly, stratified accumulations 
 of drift-sand may be heaped up along a sea-coast or in a 
 sandy desert, by the action of the wind alone ; and these also 
 may sometimes preserve in their interior the remains of 
 animals or plants. Both the cases here alluded to are rare, 
 and both are tolerably easy of reference to their true ciiuses. 
 
 II. Volcanic Uocks. — The second great class of rocks is 
 that of the volcanic rocks, comprising all those rocks which 
 we have reason to believe have been formed by the action of 
 subterranean heat, in the same way as we now see in our vol- 
 canoes, whether these be upon the surface of the land or 
 beneath the sea. The volcanic rocks, as a general rule, are 
 devoid of fossils, and are mostly unstratified ; but cases occur, 
 as remarked above, in which they are more or less perfectly 
 stratitied, and contain imbedded organic remains. These, 
 however, are exceptions and do not invalidate the general 
 statement. Under the head of " Volcanic Rocks," are included 
 all those rocks which form the cones of existing volcanoes, or 
 have proceeded from them, or which are in direct connection 
 with hills which can be shown to have been formerly volca- 
 noes, though now exliibiiing no signs of volcanic activity. 
 Under this head, also, comes a vast series of rocks which can- 
 not now be fIiowu to be directly connected with any vol- 
 canic vent, though we can certainly infer from their characters 
 that they were so connected at some former period. The 
 rocks alluded to are spoken of as the Trappean Rocks^ and 
 they occupy large areas in almost every country m the world. 
 As just said, it is impossible now to point to the original cones 
 j and craters from which these " trappean rocks " have proceed- 
 ied; but their characters enable us to assert positively that 
 th< were produced essentially in the same way as we see 
 1 similar rocks produced at the present day by existing vol- 
 canoes. 
 
 «? ^ 
 
54 
 
 GEOLOGY. 
 
 Thus, the trappean rocks consist of beds of solid " trap- 
 rock," identical in mineral composition, in structure, and in 
 all essential characters, with the lava-flows of any modern V(jI- 
 cano ; or exhibiting only such differences as can readily be ex- 
 plained. Associated with tjie beds of solid trap are other 
 beds of " trappean ashes " exactly similar to the ashes and 
 cinders showered forth by recent vents. We further find 
 that the beds of trap-rock have baked and burnt the other 
 rocks with which they have come in contact, just as a current 
 of lava would do. Lastly, we often find that these trap-rocks 
 cut through other formations, forming dikes^ which alter the 
 rocks on both sides of them ; just as do the lava-dikes formed 
 at the present day by the injection of molten matter from 
 volcanoes into fissures in the crust of the earth (Fig. IG). 
 
 There can, therefore, be no doubt as to the substantial 
 identity of the " trappean rocks " with the products of recent 
 volcanoes ; and it is sufficient to remark here that the absence 
 of cones and craters in connection with the former is readily 
 explained. In the first place, all the regions which now ex- 
 hibit trap-rocks have been subjected to enormous denudation ; 
 and the surface which we now see is in no way the original 
 surface of the ground at the time when the rocks in question 
 were formed. Secondly, there is abundant evidence to show 
 that most trappean rocks were formed by sub-marine vol- 
 canoes, and were, therefore, emitted from openings in the bed 
 of the ocean, and not from chasms in the dry land. It is only 
 in the case of sub-aerial volcanoes, as a general rule at any 
 rate, that any cone is formed at all ; and if such a cone were 
 formed by a sub-marine volcano, it would certainly be rapidly 
 destroyed on the cessation of the volcanic action by the de- 
 nuding power of the waves of the sea. 
 
 III. Plutonic or Granitic Rocks. — The two classes of 
 rocks which we have been previously considering are \m- 
 questionably natural groups, and we can point to two similar 
 classes of rocks in process of formation at the present day, by 
 agencies which we know and can observe. The remaining 
 two classes of rocks difier altogether from any thing which wc 
 can see actually in process of formation now. For this reason 
 thoy are more or less artificial divisions, and any theories as 
 to their exact origin and mode of production are more or less 
 open to question. 
 
 The plutonic or granitic rocks agree with the solid trails 
 and with the modern lavas in being unstratified and in con- 
 taining no fossils; while they differ from both of thefe in 
 
PLUTONIC OR GRANITIC ROCKS. 
 
 65 
 
 Itheir highly crystalline texture. It is well known that, when 
 
 jrystals are formed from melted matter, the size of the crystals 
 
 impends mainly upon the rapidity with which the mass is allowed 
 
 to cool • the largest crystals being formed when the cooling 
 
 bakes place most slowly. If a piece of ordinary basalt or whin- 
 
 3tone be melted, we obtain a fused mass, all the particles of 
 
 whioli are free to move upon one another, and are, therefore, 
 
 ■0 to assume a crystalline form, if allowed to do so. If such 
 
 [a melted mass be cooled with great rapidity, as by exposing 
 
 [a portion of it to the air, or pouring it into water, it will 
 
 jolidify into an actual glass, exhibiting no distinct crystals. 
 
 [f allowed to cool with moderate slowness, the rock will be 
 
 nore or less nearly reconverted into its original condition, 
 
 Stiiat of an uncrystallized paste having exceedingly minute 
 
 Icrystals imbedded in it. The longer, however, the process of 
 
 jcooling can 1)3 protracted, the larger will be the crystals ; and, 
 
 (if we could lengthen the cooling sufficiently, the whole mass 
 
 [would become crystalline. These unquestionable facts supply 
 
 [us with the chief positive elements which we have in detcr- 
 
 [niiiii'ig the origin of granite and the other plutonic rocks. 
 
 nVe know that the materials which compose granite have at 
 
 [one time been more or less perfectly' fused or semi-fused ; as 
 
 jshown by the unstratified nature of masses of granite, by their 
 
 [breaking thnnigh the stratified rocks and sending veins into 
 
 [them, and by their baking and otherwise altering the rocks with 
 
 jwhicli they come in contact. We know, moreover, that while 
 
 jtlie particles of granite must have been once free to move upon 
 
 [one another in consequence of partial or complete fusion, the 
 
 [piocess of cooling must have been one of extreme slowness. 
 
 I This is shown by the fact that granite and its allies invariably 
 
 [consist of numerous crystals of different substances confusedly 
 
 [imbedded in an uncrystallized paste or matrix. Not only so, 
 
 [but, in any large granitic mass, a specimen taken from near its 
 
 icentre, where the cooling was most protracted, will be more 
 
 [coarsely and largely crystallized than one taken from the cir- 
 
 [ciiniference of the mass, where the cooling was most rapid; 
 
 [while a specimen taken from close to where the granite 
 
 jcoines into contact with the neighboring rocks will have 
 
 [cooled so rapidly that it is quite fine-grained and hardly exhil)its 
 
 [crystals at all, or only very small ones. Lastly, we know that 
 
 [the granitic rocks are rarely or never found resting upon other 
 
 [ro 'ks, as if they had overflowed them ; whereas the volcanic 
 
 [r(jcks are constantly found in this position. For this reason, 
 
 jtliough granites often pierce other formations, the granitic 
 
56 
 
 GEOLOGY. 
 
 rocks have been not unaptly termed the " underljing rocks," 
 while the volcanic rocks are termed the " overlying rocks." 
 
 The chief positive facts, then, that we know about the 
 granitic rocks, are these : 1. Granitic rocks underlie other 
 formations, and, though they pierce them, they do not overflow 
 them. 2. The materials of the granitic rocks have certainly 
 been fused or semi-fused. Besides the proofs already men- 
 tioned, this fact is further shown by the occurrence in the crys- 
 tals of granite of microscopically small cavities filled with gas 
 or half filled with water. This last fact shows that, though 
 granite has been fused, the temperature at the time of fusion 
 could not have been very high, or else the fusion took place 
 under enormous pressure; for it shows that the melted 
 granite must have been permeated by steam. 3. Granitic 
 rocks must have cooled with exceeding slowness, as their 
 component crystals are often of very large size. 
 
 From these and similar facts the following general con- 
 clusions appear to be deducible : 
 
 Firstly. All granitic rocks have not had a similar origin, 
 but there are probably two classes of granites, of which one 
 has been formed mainly by igneous action, while the other 
 has been produced by an alteration of previously-existing 
 rocks, so that it would more properly come under the head of 
 metamorphic rocks. 
 
 Secondly. The granitic rocks of either class have been 
 formed by the agency of heat acting under great pressure, 
 and probably in conjunction with watery vapor or steam. 
 The granitic rocks, therefore, have their origin at great depth 
 below the surface of the earth ; hence their character of being 
 *' underlying rocks." 
 
 IV. Metamorphic Rocks. — The metamorphic, or strati- 
 fied crystalline rocks, or crystalline schists, as they are some- 
 times called, include a number of rocks, of whicn the best 
 known are gneiss, mica-schist, roofing-slate, and statuary mar- 
 ble. All these show certain points of affinity to the granitic 
 rocks ; and there are strong reasons for believing many of the 
 granitic rocks owe their origin to a further continuance of the 
 same process as that by which the metamorphic rocks are pro- 
 duced. 
 
 The metamorphic rocks agree with the granitic rocks in 
 possessing a more or less completely developed crystalline 
 texture. This is shown most markedly in such metamorphic 
 rocks as gneiss and mica-schist, less so in statuary marble, 
 and not at all, or only in a modified form, in rooling-slate, 
 
METAMORPHIC ROCKS. 
 
 57 
 
 ss, as their 
 
 which last, indeed, can only occasionally be properly classed 
 witli this group. On the other hand, the metamorphic rocks 
 differ from the granitic rocks in always exhibiting a more or 
 less distinctly stratified arrangement. This is not so much 
 seen in the capability of being split into separate laminae, a 
 capability which may be present or may not, and which may 
 or may not be coincident with the original stratification ; but 
 it is seen rather in the fact that they are divided into beds 
 which correspond in form and arrangement to the different 
 beds of the ordinary sedimentary formations. Thus, gneiss, 
 quartzites, mica-schist, roofing-slate, and statuary marble, may 
 and do alternate with one another in regular beds, just as sand- 
 stones, clays, and limestones, succeed one another in the un- 
 altered aqueous rocks. There is every reason, therefore, in 
 speaking of the metamorphic rocks as stratified rocks. The 
 metamorphic rocks, however, differ from the ordinary aqueous 
 rocks, not only in their crystalline texture, but also in con- 
 taining few or no fossils, and in rarely splitting along the 
 original layers or laminae of deposition. Further, it very gen- 
 erally happens that the action which forms metamorphic rocks 
 develops in the rock new minerals which are not to be found 
 in the original rocks of which metamorphic strata are merely 
 an altered form. 
 
 This leads us to speak of the origin of the metamorphic 
 rocks. As implied by the name " metamorphic " (Gr. meta^ in- 
 dicating change; morphe^ form), it is believed that this group 
 of rocks owes its origin to the alteration and metamorphosis 
 of ordinary aqueous rocks. Metamorphic rocks are not produced 
 as such in the first place, but they become so at some period 
 subsequent to their original deposition. It is believed, name- 
 ly, that metamorphic rocks arc ; roduced by the long-continued 
 action of subterranean heat, probably in conjunction with 
 moisture, upon ordinary stratified formations, at some period 
 jiosterior to their deposition. In all probability this meta- 
 morphic action has taken place at great depths beneath the 
 surface of the earth and under an enormous pressure of super- 
 incumbent rock ; and its result has been to give a totally new 
 texture, often with a different structure and sometimes with a 
 different mineral composition, to the strata thus affected. 
 
 It follows from this theory of their origm, that metamor- 
 phic rocks need not necessarily be of any particular age. A7}y 
 rock of any age may be converted into a metamorphic rock, 
 if only subjected to the necessary conditions ; and, as a matter 
 of fact, it is now known that metamorphic rocks occur which 
 
63 
 
 GEOLOGY. 
 
 \'i 
 
 m 
 
 ;h 
 
 are referable to all the great geological periods. In the same 
 way and for the same reason, it is known now that granites 
 are of all ages. It was formerly believed that the granitic 
 rocks had been formed at the earliest period of the eartii's 
 history, that they were anterior to tlie formation of all the 
 sedimentary rocks, and that no granites had been produced 
 after the deposition of the aqueous rocks had once commenced. 
 On the contrary, we now know that granitic rocks have been 
 formed in all the great epochs of the earth's history ; and this 
 renders still more probable the view that most granitic rocks 
 are only a further stage of the metamorphio rocks, and that 
 both owe their origin to the same agency. 
 
 The only action which we see at the present day at all com- 
 parable to what we believe has occurred in the metfimorphic 
 rocks, is the group of phenomena which we can observe where 
 masses of melted rock have come into contact with other rocks 
 belonging to the stratified or aqueous series. In this case, 
 we find the igneous and once molten mass surrounded by a 
 broader or narrower zone of altered rock, metmnorphosed by 
 the heat of its intrusive neighbor. Thus, chalk or limestone 
 near its junction with a mass of trap may be converted into 
 hard white statuary marble, slate may be changed into mica- 
 schist, and sandstones may become quartzites. There is reason 
 to suppose that the metamorphic rocks have been produced in 
 a manner analogous to this ; but in their case it is certain that 
 the action must have been produced by some cause very much 
 more general in its operation, and probably at great depths 
 below the surface, since whole mountain-masses have been 
 aflFected in this way over areas of many hundreds of square 
 miles. 
 
 It is quite clear that the granitic and metamorphic rocks 
 have much in common ; and it is often convenient to speak of 
 the two by some common name. Formerly it was supposed 
 that all the granitic and metamorphic rocks had been first 
 produced, and that then the aqueous and volcanic rocks had 
 been formed ; and upon this view the name of " Primitive 
 Rocks" was applied to the two former classes. Now, we 
 know that all the four classes of rocks have been produced in 
 successive portions and at successive periods. They have all 
 been produced contemporaneously, and may even now be in 
 process of formation on a large scale. The name of " Primi- 
 tive Rocks " must therefore be abandoned ; and the best sub- 
 stitute is the term " Hypogene Rocks," or nether-formed rocks 
 (Gr. hupo^ below ; gennao^ I produce). This term was sug- 
 
 -i)| 
 
 I!: „y:i!f 
 
METAMORPHIC ROCKS. 
 
 69 
 
 frested by Sir Charles Lyell upon the certainty that noiie of 
 the granitic and metamorpliic rocks had assumed their present 
 form and structure at the surface of the earth. They are not 
 bv any means necessarily the lowest rocks, or the oldest in 
 point of time ; but, in any given area in which they occur, 
 they are always, without exception, below all the rocks with 
 which they come in contact. They are always " underlying 
 rocks." They never repose upon any of the volcanic or un- 
 altered fossiliferous rocks ; and are, therefore, always under all 
 the other rocks of any particular region in which they occur. 
 For these reasons, the name of "Hypogene Rocks" may 
 sometimes be advantageously employed as a common term 
 to designate the metamorpliic and granitic rocks. 
 
CHAPTER Vn. 
 
 AQUEOUS BOCKS. 
 
 It is now necessary to speak of each of the four great 
 classes of rocks in greater detail, commencing with the aque- 
 ous rocks. The aqueous or sedimentary rocks may be prima- 
 rily divided into the two great groups of the mechanically- 
 formed rocks, and the chemically-formed rocks, the latter 
 including all those rocks w^hich owe their origin to the action 
 of living beings. 
 
 I. Mechanically-formed Rocks. — These are all those 
 aqueous rocks of which we can attain proof that their parti- 
 cles have been mechanically transported to their present 
 situation. Thus, if we take a piece of " conglomerate " or 
 pudding-stone, we find it to be composed of a number of 
 rounded pebbles imbedded in a fine paste or matrix. These 
 pebbles have been manifestly subjected to much mechanical 
 attrition or rubbing down, and they must have been carried a 
 long way, and much tossed about, before they were finally 
 deposited where we now see them. In the case of a sand- 
 stone the component grains of sand are equally the result of 
 mechanical attrition, and have been equally transported from 
 a distance. In the conglomerate we can often point to the 
 exact place from which the pebbles have been brought; in 
 the sandstone we can rarely say whence the individual grains 
 have been derived, but their mechanical origin is still obvious. 
 In the case of still finer rocks, such as shale, the particles of 
 the rock have been so far worn down that their source is quite 
 irrecognizable ; but a microscopical examination would still 
 show us that the component grains were all rounded and 
 water-worn. 
 
 Mechanically-formed rocks, then, are such as can be proved 
 to have been derived from (he wear and tear of other pre- 
 
AQUEOUS ROCKS. 
 
 61 
 
 existent rocks ; hence they are often spoken of as Derivative 
 rocks. Every bed, therefore, of every mechanic«Uy-formed 
 rock is an exact equivalent for a corresponding aii<ount of 
 destruction of some older rock. Mechanicully-formed rocks 
 may be divided into the two groups of the i\jeuaceous and the 
 Argillaceous Rocks. 
 
 a. The Arenaceous (Lat. arena^ sand) or Siliceous rocks are 
 those which are mainly or entirely composed of larger or 
 smaller particles or grains of flint or silex. The chief varieties 
 of this group are sands and sandstones, grits, and conglomer- 
 ates. Sands and sandstones vary almost indefinitely in cohe- 
 rence, colors, and grain, but they all consist of grains of flint 
 or silica, of ditFerent sizes. The hardest sandstone, when first 
 depjsitcd, was as incoherent as the sand of the sea-shore. 
 Tlio conversion of sand into sandstone may be effected by 
 pressure alone ; more usually, however, the grains of sand- 
 stone are made to cohere by the percolation, through the 
 wliole mass, of water holding in solution some substance 
 capable of acting as a cement, such as some soluble silicate, 
 carbonate of lime, or, very commonly, an oxide of iron. If 
 the cementing substance be some salt of iron, the sandstone 
 will be colored with various shades of yellow, red, or brown, 
 or, in rare cases, green. If the cementing material be carbon- 
 ate of lime, the sandstone becomes more or less " calcareous ; " 
 and, if there be much lime present, a rock Is produced, which 
 might, indiffbrently, be called an arenaceous limestone or a 
 calcareous sandstone. 
 
 Tlie distinction between an ordinary sandstone and grit^ 
 as it is termed, is one that is very difficult to define, though 
 every geologist knows the diff'erence in the field. As a 
 general definition, it may be said that the term grit or gritstone 
 should only be applied to the harder sandstones, which con- 
 sist almost entirely of grains of silica cemented together by 
 the most purely siliceous cement (Jukes). Often the particles 
 of a grit are imperfectly rounded or angular, but this is not 
 essential ; and, in the rock known as " millstone grit," we get 
 a sandstone which might fairly be regarded as a very fine- 
 grained conglomerate. No sandstones, however, or very few, 
 ate purely siliceous ; but they mostly contain small quantities 
 of some foreign substance. If lime be present, the sandstone 
 is calcareous ; if there are little flakes of mica in it, it becomes 
 micaceous ; and, if there be aluminous matter, we have an 
 argillaceous sandstone. 
 
 A purely siliceous rock may be recognized by the fact that 
 4 
 
63 
 
 GE0L0Q7. 
 
 .■ ill 
 
 * ti 
 
 Hi 
 
 no effervescence would be caused by the addition of a drop of any 
 mineral acid, and the rock could not be scratched with a knife. 
 
 When an arenaceous rock consists of a number of frag- 
 ments large enough to be called pebbles, imbedded in a sandy 
 base or matrix, it ceases to be a sandstone. If the included 
 fragments are all rounded and water-worn^ the rock is now a 
 conglomerate or pudding-stone. If the fragments are more 
 or less angular, it becomes what is called a breccia. Gravel 
 or shingle, again, may be said to be nothing more than a con- 
 glomerate in an unconsolidated condition. It is convenient, 
 for many reasons, to consider conglomerates and breccias 
 under the head of arenaceous rocks, but this is to a great 
 extent arbitrary. Many conglomerates and breccias certainly 
 have a sandy matrix, and are, therefore, arenaceous rocks ; but 
 many are calcareous^ their matrix being composed of carbon- 
 ate of lime. Many breccias, again, are of volcanic origin, and, 
 though they are certainly mechanically-formed rocks, they are 
 not aqueous. 
 
 It seems hardly necessary to point out that, in all conglom- 
 erates without exception, the included pebbles are foreign to 
 the rock itself, and have always been derived from some older 
 rock. In all conglomerates, therefore, the pebbles are older 
 than the matrix. The same holds good of all breccias, except 
 in the rare instances in which a rock has been locally broken 
 into fragments, and has been recemented in place by the per- 
 colation of water holding some cementing substance in solu- 
 tion. It follows from this that when fossils occur — as they 
 sometimes do — in any conglomerate or breccia, we have to 
 ascertain in what part of the mass they occur, before pronoun- 
 cing as to their age. If they occur in the pebbles, then they 
 belong to the older period in which the rocks were formed 
 from which the pebbles were derived. If, on the other hand, 
 they occur in the matrix, then they belong to the period in 
 which the conglomerate was formed. Thus, a conglomerate 
 of the age of the Old Red sandstone might contain Old Red 
 fossils in its matrix ; but, if it contained any fossils in its 
 pebbles, these would necessarily be the fossils of the older 
 Silurian period, or of some still more remote age. 
 
 Conglomerates, like sandstones, vary extremely in hardness, 
 as well as in the size of the included pebbles. Sometimes the 
 pebbles may be detached from the matrix with the slightest 
 blow ; at other times the union of the matrix and pebbles is 
 BO strong, that a fracture will cut through the pebbles as well 
 as the matrix, leaving a perfectly clean face. 
 
AQUEOUS ROCKS. 
 
 68 
 
 J now a 
 
 b. Argillaceous Rocks (Lat. argilla^ clay). — The second 
 group of the derivative aqueous rocks is that of the argilla- 
 ceous rocks, or those which contain a certain proportion of 
 clay. Perfectly pure clay is a hydrated silicate of alumina, 
 hut it can hardly be said to occur in nature. The nearest 
 approach to a pure clay is tlie " kaolin," or porcelain-clay, 
 used in the manufacture of porcelain. This is derived from 
 the decomposition of granitic rocks, but always contains some 
 impurity in the form of siliceous matter. In ordinary lan- 
 guage, any earth wliich can be kneaded with water into a 
 plastic mass, is a " clay," but all such contain more or less 
 sand. The ordinary argillaceous rocks or clays, in fact, con- 
 tain only about one-fourth part by weight of alumina, the 
 remainder being chiefly silica or sandy matter, mixed with 
 variable quantities of the oxides of iron and other impuri- 
 ties. 
 
 The chief tests in the field for argillaceous rocks are that 
 they give out an earthy odor when breathed upon ; that they 
 are readily scratched with a knife, or even with the finger- 
 nail ; and that they do not effervesce with the mineral acids, 
 or only to a limited extent and under certain circumstances. 
 
 Argillaceous rocks, as a general rule, are nothing more in 
 their origin than fine mud derived from the wearing down and 
 decomposition of rocks containing silicate of alumina ; and the 
 following are their chief varieties : 
 
 1. Ordinary clay, composed of a mixture of sand and 
 clay, colored by iron or other impurities. 
 
 2. Pipe-clay, containing less sand than the preceding, 
 white, and nearly or quite free from the oxides of iron. 
 
 3. Loam. A friable mixture of sand and clay, in which 
 the former so much predominates, that the whole ceases to be 
 capable of being kneaded into a plastic mass. 
 
 4. Marl. Clay with variable proportions of linie mixed 
 with it, and generally breaking up, when dry, into small cu- 
 bical fragments. The term " marl," however, is very loosely 
 employed, and is often applied to clays which contain no cal- 
 careous mutter. 
 
 5. Marl-slate occupies the same position to marl, that 
 shale does to clay. It is only hardened and finely*laminated 
 marl. 
 
 6. Shale. This is regularly laminated clay, more or less 
 indurated or hardened, and capable of being split into thin 
 layers along the original laminae of deposition. When it 
 contains bitumen or other oily matter, it becomes " bitumi- 
 
6i 
 
 OEOLOGT. 
 
 nous shale," and, when it has particles of coaly matter dissemi- 
 nated through it, it is said to be "carbonaceous." 
 
 7. Clay-slate or Roojing-slate. — This is a shale which has 
 been so far altered that it will no longer split along the original 
 lines of lamination, but splits along a series of planes usually 
 not coinciding with the original stratification. It is what is 
 called " cleaved," and is, in a wide sense, a " metamorphic " 
 rock. 
 
 8. Flagstone or Flag. — This is a loose term applied to 
 any rock which will split into thick slabs or flags. Arenaceous 
 rocks are often flaggy, as well as argillaceous rocks. 
 
 II. CiiEMicALLY-FORMED RocKS. — The sccoud great sec- 
 tion of aqueous rocks comprises those which have been formed 
 by chemical agencies. As many of these chemical agencies, 
 however, can only act through the medium of living beings, 
 whether animals or plants, we include under this head a 
 number of what may be called " organically-formed " rocks. 
 
 1. Calcareous Rocks. — The most important group of these 
 chemically and organically formed rocks com})rises the so- 
 called Calcareous Rocks (Lat. calx^ lime) ; so called because 
 they are made up of carbonate of lime, or contain a large pro- 
 portion of this substance. All rocks which are composed 
 almost exclusively of carbonate of lime are called limestone or 
 chalk, the former being hard and compact, the latter soft and 
 powdery. 
 
 Chalk is nearly pure carbonate of lime, and has mainly a 
 soft texture. It is to a great extent an organically-formed 
 rock, consisting almost entirely of the minute calcareous shells 
 of certain simple forms of animal life, which have been' already 
 spoken of as For ami nif era. These make up the mass of the 
 rock, and are invisible to the unassisted eye ; but along with 
 these are the remains of sea-urchins, shell-fish, corals, sponges, 
 and other marine animals. 
 
 When the calcareous rock, instead of being soft and earthy, 
 is hard and compact, it constitutes limestone^ of which there 
 are many varieties, formed in different ways. Some limestones 
 are formed almost wholly of organic remains, such as corals, 
 shells, stone-lilies, and other fossils, when the rock is truly 
 organic. When these have grown on the spot, as we find 
 them now, the rock may truly be said to be an old coral-reef. 
 In many cases, however, the rock is secondarily mechanically 
 formed ; since it is composed of fragments of shell, coral, etc., 
 mechanically transported to their present site, and then ce- 
 mented together by the percolation of water holding carbonic 
 
 Mi, 
 
AQUEOUS ROCKS. 
 
 65 
 
 acid in solution. Examples of both these kinds of limestone 
 are to be found in process of formation at the present day 
 amoii^ the coral-islands of the Pacific. 
 
 Other limestones are fresh-water in their orif^in, and are 
 formed in lakes into which run streams containing carbonate 
 of lime in solution. Water containing carbonic acid in it — 
 as rain and all streams do — is capable of taking up a certain 
 amount of carbonate of lime and retaining it in solution. 
 "NV^lien, however, the water evaporates, and the carbonic-acid 
 pus escapes, the lime, which was previously held in solution, 
 is rcdeposited in a solid form. In this way are formed those 
 pendent masses of lime which hang from the roofs of limestone 
 caverns, and are known as "stalactites." Every drop of rain- 
 water, namely, which percolates through the roof, takes up a 
 portion of lime, which it is forced to part with again, as it 
 litings suspended from the roof, and has time to evaporate. 
 Il'it succeeds in falling, it evaporates on the floor of the cave, 
 and forms there other masses of lime, which are known as 
 "stalagmites." In this way, also, are produced the well- 
 known phenomena of "petrifying" springe, some of which 
 give rise to the formation of extensive calcareous deposits. 
 As these burst forth from the interior of the earth, they hold 
 much carbonate of lime in solution ; but they deposit this in a 
 solid form, as they evaporate and give forth their carbonic 
 acid. If the resulting rock is soft and spongy, it is known as 
 " calcareous tufa ; " if hard and compact, it is called " Traver- 
 tine." This last owes its name to its occurrence upon the banks 
 of the river Tiber, where it forms precipices several hundreds 
 of feet in height, and is largely used as a building-stone. 
 
 The sea, of course, like fresh waters, contains carbonate of 
 lime, but there is no reason to suppose that limestones are 
 ever formed by the direct precipitation of carbonate of lime 
 from sea-water, as does occur in some fresh waters. In the 
 case of marine limestones, it is probable that the lime is inva- 
 riably in the first place abstracted from sea-water by the 
 agency of marine animals. 
 
 The term "marble" is applied to any limestone hard 
 enough to take a polish. Many marbles owe their beauty to 
 impregnation with mineral substances, or to the presence of 
 fossils ; and these do not differ essentially from ordinary lime- 
 stones. Other marbles, such as " statuary marble," are crys- 
 talline, like loaf-sugar, and hence they are sometimes called 
 " Saccharoid " limestones (Lat. saccharum^ sugar). These 
 are, properly, metamorphic rocks, and are devoid of fossils. 
 

 w 
 
 I 
 
 111 
 
 66 
 
 GEOLOGY. 
 
 When the limestone is composed of small, rounded grains, 
 like the roe of a fisli, it is said to be " oolitic," or to be an 
 "oolite." This structure is generally due to the deposition 
 of concentric layers of carbonate of lime round separate gniins 
 of sand, which a(!t as ind(;pendent nuclei for this action. When 
 the grains are of large size, like peas, the limestone is said to 
 be " [)isolitic " (Lat. pisum^ a pea). 
 
 When limestones contain much siliceous or flinty matter, 
 they are said to be " cherty " or " siliceous " lim(!stone8 ; but 
 very often tlie " chert " is only disseminated in scattered 
 masses in the limestone, and the whole rock is not siliceous. 
 
 If much aluminous matter is present, the rock becomes an 
 " argillaceous " limestone ; and if alumina and silica are pres- 
 ent in such proportions that the rock forms a mortar, which 
 will consolidate or " set " under water, then the limestone is 
 said to be " hydraulic." 
 
 The most important variety of limestone is dolomite or 
 mag^ieaian limestone^ which owes its characters to the pres- 
 ence of a certain amount of carbonate of magnesia intermixed 
 with the ordinary carbonate of lime. The presence of mag- 
 nesia is indicated by a peculiar sandy feel, and gritty texture, 
 accompanied, in the more genuine dolomites, by a character- 
 istic, pearly lustre. Further, magnesian limestone does not 
 effervesce with acids as readily and violently as ordinary lime- 
 stone; while its color is generally, though by no means inva- 
 riably, some shade of yellow or brown. Magnes<ian limestone 
 varies much in character, being sometimes soft and earthy, 
 sometimes hard and compact, sometimes splitting into thin 
 layers, and sometimes booking as if composed of a number of 
 rounded " concretions," which may be as small as grapes, or 
 as large as cannon-balls. In its origin, also, it varies. Some- 
 times the rock contained magnesia at the time of its deposition, 
 and was, therefore, a magnesian limestone from the beginning. 
 In other cases there is direct proof that the rock, when first 
 deposited, was an ordinary limestone not containing magnesia, 
 and that this substance was introduced into the rock at some 
 later period. How the original limestone became " dolomi- 
 tized," as it is often called, is not altogether certain. 
 
 In the fields limestone may usually be recognized by its 
 peculiar mode of weathering, owing to the solvent action of 
 water upon it, its surface being generally more or less worn 
 into irregular hollows and cavities. It may also be known by 
 the appearance and texture of its fractured surface, and by its 
 being generally divided into pretty regular and even blocks 
 
AQUEOUS ROCKS. 
 
 67 
 
 bj regular lines of division or " joints." In anv doubtful caso, 
 however, the addition of any strong acid, as nitric or muriatic 
 acid, will decide the point. If ciirbonate of lime be present, 
 there will be effervescence from the liberation of free carbonic- 
 acid gas ; and the more calcareous the rock may be, the nioro 
 rapid and violent will be the effervescence. Chalk, as being 
 nearly pure carbonate of lime, effervesces most Wolently, and 
 may be nearly altogether dissolved ; but magnesian limestone 
 effervesces only slowly and feebly. 
 
 2. Gypsum. — Gypsum is a hydrated sulphate of lime ; that 
 is to say, it is composed of sulphuric acid in combination with 
 lime and two atoms of water. It occurs as a rock in various 
 forms, but it is not found very commonly in large masses. 
 Generally it appears as a soft, yellowish-white or white rock, 
 somewhat of the texture of loaf-sugar, but often more coarsely 
 crystallized, or fibrous. It generally occurs in pretty regular 
 bods, sometimes of considerable thickness; but it is often 
 found in irregular masses or cakes, or in the form of veins and 
 strings disseminated through other rocks. Not uncommonly, 
 marls and clays are impregnated with gypsum, and are then 
 said to be "gypseous." Alabaster is a granular and compact 
 variety of gypsum, which is used in sculpture, but is not of 
 common occurrence. Gypsum may be distinguished in the 
 field from all forms of carbonate of lime by remaining unaf- 
 fected by the mineral acids. 
 
 Rock-salt. — This, like gypsum, is by no means generally 
 distributed. It mostly occurs in the form of irregular cakes, 
 which may be fifty or sixty feet thick in the middle, but which 
 rapidly diminish in thickness, or " thin out," in every direc- 
 tion, as the circumference of the mass is approached. The 
 salt may be quite pure, or may be more or less contaminated 
 by various earthy impurities. In a great many cases, beds of 
 rock-salt are found to be associated with red, green, or varie- 
 gated marls, or with masses of gypsum ; but the origin of 
 rock-salt will be alluded to in speaking of the New Red 
 Sandstone. 
 
 Coal. — This is tlie last of the orffanicallv-formed rocks 
 which requires mention, but its origin and leading characters 
 will be treated of at length in speaking of the Carboniferous 
 Rocks. Whether in the form of ordinary bituminous coal, an- 
 tliracite, or lignite, coal is formed out of vegetable matter. In 
 all cases, therefore, coal approximates more or less closely in 
 chemical composition to wood. It consists, namely, of from 
 seventy to eighty per cent, of pure carbon, with varying quan- 
 
68 
 
 GEOLOGY. 
 
 1 -Si 
 
 titles of oxygon and hydrogen, and a small quantity of earthy 
 or mineral matter, this last constituting the ash of coal when 
 burnt. All coals occur in the form of beds in other stratified 
 rocks, and there are innumerable gradations from pure coal, in- 
 to earthy coal, and carbonaceous shale, till ultimately ordinary 
 shale is reached. It follows from this that coal is not a nii/i- 
 eralj with a definite form and a definite chemical composi- 
 tion, but it is a rock, and as such is liable to an extensive 
 series of variations in composition without losing its title to 
 be called coal. 
 
 Gradations between toe Groups of Aqueous Rocks. 
 — The division of the Aqueous Rocks into the three great 
 groui)s of the Arenaceous, the Argillaceous, and the Calcareous 
 Rocks, is a very convenient one in practice. It is to be borne 
 in iuind, however, that in Nature iio hard and fast line can be 
 drawn between the great groups of Aqueous Rocks ; but that 
 they may, and commonly do, pass into one another by a number 
 of insensible gradations. Thus, purely siliceous sandstones 
 are exceptional, b'-.o more or less argillaceous or calcareous 
 matter is usually present, till ultimately we get an argil- 
 laceous or calcareous sandstone. Few limestones are without 
 some admixture of aluminous matter or clay; and the im- 
 purity may be so marked a feature that we are compelled to 
 call the rock an argillaceous limestone. Or, again, a limestone 
 may have so much sand mixed with it as to become " sili- 
 ceous." In the same w'ay, shales may be so impregnated with 
 quartzose matter, that they become " sandy shales," or " shaly 
 sandstones," just as we may choose to call them. Or, there 
 may be so much lime present, that the rock will effervesce 
 with acids, and becomes a " calcareous shale." 
 
 Again, no rigid line can be drawn between the chemically- 
 and the mechanically-formed rocks in practice. Most lime- 
 stones are primarily of the nature of chemically- or organically- 
 formed rocks, but they are often secondarily mechanically- 
 formed rocks; or, at any rate, they have undergone such 
 changes since their deposition that their exact origin cannot 
 be determined. 
 
 I' ■■ r 
 
 I ,-i{f 
 
CHAPTER VIIT. 
 
 VOLCANIC ROCKS. 
 
 s^ithoiit 
 he im- 
 lled to 
 cstone 
 "sili- 
 with 
 shaly 
 tlicre 
 vesce 
 
 Under the head of " Volcanic Rocks " are included not 
 only the rocks produced by modern volcanoes, but also those 
 ■which we have reason to suppose have been formed by vol- 
 canoes now no longer in existence. The jyeneral mode of the 
 occurrence of the Volcanic Rocks is threefold. They occur, in 
 the first place, in the form of solid masses surmounting or 
 penetrating- other formations, generally of no very grca^ hori- 
 zontal extent, but showing evident marks that they have, at 
 some former period, been melted or fused. Tn th.» rase of 
 modern volcanoes these masses constitute the "la\a,s," but in 
 the case of the older rocks, where no cone of eru|)tion is now 
 to be found, they constitute beds of different kinds of "trap." 
 In either case they are devoid of stratification, and destitute 
 of fossils. They mostly form tabular masses, the edges of 
 which constitute abrupt escarpments, or cliflFs ; and it is from 
 this peculiarity that the older examples are known as " traps," 
 from the Swedish word " trappa," a flight of stairs, trap-hills 
 generally exhibiting a stair-like terraced appearance. 
 
 Secondly, the fused materials, though precisely the same 
 as the preceding, instead of forming tabular masses or nearly 
 horizontal sheets, have been forced into fissures which have a 
 more or less nearly vertical direction. Th(\v then intersect 
 other formations as wall-like masses, and tlioy are known as 
 "dikes" (Fig. 16). 
 
 Thirdly, in addition to these two kinds of originally melted 
 rook, M-e liave another group of volcanic and trappean rocks, 
 which is purely mechanical in its origin. Tli«» rocks of this 
 group are produced by the showering forih from the volcanic 
 vent of clouds of impalpable ashes with larger or srraUer frag- 
 ments of stone ; the whole derived from the melted lava tilling 
 
 Wt% 
 
 ■- r s 
 
 1 <r 
 
 
 ^I'.L 
 
10 
 
 GEOLOGY. 
 
 the crater, by its forcible disintegration an(] dispersal in con- 
 sequence of the explosive escape through it of expansive pises. 
 The materials produced in this way are often ejected in 
 enormous quantities, and they mostly fall in the immediate 
 
 
 
 Fio. 16.- 
 
 -Dike In a valley near Brazen TTo.ifl. Madeira. (From a drawing by Captain Basil 
 
 Hull, i:. ^.) 
 
 neij^hboihood of the volcanic orifice, constitutinp;- a series of 
 beds of greater or less thickness. If the volcano is submarine 
 or near the sea, the ashes and scoria? thus emitted usually be- 
 come regularly stratified, and they may contain fossils. If 
 they fall on land, they will exliibit a rough and irregular strat- 
 ification, but not nearly in so perfect a manner as if they had 
 been arrang(;d and assorted by water. As produced by exist- 
 ing or extinct volcanoes, these mechanical acctmipaniments of 
 an eruption a. e spoken of as volcanic ashes, tuffs, and scorice. 
 As produc(3d by the ancient and no longer visible volcanoes 
 from which the traps proceeded, they are spoken of as fel- 
 spathic ashes, trappean ashes, trap-tuffs, and trappean brec- 
 cias. In both cases their nature is essentially the same. 
 
 As the mechanically-formed ashes, tuffs, and breccias, are 
 produced by the forcible breaking up and disintegration of the 
 melted lavas and traps, it follows that the two sets of rocks 
 are identical in chemical composition ; since they are, in fact, 
 nothing more than diflerent physical states of the same rock. 
 In making, therefore, the brief remarks v'hich follow, on the 
 mineral composition of the volcanic and trappean rocks, no 
 distinction need be drawn between these groups. 
 
 All volcanic and trappean rocks may be looked upon ns 
 essentially composed of two great families of minerals, /f/.«/)^r 
 and hornblende^ each of tb "386 names being used in a general 
 
VOLCANIC ROCKS. 
 
 U 
 
 sense to cover a great variety of different species of minerals. 
 All the volcanic and traj jcan rocks are produced by the inter- 
 mixture of different members of the felspathic and hornblendic 
 groups of minerals in different proportions. An enormous 
 variety of rocks is thus produced, most of them known by 
 special names, and only to be accurately determined by an 
 elaborate chemical analysis. For our present purpose, however, 
 it will be quite sufficient to understand the general composi- 
 tion of the felspathic and hornblendic groups of minerals, and 
 the characters of the more important rocks which are formed 
 by their intermixture. 
 
 All the fels/HU'S may be regarded as essentially silicates of 
 alumina, combined with the silicate of some alkali, such a3 
 potash, soda, or lime ; so that they may be looked upon 
 as a kind oi glass. The leading varieties of felspar are distin- 
 guifc ed by the predominant alkali which they contain, as 
 potash-felspar, soda-felspar, etc. 
 
 The chief varieties of felspar arc : 
 
 1. Orthoclase, common felspar, or potash-felspar ; a silicate of alumina 
 8', 1 potash. 
 
 2. Alhite or sodafehpnr ; a silicate of alumina aiul soda. 
 
 3. Oligodasc ; a silicate of alumina and soda, but of different propor- 
 tions to albite. 
 
 4. LthraJoritc, Labrador-felspar, or limr-fclspar ; a oompou.nd of silicate 
 of alumina, silicate of lime, and silicate of soda; distinguished by its cleavage 
 and iridescence. 
 
 5. Annrthile ; very similar to Labradorite, but having part of the lime 
 replaced by potash, soda, or magnesia. 
 
 The Hon^hlendic groups of minerals are essentiall}'' sili- 
 cates of magnesia mixed with silicates of lime, iron, or man- 
 ganeso. The two most important minerals are hornblende 
 and augite, which are probably only different states of the 
 same mineral. They differ from one another in crystalline 
 form, and in their " cleavage ;" that is, the crystals differ in 
 the direction in which they can be cleaved qv broken by a blow 
 from a hammer or chisel. As ordinarily seen in igneous rocks, 
 both hornblende and augite appear as grains, crystals, or 
 masses of different shades of olive-green, often so dark as to be 
 nearly black. Unless occurring in moderately large crystals, 
 it is a matter of great difficulty to distinguish hornblende from 
 augite, except by a careful chemical analysis. 
 
 In spite of the above-mentioned differences, there is reason to believe 
 that hornblende and augite are merely different forms of the sam(> mineral, 
 the former being produced by very slow, and the latter by rapid cooling. 
 The grounds of this belief are as iollow.s : 
 
 mm 
 
72 
 
 GEOLOGY. 
 
 J 
 
 ! .fill! 
 
 
 a. ITomblende and augite do not differ much in chemical composition. 
 
 6. The two miueralH are rarely associated together in the same rock, 
 
 c. Crystals are found which have the external form of augite with the 
 cUavage of hornblende. 
 
 (/. When found together, the hornblende occurs in the mass of the rock ; 
 while the augite ia only found in the form of crystals lining cavities, where 
 the rate of cooling may have been very rapid. 
 
 e. When hornblende is artificially melted in a furnace, it invariably takes 
 upon cooling the crystalline form of augite. 
 
 All volcanic and trappean rocks may, then, be regarded 
 as variable mixtures of the felspathic and the hornblendic 
 minerals. Of the many varieties produced in this way, it is 
 essential to know the names of some of the more important ; 
 and it will greatly conduce to clearness of ideas on this sub- 
 ject if we hold in remembrance the distinction form(^rly laid 
 down as to the two great groups of igneous products. Whether 
 we are dealing, namely, with the products of modern volca- 
 noes, or with the more ancient traps, we have to consider two 
 sets of rocks : 1. The melted rocks which are ejected from vol- 
 canic orifices as currents, and which subsequently solidify into 
 horizontal sheets, or tabular masses, or vertical dikes ; and 
 2. The mechanical accompaniments of every eruption, in the 
 form of ashes, scoria?, and breccias. 
 
 Holding this distinction in remembrance, the volcanic and 
 trappean rocks fall naturally into two sections each, according 
 as they exhibit a predominance of felspathic or hornblendic 
 minerals. Applj-ing the term " lava " as a general designation 
 to the molten matter which flows in currents from a modern 
 volcano, the felspathic lavas are those which exhibit a predom- 
 inance of felspathic minerals, sometimes to the total exclu- 
 sion of hornblendic matter. They are often called trachytes 
 (Gr. trachus, rough), from their rough and gritty feel to the 
 touch. The color of trachyte varies, but it is mostly some 
 shade of blue ; and it is usually porous or cellular. When 
 distinct crystals of felspar or any other mineral are present, 
 disseminated in a general felspathic paste, it is said to be 
 " porphyn'tic ;" and, when the rock is vitreous or glassy in 
 texture, from rapid cooling, it forms what is called " obsidian," 
 or " volcanic glass." The second group of hivas is that of the 
 auf/f'tic lavas or dolerites. consisting of some felspar (generally 
 lime-felspar), intermixed with augite, and with small quanti- 
 ties of less important ingnHlients. Tlie most important mem- 
 ber of this group is " basalt," a compact, apparently homoge- 
 neoijs, black, or nearly black rock, with a tlull fracture, and 
 sometimes with scattered crystals in it. 
 
VOLCANIC ROCKS. 
 
 73 
 
 Tlie mechanical accompaniments of modern lavas are : 
 
 1. Volcanic tuff or ash^ consisting of ashes or powder 
 mixod with small fragments of lava projected from a volcanic 
 oiilice during an eruption. It varies from the finest and most 
 impalpable powder up to a coarse breccia containing angular 
 or partially-rounded fragments of lava of all possible sizes. 
 
 2. ScorlcG, produced by the action of gases upon basaltic 
 or doleritic lavas, and hav ing very much the appearance of 
 cinders of a reddish-brown or black color. 
 
 3. Ptunicey a light, spongy substance, produced by the 
 action of gases upon felspathic or trachytic lavas, and perhaps 
 upon other I'lvas as well. 
 
 The trappean rocks, like the preceding, admit of division 
 into two primary sections, the felspathic traps or felstones, 
 and the hornblendic traps, greenstones, or diorites. ITie fel- 
 stones are characterized by the predominance of felspar, and 
 aro the most highly siliceous, and consequently the most in- 
 tractable and infusible of all the traps. No general description 
 can be given of the numerous varieties of felstone. The horn- 
 i)londic traps, or diorites, are those which consist of a mixture 
 of hornblende and felspar. They vary much in appearance 
 and texture, l)eing sometimes fine-gniined and granular, sotne- 
 tiines coarsely crystalline. The most important varieties are 
 greenstone, melaphyre, and basalt, this last being just as often 
 a trap as a volcanic rock. 
 
 The mechanical accompaniments of the trappean rocks are : 
 
 1. Felspathic (zshesy corresponding to the ashes of modern 
 volcanoes, and like them varying in texture from the finest 
 grain up to the coarsest breccia. As most of the trappean 
 eruptions were probably submarine, many felspathic ashes are 
 regularly bedded and laminated. 
 
 2. Grreenstone ashes and breccias^ differing from the pre- 
 ceding, in accompanying flows of the hornblendic traps, and 
 in containing, therefore, more hornblende. This gives them 
 a (lijrker tinge, but they are extremely variable both in color 
 and texture. 
 
 Though it is convenient to divide the volcanic and trap- 
 pean rocks into the preceding great sections, it must not be 
 forgotten that in nature there are many gradations between 
 tlie f(!lspathic and hornblendic lavas and traps. It is a very 
 useful distinction whereby to give a general classification of 
 any trap or lava we may happen to have to deal with ; but it 
 is ofttMi difficult or impossible to make out in the field whether 
 a given lava or trap belongs to the felspathic or to the horn- 
 blendic group. 
 
 Phi 
 
 
 I T, It 
 
 h' 
 
 4- ^' 
 
u 
 
 GEOLOGY. 
 
 I 
 
 h 
 
 ■ 1! 
 
 There still remain two terms which it is essential to com- 
 prehond, as they are applied in a f^enenil sense to any igneous 
 rock which possesses tlie necessary characters, whether it be 
 volcanic; or trappean : 
 
 1. Wiienever any lava or trap consists of a compact, earthy 
 base, in which are scattered distinct crystals of any mineral 
 (such, for instance, as felspar or hornblende), the rock is said 
 to be " jOor/?^y/•^7^c." In common language, the rock, in these 
 cases, is often spoken of as a " porjihyry ;" but this had better 
 be avoided. The name porphyry has been employed to desig- 
 nate more than one special rock ; and it prevents confusion, 
 therefore, if, instead of saying that a rock is a porphyry, we 
 speak of it as a porphyritic felstone, or greenstone, or what- 
 ever it may be. 
 
 2. Any lava or trap may become an " amygdaloid," or be 
 amygdaloidal. This term comprises all those igneous rocks 
 in which we now find round or almond-shaped nodules of any 
 mineral, such as calcspar or quartz, disseminated through a 
 matrix of ordinary lava or trap. The origin of this structure 
 is readily comprehended- As the molten rock is being forced 
 up the interior of a volcano, it becomes impregnated with va- 
 rious elastic gases. The expansion of these causes the forma- 
 tion of numerous bubbles or cells in the melted mass, just as 
 can be seen any day in the slag of a furnace. As the lava 
 flows along, the cells or cavities thus produced become drawn 
 out or lengthened in the direction of the current, so as to often 
 assume the shape of an almond ; hence the name " amygda- 
 loid" (Lat. amygdala^ an almond). In most modern lavas, 
 and in some traps, these cavities or cells remain empty, and 
 are seen to be lined by a vitreous glaze or varnish ; and the 
 whole rock becomes cellular. In some lavas, however, and in 
 many traps, the rock has, at some later period subsequent to its 
 cooling, been subjected to the percolation of water holding in 
 solution certain mineral substances, of which carbonate of lime 
 and silica or flint are the . omnionest. These dissolved mate- 
 rials are gradually precipitated from the water and deposited 
 in the cells of the rock ; till finally, in place of the original 
 empty cavity, yo\j get a nodule of some mineral, such as calc- 
 spar, agate, or chalcedony. Sometimes, however, the cell has 
 been partially filled with one mineral, and partially with 
 another, and very generally some of the cells of an amygda- 
 loid will contain one mineral, and other cells will be filled 
 with a different mineral. 
 
CHAPTER IX. 
 
 PLUTONIC ROCKS. 
 
 We have next to consider the composition of the crj'stal- 
 line plutonic rocks, which, as already said, are believed to 
 have been formed by igneous or hydro-iij^neous action at great 
 depths below the surface of the earth, and under enormous 
 pr(>ssure. Tlie most important plutonic rock is granite, but 
 tlicre are some others of which it is necessary to know the 
 characters and composition. 
 
 I. Granite is a crystalline rock, in which the crystallization 
 is confused ; that is to say, there is rarely any regular ar- 
 rangement of the crystals, but they are confusedly scattered 
 in every direction through an un crystallized matrix. When, 
 as sometimes happens, one of the materials of the granite has 
 crystallized in large crystals, more conspicuous than any of 
 the rest, the granite is said to be " porphyritic." Granite is 
 ordinarily composed of three minerals — quartz, felspar, and 
 mica — the proportions of which v.ary in different granites, and 
 often in different parts of the same granitic mass. 
 
 The quartz is usually one of the most abundant of the ele- 
 ments of granite, but it does not generally occur in distinct 
 crystals, and it may be present in only small quantity. Being 
 merely silica or flint, the quartz may be picked out by its ap- 
 pearance, and by its not being capable of being scratched with 
 the point of a knife. As a general rule, the quartz forms a 
 glassy mass in which the other elements of the granite have 
 confusedly crystallized. 
 
 li^\\e felspar is generally present in more than one of its 
 forms, and it is the most conspicuous crystalline element of 
 the granite. Ordinarily, only part of the felspar has orystal- 
 lizi'd, and the remainder is either amorphous, or has crystal- 
 lized in very small crystals. Tlie commonest felspar of gran- 
 
 *<! 
 
 K% 
 
U •'. 
 
 76 
 
 GEOLOGY. 
 
 i M 
 
 ^ i 
 
 itc is potash-felspar or ortlioclase, and one of its commonest 
 colors is pink or flesh-colored. 
 
 The mica is usually i)resent in the form of small, f^listcninf^ 
 Boalcs, either vvliitc or black in color, or sometnnes brown, 
 fTreen, or yellow. It more ran^ly occurs in the form of large 
 tabular plates. Mica is essentially a silicate of alumina com- 
 bined with the silicate of an alkali ; and, when this alkali is 
 potash, we get the commonest form of mica. 
 
 The most remarkable point about the crystallization of 
 granite is that the more infusible and intractable portions of 
 the mass have crystallized or consolidated last, and the most 
 fusible have const )lidated,^Vs^. In melting granite, the quartz 
 would melt last, as being the most infusible, and requiring 
 the highest temperature before it would melt. This being 
 the case, it is quite clear that in the cooling of granite the 
 quartz ought to have consolidated ^Vs^, and the more fusible 
 felspar and mica should have remained fluid for a longer 
 period. The reverse of this, however, is what has really oc- 
 curred. The felspar and mica have crystallized first, and they 
 are found now in hard, transparent, glassy quartz, which must 
 liave remained fluid to the last, as shown by its often retaining 
 accurate casts of the imbedded crystals. Sometimes, how- 
 ever, the quartz and felspar have crystallized at the same time, 
 and have mutually impressed their forms upon each other. It 
 is very difficult to explain this undoubted general fact in the 
 crystallization of granite. The most probable explanation is 
 based upon certain experiments which seem to show that 
 melted silica in cooling has the property of remaining for 
 some time in a soft, gelatinous condition, whereas this is never 
 the case with felspar. 
 
 There are, however, many grounds for believing that the 
 conditions under which granite was formed, were conditions 
 in which water played quite as important a part as heat. It 
 has, in fiict, been asserted, apparently upon insufficient grounds, 
 that granite has never been fused ; because the specific gravity 
 of its quartz agrees with that of silica precipitated from a 
 watery solution and not with that of silica which has cooled 
 after igneous fusion. The quartz of granite, also, often con- 
 tains microscopical cavities with fluid in their interior, showing 
 that water was certainly present at the time of its formation. 
 Almost all modern lavas, however, show these same cavities ; 
 so that this cannot be advanced as an argument against the 
 belief that granite has been at one time fused. This appears 
 also to be established by the crystallization of g'-anite, by the 
 
PLUTONIC ROCKS. 
 
 n 
 
 bakino^ and metamorphizinG^ cfTort which it oxercises upon the 
 other rocks with wliich it roinos in contact, and by its sen(hn<^ 
 out veins into the surroundiiif^ tbrniations. At the same time, 
 there is strong reason to believe that very many granites are 
 the result of the alteration and semi-fusion of other rocks in 
 situ, and that in many cases these rocks were primitively strat- 
 iliod rocks. Thus, granite sometimes passes insensibly into 
 gneiss, which was certainly at one time an ordinary stratified 
 rock. Some granites, therefore, may properly be considered 
 as metamorphic rocks ; but it is not certain that this explana- 
 tion will apply to all granites. 
 
 II. ISyenite is in all its geological features identical with 
 granite ; but, instead of consisting of quartz, felspar, and mica, 
 it is composed of quartz, felspar, and hornblende. When 
 extensively developed, syenite frequently loses its quartz, and 
 then passes into syenitic greenstone or felstone-porphyry. 
 
 III. Prolog ine or talcose granite is similar to granite, ex- 
 cept that it consists of quartz and felspar, with talc in place 
 of mica. The composition of talc is a silicate of magnesia. 
 
 IV. Eiirite is simply granite in which all the component 
 minerals — quartz, felspar, and mica — -are mingled together so 
 as to form a finely-granular mass, not exhibiting the coarse 
 and distinct crystallization of ordinary granite. 
 
 Passage of Granitic Rocks into Trap. — It has already 
 been mentioned that ordinary granite may pass into gneiss. 
 Similarly protogine may pass into talcose schist. These facts 
 support the view that some granites are of metamorphic ori- 
 gin, and are to be regarded as the extreme term of the meta- 
 morphic series. On the other hand, granite and all its varie- 
 ties sometimes pass by insensible gradations into ordinary 
 trap-rock. This would strongly support the view that some 
 granites are truly of igneous origin. 
 
 h(l' 
 
 1 
 
 
u I 
 
 CHAPTER X. 
 
 METAMORPniC ROCKS. 
 
 
 
 ■ 
 
 
 
 i 
 
 The true metamorphic rocks are almost always devoid of 
 orp^anic remains, and contain no distinct fragments of otlier 
 rocks, whether angular or rounded. As before remarked, tliey 
 are believed to have been produced by an alteration or meta- 
 morphism of ordinary stratified rocks, in consequence of the ac- 
 tion of heat in conjunction with moisture, under great pressure. 
 The most important metamorphic rocks are gneiss, hornblende- 
 schist, mica-schist, roofing-slate or clay-slate, quartzite, and 
 primary or metamorphic limestone. 
 
 I. Gneiss in its mineral composition agrees with granite, 
 being composed of quartz, felspar, and mica ; but these mate- 
 rials, instead of being confusedly crystallized together, are ar- 
 ranged in thin layers, along which the rock has a tendency to 
 split. As a rule, each of these layers consists of one of these 
 minerals ; and thus a layer of quartz succeeds a layer of fel- 
 spar, and this is followed by a layer of mica, and so on in in- 
 definite alternation. Tliese layers of different mineral compo- 
 sition are called " folia," and the rock is said to be foliated. 
 The origin of foliation will be subsequently considered ; in the 
 mean while it is sufficient to remark that the "folia" of the 
 rock, though of different color, texture, and mineral composi- 
 tion, are not the original laminae of deposition. It may hap- 
 pen, as a matter of accident, that the lines of foliation agree 
 with the lines of stratification or lamination ; but it is much 
 more general for the lines of foliation altogether to disregard 
 the original planes of stratification. 
 
 If hornblende replace the mica of gneiss, or be present in ad- 
 dition to the quartz felspar and mica, the rock becomes a "syc- 
 nitic gneiss." If talc take the place of mica, the rock is said to 
 be a " talcose gneiss," or sometimes a " stratified protogine." 
 
 II. Hornblende-schist differs little from " syenitic gneiss." 
 It is a foliated rock, nearly black in color, composed principally 
 
 
METAMORPUIO ROCKS. 
 
 W 
 
 of liomblonde, with a variable quantity of felspar, and some- 
 times with grains of (juartz. 
 
 III. 3Iica-schUt is another foliated rook, of very common 
 ot^currence. It consists of alternating layers or folia of mica 
 and quartz ; the mica being sometimes so abundant as to con- 
 stitute almost tlie entire rock. 
 
 W. Claif-slate or lioofing-slate is nothing more than ordi- 
 nary laminated clay or shale, which has been so far metamor- 
 j)hosed that the rock will no longer split along the original 
 lines of stratification, or does so with great difficulty ; whereas 
 it will split readily and indefinitely along a second different 
 set of planes, usually altogether discordant with the original 
 laininne of deposition. This structure is called " cleavage," 
 the rock is a cleaved rock, and the lines along which it splits 
 are known as " cleavage-planes." The nature and origin of 
 cleavage will be considered later on ; in the mean while it must 
 be remembered that all slate is not a metamorphic rock, in any 
 other sense than that cleavage is never present in a rock in 
 tlu; time of its deposition, but is always induced in it at some 
 later period, in consequence of some external agency. In this 
 general sense, slate is certainly always a metamorphic rock ; 
 but there are many more oi less perfect clay-slates in the ordi- 
 nary fossiliferous rocks ; and ^here is no positive test by which 
 such slates can be distinguished from the clay -slates which oc- 
 cur in the series of the metamorphic rocks. 
 
 V. Qiiartzite or quartz-rock is produced by the mctamor^ 
 phisni of ordinary siliceous sandstones, which have been so fiir 
 melted that the component grains of quartz have their original 
 sharpness of outline blurred, and have been fused together at 
 their edges. Excellent examples of quart zite may be found 
 in sandstones near their point of junction with trap dikes ; or 
 in tiie sandstone-slabs whicii are sometimes used as bottoms 
 for the hearths of iron-furnaces. Under no circumstances must 
 quartzlte be confounded with quartz ; the latter being a min- 
 eral which occurs under many forms, while the former is a half- 
 melted sandstone. 
 
 VI. The last metamorphic rock of any importance is pri- 
 mary litnestone or metamorphic limestone^ as it would b<^ bet- 
 ter termed. This occurs either in the form of thin foliated 
 bods, not at all unlike certain varieties of gneiss, or sometimes 
 as a massive, white, granular marble. In this latter case, the 
 rock has lost all traces of bedding and is highly crystalline. 
 When not colored by foreign substances, as it very often is, it 
 is called " statuary marble," as it is largely used in sculpture. 
 
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 CHAPTER XI. . • 
 
 DIVISIONAL PLANES OF ROCKS. 
 
 Before going on to consider the manner in which the 
 foiir great classes of rocks present themselves in the field, it 
 is necessary to study the various lines and planes along which 
 any given rock may be split, or exhibits a natural fissure. All 
 these lines and planes are spoken of in geological language as 
 the " divisional planes " of rocks ; and there are iour kinds of 
 these, the nature and origin of which it is absolutely necessary 
 to understand. 
 
 I. Planes op Deposition or Stratification. — These are 
 the original lines and planes marking the boundaries of the 
 different layers or strata of which every stratified or " bedded '* 
 rock is composed. Strictly speaking, the " planes of stratifica- 
 tion " are the planes which divide an aqueous rock into its 
 dififerent beds or strata; while the "lamina? of deposition" are 
 the lines which divide each stratum into its minor laminas or 
 layers. Strata^ varying in thickness from a few inches up to 
 several feet, are the characteristic of every sedimentary rock. 
 The laininm vary in thickness from one inch down to the thin- 
 ness of writing-paper, but they are not universally present. 
 In many cases a rock — as, for example, chalk — may exhibit 
 more or less clearly the original lines of stratification, but 
 shows none of the minor laminae of deposition ; while some- 
 times even the former may be obscure or obliterated. The 
 lines or planes which divide one lamina from another indicate 
 pauses in the work of deposition. The lower layer had time 
 to harden somewhat before the succeeding layer was depos- 
 ited ; hence the rock splits naturally along the lines between 
 the layers, since there is here less cohesion than elsewhere. 
 The lines of stratification indicate still longer pauses in the 
 work of deposition. The lower stratum had so much time 
 
DIVISIONAL TULim OF ROCKS. 
 
 81 
 
 allowed it to consolidate in, before the upper layer was depos- 
 ited, that there is a total wjint of cohesion between the two, 
 and two succeeding strata are separated by an actual break 
 of continuity. 
 
 II. Planes op Jointing. — Tlie second class of divisional 
 planes comprises a group of fissures which are known as 
 "joints," and are found in all rocks alike, whatever the nature 
 of these may be. If it were not for the presence of joint- 
 planes, the unstratified rocks, such as basalt or granite, could 
 not be quarried, since they would form undivided, intractable 
 masses of solid rock (Fig. 17). 
 
 Fio. 17.— Joints in limostonp (nftor JhIcor). Tho fhces of the Joints which coincide with tho 
 (lip are shaded; those of the joints which run ulon^; tlio strike aro UBshuded. Tho 
 nearly horizontal lines uro the lines of sti-utiiicutiou. 
 
 As a matter of fact, then, all rocks are traversed by a se- 
 ries of divisional planes or " joints," which divide the rock 
 more or less completely into a series of bloc^ks of different sizes 
 and shapes. In stratified rocks, joints are generally inclined at 
 angles more or less nearly perpendicular to the planes of strati- 
 fication or bedding; and many of them are extremely irregular 
 in direction. Often, however, there may be made out two 
 leading systv^ms of joints, of which one series coincides with 
 the direction of the inclination or " dip " of the beds, while 
 the other series runs nearly at right angles to the former. 
 When these two sets of joints are well developed, as they 
 often aie in limestones (Fig. 17), they divide the entire mass 
 of the rock into a series of rectangular blocks, the upper and 
 lower surfaces of which are formed by the planes of stratifica- 
 tion, while the sides are formed by the joints. The planes of 
 jointing are generally most close, regidar, and even, in the 
 
l! '}' 
 
 82 
 
 GEOLOGY. 
 
 finer-grained rocks, and more irregular and uneven in the 
 coarse-grained rocks. 
 
 The most common and general cause of jointing appears to be 
 the contraction of the rock in the process of consolidating. All 
 rocks, in passing from an unconsolidated to a consolidated con- 
 dition, undergo a certain amount of contraction, and it appears 
 impossible that this contraction can take place in any large mass 
 of rock without the production of numerous fissures or joints. 
 Tliat the power which produced joints acted with great force, 
 is shown by joints traversing conglomerates, which often cut 
 clean tlirough the hardest pebbles as well as the softer matrix. 
 
 In the solid igneous and plutonic rocks the joints a-e gen- 
 erally very irregular, but they are sometimes so closely set 
 and so regular as very closely to simulate bedding. There is 
 another case of regular jointing which is often seen in lavas 
 and traps, and which requires explanation. This is the co- 
 lumnar jointing of tr.aps and lavas, by which the entire mass 
 of the rock is divided into a series of columns, which have a 
 more or less perfect hexagonal outline, thus forming six-sided 
 prisms (Fig. 18). This structure is seen in its greatest perfec- 
 tion in the Giant's Causeway on the northeast coast of Ireland, 
 and in the " pillared " island of StaflFa, on the west coast of 
 Scotland. 
 
 Fio. 18.— View of the Island of Cyclops, In the Boy of Trezza, showing colunuiar lava. 
 
 m 
 
 Mill 
 
 There is one general law which holds good without excep- 
 tion in these columnar masses. The direction of the columns 
 is invariably perpendicular to the cooUnfj surfaces of the melt- 
 ed mass. Thus, if you have a mass of basalt included between 
 stratified rocks (Fig. 19, a), the direction of the columns will 
 
DIVISIONAL PLANES OP ROCKS. 
 
 83 
 
 be at right angles to the surfaces of the stratified beds, since it 
 was at these surfaces that the basalt commenced to solidify. 
 If the basalt has formed a vertical dike or wall-like mass inter- 
 secting other rocks (Fig. 19, 6), then the direction of the col- 
 umns will be horizontal, or at right angles to the sides of the 
 dike. Lastly, if the melted mass has formed u kind of pipe 
 
 Fio. 19. — a. Columnar basalt lylnp botwoen harizontal bods of nquponc rock ; ft, Colniniiiir 
 dikf, iiiterscctiuK strutiruKi rocks vertically ; <•. C'oluinnar traj) tlllinjf a \)\iw In a<iiuoii8 
 ruckH, and shown in cruss-scction. The direcUoii of thu columns ia tlictto tbruc* tigurus 
 is seen tu be at right angles to the surCiccs of cooling. 
 
 xcep- 
 umns 
 melt- 
 weon 
 will 
 
 running through other rocks (Fig. 19, c), then the direction 
 of the columns will be like the spokes of a wheel, radiating in 
 every direction from the centre to the circumference. 
 
 In most cases, the columns are of considerable length, va- 
 rying from five or six feet up to as much as one hundred or 
 one hundred and fifty feet, with a diameter of from six to 
 eighteen inches, and only internipted by an occasional cross- 
 joint. In other cases, the columns have a diameter of several 
 feet, and their outline is only rudely hexagonal ; so that the 
 columnar structure of the rock can only be perceived on a large 
 scale, and when looked at from a distance. Lastly, there are 
 cases in which the columns are divided into a number of short 
 hexagonal masses, the ends of which are occasionally deviO- 
 oped intx) ball-and-socket articulations or joints. The origin 
 of these "articulated " columns has been shown by experiments 
 made upon artificially melted basalt. If such a melted mass 
 be allowed to cool slowly^ it returns to its original stony con- 
 dition. In cooling, however, numerous points of aggregation 
 or centres of solidification appear in the mass, and the solidi- 
 fying particles arrange themselves round these, so as to form 
 a number of concentric coats round each centre, somewhat like 
 the coats of an onion. The final result of this is, that the 
 
' 
 
 111 
 
 (,; 
 
 
 I' 
 
 n 
 
 11 
 
 
 Hh 
 
 
 
 
 84 
 
 GEOLOGY. 
 
 ■whole mas3 comes to be composed of a number of Bpherical 
 balls, each of which is composed of a series of concentric 
 coats. If all the balls are of equal size, each will be touched 
 by exactly six others ; and, if all the balls tend to increase 
 equally in size at their circumferences, each will ultimately 
 be squeezed, by the pressure of the others, into an hexagonal 
 prism. This, there is every reason to believe, is what has 
 actually occurred in the case of articulated columnar basalt. 
 Indeed, the tendency to form spheroidal balls, composed of 
 many concentric coats lound a central nucleus, is observable 
 in many igneous rocks, without its ever going so far r . to 
 produce a columnar structure. It occurs in many granites 
 and perhaps in most traps, but it is rarely to be detected ex- 
 cept upon surfaces which have been long weathered. 
 
 III. Planes of Cleavage. — The structure, characters, and 
 Oiigin of cleavage-planes are of the greatest interest and im- 
 portance; and few subjects require greater practical experi- 
 ence in the field than to distinguish readily and with certainty 
 between cleavage and lamination. Cleavage-planes — like the 
 planes of foliation — are what are called " superinduced" planes 
 of division. That is to say, they are not original divisional 
 planes, connected with the mode of formation of the beds, like 
 the planes of stratification and lamination ; nor are they merely 
 resultant upon the passage of the beds from an incoherent to 
 a solid condition, like the planes of jointing. They are super- 
 induced upon the rock at some time subsequent to Us deposi- 
 tion and solidijication / and as a rule they altogether ignore 
 and disregard all the original divisional planes. As the 
 cleavage-planes are thus superinduced, it follows that they 
 occur most commonly in metamorpliic rocks, or in the older 
 stratified rocks which have been subjected to the greatest 
 changes since the time of their original deposition. Cleavage, 
 however, may, and does, occur in rocks cf all ages. 
 
 By cleavage — or, as it is sometimes called, " slatyc leavage" 
 — is understood a tendency of any rock to split into an in- 
 definite number of thin layers or plates,, which have a certain 
 definite direction over wide areas, wholly independent of the 
 original lamination or stratification of the rock. Cleavage 
 diflers from jointing in this : The mass of rock included be- 
 tween any two joints has no tendency whatever to split again 
 in a direction parallel to the planes of the joints ; whereas in 
 a cleaved rock the mass is capable of being indefinitely split 
 
 subdivided in the direction of the slaty cleavage. As a 
 
 or 
 
 rule, not only do the cleavage-planes altogether ignore the 
 
DIVISIONAL PLANES OF ROCKS. 
 
 85 
 
 original lines of lamination (Fig. 20) ; but the result of cleav- 
 age is positively to seal up tlie original planes of deposition. 
 A cleaved rock will not only split most easily in the direction 
 
 rage' 
 Ml iu- 
 ?rtaiu 
 ^f the 
 
 Fio. 20.— DiaffTftm to Illustrate cleavape. The dark Hnes indicate the beddinfr of the rook, 
 and the fine lines indicate the cleavage-planes. The latter are seen to uiaintaiii a uni> 
 form direction, while the strata ore contorted. 
 
 of the cleavage-planes, but it is impossible, or very difficult, 
 to get it to split along the original lines of lamination. The 
 original layers of deposition may, nevertheless, be usually 
 detected without much difficulty. In the case of fossiliferous 
 cleaved rocks, tliey may usually be made 
 out by the occurrence of lines of f(js- 
 sils. In the case of ordinary roofing- 
 slate, in which this test is useless, the 
 original lines of bedding or lamination 
 are marked by a number of parallel 
 stripes, some of which are lighter, and 
 others darker, than the general mass ; 
 while they differ from one another in 
 grain and texture. This constHutes 
 wliat was termed by Sedgwick the 
 "stripe" of the slate (Fig. 21). 
 
 The finer grained any rock may 
 be, the closer and more regular are 
 the planes of cleavage; the C9arser 
 the rock, the fainter, wider apart, 
 and more irregular are the cleavage- 
 planes. It follows from this that 
 cleavage is only seen in its highest 
 ])erfection in the finer argillaceous 
 rocks, such as shale ; though it occurs 
 also in sandstones and limestones, and 
 is often well developed in volcanic or 
 trappean ashes. The moment, how- 
 ever, that a shale is subjected to 
 cleavage it ceases to be a shale, and 
 becomes properly a slate. The term 
 " slate " is often loosely applied, but it ought to be restricted 
 6 
 
 Fig. 21. — Striped and faulted slata 
 from the north of Kn^land. 
 The HK'k is a cleaved volcanic 
 af>li. and the (hco tlgiired is a 
 plane of cloavaffe. The linos 
 running across it are the 
 "stripe." and are the orif^inal 
 lines of lamination. The spe- 
 cimen is traversed by three 
 parallel "fhults," by which 
 the original layers have been 
 slightly displaced. 
 
'W. 
 
 86 
 
 OEOL007. 
 
 to cleaved rocks ; though what is commercially called slate is 
 often obtained from stratified rocks which are not cleaved. 
 The best roofing-slates, however, such as the Welsh slates, 
 are cleaved rocks ; and the flat surfaces of the slate are not 
 the original layers of the rock, but are planes of cleavage, and 
 generally cut the original laminae of deposition at high angles. 
 The remaining phenomena with regard to cleavage which 
 require notice, are these : 
 
 a. The direction of the cleavage-planes is generally con- 
 stant in any given district, retaining the same general direc- 
 tion, or "strike,*' over widely-extended areas, and through 
 whole mountain-chains. 
 
 b. The cleavage-planes, as already remarked, generally dis- 
 regard the original lines of deposition. As a matter of chance, 
 the planes of cleavage may happen to coincide with the bed- 
 ding ; but, as a rule, they maintain a steady direction wholly 
 irrespective of the original stratification or of subsequent con- 
 tortions of the rocks (Fig. 20). 
 
 c. The general direction, or "strike," of the cleavage- 
 planes usually agrees more or less closely with the strike of 
 the stratified rocks of the district; but the inclination, or 
 " dip," of the cleavage-planes is altogether independent of the 
 " dip " of the beds. 
 
 d. Lastly, in all cases where the cleavage-planes are well 
 developed, they can be shown to have produced a fresh ar- 
 rangement of the minutest particles of the rock through which 
 they pass. Thus, if a fine-grained slate be carefully examined, 
 it is found that all the longer particles of the rock are lying 
 with their longer axes coinciding with the dip of the cleavage. 
 This rearrangement is shown more obviously in cases where 
 the cleaved rock contains fossils. In all such cases it in- 
 variably happens that the fossils are distorfedy being length- 
 ened or drawn out in the direction of the cleavage, and con- 
 tracted in the opposite direction, or at right angles to the 
 cleavage. 
 
 Origin op Cleavage. — 'By Prof. Sedgwick, who was the 
 first thoroughly to examine the phenomena of the slaty rocks, 
 cleavage was referred to the action of crystalline or " polar " 
 forces, acting in given directions upon large masses of a near- 
 ly homogeneous mineral nature. Recent experiments, however, 
 appear to have demonstrated that cleavage is the result of 
 great compression of the rock, exercised laterally^ or in a di- 
 rection at right angles to the direction of the cleavage-planes 
 themselves. The effect of this powerful lateral pressure is to 
 
DIVISIONAL PLANES OF ROCKS. 
 
 87 
 
 compress all the particles of the rock in a direction at right 
 angles to the cleavage-planes, and to pull them out or lengthen 
 them in the opposite direction, or in the same direction as the 
 cleavage. The result of this is, that the whole mass cleaves or 
 splits in a direction at right angles to the line in w'hich the 
 pressure is exerted. A further result of the pressure which 
 produced the cleavage is, that the cleaved rock i» condensed 
 and compressed to an amount averaging about one-half of its 
 original volume. 
 
 The correctness of this th*H)ry as to the origin of cleav- 
 age has been shown by actual experiment. Thus, Mr. Sorby 
 showed that if a mass of clay were taken and mixed confused- 
 ly with a number of scales of oxide of iron, and if the whole 
 were then reduced to half its original volume by pressure, the 
 entire mass would exhibit cleavage in the most perfect man- 
 ner, splitting with great ease in a direction at right angles to 
 the line in which the pressure had been applied. Not only so, 
 but the particles of oxide of iron were found to have arranged 
 themselves so that their longer axes universally coincided 
 with the direction of the cleavage. Subsequently, Dr. Tyn- 
 dall showed that pressure alone would produce cleavage in 
 perfectly homogeneous substances, without the presence of 
 particles having flat surfaces, such as scales of oxide of iron. 
 Pure clay or white wax thus submitted to pressure became 
 perfectly cleaved, splitting indefinitely into thin laminae in a 
 direction at right angles to the line in which the pressure had 
 been applied. There can, therefore, be no hesitation in ac- 
 cepting the theory as to the origin of cleavage in consequence 
 of lateral pressure. The cause of this lateral pressure will be 
 spoken of in considering the cause of contortions and faults. 
 
 IV. Foliation. — The last class of divisional planes of 
 rocks comprises what are known as the planes of " foliation." 
 Foliation, like cleavage, is a superinduced structure, brought 
 about upon the rock at some period subsequent to its deposi- 
 tion or solidification ; and it is only known to occur in rocks 
 which either belong to the metamorphic class, or can be 
 shown to have been locally metamorphosed by some neigh- 
 boring mass of melted rock. In many respects foliation agrees 
 with cleavage. The planes of foliation are divisional planes 
 along which the rock can be split, and which preserve a uni- 
 form direction over more or less extensive areas, wholly in- 
 dependent of the original lines of stratification or lamination. 
 In a cleaved rock, however, there is no perceptible mineral 
 distinction between one cleavage surface and another, or only 
 
88 
 
 OEOLOGT. 
 
 rarely, and then to a limited extent. In a foliated rock, on 
 the other hand, the rock is positively separated into a number 
 of thin layers or folia^ which differ from one another in min- 
 eral composition. Gneiss, for instance, is a foliated rock, and 
 it consists of a number of thin layers of quartz, felspar, and 
 mica, alternating with one another indefinitely. As regards 
 nomenclature, while a cleaved rock should always be spoken 
 of as a " slate," or a " slaty " rock, a foliated rock should al- 
 ways be termed a " schist " (Gr. achizo^ I separate). The term 
 " schist," however, is sometimes loosely applied to rocks which 
 have no foliated structure. 
 
 The planes of foliation may accidentally coincide with the 
 original lines of lamination, or bedding, but, as a rule, they 
 resemble cleavage-planes in being wholly independent of tho 
 original stratification of the rock. The planes of foliation, 
 however, in a given region very often agree in direction with 
 the cleavage-planes of other rocks in the same district. This 
 fact has led to the opinion that foliation is merely a further 
 development of the process of cleavage. This view was origi- 
 nally put forth by Sedgwick, and has been supported by 
 Darwin in his observations on the metamorphic rocks of South 
 America. It is difficult, however, to see how any amount of 
 pressure could produce a rearrangement of the mineral par- 
 ticles of the rock, such as we sec in foliation ; while there is 
 every reason to believe that cleavage is produced by pressure 
 alone. Accordingly, Sir Charles Lyell and Mr. David Forbes 
 both reject the view that there is any nec-^jssary connection 
 between foliation and cleavage ; though it cannot be said that 
 any generally applicable explanation has been advanced in 
 its stead. 
 
CHAPTER Xn. 
 
 CnABACTEBS OP AQUEOUS BOCKS IN THE FIELD. 
 
 Ha VINO now considered the four great classes of rocks as 
 regards their mineral characters, structure, and origin, weliave 
 now to consider the phenomena which they present when 
 studied in the field. It is hardly necessary to remark that the 
 aqueous rocks are from this point of view by far the most im- 
 portant, and will claim the greatest part of our attention. 
 
 Any formation or group of stratified rocks may consist of 
 a single species of rock, or of various different kinds arranged 
 in alternating beds. Thus we occasionally find a series of 
 beds, of many hundreds or even thousands of feet in thickness, 
 composed throughout of similar materials, shale, limestone, 
 conglomerate, or sandstone. More commonly, however, the 
 vertical thickness of any bed or group of beds is not so great, 
 and strata of shale, sandstone, and limestone, alternate with 
 one another with tolerable rapidity. 
 
 Lateral Metent of Beds. — Sometimes we meet with a par- 
 ticular bed of rock which. is continuous, and preserves the 
 same characters, over very considerable areas. As a rule, 
 however, if we are able to follow out any particular bed, we 
 find that it begins in time to diminish in thickness, and ulti- 
 mately ceases to exist altogether (Fig. 22). This is what is 
 called technically the " thinning out " of a bed. Each indi- 
 vidual stratum, therefore, in any group of beds may be regard- 
 ed as an unequal mass, thickest in the centre, and gradually 
 thinning out in all directions toward the circumference. What 
 occurs in the case of a single bed, holds good in the case of 
 any particular aggregation or group of beds which we may 
 choose to take. Any group of beds is continuous over a cer- 
 tain area (and the larger the group of beds is, the larger will 
 be the area over which it is likely to be spread), but, however 
 
90 
 
 OEOLOGT. 
 
 extensive this area may be, the group will be found ultimately 
 to thin out. What commonly occurs in a»iy group or set of 
 beds is this : If we follow the group for any distance, we find 
 that its characters gradually change by the thinning out of 
 particular beds and the intercalation of others of a different 
 mineral nature (Fig. 22). The ultimate result of this process 
 is, that we get a group of beds which are the geological equiva- 
 lent of the beds with which we started, but which differ alto- 
 gether in their nature. An excellent example of this is afforded 
 
 A B 
 
 V.V^*;^.'«^.V.^fJ«' •■[^ij^^^jA>*J^^t ^llmm^Ml^^ 
 '>.»NN\v>;;:»:^;^».^\st;o.Ai.'..'.i'.'iy!r«???g^Wffff^ 
 
 Fio. 22. — Diofirram to illnstrote the thinning ont of bcdB Interolly. The beds at a are tha 
 cquivoloDt of the beds at b, but tne two are wholly different in nature. 
 
 
 i|l»i 
 
 ■ 1 
 
 by the Carboniferous limestone of England, and the changes 
 which it undergoes in passing from the south northward. In 
 ths south of England the Carboniferous limestone is a great 
 mass of pure limestone, over one thousand feet in thickness, 
 and not exhibiting a single bed of sandstone or shale. As we 
 go northward, the beds of limestone thin out gradually, and 
 beds of sandstone, grit, or shale, begin to be intercalated ; till, 
 when we reach the north of England, we find the formation to 
 be composed of alternating limestones, sandstones, and shales, 
 with a few thin bands of coal, the limestones still bearing a 
 considerable proportion to the whole mass. Proceeding still 
 farther northward, the limestones go on thinning out, till, in 
 Central Scotland, the Carboniferous limestone consists essen- 
 tially of a great series of sandstones and shales, with thick and 
 workable beds of coal, while the limestones are reduced to a 
 few comparatively insignificant bands. Still, the series is the 
 geological equivalent of the great calcareous mass which rep- 
 resents this formation in Southern England 
 
 Original Horizontality op Strata. — The under and 
 upper surfaces of any given bed are always approximately 
 parallel to one another. This arises from the fact that, when 
 the bed was in process of deposition at the bottom of the sea, 
 the particles of sediment were driven by the motion of the 
 water to settle in all the hollows and depressions of the sur- 
 face, where they were least liable to be disturbed by any mov- 
 
CHARACTERS OF AQUEOUS ROCKS IN THE FIELl Ql 
 
 inf^ force. For the same reason all stratified beds have been 
 originally deposited in a hori2ontal position, or approximately 
 8o. As will be seen, however, it is rare at the present day to 
 find stratified rocks in their original horizontality. They are 
 mostly found now to be " inclined," that is to say, they have 
 been acted upon bv subterranean forces, and have been tilted 
 up, so as to be inclined to the horizon at angles varying from 
 the perpendicular to nearly absolute horizontality. 
 
 DiAQONAL OB Obliqub LAMINATION. — As a rule, the lami- 
 nae of any given stratum are parallel to the under and upper 
 surfaces of the stratum. There are cases, however, in which the 
 laminse of deposition hold a different position, oblique to the 
 general planes of Btratificatit u (Fig. 23^, and the direction of 
 the laminaB in one stratum mit/ be wholly different from their 
 direction in the contiguous beds. Tb<>sc cases ais spoken of 
 
 rep 
 
 Fio. 23.— Sootion ofblfto-bedded sand in the Kreenssnd-formation In 
 Bedfordshire, England. 
 
 as cases of " diagonal stratification," " oblique lamination," or 
 " false bedding." The phenomenon is a common one among 
 sandstones or sands, and is due to the fact that the beds were 
 deposited as shifting sand-banks by means of currents which 
 were constantly changing in direction, and probably in strength 
 as well. False bedding is chiefly of importance as being liable 
 to be mistaken for true stratification in the field. In a small 
 
•\c 
 
 02 
 
 GEOLOGT. 
 
 section it may be impossible to say whether the phines are 
 those of true or diivgoual stratification ; but, when several sec- 
 tions are compared over a considerable area, there can be lit- 
 tle difficulty in determining which of these is really the case. 
 From its mode of production, it follows that false bedding only 
 occurs in rocks which have been laid down in shallow water. 
 
 Ripple-mark. — Another common phenomenon of the de- 
 posits of shallow seas is " ripple-mark " (Fig. 25). In its ap- 
 pearance and structure this is in every respect identical with 
 the rippled appearance and structure of the rippled surface 
 which occurs upon every sandy sea-shore. It is produced 
 in all cases by the passage of moving v/ater over incoherent 
 
 
 Fio. 24. — Diagram to illustrate the formation of ripplc-mark. . 
 
 sand. The action of the water tends to pile up the sand in 
 little ridges (Fig. 24), which are constantly advancing on one 
 another, in consequence of the grains of sand being succes- 
 sively pushed up the long and gentle slope «, b — c, <7, till they 
 roll over down the short and abrupt slopes, J, c — f?, <?, where 
 they are temporarily undisturbed and protected. The preser- 
 vation of ripple-mark is due to the fact that, when the tide 
 retires, there may be sufficient time for the ripple-ridges to 
 partially consolidate, and the returning tide may not destroy 
 them, especially if they are covered with a fine film of clay. 
 On the other hand, the returning tide may bring sufficient 
 sediment to cover up and thus preserve the ripple-mark of the 
 former tide. Ripple-mark is seen in many sandstones, and is 
 often preserved in great perfection. Like diagonal stratifica- 
 tion, it implies that the beds which exhibit it were deposited 
 in shallow water. 
 
 Often accompanying ripplc-mark is a structure known by 
 the name of " desiccation cracks." This consists in the pres- 
 ence of little ridges which cross the surface of the stone in 
 every direction. These are produced in consequence of the 
 original surface of mud or sand having been exposed to the 
 heat of the sun for a sufficient length of time to allow of its 
 shrinking and cracking in various directions, just as may be 
 seen any day in a mass of mud allowed to dry. With the re- 
 turn of the tide all the cracks produced in this way are filled 
 up by the sedimeut which it brings in j and the result of this 
 
 "if:-" 
 
CnARACTERS OF AQUEOUS ROCKS IN THE FIELO. 
 
 93 
 
 is ultimately to produce in the stone a system of solid inter- 
 lacing ridges in place of a system of cracks or open fissures. 
 
 Fio. 25. — Slab of ripple-marked sandstone from the Trias of Cheshire, England. 
 
 Not uncommon also in finc^T^rainod sandstones or shales 
 are rain-prints^ the memorials of ancient showers. These 
 are produced under exactly the same conditions as ripple- 
 marks and desiccation-cracks, ;ind are preserved in the same 
 way. They are produced, namely, upon reaches of sand or 
 mud, which are uncovered by water for a sufficient length of 
 time to allow of their partial consolidation before they are 
 again submerged. They aj)pear in the rock in the form of 
 jiits or rounded depressions, each of which has been produced 
 by tlie falling of a single drop of rain. 
 
 Present Inclination of Strata. — As already remarked, 
 all stratihed rocks were originally deposited in a horizontal 
 position, but most of them in the process of elevation to their 
 present situation have been tilted, so that we find them now 
 inclined at various angles to the plane of the horizon. In 
 speaking of inclined strata there are several terras which re- 
 quire to be explained. 
 
 
04 
 
 GEOLOGY. 
 
 Fig. 26. — Diagram to illustrate the dii» of 
 Inclined strata. 
 
 When a stratum or bed of rock is not perfectly level, but 
 is inclined to one side or other, it is said to dijj (Fig. 2G). 
 
 The inclination of the bed 
 
 S N downward into the earth is 
 
 called its " dip," the amount 
 of this inclination *s called 
 the "angle of dip," and tlie 
 direction in which the bed is 
 inclined as regards the point 
 of the compass is called the 
 "point of dip," or the direc- 
 tion of the dip. Thus, in the annexed diagram (Fig. 26), the 
 strata are inclined to the horizon at an angle of forty-five de- 
 grees, and they dip toward the north ; or, in a shorter form, 
 the beds dip N. Z 45°. 
 
 As inclined strata "dip" or descend into the earth in one 
 direction, they necessarily approach the surface or "rise" in 
 the opposite direction. The place at which an inclined stratum 
 actually comes out at the surface of the earth is called its " out- 
 crop" or "basset." The line of outcrop of any given bed or 
 beds, or the line at which it w^ould appear at the surface, sup- 
 posing that surface to be level, is called the strike or " line of 
 bearing" of the bed, or simply its direction. The line of strike 
 of an inclined bed is invariably and necessarily at right angles 
 to the dip. If, therefore, a bed dips due east or west, its 
 strike will be north and south, and vice versa, if it dips north or 
 south, it will strike east and west. When we once know the 
 dip of any bed, we know at once its line of strike, and can tell 
 exactly where it ought to reappear, supposing t'i:at it is not 
 interfered with by any interruption. The reverse of this, how- 
 ever, does not hold good ; and, if we only know the strike of a 
 bed, we cannot be absolutely certain as to the dip, either as 
 regards its direction or its amount. If we know, for instance, 
 that certain beds strike east and w^est, we know that they 
 must dip at riglit angles to this ; but they may dip either to 
 the north or to tlie south, and they may be inclined to the 
 horizon at any angle. Whenever beds have no inclination, or 
 are perfectly horizontal, it also follows as a matter of course 
 that they have no strike, since they have no dip. Wlien, 
 again, beds are vertical or perpendicular, they have a strike, 
 and they are said to dip at ninety degrees ; but they do not 
 dip in any particular direction. Their strike may be in any 
 direction, but, so long as they are strictly vertical, they can- 
 not dip to any point of the compass. 
 
 *'M 
 
CHARACTERS OF AQUEOUS ROCKS IN THE FIELD. 95 
 
 In all cases of inclined beds (Fig-. 27), it follows, as a mat- 
 ter of course, that so long as we walk in the direction of the 
 dip, we must be getting constantly on to higher and higher 
 
 Fig. 27. — Inclined strata. The arrow shows the direction of the dip. 
 
 beds. When we reverse our course, and walk in the opposite 
 direction to the point of dip, we are constantly coming upon 
 lower, and therefore older, strata. 
 
 Curved Strata. — When strata are simply inclined to the 
 horizon at any angle, their dip and strike may be readily 
 made ' ut, and they may easily be mapped and followed 
 across a country. In most cases, however, in Nature, neither 
 the dip nor the strike remains constant over any considerable 
 a-.ea. This is due to the fact that most strata in the process 
 of reaching their present situation have been more or less bent 
 and curved; so that they now form portions of curved sur- 
 faces, instead of formitig straight lines and planes. 
 
 When these curves are on a sufhciently small scale to be 
 visible in a single section (Fig. 28), the beds are sirc^^y said 
 
 
 Fio. 28.— Contorted strata of Sklddaw slate in the north of England.— Length of section 
 
 alx)Ut sixty Hot. 
 
 ! 
 
 to be " contorted," or *' flexured." In these cases, though the 
 contortions may be repeated in small spaces with considerable 
 rapidity, there is generally little difficulty in making out the 
 general dip of the whole set of beds. 
 
 When the curves of the beds cease to be upon a small 
 scale, and are more extensively developed, they are no longer 
 Bpoken of as "contortions." The tAvo chief forms of these 
 major curves are of great importance, since they are of con- 
 
96 
 
 GEOLOGY. 
 
 stant occurrence ; and they are known as anticlinal and syn- 
 clinal curves. 
 
 When a group of strata is bent into a curve like a saddle, 
 with its convexity turned toward the surface of the earth, we 
 get what is called an anticlinal curve (Fig. 29). The centre* 
 
 Fig. 29. — Diagram of an anticlinal curve. 
 
 I ¥'! 
 
 of this curve is formed by an imaginary line, called the " anti- 
 clinal axis," and the beds necessarily dip in opposite direc- 
 tions on both sides of and away from this line. In any undis- 
 turbed anticlinal curv^e, therefore, there is necessarily a repeti- 
 tion of the strata forming the saddle, and the same beds are 
 found on both sides of the central line. If we commence al- 
 together outside the anticline, and walk toward its centre, at 
 first we pass from newer to older strata, and we find the beds 
 constantly dipping in the opposite direction to that in which 
 we are ourselves moving (Fig. 29). When, however, we reach 
 the centre of the curve, and cross the anticlinal axis, this state 
 of things is reverse!. We find now t/ie same strata, dipping 
 in the opposite direction to what they were before, or in the 
 same direction as that in which we are moving. Not only is 
 this the case, but the order of the strata is reversed, and we 
 are now passing constantly from older to newer strata. 
 
 When an anticlinal curve is arranged not in reference to a 
 line or axis, but to a point, we have what is called a dome- 
 shaped elevation, from the centre of which the beds would dip 
 away in every direction. In this case the strata are said to 
 have a qua-qua-versal dip. 
 
 A synclinal curve is exactly the opposite of an anticline. 
 Wlien the strata are so folded, or curved, as to form a trough, 
 the concave side of which looks upward, we have what is 
 called a synclinal curve (Fig. 30). The imaginary line which 
 forms the centre of the curve is spoken of as the " synclinal 
 axis ; " and the beds necessarily dip inward toward this line 
 upon both sides. In a synclinal curve, therefore, we have 
 a repetition of the strata on both sides of the ixis of the 
 curvC) but in a reverse manner to what occurs ia an anticline. 
 
 W.i 
 
CHARACTERS OP AQUEOUS ROCKS IN THE FIELD. 97 
 
 In the latter the strata dip away from the axis, so that the 
 oldest beds are in the centre of the curve, and the higher and 
 newer beds are removed farthest from the centre. In a sjn- 
 
 •. •.. — -- ..•• 
 
 ■•• '•.. ."• •• 
 '.,_ _^.- 
 
 Fia, 30.— Diagram of a synclinal curve. 
 
 clinal curve the strata on both sides of the axis are the same, 
 
 but dip toward the central line ; so that the lowest and oldest 
 
 strata are those farthest removed from the axis, and the 
 
 newest beds are those in the centre of the curve. In walking, 
 
 therefore, across any S3miclinal curve, 
 
 tlie beds at first dip in the direction 
 
 wo arc moving, and we find ourselves 
 
 constantly passing from older to 
 
 newer beds. When we have crossed 
 
 the central axis we have the same 
 
 bods over again, but they now dip in 
 
 the opposite direction to that in 
 
 which we are walking, and we find 
 
 ourselves constantly passing from 
 
 newer to older beds. 
 
 When the beds of a synclinal are 
 arranged in reference to a single point 
 instead of a line, we have a basin- 
 shapod depression, in which the beds 
 dip upon all sides toward the centre. 
 In other words, the beds have a qua- 
 qua-versal dip toward the central 
 point of the basin. 
 
 As regards the causes of contor- 
 tions and curves, the most general 
 cause must be lateral pressure, crum- 
 pling up the rocks. The origin of „ „ ^ 
 tlie lateral pressure requisite for this formatiouofcontortiona. 
 is not altogether cle.ar; but it has 
 
 boon ascribed to the forcible injection of melted rock into fis- 
 sures in the earth's crust, or to unequal movements of sub- 
 eidence. A very simple, and apparently adequate, explanation 
 
w 
 
 98 
 
 GEOLOGY. 
 
 »i 
 
 has, however, been given by Mr. J. M. Wilson, of Rugby, who 
 ascribes contortions to the subsidence of large areas of the 
 crust of the earth. If, namely, we consider a portion of the 
 crust of the earth, a, J, c, and imagine it to sink slowly to tlie 
 position indicated by the dotted lines in Fig. 31, it is perfect- 
 ly clear that in so doing its curvature must l3e reduced, and it 
 must, therefore, be laterally compressed. In this way, the 
 weight of the sinking mass generates sufficient power to 
 crumple up the rocks, so as to accommodate them to their 
 more confined position. 
 
 , '!! '>' ' .1 ; 
 
CHAPTER XIII. 
 
 UNCONTORMABILITY AND FAULTING. 
 
 Unconpormabtlity. — When the beds of any group of 
 stratified rocks, or of any two groups, have been continuously 
 deposited, so that they succeed each other regularly without 
 any break or interruption, they are said to be conformable. 
 AMien, on the other hand, there are indications that a break 
 has occurred between the deposition of one set of beds and 
 the formation of the beds which immediately succeed, then 
 the upper beds are said to be unconformable to the lower. 
 The most general definition of unconformability which can be 
 given is that when " the base of one set of beds rests in difier- 
 ent places on different parts of another set of beds, the two 
 are unconformable to one another " (Jukes). It follows, from 
 this definition, that the essential element of unconformability 
 is, that the lower set of beds shall have been more or less de- 
 nuded or worn away before the formation of the upper set ; so 
 that the upper beds rest upon an uneven and eroded surface 
 formed by the lower beds (Fig. 32). 
 
 FiQ. 82. — TTnconformnhle junction of conplonioraU'S of Old Red Sandstono 
 with Silurian Slates, near St. Abb's Fead, Berwickshire. 
 
 It does not necessarily result that there is any discordance 
 between two unconformable groups of beds as regards their 
 inclination, especially if both sets are pretty nearly horizontal. 
 
w 
 
 ti 
 
 m\\ 
 
 ¥•'■ 
 
 *, 
 
 mi-y 'i 
 
 
 m 
 
 ;i;! 
 
 
 
 100 
 
 GEOLOGY. 
 
 If the two j^roiips of beds aro perfectly horizontal, it can still 
 generally be shown that tlie lower beds have had a fresh sur- 
 face formed upon them by denudation before the upper beds 
 were laid down upon them. It could, therefore, be shown 
 that the lowest bed of the upper set rested in different places 
 upon different parts of the lower series (Fi<^. 33, A). If the 
 strata are inclined, and not horizontal, tiiere would usually, 
 but not necessarily, be a difference in the direction of the dip 
 of each set, though this might be very difficult or impossible 
 to detect in a much-disturbed district. However slight tiiis 
 difference might be, it would, however, cause a difference in 
 tlie strike of the two sets of beds, and the result of this would 
 be that the upper set of beds would "overlap" the lower; 
 that is to say, if followed far enough, the u]iper beds would 
 be found to rest upon different members of the lower group 
 (Fig. 33, B). . ,, 
 
 Fio. S3. — A. S'cf ion of unconformable strntn, in which the inclination of the two sots of 
 beds is tlu' same; but the iipjier beds an' seen to rest upon an eroded and denuded 
 Burfaec of the lower beds. B. (Troniiil-phtn of uneonfoniuihle strata, in which there is 
 unconfortnable overlap in consequence of a slifrht ditference in the dli'cctiou of the dip 
 of the two groups. The arrows indicate the direction of the dip. 
 
 As a very general rule, however, when unconformability is 
 present, the upper and lower sets of beds are also discordant 
 with one another as regards their general inclination or dip 
 (Fig. 32). The common thing is to find that the lower group 
 of beds has been uptilted, so that its strata now dip at high 
 angles ; that tliese have been planed down by denuding agents 
 to an approximately level surface ; and that the upper beds 
 have been deposited upon the surface thus formed, in such a 
 manner that their dip is much lower and quite different to that 
 of tlie inferior series. 
 
 The sequence of phenomena indicated by this, the com- 
 monest case of unconformability, is this : Firstly, the lower 
 beds were originally deposited in a horizontal position at the 
 bottom of the sea. Secondly, at some time subsequent to 
 their deposition they were raised above the level of the sea, 
 in which process they were probably tilted from their former 
 horizontal position, and certainly underwent so much erosion 
 
UNCONFORMABILITY AND FAULTING. 
 
 101 
 
 .\ 
 
 high 
 
 and denudation that thev were worn down into a level or 
 nearly level surface. Thirdly^ they were again submerged 
 beneath the sea by a process of subsidence. Fourthly^ fresh 
 beds of a diflFerent and later age were deposited upon their 
 upturned edges, so as to be altogether discordant in position 
 and inclination. Fifthly^ and lastly, the whole series com- 
 posed of the two unconformable groups was again elevated 
 above the sea, so as to occupy the position in which we now 
 find it. 
 
 • In all cases, therefore, the mere fact of unconformability 
 indicates the lapse of an almost inconceivable interval of time, 
 during which the processes just described took place. Even 
 in cases where the two unconformable groups do not differ 
 much in geological age — as where Upper Silurian strata rest 
 unconformably upon Lower Silurian beds — it is diflicuH to 
 overestimate the lapse of time indicated by the line of uncon- 
 formability. Still more vast must be the inten'^al when wo 
 find strata of different geological formations in unconformable 
 junction, as, for instance, when rocks of Devonian or Carbo- 
 niferous age repose upon strata belonging to the Silurian sys- 
 tem. And the imagination fails 'to grasp the period repre- 
 sented by the unconformable juxtaposition of the Palaeozoic 
 and Tertiary formations. In many cases the vastness of the 
 time indicated by unconformability may be to a limited extent 
 deduced from what we find has been going on elsewhere dur- 
 ing the same period. When, for instance, we find Carbonifer- 
 ous rocks reposing unconformably upon Silurian rocks, we can 
 form some idea of the interval indicated by this, when we 
 know that elsewhere during the period represented by the 
 mere line of unconformability were deposited the odd fifteen 
 thousand feet of strata which make up the Old Red Sandstone, 
 a formation which is properly intermediate between the Car- 
 boniferous and Silurian systems. Even without this evidence, 
 we should know that a vast interval must have elapsed ; for 
 we should find that the period indicated by the line of uncon- 
 formability had been sufficiently long to allow of a complete 
 revolution in the life of the globe. We should find, namely, 
 that the animals which peopled the Silurian seat, had disap- 
 peared, and that their places were taken in the Carboniferous 
 beds by a totally different group of organisms. 
 
 A common accompaniment of unconformability, though 
 one by no means necessarily present, is to find a bed of con- 
 glomerate at the base of the upper group, containing pebbles 
 derived from the beds of the lower group. Thu3, if we found 
 
102 
 
 GEOLOGY. 
 
 conglomerates of the age of the Upper Old Red Sandstone 
 resting unconformably upon Silurian strata, we should find 
 that ^e pebbles in the conglomerate would be of Silurian 
 age. This indicates that, when the lower beds were elevated 
 above the sea, they were worn down into great beds of shin- 
 gle, and that these constituted the first strata of the upper 
 group, which was ultimately deposited upon the upturned 
 edges of the older set. 
 
 Overlap. — As has been already pointed out, unconforma- 
 bility is generally accompanied by what is called " overlap ; " 
 that is to say, by the extension of one set of beds beyond the 
 ends of another set, so that the upper beds come successively 
 to rest upon diflFerent strata of the lower group (Fig. 33, B). 
 This, however, may occur without any unconformability, or 
 without any previous denudation, in cases where the lower 
 group of beds has been from the beginning a mere local de- 
 posit of very limited extent. Thus, the Carboniferous lime- 
 stone (Fig. 34, a) is a very widely-extended deposit, which is 
 always conformable to the Upper Old Red Sandstone, when 
 the two occur together. The latter, however (Fig. 34, 6), is a 
 very local deposit, and has. often been laid down in patches 
 which may be of considerable thickness in the middle, but 
 thin out rapidly in all directions. It commonly occurs, there- 
 fore, that the Carboniferous limestone overlaps one of these 
 
 Pio. 84. — Ground-plan, showlnfr the Carboniferous limestone (a) overlapping a patch of 
 Upper Old Red Sandstone (6), and coming ultimately to roHt dii-eciiy upon Silurian 
 strata (c). The arrows show the dip. a and b are both uncouiormablo to c 
 
 patches of Upper Old Sandstone, without there being any 
 unconformability; since, when the latter has completely 
 thinned out, the Carboniferous limestone comes, of necessity, 
 to rest upon the beds below the Upper Old Red Sandstone, 
 which beds will probably be of Silurian age. 
 
 FAULTS. 
 
 We come now to the very important subject of what are 
 known to geologists &8 faults or dislocations, the " troubles " 
 
 \m 
 
UNCONFORMABILITY AND FAULTING. 
 
 103 
 
 and " shifts " of the practical minor. It has long been recog^ 
 nized that there is some kind of connection between those 
 fissures and cracks in the rocks which constitute faults, and 
 tlie existence of bendings and contortions of the strata. When 
 the beds have been much folded and contorted, there are 
 usually few fissures of much magnitude, and when the rocks 
 have been much fissured, there are generally few contortions. 
 It is as if the yielding and bending of the rocks under pressure 
 obviated the n<.'iessity of their breaking; and when they 
 would not bend, they were forced to break instead. As 
 already remarked, it has been suggested by Mr. Wilson that 
 contortions are the result of the subsidence of a curved area 
 of the earth's crust. The same observer brings flexures into 
 close connection with faults, by further suggesting that faults 
 are the result of the elevation of a curved area of the earth's 
 surface. This view is explained by the following diagram 
 (Fig. 35). If the portion of the earth's crust A B be elevated 
 
 Fio. 85.— Diagram to lUustrate the production of ftulta (after Mr. J. M. Wilson). 
 
 « 
 
 SO as to assume the more curved form C D, it will be fissured 
 in various places. The masses a and <?, marked out by these 
 fissures, wUl be pushed up, but the increased space between 
 them will be occupied by the sliding down of the masses h and 
 c. This view seems to explain fully the production of faults, 
 and has the merit of extreme simplicity. 
 
 A/'ault or dislocation is a fissure or crack in the crust of 
 the earth accompanied by the elevation- of the mass upon one 
 side of the fault, while the other side remains stationary or 
 sinks down. The strata, therefore, upon the two sides of the 
 fault are shifted in position (Fig. 36), and no longer are con- 
 tinuous or correspond with one another. If, then, we were 
 following any particular bed, such as a bed of coal (a), we 
 should find that its level would be changed where it was in- 
 tersected by a fault, and that it would be placed higher upon 
 
104 
 
 GEOLOGY. 
 
 one side of the fault than upon the other. The amount of 
 difference in the position of any particular bed upon the two 
 sides of a fault, measured vertically, constitutes the " throw " 
 
 Fio. 86.— Dlapram of Ciultcd ond displaced strata.-//, Faults. 
 
 of the fault ; and this throw may vary in amount from a few 
 inches up to many thousands of feet. It need hardly be said 
 that, when the throw of the fault is great, it is not merely a 
 displacement among the beds of a particular formation, but 
 •wholly different formations may be brought in contact with 
 one another. In Fig. 37, the line a h shows the " throw " or 
 amount of displacement effected by the fault, as measured by 
 the distance between the separated portions of the bed e. 
 
 r\'h 
 
 Fio. 87.— TMagram of a fhnU.— / Fault; a &, Throw of the fcult; e «, Shifted bed; c, Up- 
 throw Bide of fault; (2, Downthrow side of fiiult. 
 
 li M'- 
 
 if'li 
 
 The side of the fault upon which the beds are elevated (Fig. 
 37, c) is called the " upthrow " or " upcast" side of the fault ; 
 and the side of the fault upon which the beds are depressed 
 («?) is the " downthrow " or " downcast " side of the fault. 
 The direction or dip of a fault varies a good deal. Commonly, 
 a fault is vertical. When inclined from the perpendicular, 
 there is one constant rule. The fault dips, or " hades," as it 
 is properly called, in the direction of the downthrow, or under 
 the downcast beds. A reference to Figs. 36 and 37 will 
 show the obvious reason of this, namely, that the upthrow 
 side of the fault could not be elevated if the " hade " of the 
 fault were directed toward it. 
 
 The exact line of fault, or, in other words, the original 
 crack along which the strata yielded, is rarely or never seen 
 
UNCONFORMABIUTT AND FAULTING. 
 
 105 
 
 now in the form of an open fissure. Either the two sets of 
 beds on the opposite sides of the fault are now in close con- 
 tact ; or, as commonly happens, the original fissure has been 
 completel}' filled up by the broken-down debris and rubbish 
 produced by the grinding against each other of the two sides 
 of the fault; or, lastly, the fault may be filled up with mineral 
 matters of various kinds, constituting mineral veins, or 
 "lodes," which may contain various metals, or may be simply 
 composed of spars of different kinds. It is also readily in- 
 telligible that the rocks in the immediate vicinity of any large 
 fault are completely broken up, and disturbed in every pos- 
 sible manner. Not only is this the case, but the faces of the 
 fault itself and the rocks near it are generally polished and 
 grooved, in consequence of the enormous pressure and friction 
 to which they have been exposed. Tliis polished and striated 
 appearance of the rocks near a fault is known to geologists by 
 the name of " slickensides." 
 
 In practice, the phenomena presented by a fault vary a 
 good deal from what might be expected from merely theoreti- 
 cal considerations. Theoretically, the u]ithrow side of any 
 fault ought to form a precipitous hill, while the downthrow 
 side would constitute a plain or a depression (Fig. 38). In 
 
 Fio. 88. — A, Section of a &u1t, showlnff the upthrow side only partially denuded and still 
 elevated above the downthrow side. B, Section of a fiiult, Bhowin^ the upthrow side 
 completely planed down. The dotted lines show the amount removed by denudation. 
 
 all cases, in fact, the upthrow side must be elevated above the 
 downthrow side, unless some external agency interfere with 
 this state of things. In practice, however, it is not common 
 to find the upthrow side of a fault remaining in this way as a 
 precipice or mountain ; though such cases do occur. In by far 
 the greatest number of cases the country upon the two sides 
 of the fault has been reduced to one uniform level by the de- 
 nudation of the upthrow side during its slow elevation ; so 
 that there is not now the smallest indication upon the surface 
 of any dislocation of the rocks (Fig. 38, B). In these cases, 
 therefore, the chief guide which enables us to discover the 
 
106 
 
 GEOLOGY. 
 
 
 i ¥\ 
 
 fault 13 the finding a line with altogether different strata 
 upon its two sides, or with the same strata repeated with the 
 same dip (Fig. 40, A). If we can get anywhere near the exact 
 line of fault, we find " slickensides," along with traces of that 
 breaking up of the beds which necessarily accompanies every 
 large fault. If the beds upon the two sides of the fault belong 
 to the same formation, and if there is no disturbance of the 
 dip, it may be very difficult, or impossible, to make out the 
 fault at the surface of the country. In large faults, however, 
 the beds on the two sides of the dislocation will belong to 
 different parts of the same formation, or to altogether different 
 formations. Thus, the coal-measures, for example, may be 
 "brought down" by a large fault against the lower Carbo- 
 niferous rocks, or against beds of the Old Red Sandstone, or 
 even against Silurian rocks. 
 
 Another phenomenon which enables us to detect a fault 
 traversing inclined beds is what is known as the "lateral 
 shift " in the outcrop of any particular bed upon the two sides 
 of the fault ; though it is, perhaps, impossible to render this 
 clear by any verbal description. In the first place, no altera- 
 tion in the lino of outcrop can be produced by any fault, ex- 
 cept by those which run across the strata, or more or Jess at 
 right angles to the strike, jf the beds. Even in these cases no 
 change is produced in the outcrop of the faulted beds, if their 
 inclination be vertical. In this case the fault, however great, 
 simply causes the beds to slide up and down upon one an- 
 other, and, when the two sides of the fault are cut down to the 
 same level, the beds are seen to cross the fault with an un- 
 broken line of outcrop. It is almost impossible, therefore, to 
 detect faults in vertical strata, whatever their magnitude may 
 be. If the beds, however, are inclined, but are not vertical, 
 there is a " lateral shift " in the outcrop of the beds at the 
 point where they are crossed by a fault. If we follow a par- 
 ticular bed across a district, its line of outcrop will be found 
 to agree with the strike of the beds, and will be continuous, 
 if there be no fault. This is shown in Fig. 39, A, where the 
 dotted lines indicate what would be the outcrop of the bed «, 
 if it were not crossed by faults. It must be remembered that 
 this figure is a ground-plan, and not a section. If, hdwever, 
 the bed a be crossed by a fault, its line of outcrop is shifted 
 laterally, and is found out of its true line of bearing upon the 
 opposite side of the fault. Tlie practical rule about this shift 
 is, that the beds will be shifted in the direction of their dip 
 upon what was the upthrow side ofthcfauU. That is to say, 
 
UNCONFORMABILITY AND FAULTING. 
 
 107 
 
 if a bed dipping south, and striking east and west, be crossed 
 by a north and south fault, its line of outcrop will be shift- 
 ed to the south upon the upcast side of the fault; as is 
 shown in Fig. 39, A. Here the bed a, striking east and west. 
 
 
 6v 
 
 
 SS31P? 
 
 c\ 
 
 Fig. 39. — A, Ground-plan of a bed a shifted by two ftiults (//) which cross It at rlpht 
 angles to its liDo of strike. The dotted lines show what would have been the line of 
 outcrop if undisturbed. B, Section of the same along the line b c. The dotted tines 
 show the upthrow side of the fault, and the former prolongation of the bed a, before it 
 was planed down by denudi^tion. 
 
 and dipping south, is crossed by two north and south faults 
 {ff)j the upthrow side of which is en the east. The bed a 
 is, therefore, shifted to the south on the eastern side of each 
 fault, the amount of shift varying with the magnitude of the 
 fault. The cause of this apparent lateral shift is as follows : 
 When the fault originally took place, the i^pthrow side was 
 elevated above the downthrow side, and there was no shift 
 in the outcrop of any of the strata crossed by it. The bed o, 
 for instance, as shown in Fig. 39, B, had its outcrop continuous 
 on both sides of the fault, and was simply elevated on the up- 
 throw side, as is indicated by the dotted lines. If, however, 
 the beds composing the upthrow side of the fault be now cut 
 down by denudation to a level with the downthrow side, it is 
 clear that the outcrop of the beds ou the two sides of che fault 
 can no longer correspond. Any particular bed in the upthrow 
 side must be cut across — in consequence of its inclination — at 
 a point removed some distance from its original line of out- 
 crop, the removal being in the direction of the dip of the 
 strata. The larger the fault, the greater will be the distance 
 at which each bed will have to be cut across, in order to 
 reduce the whole to a level surface ; and, as the point, or line, 
 along which any bed is cut across, will constitute its new line 
 of outcrop, it follows that the outcrop of the strata cannot 
 correspond upon the two sides of the fault. 
 
 Repetition op Strata by Faults. — When faults run at 
 right angles to the dipj or coincide more or less nearly with 
 
108 
 
 GEOLOGY. 
 
 the strike of the beds, there is a repetition of the strata ; so 
 that the same beds may follow one another, perhaps several 
 times over, in any given district. This is shown in Figs. 36 
 and 40, where it is seen that the repeated beds all dip in the 
 
 Fio. 40.~A, Strata repeated with the same dip hy parallel fiinlts ; B, Strata repeated by a 
 synclinal curve; 0, Strata repeated by an anticlinal curve. 
 
 same direction. "WTien this is the case, even though the 
 amount of the dip be changed, there need be little hesitation 
 in ascribing the repetition to faults. If, on the other hand, 
 the repeated beds dip away from one another, then the repe- 
 tition is probably due to an anticlinal fold (Fig. 40, C) ; 
 while, if the repeated beds dip toward one another, a syncli- 
 nal curve is probably present (Fig. 40, B). 
 
CHAPTER XIV. 
 
 ON THE RELATIVB AGES OF THE AQUEOUS ROCKS. 
 
 We have seen that the series of the stratified or aqueous 
 rocks is composed of a succession of deposits of diflFerent 
 ages, and we come now to the question as to how these ages 
 may be determined, and a true succession of the stratified for- 
 mations established. In solving this question as to the method 
 of determining the age of any particular bed or set of beds, 
 we find that there are three principal tests which may be em- 
 ployed: 1. Superposition; 2. Mineral composition; 3. In- 
 cluded organic remains. 
 
 I. Superposition. — The first and most obvious test of the 
 age of any aqueous rock is, its relative position. Any bed, or 
 set of beds, of sedimentary origin, is obviously and necessarily 
 younger than all the beds upon which it rests, and older than 
 all those which surmount it. When the beds are horizontal, 
 there is little difficulty in making out the position of any one of 
 them ; but, if the beds are inclined, and especiallj' if they are 
 much folded or faulted, it is often impossible to determine the 
 relative position of any group of beds. Necessarily, too, the 
 order of superposition can only be applied to a limited set of 
 beds, and through limited thicknesses. Lastly, nt its best, 
 superposition can only tell us the relative and not the ahsohite 
 age of any bed or set of beds. It will tell us with certainty 
 that this or that bed is older or younger than some other bed, 
 but it cannot of itself tell us hoio much older or voungcr. 
 
 If, for example, we find, in one district, rocks of the coal- 
 formation resting upon Silurian strata, we know from the or- 
 der of succession that the latter are the oldest ; but we do not 
 know how much older. The coal-measures might, for all we 
 can tell, be the formation which immediately followed the 
 Silurian rocks, or they might be separated by an enormous in- 
 
1^ !^ 
 
 si'l' 
 
 fiiflli 
 
 
 
 
 110 
 
 GEOLOGY. 
 
 terval of time. In practice we can only determine this by an 
 appeal to the order of succession in other regions, and by 
 means of the fossil remains in each set of beds. From the 
 first, we should learn that the coal-formation is never conform- 
 able to the Silurian rocks, and that between the two there 
 really intervenes the great formation of the Old Red Sand- 
 stone ; while the second would show us such a complete dif- 
 ference in the life of the two periods, that a great period of 
 time would have to be allowed for on this ground alone. 
 
 II. MiNEEAL Chakactees. — The second test of the age 
 of the aqueous rocks — that of mineral composition — is an ex- 
 tremely unreliable one, and can only be applied to a very 
 limited extent. It is true that great masses of chalk might 
 be taken as tolerably good evidence that we were about the 
 horizon of the Upper Cretaceous rocks ; extensive beds of 
 workable coal would afford a fair presumption that our horizon 
 would be that of the Carboniferous rocks; well-developed 
 magnesian limestones would lead us to infer that we hud to 
 do with beds of Permian age ; and red sandstones, with gyp- 
 seous clays and rock-salt, would be a strong proof that we were, 
 working in the Triassic formation. It is true, also, that if 
 in any unknown region we found the rocks very much cleaved 
 and indurated, consisting mostly of slates and grits, we should 
 have grounds for believing that we were dealing with Silurian 
 or Cambrian rocks ; while if they consisted chiefly of more or 
 less incoherent sands, clays, and gravels, we should be equally 
 justified in supposing that we were dealing with rocks of the 
 Tertiary or Post-tertiary period. 
 
 Still, in all these cases, and in many other similar ones, we 
 might and sometimes should be wrong. The Cretaceous sys- 
 tem of rocks sometimes contains no chalk ; workable seams of 
 coal occur in several formations younger than tlie true coal- 
 formation ; magnesian limestone is not exclusively Permian ; 
 and red marls and sandstones occur in the Tertiary series. 
 Again, perfectly cleaved and indurated beds occur in some 
 very modern formations; while some of the older rocks are 
 as little hardened and consolidated as most of the Tertiary 
 strata. The test by mineral characters is, therefore, never al> 
 solutely conclusive as to the age of any given bed or group 
 of beds. Still, there is no question but that each of the great 
 formations is in a general way characterized in any given 
 country by the occurrence of particular kinds of rocks ; and 
 when this evidence is combined with what we learn from fos- 
 sils, and from the superposition of the rocks, we can arrive at 
 
 Mu,i 
 
RELATIVE AGES OF THE AQUEOUS ROCKS. 
 
 Ill 
 
 3S, we 
 IS sys- 
 Lins of 
 } coal- 
 mian ; 
 series, 
 some 
 s are 
 rtiary 
 er a1> 
 group 
 great 
 given 
 ; and 
 fos- 
 ive at 
 
 reliable conelusions as to the age of the beds in any particular 
 region. In one case, also, this test will afford decisive evi- 
 dence of the relative age of two sets of beds ; namely, when 
 we find one group of beds containing fragments of another 
 group, in which case the former is, of course, the youngest. 
 
 III. Included Organic Remains. — The last test, as to 
 tlie age of any bed or group of beds, is the nature of the or- 
 ganic remains or " fossils " which occur in it. As in the case 
 of mineral composition, however, this test is neither always 
 applicable, nor in all cases absolutely conclusive. Many 
 aqueous rocks exhibit no traces of life, or are " unfossiliferous," 
 for a thickness of many thousands of feet ; and even amonf' 
 fossiliferous rocks many strata occur, of a few feet or yards ir 
 thickness, which are wholly without organic remains. Even 
 when fossils do occur, it may not be alwu^'s possible to decide 
 as to the age of the beds. Many fossils range vertically 
 through several groups of strata, and in some cases even 
 through several formations ; and these, therefore, taken by 
 'ihemselves, would not be conclusive evidence as to the age of 
 any particular sot of beds. 
 
 As the result, however, of a vast number of observations, 
 it is now absolutely certain that the entire stratified series may 
 be divided into a number of groups or formations, each of 
 which is characterized by the occurrence, not of any particu- 
 lar fossil, but of an assemblage of fossils peculiar to tliat for- 
 mation, and not occurring in company in any other formation. 
 Such an assemblage of fossils, characteristic of any formation, 
 represents the life of the period during which that formation 
 was deposited. It follows from this, that whenever we can 
 obtain a series or collection of fossils from any particular bed 
 or set of beds, there is rarely any difficulty in determining 
 precisely the geological horizon of the rock in which the fos- 
 sils occur. 
 
 With certain limitations, we may go much further than 
 this. Not only are the great formations characterized by 
 special and peculiar assemblages of animals or plants ; but in 
 a general way each subdivision of each formation has its own 
 characteristic fossils, by which it may be recognized by a com- 
 petent observer. For instance, whenever we find the singular 
 fossils known as Graptolites, we may be certain that we are 
 dealing with Silurian strata (with one or two unimportant ex- 
 ceptions). Not only so ; but, if the Oraptolites belong to cer- 
 tain genera, we may be sure we are working in Lower Silurian 
 beds J and, if certain species are present, we may even be able 
 
112 
 
 GEOLOGY. 
 
 i! 
 
 to fix upon tlie exact part or subdivision of the Lower Silurian 
 rocks with which wc are occupied. But all this would have 
 to be done under a reservation. Graptolites might at any 
 time be found in strata much younger or older than the Silu- 
 rian rocks. In the same way, the species which we now re- 
 gard as characteristic of the Lower Silurians might at any 
 time be found to have survived into the Upper Silurian period. 
 So that we should never forget that, in determining the age 
 of a rock by fossil evidence alone, we are reasoning upon 
 generalizations which are the result of experience, and which 
 may at any time be overthrown by fresh discoveries. 
 
 As many allusions will necessarily have to be made to the fossils charac- 
 teristic of the different formations, it may be as well to give here 'in a very 
 brief form a synoptical view of the animal and vegetable kingdoms, with 
 more especial reference to the geological aspect of the subject. It may be 
 premised that though most fossil animals and plants are extinct^ and are not 
 found at the present day upon the globe, nevertheless no fossil is known 
 which moy not be referred to one or other of the primary divisions of the 
 animal J»nd vegetable kingdoms. It is chiefly of importance, therefore, that 
 the siudent should obtain a clear idea of the characters of these great sections. 
 
 The animal kingdom is divided into six primary divisions or 6i«6-A:/ngrcfo»is, 
 as follows, beginning with the lowest : 
 
 I. Protozoa (Gr. /jro/os, first; zon, animals). The animals belonging to 
 this section are mostly very minute in point of size, have the body composed 
 
 ^0:^^-^.'% 
 
 i., 
 
 m~ 
 
 
 Fio. 41.->I'oraminirera (mapiifled). — h and c show the shell In its living state ; 
 but a, e, and/, merely exliibit the shell. 
 
RELATIVE AGES OF THE AQUEOUS ROCKS. 
 
 113 
 
 of a gtructureless, jelly-like substance, have no nervous system, only rarely 
 possess a mouth, and never pos.sesa any distinct digestive ca-ity or stomach. 
 Most of the Frotozoa live in the sea or in fresh water, and they are generally 
 not provided with any hard structures, so that they cannot be preserved in a 
 fossil condition. The most important, from a gcol(>«:iral point of view, are 
 t\\c Foramiiiifcra {¥V^. 4l)and the Sponges. The former are mostly very 
 small, and have the body protected by a little case of lime or sand, which ia 
 often of great beauty. They are found in many rocks, but are especially 
 al)undant in the chalk and in some Tertiary strata. The Sponges are well 
 known by the horny sponges of commerce, but the fossil forms possess a 
 skeleton of lime or flint. They are found from the base of the Silurian rocks 
 upward, but are especially abundant in parts of the Cretaceous system. 
 
 11. CffiLENTKRATA (Gr. koilos, holiow ; enteron, the intestine). This sub- 
 kingdom includes most of the animals formerly called Radiates^ and popularly 
 known as " zoophytes," such as sea-firs, sea-anemones, corals, and sea-jellies. 
 They are characterized by the fact that the alimentary canal opens directly 
 into the general cavity of the body. There are rarely any traces of a ner- 
 vous system ; and there is generally a distinct starlikc or radiated arrange- 
 ment both of their external parts and internal organs. The most important 
 members of this order are the sea-firs and the corals (Fig. 42). The sea-firs 
 are branched, ) 'ny, plant-like organisms, which are composed of numerous 
 minute creatures living associated in colonies. They inhabit the sea, and 
 are believed to be very nearly related to the large and important e.xtinct 
 group of fossils known as Oraptolitcs. The corals are much more important, 
 and are represented by numerous fossil forms, occurring in almost all the 
 great geological formations. As before explained (p. 44), corals may be 
 
 Fio. 42.— Eeccnt corals. 
 
 looked upon as essentially sea-anemones, with the power of secreting a hard 
 support or skeleton composed of lime. These skeletons are the parts pre- 
 served in a fossil condition ; and many limestones are to so great an extent 
 
114 
 
 GEOLOGY. 
 
 composed of corals, that wc are led to suppose that they must have been 
 ancient coral-reefs. Many fossil corals, however, differ in some important 
 respects from all known living form?. 
 
 III. Anni r.oiDA (Lat. annidus, a ring; Gr. m/os, form). The only mem- 
 bers of this sub-kingdom which are ever preserve;! in a fossil condition are 
 
 the sea-urciiins, star-fishes, stone- 
 lilies, and their allies, which togeth- 
 ci- form the class Echinodcrma(a 
 ((Jr. echhws, a hedgehog ; ilcnna, 
 skin). The name of the class is de- 
 rived from the generally prickly na- 
 turc of the skin, due to the power 
 which they all possess, in different 
 degrees, of secreting carbonate of 
 lime in the integument. When fully 
 grown they all exhibit a more or less 
 distinct star-shaped or radiate ar- 
 rangement of their parts (Fig. 43). 
 The alimentary canal never commu- 
 nicates with the body-cavity, and 
 there is always a well-develoi)ed ner- 
 vous system. Lastly, they all possess 
 a peculiar system of tubes to which 
 water is generally admitted from the 
 exterior, and which is usually con- 
 cerned in locomotion. 
 
 The most important members of 
 this group geologically are the stone- 
 lilies (Crinokh\ the star-fishes and 
 brittle-stars (Astri'oifls), and the sea- 
 urchins {Et-hinoids). The Criuoidx 
 (Fig. 43) are distinguished by being 
 fixed to the bottom of the sea by a 
 jouited calcareous column or stem, 
 which supports a body not unlike 
 that of a brittle-star. In some cases, 
 only the young is so fixed, and the 
 adult loses its t^talk and becomes 
 free. The stone-lilies are very abun- 
 dant as fossils, and often whole beds 
 are composed of their broken stems. 
 They abounded chiefly in the older 
 periods of the earth's history, and 
 gradually dwindled down, till, at the 
 present day, there are no more than 
 three or four living types of the 
 order. The star-fishes and brittle- 
 stars are well known for their com- 
 pletely starlike form. They occur as fossils in many formations, especially 
 in the Secondary rocks ; but they are not of great importance. The sea- 
 urchins are distinguished by their globular, heart-shaped, conical, or cake- 
 like form, and by having the body (Fig. 44) encased in an immovable shell, 
 composed of numerous calcareous plates firmly jointed together. The whole 
 shell is covered with numerous tubercles, which support longer or shorter 
 
 Pio. m.—Rhisocrinns LofofenMs, allying 
 Crinoid (after Wyvillo Thomson), 
 
RELATIVE AGES OF THE AQUEOUS RO'-KS. 
 
 115 
 
 morable spines. The Sea-urchins occur as fossils in many formations, but 
 are chiefly found in the Oolitic and Cretaceous rocks. 
 
 Fio. 44.— A living Sea-urchin (JJidaria), 
 
 lecomcs 
 
 y abun- 
 
 beds 
 
 stems. 
 
 older 
 
 ', and 
 
 at the 
 
 re than 
 
 the 
 
 (rittlc- 
 
 coni- 
 
 [ecially 
 
 )e pca- 
 
 cake- 
 
 shcU, 
 
 J whole 
 
 ihoiter 
 
 lof 
 
 IV. Anntjlosa (Lat. annuhis, a rinp). Tho members of this sub-king- 
 dom, such as worms, crustaceans, spiders, centipedes, and insects, have a 
 boily composed of a number of rings arranged longitudinally one behind the 
 other. There is a distinct alimentary canal, generally circulatory organs, 
 and always a nervous system. The nervous system consists, typically, of 
 two nervous cords placed along the lower surface of the body, and having 
 two little nervous masses developed in each ring. The sub-kingdom is 
 divided into two great divisions, according as the body is furnished with 
 jointed limbs or not. In the former section are the Leeches, Earthworms, 
 Sea-worms, etc., none of which are geologically important, though the Tube- 
 worms not uncommonly occur as fossils. The second section comprises the 
 Crustaceans, Spiders and Scorpions, Centipedes, and Insects, all having jointed 
 appendages articulated to the body ; hence the name o( Articulated Animals, 
 often applied to this section. 
 
 The Crustaceans comprise the Lobsters, Shrimps, Crabs, Wood-lice, Horse- 
 :;hoe Crabs, Water-fleas, Baniacles, and Acorn-shells, etc., and are all more or 
 less truly aquatic. They almost always have breathing-organs in the form 
 of [fills ; they have two pairs of feelers; the limbs are usually more than 
 eight in number ; and the body is generally protected by a hard shell or 
 "crust" (Fig. 45), The most important extinct groups of the CruKlacca 
 arc the Tnlobitcs and Buri/pteHds, both characteristic of the older strata 
 of the earth's crust ; but all the forms mentioned above are represented by 
 fossil examples. 
 
 The Spiders and Scorpions (Arachnidn) are terrestrial, and have breath- 
 ing-organs, adapted for respiring air directly ; they have no feelers, as such ; 
 and they have four pairs of legs. They occur in a fossil condition, but aie 
 rare, and comparatively unimportant. 
 
 The Centipedes (Mt/riapoda) have breathing-organs, adapted for respiring 
 air, have one pair of feelers, and have numerous pairs of legs (never less 
 than nine pairs). They rarely are found as fossils, and require no further 
 notice here. 
 
116 
 
 GEOLOGY. 
 
 The tnic Insects (Tnsecta) bronihe air directly, have one pair of fcclcrR, and 
 three pairs of legs, genoraUy with one or two pairs of wings. Thougli not 
 of common occurrence as fossils, insects are of considerable importance from 
 a geological point of view. They have been found in all formations, from 
 the Old lied Sandstone upward. 
 
 V. MoLLUscA (Lat. mollis, soft). The Mollusks, or true Shell-fish, have 
 soft bodies, usually protected by a calcareous ehtll, of one, two, or more 
 pieces. There is a distinct alin'Mtary canal, and generally a heart and cir- 
 culatory system. The nervous system consists of three scattered masses, 
 united to one another by nervous cords. There may be no respiratory or- 
 gans, or there are distinct breathing-organs, adapted for breathing air di- 
 rectly, or more commonly through the medium of water. The most important 
 members of the Mollusca, from a geological point of view, are the Lamp- 
 shells and their allies, the Bivalves, the Univalves, and the Cephalopoda. 
 
 i/i' 
 
 .nti. 
 
 n 
 
 Av; 
 
 
 
 ry 
 
 
 
 i _ 1 
 
 ^ 
 
 
 -r^ 
 
 ■-:^-~-- 
 
 -."" 
 
 tE 
 
 ^y'.i^- 
 
 ^•^•l 
 
 y 
 
 V> 
 
 
 ' ' jr 
 
 
 n 
 
 m 
 
 Fig. ^.—EnryiitcMn.—Pien/ffo- 
 tus An(iHcuH, restored (after 
 H. WoodwardX 
 
 Fio. 46. — Brachiopoda. — Lingula, 
 showinfr the muscular stalk 
 by which the shell is attached. 
 
 The Lamp-shells and their allies form the class Brachiopoda (Gr. brachion, 
 an arm ; jTodes, feet), so called because the mouth is furnished with two long, 
 fringed processes or " arms." The body is protected by a " bivalve " shell, 
 composed of two pieces or valves (Fig. 46), which generally differ in size 
 and in other characters as well. They a:'e often placed with the true Bi- 
 valve Shell-fish, but their general organization is much lower. The Brachio- 
 poda are of great geological importance, occurring in all formations after thQ 
 
RELATIVE AGES OP THE AQUEOUS ROCKS. 
 
 117 
 
 earliest, arid often in very great abundance. They are an example of a group 
 wliioli has long been on the decline, the living npecies falling tar short of one 
 hundred, while nearly two thousand fossil forms are known. 
 
 The Di valve Molluaks form the class Lnmellihrnnchiata (Lat. lamella, a 
 thin plate ; Gr. bragchia, gill), so called from their leaf-like gills. Thev 
 have a shell composed of two pieces or "valves," which are usually identical 
 in size and shape. (Jood examples are the Oystei, Mussel, and Scallop. 
 Numerous fossil forms of this class are found in all formations after the 
 oldest. 
 
 The Univalve Molluska are known as Gasteropoda {Gr. r/asler, belly ; pode$, 
 feet), from their cree|)ing about upon a flattened disk formed of the lower 
 surlace of the body. Some of them, such as the Slugs, have no visible shell ; 
 but most of them have a fihell, which is almost alwavs composed of a .«ingle 
 piece or "valve" (Fig. 47). The shell varies a good deal in shape, but'is 
 mostly coiled into a spiral, as is seen in the common reriwiuklea and 
 
 -V-i 
 
 rA, 
 
 Fio. 41— Sheila of Gaateropoda.—a, Holostomatoiis shell ( Ttirrifella commwiis) ; 6, 81- 
 phoDostouiatous shell {^Buccinum undutuvi). 
 
 "V\Ticlks. The Gasteropoda have a great antiquity, and are found, more or 
 less abundantly, in all the great geological formations after the first. 
 
 The class Cephalopoda (Gr. kephale, head ; pedes, feet) comprises the 
 Cuttle-fish and Pearly Nautilus, with a host of fossil forms. They derive 
 their name from the fact that the head is surrounded by a series of " arms " 
 or long processes, which are usually provided with suckers, and by which 
 the animal walks about, head-downward, at the bottom of the sea. The. 
 Cuttle-fishes have no external shell, but generally possess a calcareous or 
 horny internal skeleton. The most important fossils referable to this sec- 
 tion of the Cephalopoda are the singular Beletnnites, so characteristic of the 
 secondary period of geology. The Pearly Nautilus (Fig. 48) and its fossil 
 allies have a well-developed external shell, which is always divided into a 
 series of chambers by shelly partitions. The animal lives in the last cham- 
 ber only of the shell, and the partitions of the shell are always pierced by an 
 aperture for the conduction of a peculiar tube known as the " siphuncle." 
 
118 
 
 ^,20L0QY. 
 
 
 r 
 t 
 
 In the Nautilufl and its ncarcnt allies the partttionfl of the shell are sinnpiy 
 curved, and the " fliphiincle " is centml, or nearly so. In the Urpe and 
 important extinct group of the Ammonilca the partitions of the ehull aro 
 
 Fio. 49.— Pearly Nautilus 
 
 /, Fuuuel. 
 
 Mantlo; o, Eye; t. Tentacles; 
 
 wonderfully folded and lobed, instead of being sinnply curved, and the "si- 
 phuncle " is placed on the back of the shell. The Nautilus and its allies occur 
 in all the great formations, but the true Ammonites, with a great number of 
 related forms, are characteristic of the Secondary rocks. 
 
 VI. VERTEniiATA (Lat. vertebra, one of the bones of the spine or back- 
 bone). The Vertebrates are characterized by the almost universal possession 
 o^ a spinal co1uiT)-« or backbone (Fig. 49), composed of numerous bones 
 placed one bcliiud the other, and enclosing the spinal cord. The skeleton is 
 internal, and the in'iseles are attached to its several parts. The limbs may 
 be wanting, ov \) .rtially undeveloped, but they are always jointed to the 
 body, when present, Pud there are never more than two pairs. The Verte- 
 brates are divided into the following five great classes : 
 
 1. Pisces (Fishes), distinguished by having gills, and by having the limbs 
 (when present) in the form of fins. The heart is mostly two-chambered. 
 The most important groups of Fishes are the Bony Fishes, such as the 
 Salmon, Cod, Herring, etc. ; the Ganoid Fishes, such as the Sturgeon and 
 Bony Pike ; and the Sharks and Rays. The Bony Fishes are distinguished 
 by their thin, horny scales, their bony skeleton, and symmetrically-lobed 
 tail. The Ganoid Fishes have bony scales covered with enamel, the skeleton 
 usually more or less gristly, and the tail sometimes symmetrical, sometimes 
 unsymmetrical. The Sharks and Rays have scales in the form of detached 
 bony grains or plates, a gristly skeleton, and an unsyrametrically-lobed tail. 
 
 2. Amphibia (Frogs, Newts, etc.), distinguished by having gills when 
 young, and lungs when fully grown, the gills sometimes remaining through- 
 
RELATIVE AGES OF TOE AQUEOUS ROCKS. 
 
 119 
 
 Fio. 49. — Skeleton of the Beaver, showinfr the reasons of the vertebral eolnmn. — e, Cervical 
 region^ or neck ; </. Dorndl regiov. or n-tjloii of the back ; h. Lumbar region, or region 
 of the loins; «, Sacrum ; t, Caudal region , or region of the tall. 
 
 out life. The limbs may be wanting, but are never in the form of fins. The 
 skull is jointed to the backbone by two articulating surfaces or "condyles." 
 Tin; most important fossil amphibians are the great Labyrinthodouts of the 
 Carboniferous and Triassic periods. 
 
 3. Replilia (Reptiles), distinguished by never possessing gills, by having 
 the skin furnished with horny scales or bony plates, and by having the 
 skull jointed to the backbone by one articulating surface or " condyle." 
 The blood is cold, and the heart is almost always three-chambered. The 
 following living orders are included in this class : 
 
 a. Chelonia (Tortoises and Turtles). 
 
 b. Lacertilia {hh&rds). 
 
 c. Ophidia (Snakes and Serpents). 
 
 d. Crocodilia (Crocodiles and Alligators). 
 
 All these living orders are represented by extinct forms ; but besides 
 these there are five wholly extinct orders, some of them of very remarkable 
 character, belonging to the Secondary period of Geology. The more remark- 
 able of these forms will be noticed in speaking of the rocks in which they 
 occur. 
 
 4. Aves (Birds), characterized by never possessing gills, by having a 
 covering of feathers, and by having the skidl jointed to the vertebral column 
 by a single joint or " condyle." The blood is warm, and the heart is four- 
 chambered. The fore -limbs are generally so modified as to form " wings." 
 The class of Birds is of no high geological anti(juity, the earliest example 
 being from the Secondary rocks (Oolites). The class is divided into the fol- 
 lowing orders : 
 
120 
 
 GEOLOGY. 
 
 i:!;1 
 
 a. Nafatorfs or Swimming Birds. Ex. — Ducks, Oulls, Pelicans. 
 
 b. Grallatores or Wadiruf Birds. Ex. — Herons, Storks, Woodcocks. 
 
 c. Cursores or Running Birds. Ex. — Ostrich, Emeu, 
 
 d. Basorcs or Scratching Birds. Ex. — -Fowls, Game-birds, Pigeons. 
 €. Scansores or Climbing Birds. Ex. — Parrots, Woodpeckers. 
 
 f. Lisessores or Perching Birds. Ex. — Finches, Larks, Crows. 
 
 g. Jiaptorcs or Birds of Prey. Ex. — Hawks, Eagles, Owls. 
 
 h. Saunirce or Lizard-tailed Birds, comprising only the extinct Archaop. 
 teryx of the Oolitic Rocks. 
 
 5. J/iemma/ia (Mammals); distinguished by having some part or other 
 of the skin provided with hairs, by having the skull Jointed to the backbone 
 by two joints or " condyles," and by never having gills. The blood is warm, 
 and the heart is fouf-cha nbered. The young are notirished for a longer or 
 shorter time by means of a special fluid — the milk — secreted by special' 
 organs, the mammary glands. The class includes all the ordinary quadru- 
 peds, and is divided into the following orders : 
 
 a. Monotrcmata. Ex. — Duck-mole, and Spiny Ant-cater. 
 
 b. Marsupialia. Ex. — Kangaroos and Opossums. 
 
 c. Edentata. Ex. — Sloths, Armadillos, Ant-eaters. 
 
 d. Sirenia. Ex. — Dugong, Manatee. 
 
 e. Cdacea. Ex. — Wlialcs and Dolphins. 
 
 /. Ungnlata{\\oo{Q([ Quadrupeds). Ex. — Rhinoceros, Hippopotamus, Pigs, 
 
 Tapirs, Giraffe, Deer, Antelopes, Sheep, Goats, Oxen. 
 g. IB/racoidca. Ex. — Ilyrax. 
 h. Proboscidca. Ex. — Elephant. 
 
 i. Carnivora. Ex. — Scal.«, Wv'.rus, Bears, Raccoons, Dogs, Wolves, 
 
 Hyainas, Lions, Tigers. 
 j. Podeutia. Ex. — Mouse, Rat, Beaver, Squirrel. 
 K. Cheiroptera. Ex. — Bats, 
 
 I. Insectivora. Ex. — Moles, Shrew-mice, Hedgehogs. 
 m. Quadnimann. Ex. — Lemurs, Baboons, Apes. 
 n. Bimana. — Man. 
 
 VEGETABLE KINGDOM. 
 
 The following arc the main subdivisions of the Vegetable Kingdom : 
 I. Cryptogamic Plants (Gr, kruptos, concealed ; gamos, marriage), dis- 
 tinguished by having no distinct flowers or fruit. They include : 
 
 a. TTtallogens. Ex. — Sea-weeds (^/V/ce), Lichens, Mushrooms. 
 
 b. Anogens. Ex. — Liverworts, Mosses. 
 
 e. Acrogtns. Ex. — Club-mosses (Lycopodiacea;), Ferns, Horse-tails {Egui' 
 setaceai). 
 
 n, Phanerooamio Plants (Gr. phaneros, conspicuous ; gamos, marriage) ; 
 distinguished by having distinct flowers and seeds. They are divided 
 into: 
 
 a. Endogens. Ex. — Grasses, Palms, Lilies. These have «j(fo(7f«0Ms stems, 
 showing no rings of growth, and the young plant possesses but a single 
 seed-lobe or " cotyledon," Hence they are often called Monocotyledons. 
 
 b. Exogens. Ex. — Pines and Cycads, with most ordinary shrubs, trees, 
 and flowering plants. The Pines and Cycads, with the fossil Sigillarice, have 
 the seed naked, and are hence called Oymnospcrms (Gr. gnmnos, naked ; 
 sp'TTna, seed). Ordinary trees and shrubs, on the other hand, have the seed 
 covered, and are therefore called Angiosperms. Both the Gymnosperms and 
 Angiosperms have an exogenous mode of growth, with a true bark and annual 
 
RELATIVE AGES OF THE AQUEOUS ROCKS. 
 
 121 
 
 rinps of growth. The seed also possesses two seed-lobes or " cotyledons ; '* 
 and they are therefore often Bpokcn of as Dicoti/kdons. 
 
 Chbonological Succession op the Aqueous Rocks. — 
 As the result of observations made upon the superposition of 
 rockf. in different localities, from their mineral characters, and 
 from their included fossils, geologists have been able to divide 
 t!ie entire stratified series into a number of different divisions 
 or formations, each chanictcrized by a gemrral uniformity of 
 mineral composition, and by a special and peculiar assembla//e 
 of organic forms. Each of these primary groups is in turn 
 divided into a series of smaller divisions, characterized and 
 distinguished in the same way. It is not pretended for a mo- 
 ment that all these primary rock-groups can anywhere be seen 
 surmounting one another regularly. There is no region u[)on 
 the earth where all the stratified formations Ciin be seen to- 
 gether ; and, even when most of them occur in the same coun- 
 try, they can nowhere be seen all succeeding each other in 
 their regular and uninterrupted succession. Tlie reason of 
 this is obvious. There are many places — to take a single ex- 
 ample — where one may see the Silurian rocks, the Old Red 
 Sandstone, and the Carboniferous rocks succeedmg one an- 
 other 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 whicli one would 
 find the Carboniferous rocks resting unconformably upon the 
 Silurians without *.he intervention of any strata which could be 
 referred to the Old Red Sandstone. 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 Old Red period, in which 
 case, of course, no strata of the age of the Old Red Sandstone 
 could possibly be deposited. 2. The Old Red Sandstone 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 Old R<h1 Sand- 
 stone entirely. In this case when the land was ag;iin sub- 
 merged, the Carboniferous rocks, or any younger formation, 
 might be deposited directly upon Silurian strata. From one 
 or other of these causes, then, or from subse(juent disturbances 
 and denudations, it happens that we can rarely find many of 
 the primary formations following one another consecutively 
 and in their regular order. 
 
12 
 
 6E0L0GT. 
 
 IDEAL SECTION OF THE CRUST OP THE EARTH. 
 
 Fio. 60. 
 
 o ^ 
 
 uu 
 
 S 
 
 ' / /'//////// //////( 
 
 ilHUWMM 
 
 ,/. 
 
 211 
 
 -« Post-tertiary and Recent. 
 •— Pliocene. 
 
 "•• Miocene. 
 -••- Eocene. 
 
 •— Cretaceous. 
 
 •— Jurassic or Oolitic. 
 
 orp.'gf ftSc'cPoioro iiio. 
 
 - Triassic (New Red Sandstone). 
 
 Permian. . > 
 
 Carboniferous. 
 
 ~ Devonian or Old Red Sandstone. 
 
 5 — Silurian. 
 
 — Cambrian. 
 
 ..- Huronian. 
 — Laurentian. 
 
RELATIVE AGES OP THE AQUEOUS ROCKS. 
 
 123 
 
 4. 
 
 5. 
 
 6. 
 
 7. 
 
 8. 
 
 9. 
 10. 
 11. 
 12. 
 
 The main subdivisions of the Stratified Hocks are known 
 hy the following names : 
 
 1. Laurentian. 
 
 2. Cambrian (with Huronian ?). 
 
 3. Silurian. 
 Devonian or Old Red Sandstone, 
 Carboniferous. 
 
 e m an, / j^^^ j^^j Sandstone. 
 
 Jurassic or Oolitic. 
 
 Cretaceous. 
 
 Eocene. 
 
 Miocene. • - 
 
 Pliocene. 
 13. Post-tertiary. 
 
 Of these primary groups, the Laurentian, Cambrian, Silu- 
 rian, Devonian, Carboniferous, and Permian, are collectively 
 grouped together under the name of Primary or JPalceozoic 
 rocks (Gr. palaios^ ancient ; zoe^ life)) because of the entire 
 divergence of their animals and plants from any now exist- 
 ing upon the globe. The Triassic, Jurassic, and Cretaceous 
 systems, are grouped together as the Secondary or Mesozoic 
 formations (Gr. mesos^ intermediate; zoe, life), because their 
 organic remains are intermediate between those of the Pa- 
 Itcozoic period, and those of more modem strata. The Eocene, 
 Miocene, Pliocene, and Post-tertiary rocks, are grouped to- 
 gether under the head of Tertiary or Kainozoic rocks (Gr. 
 kaifioSf new; zoe, life), because their organic remains ap- 
 proximate in character to those now existing upon the globe. 
 
 All these separate formations require to be noticed some- 
 what in detail, and in so doing it is best to begin with the 
 lowest and gradually work our way upward. The foregoing 
 illustration represents an ideal section of the crust of the 
 earth, showing the succession of the great formations (Fig. 50). 
 
CHAPTER XV. 
 
 LAFRENTIAN, HTJEONTAN, AND CAMBRIAN GROUPS. 
 
 i'Si;> 
 
 LArRENTiAN Series. — The oldest formation with which 
 wo are as yet acquainted is that of the Laurentian rocks, so 
 called because they are largely developed in Canada, north of 
 the river St. Lawrence. A large area of these rocks also oc- 
 curs in Northern New York, rising into the lofty and rugged 
 elevations of the Adirondacks, and there is a third area to tlie 
 south of Lake Superior. The Laurentian series is of vast 
 thickness, and is divided into a lower and upper division. 
 The Lower Laurentian group attains the enormous thickness 
 of about 20,000 feet, and is composed entirely of metamor- 
 phic rocks, consisting mainly of gneiss interstratified with mi- 
 ca-sciiist, with great beds of quartz, and massive beds of crys- 
 talline limestone, of which one varies from 700 to 1,500 feet in 
 thickness. Cona,lomerates also occur, and there are vast de- 
 posits of magnetic and specular iron-ore. Graphite or black- 
 lead — which is merely a form of carbon — occurs disseminated 
 in strings, veins, and beds, through hundreds of feet of Lower 
 Laurentian strata, and its amount is calculated by Dr. Daw- 
 son to be equal in quantity to the coal-seams of an equal area 
 of the Carboniferous rocks. 
 
 Not only is the Lower Laurentian series of vast thickness 
 and greatly metamorphosed, but it must have been elevated 
 above the sea, and subjected to vast denudation, prior to tin; 
 deposition of the upper group. This is shown by the fact 
 that the Upper Laurentian lies unconformably upon the trun- 
 cated edges of the Lower Laurentian. The Upper Lauren- 
 tian group is about 10,000 feet thick, and consists wholly of 
 stratified crystalline rocks. These consist mainly of gneissic 
 and felspathic rocks, often characterized by the occurrence of 
 lime-felspar or Labradorite. The series is extensively devcl- 
 
LAURENTIAN, HURONIAN, AND CAMBRIAN GROUPS. 125 
 
 oped in Labrador, and is sometimes spoken of as the " Labra- 
 dor Series." 
 
 European Laurentian Rocks. — As rc^^ards the occur- 
 rence of Laurentian rocks in Britain, there is still some uncer- 
 tainty. In the Hebrides and along the western shores of 
 Sutherlahdshire (Scotland) Sir Roderick Murchison showed that 
 there occurred great masses of higlily-crystalline gneiss (Fig. 
 51, a). Upon the truncated and highly-inclined beds of this 
 
 Fio. 51.— Diagrammatic section of the old rocks of the Northern ITiffhlands of Scotland, 
 after Sir K. Murchison. — «, Laurentian (?) ffneiss ; ft, lied sandstones and conpioiiuir- 
 ates of Cambrian (?) age; c, Lower Silurian quartz-rock and fossiiiferous liuiestono; 
 d, Metamorphosed Lower Silurian strata. 
 
 "fundamental gneiss" lie great beds of red sandstone and 
 conglomerate {b) ; and these are in turn succeeded unconform- 
 ably by quartz-rock and interstratified limestone (o). These 
 last contain Lower Silurian fossils ; so that the red sandstones 
 and conglomerates beneath them must almost certainly be 
 Cambrian. The lowest gneiss is, however, in a doubtful posi- 
 tion. It is believed by Sir R. Murchison to be Laurentian, but 
 it may, perhaps, be Huronian. There are some other British 
 rocks which are believed to be referable to the Laurentian 
 series ; and it is highly probable that Laurentian rocks will 
 hereafter be shown to exist in other parts of Europe. 
 
 Life of the Laurentian Period. — The Laurentian rocks 
 are often spoken of as the yizoic series (Gr. a, without ; 2oe, 
 life) ; but the name appears to be inappropriate, because there 
 is good evidence to sliow that living beings were in existence 
 ill the Laurentian period. In the first place, it is certain that 
 tlie Laurentian rocks, though now highly metamor])liic, were 
 originally deposited as ordinary sedimentary beds of sandstone, 
 conglomerate, shale, and limestone. There is, therefore, no 
 reason whatever for supposing that the seas of the Laurentian 
 period differed in any respect from modern seas, so far at any 
 rate as to render the occurrence of living beings impossible ; 
 while we know that one of tlie results of metamorphic action 
 is the obliteration of the fossils in the rock affected. Secondly, 
 
 
 4: 
 

 i 
 
 .!■ ! 
 
 m 
 
 126 
 
 GEOLOGY. 
 
 by the researches of Sir William Logan there was discovered 
 in one of the limestones of the Lower Laurentian group a body 
 which has been described under the name of Eozobn Cana- 
 detise^ and is believed to be a gigantic Foraminifer. The 
 organic nature of this body was first detected by Dr. Dawson, 
 of Montreal, and his opinion as to its nature has since been 
 confirmed by the highest authorities. Thirdly, there is good 
 reason to believe that the graphite of the Laurentian rocks is 
 nothing more than metamorphic coal^ and that it is derived 
 from vegetables which flourished during the Laurentian 
 period. 
 
 HuRONiAN Series. — Resting unconformably upon the de- 
 nuded edges of the Laurentian rocks on the borders of Lakes 
 Superior and Huron, is another great series of metamorphic 
 'ocks, to which the name of Huronian has been applied by 
 oir William Logan. They are about 18,000 feet in thickness, 
 and consist of quartzites (altered sandstones), siliceous slates, 
 con "-^ operates, and limestones. Tlie conglomerates sometimes 
 con) ain pebbles derived from the subjacent Laurentian rocks. 
 No fossils have hitherto been found in any part of the Hu- 
 ronian series, and its exact age is, therefore, doubtful. Not 
 improbably it may correspond with the Lower Cambrian rocks 
 of other regions, but it may represent an independent forma- 
 tion to be intercalated in point of time between the Lauren- 
 tian and Cambrian groups. 
 
 Cambrian Series. — The exact limits of the Cambrian 
 rocks are as yet not well defined, different authorities taking 
 different views as to the strata which should be considered 
 under this head. The name " Cambrian " is derived from the 
 fact that thes3 strata are the lowest rocks visible in North 
 Wales and its borders (Cambria). The Cambrian rocks are 
 generally divided into a Lower and Upper division, and they 
 are well developed in various parts of Europe and America. 
 The following gives a general idea of the nature, distribu- 
 tion, and mineral characters of the Cambrian rocks : 
 
 I. Cambrian RocJcs of Britain. — The Lower Cambrian rocks of Britain 
 arc best seen in the Longmynd Hills in Shropshire, and consist of about 
 25,000 feet of variously-colored sandstones, grits, and shales, often ripple- 
 marked, and exhibiting rain-prints, but with very few fossils. These are 
 succeeded by a great series of micaceous flagstones, slates, and shales, 
 which vary in thickness from 6,000 to 2,000 feet, and are of Upper Cam- 
 brian age. They are known as the Lingula Flaga^ from the occurrence in 
 them of a Brachiopod I'jelonging to the genus Lingula (Fig. 57). In North 
 Wales the Lower Camb.nan strata are often highly metamorphosed, and the 
 celebrated Welsh roofinj!:-slate3 are also derived from this division. Gam- 
 
LAURENTIAN, HURONIAN, AND CAMBRIAN GROUPS. 127 
 
 briati rocks occur in other parts of Britain, and the following table exhibits 
 their leading members : 
 
 ^ h a. a a 
 
 Tia. 52.— Section of the Cambrinn rocks of the Lonpmynd. — a. Lower Cambrian prits, sand- 
 stones, and shales; ft, Llnj^ila ttnps (Upper Cambrian); c, Lower Llandeilo rocks 
 (Lower Silurian) ; d, Upper Silurian strata. 
 
 . 1. Lower Cambrian : 
 
 a. Longmynd beds (25,000 feet). 
 6. Llanlo'ris slates (3,000 feet). 
 
 c. Harlech grits (6,000 feet). 
 
 d. Oldhamia slates of Ireland. 
 2. Upper Cambrian : 
 
 c. Lingula Flags of Wales (about 6,000 feet). 
 
 /. Treraadoc slates of North Wales (2,000 feet). 
 
 ff. Skiddaw slates of the north of England (7,000 feet). 
 The last-mentioned group of rocks, namely, the Skiddaw slates of the 
 north of England, are in a doubtful position. They consist of about 7,000 
 feet of dark-colored shales and slates, and they are most clearly the equiva- 
 lent of the Quebec group of Canada, containing many of the same fossils. 
 Upon the whole, it seems safer in the mean while to regard them as Upper 
 Cambrian. 
 
 II. Cambrian Eocks of Bohemia and Sweden. — In Bohemia, M. Barrande 
 has succeeded in demonstrating as underlying the Lower Silurian rocks of 
 that country a zone of rocks, which correspond to the Lingula Flags of 
 Britain, and are, therefore, of Upper Cambrian age. This zone contains 
 many remarkable and characteristic fossils, and is often spoken of as the 
 "Primordial Zone." In Sweden and Norway the Lower Cambrian rocks are 
 represented by a sandstone containing impressions supposed to be referable 
 to sea-weeds or "fucoids." This "Fucoidal sandstone" is succeeded by 
 beds of so-called " alum-schist," which are of Upper Cambrian age, and cor- 
 respond with the Lingula Flags of Britain. Among the most characteristic 
 of the fossils of this " Primordial Zone " are the singular crustaceans known 
 as Trilobites, of which an example is figured on p. 128 (Fig, 53). 
 
 III. Cambrian Rocks of North America. — The Cambrian rocks are rep- 
 resented in North America by the Potsdam sandstone and the Calciferous 
 series. The PoUdam sandstone is mostly a laminated sandstone, or grit, in 
 the State of New York, but limestones are present in addition in the Mis- 
 sissippi basin, and it consists of a great thickness (2,000 to 7,000 feet) of 
 slates, sandstones, and limestones, along the Appalachian chain. It contains 
 a good many fossils, among which are Trilobites resembling those of the 
 "Primordial Zone" in Bohemia. A characteristic form is figured hereafter 
 (Fig. 54). 
 
 The Calciferous series consists of a hard calcareous sandstone, or *' sand- 
 rock," in the State of New York ; but it consists of sandstone with well-de- 
 veloped magnesian limestone in the basin of the Mississippi ; and along the 
 Appalachian chain it consists of sandstones and limestones, subordinated to 
 great masses of shale. In their last-mentioned development the Calciferous 
 rocks have been termed the " Quebec group," and, as before said, they are 
 
128 
 
 GEOLOGY. 
 
 undoubtedly the equivalent of the Skiddaw slates of Britain. They attain a 
 thickness of from 5,000 to 7,000 feet ; but it is not clear whether they are 
 truly referable to the tipper Cambrian or to the base of the Silurian system. 
 Most probably they are transition-beda between the two formations. 
 
 Fio. BS.—Paradoofides, a Trilobite from 
 the *' Priiaordiul 2jono " of i^obemio. 
 
 Fio. 54. — DikelocepTtalua MinnesotenDi/t 
 (Dale Owen) ; one of the Trllobites of 
 the Potsdam Sandstone. 
 
 Life op the Cambrian Period. — The life of the Cam- 
 brian period is but scanty, and the forms represented are all, 
 comparatively speaking, low in the zoologi- 
 cal scale. In the Lower Cambrian rocks fos- 
 sils have hitherto proved extremely scarce. 
 With the exception of one doubtful fossil, 
 the commonest organic remains are the bur- 
 rows of sea-worms, allied to the common 
 Lob-worm of our coasts. These are very 
 abundant, and are found even among the 
 hardest and most quartzose rocks of the for- 
 mation. In rocks believed to be of this age 
 in Ireland occurs the singular fossil called 
 Oldhamia (Fig. 55), the exact nature of 
 which is uncertain. It is sometimes be- 
 lieved to be most closely allied to the Sea- 
 firs {Sertularians) ; but the more probable 
 view is that it is a calcareous sea-weed, \i]s.e'Fio.!i'y.—omamia an- 
 the " corallines" of the present day. 
 
 In thu Upper Cambrian rocks, fossils become pretty plen- 
 tiful, and some higher types appear. Trilobites are especially 
 abundant, and belong to peculiar types in most instances. 
 
LAURENTIAN, UURONIAN, AND CAMBRIAN GROUPS. 120 
 
 Some of the characteristic forms have been already figured 
 (Figs. 53, 54), and one of the species from the Lingula flags is 
 given below (Fig. 58). Besides Trilobites, the Liugula Ihigs 
 contain in abundance the remains of another Crustacean, ILjmer 
 nocaris vermicauda (Fig. 56). The Lingula (Fig. 5T), from 
 
 Lingula Flag Fossils. 
 
 Fig. t^,—ITymenocarw vermicavda. 
 ^ nut. size. 
 
 Fig. bl.—LinqtUa DaHHi- 
 
 a. V nat. size. 
 
 b. bistortt'd by cleavage. 
 
 Fio. 58. — Olenua mi' 
 
 criiniM. 
 
 }i uat, size. 
 
 which the name of this group is derived, is a Brachiopodous 
 shell, and is found in great abundance. In the Primordial 
 ^one of Bohemia, and in the alum-schists of Scandinavia are 
 contained many Trilobites, while the former has also yielded 
 a few Brachiopods and some Echinoderms. The Potsdam 
 Sandstone contains Trilobites, a small Brachiopod, burrows 
 and tracks of sea-worms, and other fossils. In the Upper 
 Cambrian rocks appear for the first time the singular fossils 
 known as Graptolites (Gr. grapho, I write ; lithos^ stone). 
 These curious organisms are believed to be most nearly allied 
 
 to the living sea-firs, but they are in 
 many respects quite peculiar and un- 
 like all recent organisms. In the 
 Quebec group of Canada, and in the 
 Skiddaw slates of Britain, Grapto- 
 lites occur in great plenty, and in 
 the most varied forms. One of the 
 most characteristic species is figured 
 below (Fig. 59). In the Skiddaw 
 slates also occur the remains of what 
 ^f ^^Tu?'5'r"''"*?P/"^ hrycnoi. njygt almost certainly be regarded as 
 
 rfe«, a Skiddaw-slate Graptolite. . *^ i • i^ , i 
 
 marine plants of some kmd or otlier. 
 Fossils of an apparently vegetable nature have also been dis- 
 covered in the Cambrian rocks of Sweden. 
 
 Lastly, in the Potsdam Sandstone have been detected the 
 earliest footprints as yet discovered. These have been de- 
 scribed under the name of Ftotichnites. They were at first be- 
 
I \i 
 
 ( 
 
 m 
 
 liiUi I 
 
 li 
 
 130 
 
 GEOLOGY. 
 
 lieved to have been made by some animal of the Turtle family, 
 but they are considered by Owen to be the tracks of some 
 large Crustacean. Their size is very remarkable, as they indi- 
 cate an animal of probably several feet in length. 
 
 Tabular View op the Chief Cambrian Strata. 
 
 1. Lower Camhrian (= Huronian?) : 
 
 a, Longmynd beds, Llanberis Slates^ and Harlech 
 
 Grits of Britain. 
 h. Fucoidal Sandstone of Sweden. 
 
 2, Upper Cambrian: 
 
 c. Lingula Flags and Tremadoc Slates of Britain. 
 
 d. " Primordial Zone " of Bohemia. 
 
 e. Alum-schists of Sweden. 
 
 f. Potsdam Sandstone and Calciferous Sand-rock of 
 
 North America. 
 
 g. Quebec Group of Canada (?). • 
 h, Skiddaw Slates of north of England (?). 
 
CHAPTER XVI. 
 
 BILiriSIAN SEBIES. 
 
 Following the Cambrian comes the great Silurian series 
 of rocks, first clearly established and definitely worked out by 
 Sir Roderick Murchison, the founder of the Silurian system. 
 The exact limit between the Cambrian and Silurian forma- 
 tions is one which is not clearly defined, since there does not 
 appear to be any general physical break between the two 
 groups. The line of demarcation between them is in the pres- 
 ent state of our knowledge an arbitrary line, and is derived 
 cliiefly from the characters of the Trilobites. There are rocks, 
 however, such as the Tremadoc slates, the Skiddaw slates, and 
 the Calciferous and Quebec group, in which there is an inter- 
 mixture of Cambrian with true Lower Silurian types. These 
 rocks, therefore, might be regarded as Upper Cambrian or as 
 Lower Silurian, or as passage-beds between the two. It is to 
 be remembered, also, that the Tremadoc slates and Lingula 
 flags are regarded by Sir Roderick Murchison as being the 
 basement-beds of the Lower Silurian. 
 
 The name " Silurian '' was proposed by Sir R. Murchison 
 for a great series of strata lying bi. \vi v the Old Red Sandstone, 
 and occupying those parts of Wales and England which were 
 at one time occupied by the " Silures," a tribe of ancient Brit- 
 ons. The Silurian rocks are largely developed in Wales, the 
 north of England, Scotland, and Ireland, in various parts of 
 Europe, especially Bohemia, Saxony, Russia, and Sweden, and 
 in the North American Continent. The entire series is divis- 
 ible into the two sections of the Lower and Upper Silurian 
 rocks, each in turn split up into smaller subdivisions, the names 
 of which have usually been taken from localities where they 
 are unusually well developed, or where they were first studied. 
 We shall consider each ot these divisions separately, fij:st as 
 
 
f 
 
 i 
 
 t 
 
 1^ 
 
 •■mill 
 W 
 
 i! 
 
 132 
 
 GEOLOGY. 
 
 they occur in Britain, and then as thoy are developed in North 
 America ; the former country having been generally adopted 
 by geologists as the typical Silurian region of the world. It 
 is also the region which forms the special subject of Sir Rod- 
 crick Murchison's classical work " Siluria." 
 
 Silurian Rocks of Britain. — Tl "^man rocks of Brit- 
 ain, as indicated in the annexed secti^.., are divided into tlic 
 following groups from below upwai J : 
 
 a. Lower Llandeilo group, 
 
 b. Upper Llandeilo group, 
 
 c. Bala, Caradoc, or Coniston group, 
 
 d. Lower Llandovery group, 
 
 e. Upper Llandovery group, 
 
 f. Weidock griuip, \- Upper Silurian. 
 ff. Ludlow group. 
 
 ."N 
 
 > Lower Silurian. 
 
 Fio. 60. — Generalized section of the Silurian Bocks of Britain. 
 
 1. The Lower Llandeilo group (Fig. 60, a) derives its 
 name fron. the town of Llandeilo, in Wales, where it consists 
 of dark-colored micaceous flags, with earthy shales and gritty 
 sandstones. It contains Brachiopods, Trilobites, Graptolites, 
 and other fossils, and one of the most characteristic of the 
 latter is figured below (Fig. 61). 
 
 FiQ. 61.— Dldymograpsus patulua (Hall). — Lower Llandeilo, Quebec, and Sklddaw groups. 
 
 2. The Tipper Llandeilo group consists in Wales of a great 
 series of micaceous flags and dark-colored shales, often with 
 interstratified igneous matter. In Scotland this group consists 
 of a great assemblage of shales and grits, the former mostly 
 very dark in color, with anthracitic lands containing numerous 
 Graptolites. Besides these singular organisms, the Upper 
 Llandeilo rocks of Wales contain numerous JSrachiopod% Cc- 
 phalopods^ and Trilobites. Two of the most characteristic of 
 the last-mentioned fossils are figured on p. 133 (Figs. 62, 63). 
 
SILURIAN SERIES. 
 
 133 
 
 ITpper Llandeilo Fossils, 
 
 Fig. (}2.--A8aphus tyrannxu. 
 
 Fio. i&.—Ogygia Buchil. 
 
 3. Tlic Hala or Coniston group consists in Wales of 
 slates, grits, and sandstones, to the thickness of about 5,500 
 feet, with two int i stratified limestones. In the north of 
 England it consists of black flags, a well-marked limestone 
 with intercalated shales, and black mudstones containing nu- 
 merous Graptolitcs. The group is also well developed in i^cot- 
 land and Ireland. Wherever it occurs, the Bala Ibrniation is 
 richly fossiliferous, its most characteristic fossils being lirathio' 
 podSj belonging chiefly to the genus Oi'this (Figs. 64, G5), and 
 having a peculiar, simple, plaited form. 
 
 Brachiopods op the Bala Group. 
 
 ■ groups. 
 
 a great 
 n with 
 onsists 
 mostly 
 merous 
 Upper 
 d% Ce- 
 istic of 
 2, 63). 
 
 Fig. M.—Orthia 
 tricenaria. 
 X oat. size. 
 
 Fig. 65.— <)r«lfa 
 vettpertilio. 
 X nat. size. 
 
 FiQ. QQ.—Strophomena 
 
 grnrulw. 
 
 % nat. size. 
 
 It is also characterized by several Trilobltes^ and by a group 
 of peculiar Echinoderms^ which are related to the Crinoids or 
 stone-lilies, and which are known as Cystideans (see p. 139 
 Fig. 78). 
 
 4. The Lower Llandovery group is so called from its oc- 
 7 
 
 yill 
 
134 
 
 GEOLOGY. 
 
 m u 
 
 currence near the town of Llandovery, in South "Wales. It 
 consists of slates and sandstones, with great beds of conglom- 
 erate, and it is unconformably overlaid by the Upper Llando- 
 very group, in which also most of its fossils occur. 
 
 5. The Upper Llandovery group forms in Britain the base 
 of the Upper Silurians, and rests unconformably upon the 
 Lower Llandovery, which forms the summit of the Lower Si- 
 lurians. This want of conformity, however, between the 
 Lower and Upper divisions of the Silurian series, though cer- 
 tainly the rule in Britain, does not seem to exist elsewhere. 
 The Upper Llandovery group consists of limestones, shales, 
 conglomerates, sandstones, and slates, and attains a consider- 
 able thickness (nearly 2,000 feet). Among its most charac- 
 teristic fossils, abounding especially in the limestones, are 
 Brachiopods of the genus Pentamerus (Fig. G7). 
 
 Fio. 67. — PentameruB Imvia, a Brachlopod of the Upper and Lower Llandovery groups. 
 
 J; "iM^^ 
 
 6. The Wenloek group consists of a great mass of shale 
 and fla one, underlaid and surmounted by limestones, the 
 whole .aining a thickness of 3,000 feet. It is richly charged 
 with lossils, of which, perhaps, the most characteristic are 
 corals (Figs. 68, 69, 70.) Besides these, however, occur numer- 
 ous brachiopods and Trilobites, with various forms of bivalve 
 and univalve Shell-fish. 
 
 7. The Ludlow group consists of shales, limestones, and 
 sandstones, in Wales, and of grits and shales in the north of 
 England, having a total thickness of from 2,000 to 4,000 or 
 6,000 feet or more. 
 
 The entire series is charged wiiL very numerous fossils, 
 
SILURIAN SERIES. 
 
 136 
 
 Wenlock Corals. 
 
 
 Fig. 69. — ffalysitta 
 
 cate7iularius, 
 
 the ^' chain conU." 
 
 Pro. CQ.—FavosiUt 
 Oothlandica. 
 
 Fro. lO.—Omphyma 
 turbinatvm. 
 
 comprising Sponges, Brachiopods, univalve and bivalve Mol- 
 lusks, Criuoids and Star-fishes, Trilobites and other Crustacea^ 
 and a few Graptolites. Some of the more characteristic Ura- 
 chiopoda are figured below. 
 
 Ludlow Brachiopods. 
 
 Fio. "H.—Orthia elegantula. 
 
 Fro. 12.—Rhyncihon«llanavicula, 
 
 Fro. 1Z.—RhynchoneUa Wilaoni. 
 
 Besides the above, and more remarkable than any of these, 
 are certain remains of fishes, which present us with the first 
 undoubted traces of vertebrate animals upon the globe. The 
 remains in question are those of fishes belonging to the genus 
 JPteraspiSf and to the order of the Ganoid fishes. The head 
 
 ^(s 
 
136 
 
 GEOLOGY. 
 
 i ;i 
 
 ':' 
 
 Vr 
 
 was covered with a singular buckler or shield (Fig. 74), and 
 
 in common with other Ganoids the scales 
 
 were in the form of bony plates covered 
 
 by shining enamel. The tail, also, as in 
 
 most Ganoids, consisted of two unequal or 
 
 unsymmetrical lobes. 
 
 At the very summit of the Upper Lud- 
 low rocks is a well-known stratum, vary- 
 ing from one inch to nearly one foot in 
 thickness, and known as the " bone-bed." 
 In this bed occur the remains of 'ics 
 probably most nearly allied to the ang 
 Port Jackson shark. Spines of such fishes 
 occur in abundance, and have been referred 
 to the genus Onchus (Fig. 75) ; with these 
 also occurs the shagreen of a shark-like 
 fish, for which the genus Thelodus (Fig. 76) has been consti 
 tuted. * 
 
 Yia. 74.— Buckler covering 
 the head of Pterattpis 
 Banksii, from the Lud- 
 low rocks (after Murcbi- 
 Bon). 
 
 Fishes op the Ludlow Bone-Bed. 
 
 Fig. 15.— Onchus tenuisiHatua, 
 
 Fio. 76.— Shagreen scales of Thtlodus. 
 
 This bed is further of interest as containing the earliest 
 remains of land-plants. These are in the form of numerous 
 minute globular bodies, which have been determined by Dr. 
 Hooker to be the seed-vessels of a cryptogamic land-plant, 
 probably most nearly allied to our club-mosses. 
 
 Silurian Rocks op North America. — The Silurian series 
 of North America is a remarkably full and varied one, and a 
 general correspondence can readily be established between it 
 and the British series. The two series, however, differ in cer- 
 tain important points, and nothing more than a general equiv- 
 alency can be asserted to exist between them. The main 
 divisions of the Silurian rocks of North America are as follows 
 (Fig. 77) : 
 
 a. Trenton _Period, [ Lower Silurian. 
 
 h. Hudson Period, J 
 
 c. Niagara Period, 
 
 d. Salina Period, 
 
 e. Lower Helderberg Period, 
 
 Upper Silurian. 
 
SILURIAN SERIES. 
 
 137 
 
 1. The Trenton period corresponds to the Llandeilo period 
 of Britain, and is characterized by the piedoniinance of lime- 
 stones, of which the two most important are the Chazy Liine- 
 stone and the Treutou Limestone. The Trenton Limestone is 
 
 Fio. 77.— Generalized section of the Silurian rooks of North America.— a, Limestones of the 
 Trenton period; ft, Hudson Kiver and Utica slates; c, Niagara group; d^ Solina group; 
 e, Lower Ilelderberg group. 
 
 splendidly exposed at the Falls of Trenton in Central New 
 York, and is believed to be higher than the Llandeilo, and to 
 represent the Bala Limestone of Wales. Fossils are extremely 
 abundant in the Trenton period, consisting especially of 
 Brachiopods, Trilobites, and Cephalopods allied to the Nautilus. 
 3. The Hudson period comprises the two groups of the 
 Uiica Shales and Hudson River Shales, both well exhibited in 
 the State of New York. The Uiica Shale varies in thickness 
 from 15 to 300 feet or more, and consists chiefly of dark- 
 colored shales, sometimes with intercalated beds of limestone. 
 The Hudson Itiver Shales vary from 20 to 1,600 feet in thick- 
 ness, and consist generally of shales or slates, becoming, how- 
 ever, highly calcareous in the West. The shales of both 
 groups are often highly carbonaceous. The fossils are chiefly 
 Trilobites, Corals, and Bivalve Mollusks, with an abundance of 
 Graptolites. The Hudson period is believed to correspond 
 with the Bala or Coniston period of Britain. 
 
 3. The Niagara period in its fullest development com- 
 prises conglomerates and sandstones at the base (Oneida 
 group), marls and sandstones (Medina group), sandstones and 
 shales, sometimes calcareous (Clinton group), and shales and 
 limestones (Niagara group). The fossils are extremely abun- 
 dant, the predominant forms being Corals, Crinoids, and Bra- 
 chiopods. The Niagara limestone, over which the Niagjira 
 River is precipitated to form the great falls, is undoubtedly 
 tlie equivalent of the Wenlock gioup of Britain. The lower 
 beds, namely the Clinton, Medina, and Oneida groups, proba- 
 bly correspond with the Llandovery groups of Wales. 
 
 4. The Salina period comprises marls, sandstones, and 
 limestones, with masses of gypsum, the whole impregnated in 
 
 TV" 
 
 j')' 
 
fT' 
 
 V 
 
 1 1 
 
 1i 
 
 J;!; 
 
 138 
 
 GEOLOGY. 
 
 many places with salt. The salt is obtained for commercial 
 purposes from wells sunk in the strata to a depth of some- 
 times more than 300 feet, the brine thus obtained being sub- 
 sequently evaporated by the heat of the sun, or artiiioially. 
 Fossils are very scjarce in this period. 
 
 5. The Lower Helderberg period derives its name from 
 the Helderberg Mountains, South of Albany, where the rocks 
 of this period attain a thickness of more than 200 feet. The 
 Lower Helderberg strata are essentially limestones, capable 
 of being subdivided in the State of New York into several 
 minor subdivisions, characterized by their included organic 
 remains or mineral characters. The fossils of the period are 
 extremely abundant and consist chiefly of Corals, Crinoids, 
 and Brachiopods, among which last the genus Pentamerus 
 (Fig. 67) is conspicuously represented. Tlie Lower Helderberg 
 period is believed to correspond with the Ludlow period in 
 Britain. • , .^ - , ^ > iti ^ 
 
 The annexed table shows the subdivisions of the Silurian series as de- 
 veloped in the State of New York, and their supposed British equivalents ; 
 the table being in ascending order : 
 
 Silurian strata of New York. British equivalents. 
 
 1. Trenton period (comprising the Chazy,1 The Lower Silurian se- 
 Birds-eye, Black-River, and Trenton limestones). 
 
 2, Hudson period (comprising the Utica 
 shales and Hudson River shales). 
 
 8. Niagara period (comprising the Oneida 
 conglomerate, Medina sandstone, Clinton group, 
 and Niagara limestone). 
 
 4. Salina period (comprising the Guelph lime- 
 Stone and Onondaga salt group). 
 
 5. The Lower ileldorberg period (comprising' 
 the Tentaculite and Water-lime groups, the Lower 
 Pentamerus limestone, the Delthyris shaly lime- 
 stone, and the Upper Pentamerus limestone). 
 
 rics (comprising the Llan- 
 deilo, Bala, and Lower 
 Llandovery groups). 
 
 The lower portion of the 
 Upper Silurian series(com- 
 prising the Upper Llan- 
 dovery and Wenlock). 
 
 No British equivalent. 
 
 The higher portion of 
 the Upper Silurian series 
 '(comprising the Ludlow 
 group). 
 
 Life of the Silurian Period. — In the lower portion of 
 the Cambrian series, as we have seen, organic remains are 
 exceedingly scanty ; but in the upper portion of the same fos- 
 sils are tolerably abundant, and belong in part to types which 
 pass upward into the overlying Silurian series. The fossils 
 of the Silurian series are almost exclusively marine, the only 
 exceptioti being the traces of land-plants allied to recent Club- 
 mosses which have been discovered in the ^^ery highest beds 
 of the system. The only other vegetable remains which have 
 been hitherto detected are referable to sea-weeds, and these 
 are tolerably plentiful and well preserved in some beds. The 
 
SILURIAN SERIES. 
 
 180 
 
 lower forms of animal life {JProtozoa) are represented by Fora- 
 miniferous Shells and by Sponges, as well as by certain singular 
 fossils which are apparently transition-forms between the two. 
 The Zoophytes ( Cvelenterata) are represented by the Grap- 
 toliteSy and by numerous Corals. The former are almost ex- 
 clusively Silurian fossils, and are preeminently characteristic 
 of the Lower Silurian rocks. They commence in the Upper 
 Cambrians, in which they seem to attain their maximum (sup- 
 posing the Skiddaw and Quebec groups to be rightly referred 
 to this formation). They are represented by many forms in 
 the Lower Silurians, and they are found in greatly-diminif-hcd 
 numbers in the Upper Silurian rocks, only a single genus being 
 known to have survived into the succeeding period of the Old 
 Red Sandstone. Corals are very abundant in many parts of 
 the Silurian series, certain formations, such as the Niagara 
 limestone, being so largely composed of these fossils, that they 
 have been supposed to be ancient coral-reefs. The JEchino- 
 derms are more especially represented by the group of the 
 Crinoids^ or Stone-lilies, of which many beautiful foims occur 
 in both Lower and Upper Silurian strata. Nearly allied to 
 the Crinoids is a singular group of Echincderms known as 
 Cystideatis (Fig. 78), which are preeminently characteristic 
 of the Lower Silurian period, but are found in diminished 
 numbers in the Upper Silurians. They resembled the Crinoids 
 in having a jointed stalk or column, which in most cases served 
 as a stem of attachment ; but the body was protected by cal- 
 careous plates immovably jointed together, and there were 
 rarely any true arms. The groups of the Star-fishes and Brittle- 
 stars were also found in Silurian seas, and are especially 
 abundant in the Upper Silurian period; but no true Sea- 
 urchins have hitherto been discovered. 
 
 The lower division of the Annulose sub-kingdom is rep- 
 resented by the tracks of sea- worms, and by the tubes of Tube- 
 worms. The higher division of the Articidates appears to 
 have been represented wholly by the Crustaceans, no Spiders, 
 Centipedes, or Insects, having been hitherto detected. When 
 we consider, however, that these creatures are almost all air- 
 breathers, and that the Silurian strata are all marine, we need 
 not be surprised at this. The two most important groups of 
 Silurian Crustacea are the Trilohltes and the Eurypterids. 
 The former abound in all the divisions of the Silurian series, 
 and some of the characteristic forms have been already figured 
 (Figs. 62, 63). They are somewhat allied to the living Horse- 
 shoe Crabs, and are distinguished (Fig. 79) by having the 
 
140 
 
 '.qEOLOGY. 
 
 head protected by a semicircular shield, while the body is 
 more or less distinctly three-lobed. 
 
 The Eurypterlds (Fig. 45) were mostly of very large size, 
 some having attained a length of several feet. They are de- 
 cidedly allied to the recent Horse-shoe Crabs {Limulus). They 
 
 Fig. 19>.—Echino8phcerite^ Balticus, 
 a Lower Silurian Ci/xtideiin. — a, 
 Mouth; b, Poiut of attachment 
 of the stem. 
 
 Fio. 19.— 7Yinvc?ev4 concentrictis, a Lower 
 Silurian Triloblte. 
 
 are confined to the upper portion of the Silurian series, and 
 pass upward into the succeeding formation of the Old Red 
 Sandstone. 
 
 Tlie sub-kingdom Mollusca is very largely represented in 
 the Silurian deposits. The lowly-organized shell-fish known 
 as Srachiopods are so abundant in all parts of the system, 
 that the Silurian period has been spoken of as the " age of 
 Brachiopods." Illustrations will be found in Figs. 64-66, 
 and 71-73. The true bivalves and the univalve shell-fish 
 are also represented by many and varied forms. Tlie highest 
 division of the Mollusks — that of tho Cephalopoda or Cuttle- 
 fish order — is represented by an enormous number of forms 
 more or less closely allied to the Pearly Nautilus. Some idea 
 of the abundance of these organisms may be obtained from 
 the fact that M. Barrande has described over a thousand species 
 from the Silurian rocks of Bohemia alone. Tlie most abundant 
 and characteristic of the Silurian Cephalopods are the OrtJio- 
 ceratites (Gr. orthos, straight ; keras, horn). These resembled 
 the Nautilus in essential structure, but the shell was straight 
 and not curved into a spiral (Fig. 81). The size of some of the 
 
SILURIAN SERIES. 
 
 141 
 
 Orthocerata was very remarkable, specimens having been 
 found of a length of seven or eight feet. In nearly allied forms 
 the shell was more or less curved (Fig. 80), but it is never 
 coiled into a close spiral as in the Nautilus. 
 
 Silurian CErnALOPODS. 
 
 Fio. 80.— 7VocAoc«raa giitanieua. X nat 
 size. 
 
 t*tO. 81.— Fragmont of Orthoceras Zuderut, 
 
 The tJub-kingdom Vertehrata is only represented in the 
 highest division of the Silurian rocks, and there only in its 
 lowest forms, namely by Fishes. The discovered remains, 
 however, indicate the existence in the later Silurian seas of 
 two orders of fishes. Ganoid fishes, allied to the living Stur- 
 geon, and Shark-like fishes, allied to the living Port Jackson 
 Shark. It is noticeable, also, that no undoubted traces have 
 hitherto been discovered of the lower orders of fishes, and 
 that remains of these may be looked for in the inferior portion 
 of the Silurian system. 
 
«! 
 
 CHAPTER XVII. 
 
 OLD RED SANDSTONE. 
 
 The Silurian rocks are succeeded upward by a great sys- 
 tem of rocks, mainly of the nature of sandstones and conglom- 
 erates, to which the name of Old Red Sandstone has been ap- 
 plied. The name Devonian formation is also employed to 
 designate these same strata, rocks supposed to belong to this 
 period being largely developed in Devonshire, in England. 
 It is probable, however, that the Devonian rocks represent a 
 portion only of the Old Red Sandstone, and tha+. they cannot 
 be regarded as the full equivalent of the Old Red Sandstone 
 of other regions. The term " Devonian " may, however, when 
 thus understood, be usefully employed as a general term for 
 all the strata which intervene between the Silurian System 
 and the succeeding formation of the Carboniferous rocks. 
 
 The uncertainty as to the exact position of the Devonian 
 rocks of Devonshire in the series of the Old Red Sandstone, 
 or the uncertainty as to whether they represent the Old Red 
 Sandstone in whole or in part, arises from this — that though 
 both formations are fossil iferous, the peculiar fossils of each 
 are never found associated together. The peculiar fossils of 
 the Old Red Sandstone proper are not found in the rocks of 
 Devonshire; and the fossils of the latter, though found in 
 equivalent strata on the Continent of Europe, do not occur in 
 the beds to which the name of Old Red Sandstone was origi- 
 nally applied. This, however, may be largely due to the fact 
 that, while the Devonian strata are undoubtedly marine in 
 their origin, there seems reason to conclude that the Old Red 
 Sandstone proper was, in part at any rate, a fresh-water de- 
 posit. The two groups, therefore, might be truly contempora- 
 neous, and yet might not contain the same fossils. 
 
 Old Red Sandstone op Britain, — ^The Old Red Sand- 
 
 II IT I liiifirtiMlliiitHiiliri* 
 
n 
 
 OLD RED SANDSTONE. 
 
 143 
 
 stone is preeminently a British formation, and is better devel- 
 oped in Scotland than anywhere else in the world. It is 
 divisible into three divisions, the Lower, Middle, and Upper 
 Old Red Sandstone. 
 
 The Lower Old Jied reposes with perfect conformity upon 
 the highest beds of the Upper Silurians, the two formations 
 appearing to pass into one another by an intermediate series 
 of " passage-beds," which contain large Crustaceans of the 
 family of the Earypterlda. The Lower Old lied consists niaiidy 
 of massive conglomerates, with sandstones, shales, and concre- 
 tionary limestones. Its organic remains consist chiefly of 
 plants. Crustaceans, and fishes. The plants are sometimes 
 abundant, but are always imperfect, though thev show occa- 
 sionally woody tissue, and exhibit decided indications of a 
 terrestrial origin. Tlie Crustacea are abundant, and are all 
 E'lrypterlds^ similar to, though specifically distinct from, the 
 Earypterids of the Upper Silurian (Fig. 45). The most char- 
 acteristic fossils, however, of the Lower Old Red are fishes^ 
 some of which are peculiar to this period. Among these 
 is the singular genus Cephalaspis, which agrees with the 
 Pleraspis of the Ludlow rocks in having the head covered 
 with a buckler of enamelled plates (Fig. 82). 
 
 Dccur m 
 
 Pio. %2.—Cephalaspln Lyellll, a Ganoid flsb of tbo Lower Old Tied Sandstone. — n^ One of 
 the scales covering the head ; 6, c, Scales from dltfereut parts of the body and tail. 
 
 The Middle Old Red of Scotland consists of dark-gray 
 flagstones, bituminous, flaggy shales, and conglomerates, 
 sometimes accompanied by shales having irregular calcareous 
 nodules imbedded in them. The fossil remains are chiefly 
 fishes, with one Crustacean, and a few plants. 
 
 The Upper Old Red of Scotland consists of pebbly con- 
 glomerates, sandstones and shales, and contains many fishes, 
 

 144 
 
 GEOLOGY. 
 
 a good many fragments supposed to belong to sea-woods, 
 and some undoubted land-plants. One of these, a fern 
 (Fig. 83), has Ijeen found in beds of the same 
 age in Irehmd, and has been described under 
 the name of Adiantites Ilihernicus. It is 
 accomj)a'nied with a large fresh-water mussel 
 {Anodonta Jukesi), and with fish-remains. 
 The plants of the Upper Old Red as a wIkjIc 
 approximate in general characters to those 
 of the coal-formation. The fishes of the Up- 
 per Old Red are all specifically and generi- 
 cally distinct from those of the Carboniferous 
 formation. One of the most characteristic 
 forms is figured below (Fig. 84). 
 
 In Britain generally, while the Lower Old 
 Red is always conformable with the Upper 
 Silurian, and the Upper Old Red is almost 
 always conformable to the Lower Carbonifer- 
 ous rocks, there appears to be always a want Adianiiulm^rnicm. 
 of conformity between the Lower and Upper 
 Old Red. Wiierever this unconformity, however, has been 
 observed, the Middle Old Red appears to be wanting ; while 
 
 O 
 
 [S^Mtilifc 
 
 ^F 
 
 
 s^ 
 
 i 
 
 m.^i^ 
 
 a 
 
 Fio. 84. — JIoloptijcAius, as restored by Prof. Huxley. 
 
 no systematic break can be detected in the equivalent rocks 
 in North America. 
 
 Rocks op Devonshire. — In North and South Devon 
 there occurs underlying the Carboniferous rocks a great series 
 of strata which has been regarded as the equivalent of the Old 
 Red Sandstone. Though certainly referable, in great part at 
 any rate, to the period of the Old Red Sandstone, it does not 
 appear that the Devonian rocks can be regarded as the equivor 
 
OLD RED SANDSTONE. 
 
 145 
 
 ; rocks 
 
 lent of the Old Red Sandstone of Scotland. Tlie Devonian rocks, 
 however, are largely represented on the Continent of Europe, 
 and they are richly lossiiiferous ; though they do not contain Jiny 
 of the characteristic Crustaceans^ and only one or two generic 
 representatives of the characteristicyifV/ea of the Scotch Old Red. 
 The Devonian rocks of Devonshire consist essentially of 
 greenish slates, alternating with sandstones, conglomerates, 
 and well-developed bands of blue crystalline limestone and 
 calcareous slates. They have been divided into three groups, 
 distinguished by local names. The most characteristic fossils 
 of the Devonian rocks are Corals, Brachiopods, and Trilobi^es, 
 with Crinoids, and bivalve and univalve Mollusks. Among the 
 Brachiopods, the most characteristic forms belong to the genus 
 l^pirifer {F'lQ, 85), and are distinguished by their being greatly 
 
 Fio. 85. — '^phi/er (flojunctua. 
 Upper Devonian. 
 
 Fia. 86. — Calceola Bandalina. — a. Cup of the coral; 
 6, Lid. 
 
 extended from side to side. These fossils are so abundant in 
 certain strata of the same age in Germany, that the name of 
 
 " Spirifer-sandstone " is given to the 
 beds. Among the corals, one of the 
 most remarkable is the Calceola (Fig. 8G), 
 which is furnished with a lid or cover, 
 and was long regarded as being referable 
 to the Brachiopods. 
 
 Trilobites are abundant in many De- 
 vonian beds, and in many cases belong 
 to Silurian genera. A very abundant 
 and characteristic species is the PJiacops 
 latifrons (Fig. 87). 
 
 Devonian Rocks of North Amer- 
 ica. — In no country in the world prob- 
 ably is there a finer and more complete 
 exposition of the strata intervening be- 
 tween the Silurian and Carboniferous for- 
 
 Tin.^i.~rhacop8iatifrovj>. nations, than in the United States. The 
 Devonian of Europe, Asia, following are the main subdivisions of 
 America? *" " the Dcvoulan rocks of the State of New 
 
 
 vj4| 
 
140 
 
 GEOLOGY. 
 
 >■ Lower Devonian. 
 
 York, in wliich, prob.'il)ly, the scries is most typically dis- 
 played (see secti(M», Fi;^'' ^'^i ) - 
 
 1. Oriskany period (Oriskany Sandstone), ' 
 
 2. Cornifurous period (comprising the 
 
 Caiida-GalU grit, Schoharie grit, and 
 Upper Helderberg group), 
 
 3. Hamilton period (comprising the Mar- 
 
 celliis, Hamilton,and Genesee groups), 
 
 4. Chemung period (comprising the For- J- Upper Devonian. 
 
 tage and Cliemung groups), 
 
 5. Catskill period (Catskill Sandstone), 
 
 Fig. 87X-— 0<'n<'m"i'c<l section of the Devonian rocks of the State of New York.— (7, Oris- 
 kany sandstone; b, Uornlferous aeries; c, Uainlltoa series; d, Chemuiig series; e, 
 CatskUl series. 
 
 ir 
 
 I 1^: 
 
 ■H 
 
 1. The Oriskamj Sandstone has a thickness of from five to 
 thirty feet, and is named from the town of Oriskany, in Oneida 
 County, New York. The rock is mostly a coarse-grained, yel- 
 lowish sandstone, replete with fossils, of which the most nu- 
 merous and characteristic forms are Brachiopods. The fossils 
 of the Oriskany sandstone are in many respects relatinl to 
 those of the highest Silurian rocks, and the determination of 
 this formation as the base of the Devonian series is to a great 
 extent an arbitrary one. 
 
 2. The Corniferous Period is characterized by sandy strata 
 in its lower portion, and calcareous beds above. The lowest 
 beds (Cauda-Galli grit) are characterized by a singular spiral 
 fossil, which has been supposed to b^^ a 5 - '^-eed. The calca- 
 reous division (Upper Hclderbf '^ oup) extends from East- 
 ern New York to beyond t\v issippi, ar 1 contains a pro- 
 fusion of fossils, especially C 3, Brachiop(< ., and Trilobites. 
 The corals especially are so al> 
 
 idant 
 
 ^^ 
 
 in some beds as to leave 
 no doubt that the rock is the remain of an ancient coral-reef. 
 In this period, also, are the first discovered remains of 'Fishes 
 as yet found in the American Continent. These remains are 
 referable partly to shark-like fishes, and partly to Ganoids^ and 
 it is noticeable that their occurrence in America is considerably 
 later than in Britain, where fishes are found in the Upper Si- 
 lurians. The name "Corniferous" is derived from le fact 
 
gLD RED SANDSTONE. 
 
 147 
 
 evonian. 
 
 cvonian. 
 
 ins are 
 
 that one of the limestones of this period (Corniferous lime- 
 stone) contains numerous nodules ol" hornstone, a kind of im- 
 perfect flint. The hornstone occurs much in tlie same way as 
 the flints in chalk, and, as we shall see hereafter, its origin is 
 a sinular one, for it has been shown to contain remains of simi- 
 lar organisms. The name Corniferous is, therefore, derived 
 from this fact (Lat. cortm, horn ; fero^ I bear). The maximum 
 thickness of tlie rocks of the Corniferous periotl appears to 
 fall short of 400 feet, and it is much less than this in most lo- 
 calities. 
 
 ij. The rocks of the Hamilton Period are shales, sometimes 
 highly carbonaceous, at the base (Marcellus shales), shales, 
 flags, and limestones (Hamilton beds) in the middle, and 
 shales again at the top (Genesee shales). The maximum 
 thickness of the entire series is short of fourteen hundred feet. 
 In this series have been detected the remains of true Conifer- 
 ous trees, allied to the living Pines, along with plants resem- 
 bling the living Club-mosses, but attaining a comparatively 
 gigantic size (Lepidodendron and Sigillaria). Tlie most 
 characteristic fossils of the period are bivalve Mollusks and 
 Brachiopods, and among the latter are some of the broad- 
 winged Spirifers so characteristic of the Devonian of Europe. 
 
 4. The Chemung Period is composed wholly of sandy and 
 shaly beds, and has a maximum thickness of little more than 
 throe thousand feet. Land-plants are not uncommon in this 
 period, and sea-weeds are abimdant. The animal remains are 
 chiefly Pivalve 3Tollusks allied to the recent scallops and 
 pearl-os'ster, Brachiopods and Cephalopoda. 
 
 -5. The rocks of the Catskill Period are also sandy and shaly, 
 the arenaceous beds being generally red in color, and often 
 conglomeratic. Their thickness varies from 2,000 to as much as 
 6,000 feet. Fossils are very scarce, and consist chiefly of 
 land-plants and fragments of fishes. Among the latter are the 
 remains of a Holoptychiufi^ similar to a species which is char- 
 acteristic of the Upper 01'' Red in Scotland (Fig. 84). 
 
 Life of the Devonian Period. — Taken as a whole, and 
 especially as regards its development in North America, the 
 life of the Devonian period appears to be transitional between 
 that of the underlying Siluriar and overlying Carboniferous 
 series. The Plants of the Devonian period are, upon the 
 whole, very closely allied to those of the Coal-measures, in most 
 cases agreeing generically, and sometimes being even specifi- 
 cally identical. We find here, for the first time, the remains of 
 regular e:3CDgenous trees, resembling the modem Pines and 
 
 ^apml' 
 

 
 148 
 
 GEOLOGY. 
 
 I % 
 
 Cypresses, and referable to the gymnospermous section of the 
 Dicotyledons. We find also here for the first time true ferns 
 (Fig. 83), many of which resemble those of the Coal-measures. 
 Lastly, we have here the characteristic carboniferous plants 
 jSif/illaria and Lepidodendron, These are believed to be most 
 nearly allied to the Cryptogamic Club-mosses of the present 
 day, but they attained the altitude of trees. A species of 
 ^ujlllaria from the Chemung group is figured below (Fig. 88). 
 Allied to these, but not found in the coal, is the genus JPsilo- 
 phyton^ which has been established by Dr. Dawson, of Mont- 
 real, for a plant which is very common 
 in the Devonian of Canada and New 
 York. The same high authority has 
 determined the occurrence of wood of 
 an exogenous tree referable to the 
 angiospermous division of the Dicotyl- 
 edons, and resembling, therefore, our 
 ordinary trees and shrubs. In connec- 
 tion with these remains of an old land- 
 surface, w^e may notice that the Devo- 
 nian formation in America has yielded 
 the first traces of air-breathing animals, 
 in the form of Insects^ somewhat allied 
 to the May-flies of the present day. 
 
 The lowest forms of animal life are 
 represented by sponges. The next divi- 
 sion of the animal kingdom ( Coelente- 
 rata) is represented by one or two Graptolites — the last of this 
 singular family — and by very numerous and varied forms of 
 corals. Crustaceans are abundant, and are represented by 
 numerous Trilobites, by gigantic Eurypterids, and by some 
 
 Fio. BS.—Sigillarin C/iemvng- 
 ent^is. Frapnicnt of tho 
 stem (after UoU). 
 
 
 FiQ. &9.^'JI£egalodon cucullatus : a Devonian Lamellibran^. 
 
OLD RED SANDSTONE. 
 
 149 
 
 small forms allied to the living water-fleas. The MoUusca are 
 largely represented in Devonian time, and the Brachiopods 
 are especially predominant. Tlie true bivalve MoUusks are 
 abundant, and some of the forms are very characteristic of the 
 period. This is the case with the species figured above (Fig. 
 89). Univalve Mollusks are also not uncommon, but some of 
 the Cephalopods are more important and more characteristic. 
 The form^ allied to the Nautilus of the present day are rep- 
 resented by the genus Clymenia (Fig. 90), which agrees with 
 
 Fia. 90. — Clymenia linearis — Devonian of Europe. 
 
 the Nautilus in having simply curved partitions between the 
 cliambers of the shell. Here also occur for the first time the 
 forerunners of the great family of the Ammonites^ in the 
 form of the genus Goniatltes. The shell in this genus resem- 
 bles that of the Nautilus in sh'ape, but the partitions are lobed, 
 and the siphuncle is placed on the back of the shell. Ortho- 
 ceratites still continue to be represented. 
 
 The sub-kingdom of the Vertebrates is still represented by 
 fishes only ; but these are so abundant that the Devonian Pe- 
 riod has been termed the " Age of Fishes." The order of the 
 Ganoids, with shining bony scales, is represented most numer- 
 ously by many singular forms, of which two have been already 
 figured (Figs. 82 and 84). Besides the Ganoids, however, are 
 found the fin-spines of fishes believed to be most nearly allied 
 to the living Port-Jackson Shark, and belonging, therefore, to 
 another and a higher order. It is further to be remembenjd, 
 as already remarked, that the appearance of fishes is later in 
 America than in Britain. The earliest remains of fishes in 
 Britain have been found in the Upper Silurian rocks (at the 
 base of the Ludlow Series) ; but no American fossil fishes 
 have hitherto been found in any stratum earlier than the lower 
 portion of the Corniferous series. 
 
 
 ■r-M 
 

 I J 
 
 ■■ I 
 
 ,;.;•! 
 
 il ; '■} 
 
 CHAPTER XVm. 
 
 CAEBONTPEEOUS FORMATION. 
 
 Overlying the great formation of the Old Red Sandstone, 
 or Devonian rocks, sometimes unconformably but more often 
 in perfect conformity, we have the large and important series 
 of the Carboniferous JRockSy so called because workable beds 
 of coal are more commonly developed in this than in any 
 other formation. It must not be forgotten, however, that coal 
 is not exclusively a Carboniierous product, but that workable 
 seams of coal occur in several formations younger than the 
 Carboniferous. In all cases, too, the coal forms but a very 
 small proportion of the actual thickness of the Carboniferous 
 rocks, occurring in comparatively thin beds intercalated in a 
 great series of sandstones, shales, and limestones. 
 
 The Carboniferous rocks are largely developed in Britain, 
 on the Continent of Europe, and in North America, and are 
 known to occur in other parts of the world also. Their general 
 composition, however, is, comparatively speaking, so uniform, 
 that it will be sufficient to take a general view of the forma- 
 tion without considering each area separately. As a general 
 rule, the Carboniferous rocks may be divided into the follow- 
 ing three groups, from below upward : 
 
 1. Tlie Carboniferous Slates and Mountain JLimestone^ 
 mainly and most typically calcareous. Sometimes termed the 
 sub-carboniferous group. 
 
 2. The Millstone Grit^ essentially arenaceous and con- 
 glomeratic. 
 
 3. The Coal-measures, composed of alternating shales, 
 sandstones, and other strata, with workable beds of coal. 
 
 I. The Carboniferous, Sub-carboniferous, or Moun- 
 tain, Limestone, constitutes ordinarily the base of the Car- 
 boniferous system. In Ireland, however, and elsewhere the 
 
CARBONIFEROUS FORMATION. 
 
 lowest beds of the Carboniferous series are slates and grits, 
 which attain a maximum thickness of 5,000 feet, and have 
 been termed the Carboniferous Elates (Fig. 91, a). Tlieir 
 fossils are partially referable to good Carboniferous types, and 
 
 Fig. 91. — General section of the Carboniferous rocks. — a, Carboniferous slates; &, Carbo- 
 niferous limestone; c, Millstone grit; cf, Coal-measures; «, Devonian rocks;/, Permian 
 rocks. 
 
 partly to Devonian forms, so that they may be regarded as 
 passage-beds. The Carboniferous limestone proper in its most 
 typical development, as in Wales and the west of England, 
 consists of a great mass of nearly pure limestone, from 1,000 
 to 2,000 feet thick, with a few beds of shale. In other places, 
 however, it is more or less broken up into a series of different 
 beds of limestone, alternating with sandstones, grits, and 
 shales, and sometimes containing beds of coal. In North 
 America it is never purely calcareous, but consists mainly, or 
 entirely, of sandstones and shales, sometimes with thin beds 
 of coal, or deposits of clay iron-ore. Westward, however, it 
 becomes more highly calcareous. 
 
 As the Carboniferous limestone is generally a marine for- 
 mation, its fossils are usually those of sea-animals. In those 
 places, however, in which beds of coal occur in this series, 
 plant-remai • are tolerably abundant and agree in their charac- 
 ters with those of the Coal-measures. In some places, also, the 
 series includes beds of undoubted fresh-water origin. As a 
 rule, however, marine fossils characterize the Carboniferous 
 limestone, and they are generally very abundant. The great 
 limestones of this formation in particular are almost made up 
 of fragmentary or perfect fossils, chiefly referable to Corals, 
 Crinoids, and Brachiopods. The Corals (Fig. 92) are especially 
 abundant, the rock sometimes having all the features of an 
 old coral-reef. Two of the more common and widely-dis- 
 tributed forms are figured here (Figs. 92, 93). Crinoids are 
 extremely abundant, the entire rock in many places being 
 composed of little else than the broken stems of these beauti- 
 ful fossils, when it is spoken of as " Crinoidal Limestone." It 
 is rare, however, to find unbroken specimens. The body and 
 
152 
 
 GEOLOGY. 
 
 Carboniferous Limestone Corals. 
 
 B! W 
 
 |l'l1^i •: 
 
 Fig. 92.—Lithostrotion haaaltiform^. Pio. ^'i.—Lonadahia floriformia. 
 
 arms of a characteristic species are figured below (Fi<^. 94). 
 Nearly allied to the true Crinoids are the Pentremites, which are 
 verj'^ characteristic of some beds of this formation. They dif- 
 fered, however, from the Crinoids in not possessing the jointed 
 feathery arms of the latter. Here, also, for the first time we 
 meet with true Sea-urchins belonging to two genera, and 
 differing in some important respects from all living forms. 
 
 Among the most abundant and characteristic fossils of the 
 Carboniferous limestone are the very numerous Brachiopods^ 
 of which certainly the most characteristic are a number of 
 species of the very well-marked genus Producta (Fig. 95). 
 
 Fio. 94. — Cyathocrinites planus. 
 
 Fio. 9^,— Producta aemireticulata. 
 
 Members of this genus are found all over the w^orld, wherever 
 the Lower Carboniferous rocks are developed ; and they some- 
 
 ii » 
 
CARBONIFEROUS FORMATION. 
 
 153 
 
 times attain a very large size. Along with these are Spirifers 
 and other species. Bivalve and univalve Mollusks are of com- 
 mon occurrence, and some of both have even been found re- 
 taining their original bands of color. Cephalopodous shells 
 are not uncommon, especially large Orthoceratltes and Go- 
 niatites. One of the commonest forms of the latter, both in 
 Europe and North America, is GoniatUes crenistria (Fig. 
 9G). 
 
 The Crustacea are chiefly represented by small forms, 
 allied to the living water-fleas, the bivalve cases of which are 
 extraordinarily abundant in certain beds. Hero, also, we have 
 for the last time Trilobites^ but these die out finally before the 
 deposition of the Coal-measures. 
 
 The remains of Vertebrate animals, with one exception, 
 are referable to fishes. The exception to this is constituted 
 by the footprints of an Amphibian, allied probably to the liv- 
 ing newts, which has been discovered in North America. 
 These tracks have been described under the name of Sauropus 
 primcevus, and they constitute as yet the earliest indication 
 of animal life higher in the scale than fishes. The fishes of 
 the Carboniferous limestone are mostly referable to genera 
 which more or less resemble the Port- Jackson Shark, and 
 which are represented merely by their broad crushing teeth 
 (Fig. 97). Besides these there are teeth of true Sharks (6Va- 
 dodus)^ along with numerous fin-spines. 
 
 P 
 
 Fig. 9C. — Goniatitea crenistria. 
 
 FiQ. 97.— Tt't/A of Cochliodm contortan. 
 
 II. The Millstone Grit. — The highest beds of the Car- 
 boniferous limestone are succeeded, usually conformably but 
 sometimes unconformably, by a series of sandy and gritty 
 beds which have been termed the 3Illlsto7ie rjrh. In its most 
 typical form the Millstone grit consists of a series of hard 
 quartzose sandstones, the component grains of which are 
 sometimes so large as to be more properly called small 
 pebbles, when the rock becomes a fine conglomerate. In other 
 
 I 
 
1 • t 
 
 i 
 
 154 
 
 GEOLOGY. 
 
 
 cases regular conglomerates are present, and there are some- 
 times shales, limestones, and thin beds of coal. The thickness 
 of the Millstone grit varies from 1,000 to 1,700 feet as a rule; 
 but sometimes its thickness is very greatly diminished. Fos- 
 sils are scarce, and offer no peculiarity. 
 
 III. Thb Coal-Measures. — The Coal-measures proper suc- 
 ceed the millstone-grit conformably, and consist of a great 
 scries of shale, sandstone, grit, and coal, attaining a total 
 thickness, when well developed, of from 7,000 to 16,000 feet. 
 Except in Scotland, where workable coal-seams occur below 
 the horizon of the millstone-grit, it is mostly from the true 
 Coal-measures that coal is obtained ; the largest and most pro- 
 ductive coal-fields of the world occurring in Britain, North 
 America, and Belgium. In their mineral nature, the Coal- 
 measures, all over the world, exhibit a wonderful general uni- 
 formity of composition. They consist, namely, of dark, often 
 nearly black, earthy and laminated shales, yellow, brown, and 
 purple sandstones, sometimes spotted, but very rarely red in 
 color, along with occasional beds of limestone and clay iron- 
 ore, and beds of coal of varying thickness. These alternating 
 beds may follow one another in any order, and may be repeat- 
 ed over and over again, the total thickness sometimes reaching 
 the enormous amount of 14,000 feet, or nearly three miles. In 
 the South Wales coal-field the series consists as usual of sand- 
 stones, shales, and coals, alternating with one another, and in- 
 dicating a slow but probably intermittent depression of the 
 area which they now occupy. In this coal-field there are about 
 80 distinct beds of coal, each of which — as we shall subse- 
 quently see — represents an ancient land-surface. Each of 
 these bods reposes upon a sandy shale or clay, which is known 
 as the "underclay" or "floor" of the coal, and through which 
 spread numerous fossils referred to the genus Stigmariay and 
 now known to be the roots of plants {Sigillaria). Each seam 
 is also surmounted by a bed of shale, forming the so-called 
 "roof" of the coal, and in this are found numerous flattened 
 and compressed branches and stems of plants. 
 
 The phenomena just indicated lerfd us to a consideration 
 of the vegetable remains of the Coal-measures, and of the origin 
 of coal. The Lower Carboniferous rocks, as already said, are 
 mainly marine in their origin, and contain marine fossils. The 
 Coal-measures, on the other hand, are characterized by the oc- 
 currence of terrestrial organisms, chiefly but not exclusively of 
 a vegetable nature, along with the remains of brackish-water, 
 fresh-water, or sometimes marine animals. The most abun- 
 
CARBONIFEROUS FORMATION. 
 
 155 
 
 dant and characteristic fossils of ti.e Coal-measures are plants, 
 of which there is a great variety of very remarkable forms, 
 mostly differing widely from existing plants. Not only 
 is the coal* itself merely compressed vegetable matter, but 
 more or less perfect plant-remains occur throughout the entire 
 scries. The more important plants of the (Joal-measures are 
 the following : 
 
 Ferns are very numerous in the Carboniferous series, and 
 several hundred species have been described. Some of them 
 were tree-Hke, others more of the si/e of the common ferns, 
 and many are extremely like living species. 
 
 About forty species of plants have been referred to the 
 genus Lepidodendron (Fig. 98), which is believed to have 
 been most closely allied to our living Club-mosses {Z/ycopodia- 
 cecp), but of gigantic size. The remains referred to Lepido- 
 dendron consist of cylindrical stems or trunks covered with 
 
 FiQ. 98.— Branching-stem, 49 feet 
 long, of Lepidodendron. 
 
 Fio. 99. — Stem with bark and leaves of 
 Lepidodendron Sternbergii, 
 
 leaf-scars, marking the points where the leaves were formerly 
 attached. Sometimes the leaves may be found attached to 
 the stem, and in some rare cases the cones or fruit may be 
 found in connection with the ends of the branches. Tliese 
 cones, however, are more commonly found in a detached condi- 
 
 * Coal consists of nearly pure carhon, with small proportions of hvdrojren and oxvpcn, 
 and a minute quantity of mineral matter. Bituminom ooal is coal containin'-r a considerable 
 quantity of gaseous ingredients, and burns with a bright-yellow Hame. Anthracite is coal 
 containing a smaller quantity of gaseous matter, burning >vith greater difficulty, and with a 
 bluish flame. All coal is composed of successive layers, or laminiB, and sometimes distinct 
 vegetable structure con be detected. 
 
 
V I 
 
 i 
 
 I 
 
 i M 
 
 150 
 
 GEOLOGY. 
 
 tion, and they have been described under the name of J^tjcido- 
 strobus. No living member of the Club-mosses or Ground-pines 
 attains a greater height than three feet ; but some species of 
 Lepidodendron must have been lofty trees, for specimens are 
 known to have exceeded fifty feet in length. 
 
 Of common occurrence, also, \\\ tlie coal-measures are 
 the vegetable remains known as Calamites (Figs. 100-102). 
 These consist of cylindrical, furrowed, and striated stems, 
 divided at intervals by joints, or articulations. The lower 
 extremity (Fig. 102) tapers oflF into a conical point, where 
 the stem was. doubtless attached. The original view as to 
 the nature of Calamites referred them to gigantic Horse-tails 
 {Equisetacea) ; and the tendency of modern investigation is 
 
 Fio. 100. — Calnmitea canned 
 /ormia. 
 
 Fig. 101. — Calamites Sucoicii. Fig. 102.— Root-ter- 
 mination of a Cal- 
 amite. 
 
 to confirm this view, though it is rejected by competent 
 authorities. True Horse-tails {Eqiiisetltes) certainly do occur 
 in the coal, and, as the size of these is considerable, the great 
 size of the Calamites need not necessarily render this view at 
 all improbable. 
 
 Among the most abundant and most important of the coal- 
 plants are those referred to the genera Si(/illaria and Stigma- 
 ria^ which are now known to be nothing more than diflerent 
 parts of the same plant. Many species of S'lgillaria are knt^wn, 
 and some of these attained a great height (as much as uO or 
 70 feet in some instances), though they do not a])pear to have 
 branched except close to their summit. They consist of fluted 
 stems (Fig. 103), marked with longitudinal ridges, between 
 which are rows of single or double scars, indicating the points 
 of attachment of the leaves. In numerous instances Sigilla' 
 
CARBONIFEROUS FORMATION. 
 
 157 
 
 ricB have been found in their original upright position ; and in 
 
 many cases il appears that the interior 
 must have decayed much more rapidly 
 than tlie exterior, so that, if upriglit, 
 the interior may be filled with sand- 
 stone, and, if jirostrate, the stem has 
 been completely crushed and flattened. 
 As regards size, stems of ISiyillaria 
 vary from a foot to as much as five feet 
 in diameter, witli a height of from 30 
 to 70 feet. Tlie well-known fossil 
 Stigmaria (Fig. 104) has now been 
 shown to be nothing more than the 
 root of Sigillarlay the actual connec- 
 tion between the tw^o having been in 
 many instances demonstrated. tStig- 
 maria occurs in the form of long, 
 
 Fio. 103 —Fragment ot Fiioiiia- compressed, or rounded fragments, the 
 
 rial<.vigaia. (lirongniait.) ^.^ternal SUrfaCC of which is COVCrcd 
 
 with shallow tubercles, each of \\ liich has a little pit or de- 
 pression in its centre. From each of these pits, in perfect 
 examples, there proceeds a long cylindrical process, or rootlet ; 
 
 , Fig. 104. — Fragment ot Siigmaria Jicoides, >^ natural size. 
 
 but these in ordinary examples have disappeared. The ex- 
 act botanical position of the Slgillarice is uncertain ; but the 
 most probable view would regard them as a peculiar group of 
 Gymnospermous Exogens. 
 
 Of the remaining plants of the Coal-measures may be men- 
 tioned true Coniferous trees, related to the recent Norfolk 
 Island Pines (Araucaria). Flowering plants are of very rare 
 occurrence, and it is doubtful if any true Dicotyledonous An- 
 giosperms have hitherto been detected. 
 8 
 
1. 'r 
 
 \k 
 
 :i I 
 
 158 
 
 GEOLOGY. 
 
 Origin op Coal. — As regards the origin of coal, only two 
 theories need be mentioned : Jirstly^ that coal is the result of 
 the drifting together and accumulation by water of enormous 
 quantities of vegetable matter of all kinds ; and, secondly ^ that 
 beds of coal are due to the gradual decay, upon the surface 
 where it grew, and through long periods, of a dense vegeta- 
 tion, so that each coal-seam represents an ancient land-surface. 
 It is possible that in some instances the first theory may be 
 correct. It is possible, namely, that in some rare instances a 
 great river may have brought down drift-wood and other vege- 
 table matter in sufficient amounts to have ultimately formed 
 a bed of coal. The purity of coal, however, and its general 
 freedom from earthy or sandy matter — difficult to explain upon 
 any theory — becomes wholly inexplicable upon this view. In 
 the great majority of cases, and most probably in all, coal- 
 beds have been formed by the gradual growth and decay, 
 throughout long periods, of a rank vegetation. The correctness 
 of this view is shown, not only by the absence of impurities 
 in coal, but by the common occurrence of upright stems and 
 trunks still retaining their vertical position (Fig. 105). In 
 
 Ik 
 
 Fig. 106.— Erect fossil trees. Coal-measures, Nova Scotia. 
 
 other cases, again, further and still more convincing evidence 
 can be obtained in support of this view from the phenomena 
 of the " underclay," which forms the " floor " of the coal-seam. 
 This " underclay," upon this view, ought to represent the an- 
 cient soil upon which grew the plants which formed the coal. 
 In the underclay, accordingly, we find Stigmaria branching 
 freely in every direction, while in the coal itself, or in the 
 shale which forms the "roof" of the coal, are the stems and 
 trunks of SigiUariay of which the StigmaricB are the roots. 
 
 m 
 
 m^ ^ 
 
CARBONIFEROUS FORMATION. 
 
 159 
 
 The general belief, then, about the Coal-measures, is that 
 they have been deposited in a manner which is very closoly 
 similar to, if not exactly identical with, tl»e way in which are 
 produced the deltas of our great rivers, such as the Ganges or 
 Mississippi. Such deltas at the present day form vast alluvial 
 fliits, or plains, very little elevated above the sea, composed of 
 the fine mud and sediment brought down by the river, and 
 supporting a dense and luxuriant vegetation. To explain the 
 phenomena of the coal-measures, we must suppose that after 
 the lapse of a certain period, when a sufficient amount of vege- 
 table matter had been accumulated upon such a marshy tract, 
 a submergence took place beneath the waters of the sea. The 
 vegetable accumulations would then gradually be buried be- 
 neath a series of sedimentary deposits, such as sandstones or 
 shales, which would contain the remains of marine animals. 
 Or it might be, if the subniergence were slight, that the sunk- 
 en area should be covered by the river itself, or by brackish 
 water. In this case, the fossils of the beds deposited above 
 the vegetable layer would be those of fresh water, or those 
 proper to brackish water. If, now, an elevation took place, or 
 sufficient sediment were deposited to counteract the previous 
 subsidence, a fresh land-surface would be formed upon which 
 a fresh swamp or jungle would be produced. The same de- 
 pression, repeated a second time, would convert tliis in turn 
 into another bed of coal, again surmounted by marine, fresh- 
 water, or brackish-water beds ; and so the process might be re- 
 peated indefinitely, till such a vast series as the coal-measures 
 of Nova Scotia might be produced. 
 
 In accordance with this generally-received theory as to the 
 origin of coal, we find in the Coal-measures the remains of 
 various air-breathing animals, both Vertebrate and Invertebrate. 
 If each seam of coal with its underclay represents an ancient 
 land-surface, this is just what we might have expected. We 
 find, then, the remains of various true Insects, Scorpions, Spi- 
 ders, several species of the class of the Centipedes {3iyria- 
 2)oda\ and air-breathing Shell-fish, allied to living Snails. As- 
 sociated with these are a number of Newt-like animals, most, 
 if not all of which, are referable to a peculiar and now extinct 
 group of the Amphibians. These have been called Ldby- 
 rinthodonts^ from the complex and labyrinthine structure of 
 the teeth. Several of these attained a very large size, and a 
 figure of one of the smallest is given hereafter (Fig. 106). 
 
 Also in accordance wdth the above theory we find the beds 
 associated with the coal to contain the remains of marine, 
 
 \m. 
 

 i 
 
 i 
 
 I 
 
 160 
 
 GEOLOGY. 
 
 fresh-water, or brackish-water animals. Amonpf these may be 
 mentioned Crustaceans allied to the living Water-fleas and 
 King-crabs, bivalve Sliell-lish, Ccphalopods, Brachiopods, and 
 numerous fishes, some of which w<Te of large size and highly 
 predaceous. The marine fossils, as a rule, liave a general agree- 
 ment with the forms of the Carboniferous Limestone. 
 
 Pig. 106. — Archegosavrua minor, a fossil Amphibian from the coal-measnres (Saarbruck), 
 
 Life of the Carboniferous Period. — As regards the 
 plants of this period, it is sufficient to point to the great pre- 
 dominance of Cryptogamous, as compared with Phaneroga- 
 mous plants, the Gymnospermic Exogens being almost the 
 only representatives of the latter. 
 
 The lowest forms of animal life {Protozoa) are represented 
 by the shells oi Foraminifera^ which are sometimes so abundant 
 as almost to make up the whole of certain limestones. The 
 Ccelenteratesaie represented by numerous Corals, which abound 
 
CARBONIFEROUS FORMATION. 
 
 161 
 
 cspooially in some of tlio llmestonos of the Lower Carbonifer- 
 ous scries. Tlie Kchinodermata cliiolly figure in the form of 
 Crinoiels and allied forms, but we now meet for the first time 
 with true S(Na-urchins. The Articulates are well represented 
 by both air-breathinfr and water-breathing forms. The Trilo- 
 bites make their last appearance in this period, but they W(to 
 represented by but a few forms, and these died out before the 
 Coal-measures were deposited. The Crustacea are represented, 
 however, by numerous minute forms with bivalves shells, like 
 the living Water-fleas (Fig. 108), and by larger forms nearly 
 allied to the recent Horseshoe Crabs (Fig. 107). The air- 
 
 Fio. 107. — LimuliM rotundatun, a fossil 
 horseshoe crab from the coal. 
 
 Fio. 103.— Small bivalve CVnstacoans 
 (Ci/thcre inrtatii), naturiil size 
 utul inagnilied. (After Murchl- 
 
 BOU.) 
 
 breathing Articulates are represented by Insects, Spiders, Scor- 
 pions, and Centipedes — in fact, by all the great classes at pres- 
 ent in existence. The Mollnsca are largely represented in all 
 their great divisions. Jirachiopoda are numerous, and the 
 two leading genera are Producta (Fig. 95) and Spirifer (Fig. 
 109). Bivalve Mollusks, especially those allied to the Scallops 
 
 FiQ. IdQ.— Spirifer trigonalis. 
 
 Fio. 110.— Spiri/er glaber. 
 
 and Pearl-mussels, occur in great plenty, and there are also 
 many Univalves. The Cephalopoda are represented chiefly 
 
162 
 
 GEOLOGY. 
 
 I«lll 
 
 II 
 
 1 1 r 
 
 II 
 
 ' ^ m ^' 
 
 
 ' '■ ^11 \ 
 
 ill 
 
 1 
 
 '1 
 
 1 
 
 I|HI 
 
 U t 
 
 
 III 
 
 11 ' 
 
 
 iii 
 
 I i 
 
 
 I • 1' 
 
 
 M li 
 
 i 
 
 '1 p 
 
 1 
 
 ^■'V 
 
 H 
 
 ite: 
 
 'lilt 
 
 IHi ' 
 
 '11 
 
 ii|l 
 
 '^^■H 
 
 vM 
 
 i''HI 
 
 |il|| 
 
 1 1'HI 
 
 piiili 
 
 1 1 '^^Pi'^ 
 
 
 ■4abki'^^><;^ '« 
 
 
 by Orthoceratites, often of great size, and by Goniatites (Fig. 
 96). Vertebrate life is pretty abundant, and we have now 
 numerous Amphibians, in addition to tlie 6shes, which are so 
 characteristic of the preceding Devonian period. Tlie fishes 
 are mainly GanoidSy&ndi have all unsymraetrical or unequally- 
 lobed tails. The Amphibians all belong to the extinct order 
 of i)iQ ZiabyrintJiodonts, 
 

 i. ''^'■;li 
 
 CHAPTER XIX. 
 
 PEBMI AN BOCKS. 
 
 The Carboniferous series is succeeded by a group of beds, 
 which complete the Paljcozoic formations, and which were 
 termed Permian Jiocks bv Sir Roderick Murchison, frcm the 
 province of Perm, in Russia, where they are extensively devel- 
 oped. Formerly these rocks were grouped with the succeed- 
 ing 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 sandst<jne, and because they are 
 superior to the Carboniferous rocks, while the Old Red Sand- 
 stone 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-meas- 
 ures, 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 the top of the Palaeozoic series, and the latter 
 constituting the base of the Mesozoic. 
 
 The Permian rooks, as a rule, repose unconformably upon 
 the underlying Carboniferous rocks, but seem to pass upward 
 conformably into the Trias, in most instances. The division, 
 therefore, between the Permian and Triiissic rocks and, conse- 
 quentlv, between the Palaeozoic and Mesozoic series, is not 
 founded upon any marked physical break, but upon the cUffer- 
 cnce in the life of the two periods. 
 
 The Permian rocks exhihit their most typical features in 
 Russia and Germany, though they arc very well developed in 
 parts of Britain, and they occur in North America. Wlien 
 well developed, they exhibit three main divisions : a lower set 
 
 
 
 .•m:^ 
 
164 
 
 GEOLOGY. 
 
 of sandstones, a middle group, generally calcfireous, and an 
 upper series of sandstones, constituting respectively the Low- 
 er, Middle, and Upper Perraians (Fig. 111). 
 
 i 
 
 m i 
 
 '*■ '" II J' 
 
 kyJM 
 
 Fig. 111. — Generalized section of the Permian rocks. — «, Lower Permian ror-l^s; 6, Middle 
 Pennians; c, Upper Peruiians; d, Coal-measuris. 
 
 In Russia, Germany, and Britain, the Penman rocks con- 
 sist of the following members : 
 
 1. The Lower Permiatis (Fig. Ill, «), consisting nr 'nly 
 of a great series of sandstones, of different colors, 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 liappeu to repose; and similar brc 'as ome- 
 tinies occur in the upper portion of the series as well. The 
 thickness of this group varies a good deal, but may amount 
 to 3,000 or 4,000 feet. 
 
 2. The Middle Permians (Fig. Ill, h), consisting, in their 
 typical dev(?l()pmcnt, of laminated marls, or " marl-slate," sur- 
 mounted by beds of magnesian limestone (the " Zechstein " 
 of the German geologists). Sonieliines the limestones are 
 degenerate or wholly deficient, and the series may consist of 
 sandy shales and gvi)sif(3rous 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 Lime- 
 stone. 
 
 3. The Tipper Permians (Fig. Ill, c), consisting of a 
 series of sandstones and shales, or of red or mottled marls, 
 often gypsiferous, and sometimes including a bed of lime- 
 stone. 
 
 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 
 himdred feet. They consist of sandstones, conglomerates, 
 limestones, marls, and beds of gypsum. 
 
 Life of the Pi:rmian Period. — The Permian rocks have 
 yielded a very considerable number of plants, most of which 
 are specifically distinct from the plants of the Coal-measures. 
 
PERMIAN ROCKS. 
 
 165 
 
 Thoug'i the species, however, are distinct, many of the Per- 
 mian genera dale from the antecedent Carboniferous period. 
 Thus, besides several genera of Carboniferous ferns, the Per- 
 mian rocks contain the well-known genera Lepidodendron 
 and Calainites ; but Sigillarla and Stigmaria have hitherto 
 not Ijeen shown'to have survived the Coal period. Conifers 
 allied to the living lirs are not uncommon, and one of the 
 more characteristic is figured below (Fig. 11!^). 
 
 Fig. 112. — Walch><t jiinifonnix.Ci Pcnni^ui ('(iijifcr (uflcr Gutbicr). — a, Branch; ft, Twig; 
 
 f, Leaf, inaguifled. 
 
 Corals arc rare in the Permian rocks, and the older types 
 have now almost wholly dis:ipi)eared. Echinoderms are also 
 scarce, and require no special notice. The most abundant and 
 most characteristic fossils of the Permian period — after the 
 plants — are Mollusks and Fishes. Besides forms, such as the 
 Lace-coral, allied to the living Soa-mosses and S(^a-inats, the 
 lower Mollusks are represented by various Brachiopods. 
 Among these are representatives of the genera Producta (Fig. 
 113), and /Sjnri/er (Fig. 115). Some of the Brachiopods agree 
 
 Fig, ^IS.— Producta horrida. 
 
 Fio. 114. — TAngnla Fig. llo. — Sjnri/er undulatus. 
 Crednerii, 
 
 M 
 
 * 
 
 
 *ii>.r 
 
 A^ 
 
 ?H 
 
 »-! 
 
 u 
 
 specifically with those of the Carboniferous period, and they 
 are all of Paheozoic types. lu addition to the Dr^chiopods 
 

 1 1 
 
 ■pr 
 
 ! |i, 
 
 A- 
 
 I. 
 
 
 '4B 
 
 166 
 
 GEOLOGY. 
 
 there are numerous Bivalve Mollusks, with some Univalves 
 and Ceplialopods. The fishes of the Permian rocks are all of 
 Palaeozoic types, being mostly Ganoids, and having invariably 
 unsymmetrical or unequally-lobed tails (Fig. 116). i'he species 
 
 Fio. 11 C— Restored outline of ralaoniscus. 
 
 are peculiar, but most of the Permian genera are also found 
 in the Coal-measures. One of the most characteristic genera, 
 viz., Pakeoniscus, is figured above. Besides fishes, the Mid- 
 dle Permians have yielded the bones of a true reptile, which 
 is known by the name of Ptotorosaurvs. It is the oldest 
 known example of a true lizard, and is believed to be most 
 nearly allied to the great Monitors of the old world. 
 
CHAPTER XX. 
 
 TRIASSIC FORMATION. 
 
 We come now to the consideration of the great MesozoiCy 
 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 cor- 
 responds with the higher portion of the New Red Sandstone 
 of the older geologists. Like the Permian Rocks, and as im- 
 plied by its name, the Trias admits of a subdivision into three 
 groups, a Lower, Middle, and Upper Trias (Fig. 11 T). Of 
 
 Fio. 117. — Generalized section of the Triassic rocks. — <7, Bunter Sandstcin; &, Muflchel- 
 kulk ; c, Keuper ; rf, llhaBtic beds ; e, Lias ; /; Periiiian rocks. 
 
 
 ■.v. 
 
 ii^^''^'' 
 
 
 these subdivisions the middle one is wanting in Britain ; and 
 all have received German names, being more largely and 
 typically developed in Germany than in .'uiy other country. 
 Thus, the Lower Trias is known as the Jiiuiter tSandstein^ the 
 Middle Trias is called the Miischelkalfc, and the Upper Trias 
 is known as the Keuper. 
 
 I. The lowest division of the Trias is known as the Bunter 
 Sandstein (Fig. 117, a), from the generally variegati-d colors 
 of tlie beds which compose it (German, bunt^ variegated). The 
 Buuter 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 1,500 feet. The term 
 " marl " is very generally employed to designate the clays of 
 
ii 
 
 it';:' 
 
 168 
 
 GEOLOGY. 
 
 
 ii 
 
 I 
 
 
 
 the Lower and Upper Trias, but the term is inappropriate, as 
 tliey contain no linie, and are, therefore, not genuine marls. 
 In Britain the Hunter Sandstein consists of red and mottled 
 sandstones, with unconsolidated conglomerates, or " pebble- 
 beds," the whole having a thickness of about 1,200 feet. The 
 Bunter Sandstein, as a rule, is very barren of fossils. In 
 Britain it has yielded little, except some singular hand-like 
 footprints (Fig. 118), which were originally ascribed to an 
 
 C^^ ^ 
 
 Fio. 118. — Footprints of Cheirotherium, In Saxony. 
 
 unknown animal under the name of Cheirotherium (Gr. cJieir, 
 
 hand ; tlia\ beast), but whicli are now known to have been made 
 
 by a large Amphibian belonging to the order of the Lahyrin- 
 
 t/wdonts. On the Continent the 
 
 Bunter has yielded a considerable 
 
 number of plants, chiefly ferns and 
 
 conifers, not one of which occurs in 
 
 the Upper Trias. The most cliar- 
 
 acteristic of these plants is the 
 
 Coniferous tree, ^^oltzia^ of which 
 
 an example is given in Fig. 119. 
 
 II. The Middle Trias is not de- 
 veloped in Biitain, but constitutes 
 in Germany a formation termed the 
 3lnsi'hdkalk (Germ. JIusc/iel, mus- 
 sel ; Knlh\ limestone), from the 
 
 abundance of fossil shells which it contains. It consists of 
 gray or yellowish limestones (Fig. 117), sometimes magnesian, 
 including occasional beds of gypsum and rock-salt. Among 
 the most characteristic fossils of the Muschclkalk are the 
 shells of Ceratites (Fig. 120), a Cephalopod somewhat allied 
 to the Pearly Nautilus, but belonging to the same family as 
 the Ammonites. Ceratites^ however, is distinguished by hav- 
 ing the partitions which divide the chambers of the shell 
 (Fig. 120, c) simply denticulated, and not by any means 
 elalxirately frilled as \\\\\\v, Ainmonites. Tvne Ammonites awd 
 JJdem/iifes^ both, as we shall see, highly characteristic of the 
 later Secondary rocks, are wanting in the Muschelkalk. Very 
 characteristic, also, of the Muschelkalk is the beautiful stone 
 
 Fig. lid.— Vofkia heterophylla.—b, 
 Portion of the same, luapnifled to 
 show the fructillcation. 
 
 !l|ir^-'^ 
 
TRIASSIC FORMATION. 
 
 109 
 
 Fig. 120. — Ceratites nodoiftix. — rr. Side view; h. Front viow; c. Outline of one of the partl- 
 
 tious divi(liD{f the chauibers ol'the fihcU. 
 
 .r">;': 
 
 lily {Encrhuis liUlformis^ Fig. 121), heads and stems of wliicli 
 
 are found in eonsiderublt; iibundance. Fishes are far from im- 
 
 cominon in the Musclielkalk^ and llujre are also the remains of 
 
 several reptiles. 
 
 III. Tlic Upper Trias or Kenper consists 
 of about 1,000 lect of sandstones, marls, or 
 elavs, generally red or green, Avith rock-salt 
 and gypsum, and sometimes beds of df)lomite. 
 The Keu})er in Britain is very imfossiliferous ; 
 but it contains in Germany a good many 
 plants, some of which (such as Calamites) are 
 of Carboniferous genera, wliile most agree 
 more Avith the ])lants of the Lias and Oolites, 
 consisting chioily of Ferns, Horse-tails, Coiii- 
 fcrs, and Cvcads, Besides these, there are tlie 
 remains of Fishes, Avith some Keptiles. Tlio 
 Kenper passes upward, both in Biitain and 
 Germany, into a set of beds of a very remark- 
 able natine, which are known by various 
 names, but may be spoken of here as the 
 Rhcetic lieds, as they occur in the Iiha?tic 
 Alps. The most characteristic fossils of these 
 beds are three shells — a Cockh^ ( Cardluni 
 lihmti'cff)/)^ Fig. l;i;2), a Scalloj) [Pecten Yalo- 
 
 FiG. \i\.~Encrinua nietisis^ Fig. Itilj), and a P(>arl-mussel {Avicu' 
 uiuformu. (a, conlorta^ Fig. 1;?4). This last is so abun- 
 dant that tlie beds are often spoken of as 
 
 the Avicula contorta beds. 
 
 Besides these, there occurs in this series of beds a peculiar 
 
 stratum known as the " bone-bed," from its being almost entirely 
 
 '"it "'SI?! ! I 
 
 J p 
 
 ^ A 
 
 ■if t;y'. 
 
 
170 
 
 GEOLOGY. 
 
 made up of the teeth and scales of various fishes, some of which 
 arc fif^ured below (Figs. 125-127). In addition to fish-remains, 
 the bone-bed has yielded the teeth of two small Mammals, the 
 earliest fossil quadrupeds as yet known to us. Of these, the 
 
 Fig. 122 —Carrlium lihoati- Fio. \'i,^.—Pecten Vnlo- Fio. \24,.—Aricula contorta. 
 cum. Nat. size. nieium. >i nat. Bize. Nat. size. 
 
 first discovered and most celebrated is a little predacious ani- 
 mal, probably marsupial, which has been described under the 
 
 ^ii 
 
 Ym.Vlh.— Ttnih of Ilyhodusplicatilia, Fig. 120.— Tooth of Fio. 127.— Scale of ffyro- 
 
 SaurichthijHapi- lepis; nat. size and 
 
 calin; nat. size magnified, 
 and luaguiticd. 
 
 name of 3flcrolestes antiquus, and which is only known by 
 one of its grinders (Fig. 128). 
 
 Fig. 128.— Different views of the molar tooth of MicroUste* antiqvtit. 
 
 In the Austrian Alps, the Avicrda contorta beds are under- 
 laid by nearly 3,000 feet of calcareous strata which must be 
 referred to the period of the Upper Trias, and which are 
 
.011 
 
 TRIASSIC FORMATION. 
 
 171 
 
 replete witli fossils, most of which arc Mcsozoic, while a few 
 are of Pahrozoic types. Thus, we find in these beds the 
 Pala30zoic forms Orthoccras and GoniatiteSy wliij-li make here 
 their final a])pearance. Mixed with these ancient Cephalopods, 
 occurs the characteristic Triassicform Ceratltes (Fij;r, l;iO),and, 
 in addition to these, we find true Ammonites and JieletnnUes^ 
 which form such a marked feature in the life of the later 
 Jurassic period. The same wonderful intermixture of ancient 
 with modern types is seen also in the other fossil Mollusks 
 of these strata, but we may especially remember that in the 
 Upper Trias we lose sight of the genera Orthoccras and Go?n- 
 atites, and for the first time meet with Ammonites and JBelem- 
 niP s. 
 
 Triassic Rocks of North America. — Rocks of Triassic 
 age occur m several areas in the United States between the 
 Appalachians and the Atlantic seaboard ; but they show no 
 sucli triple division as in Germany. The rocks of this age 
 consist of red sandstones, sometimes shaly or conglomeratic, 
 and occasionally with beds of impure limestone. One of tiie 
 most celebrated of the Triassic areas of the United States is 
 in the valley of the Connecticut River, where the beds have 
 yielded the footprints of various different animals. Among 
 these are a number of paired footsteps of different sizes and 
 with different characters, and undoubtedly produced by ani- 
 mals which walked upon two legs only. Some of these prints 
 are four-toed, and these have been produced by reptiles, ff)r it 
 is now known that some extinct reptiles walked, habitually or 
 occasionally, upon two legs. Others (Fig. lJ29), again, are 
 three-toed, and these have generally been ascribed to birds. 
 
 ■ ■', -i ", > 
 
 ■Ma 
 
 . ■••.■■;|. 
 
 
 •iVv'r.J 
 
 
 "•<iS'> 
 
 ,!*' < 
 
 
 
 r^ 
 
 Fio. 129.— Three-tood footprints from the Trias of the Connecticut Valley. 
 
 If this supposition be correct, we have here the earliest indi- 
 cations yet known to us of the existence of birds. 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 gypsif- 
 erous marls. Besides numerous reptiles, and the supposed 
 
? '■' 
 
 172 
 
 GEOLOGY. 
 
 11 
 
 tracks of birds, tlic Amorican Trias lias yielded the remains of 
 plants, insects, lishes, and Maninials. The fishes are remark- 
 able because wfc here meet for tlie first time with forms having 
 symmetrical or equally-lobed tails. Tlie Mammals are repre- 
 sented by the lower jaw of a small quadruped w hich has been 
 named JJromatlieriutn sylvestre, and is believed to find its 
 nearest living ally in the little insectivorous and marsupial 
 Myrmecobius or Banded Ant-eater of New South Wales. 
 
 Origin of Kock-Salt. — As has been already mentioned, 
 rock-salt is connnonly found in beds accompanying strata of 
 Triassic age, and sometimes attaining a thickness of 00 to 100 
 feet or more. The salt tnay be quite; pure, or may be mixed 
 with more or less earthy inijiurity, and the association of rock- 
 salt with Triassic strata is so conmion that the Trias is often 
 spoken of as the ISaliferoiis system. As a very general rule, rock- 
 salt is found to be associated with su][)hate of lime or gypsum, 
 and very generally also with magnesian limestones, red sand- 
 stones, and red and variegated clays. Still, strata of this kind 
 are often destitute of salt, and siilt may occur in rocks of a diircr- 
 cnt nature. As to the origin of rock-salt, the generally-received 
 theory is, that it has been formed by the evaporation of the 
 water of inland seas or lagoons, which communicate at inter- 
 vals with the ocean. It cannot be said, however, that we have 
 as yet any theory which will explain all the phenomena of the 
 occurrence of rock-salt, or which can be applied to all cases. 
 
 Life of the Triassic Period. — The Triassic period, as 
 regards its plants and animals, is in many respects intermedi- 
 ate between the Paheozoic and later Mesozoic deposits, while 
 being itself decidedly Mesozoic. Among the plants we have 
 some PaljBozoic types (such as Calaniites)^ but there is no 
 longer a marked predominance of Ciyptogams, and the lead- 
 ing forms are Ferns, Conifers, and Cycads.* As regards the 
 Invertebrates of the Trias, the intermixture of Pala?ozoic and 
 Mesozoic t3^pes is especially well seen in the 3IoUusea, and 
 particularly in the Cephalopods. The straight OrtJiOceratites 
 appear here for the last time, as do the Gonuitltcs^ in which 
 the shell was coiled up like the Nautilus, but the partitions 
 between the chambers were lobed nnd not simple. Character- 
 istically Triassic is the Ceratite (Fig. 120), in which the shell 
 is somewhat intermediate between the Goniatltes and the 
 Ammonites^ the partitions between the chambers of the shell 
 
 !■ V 
 
 m 
 
 * Tlip Piioadu !\rc nonrlv roktod to the Conifern (Fir-trlho). hut differ Greatly in external 
 form and hailiit. They look like tree-ferns, and are all natives of warm climates. An Au8- 
 ti'allan species is figured at p. 181. 
 
TUIASSIC FORMATION. 
 
 173 
 
 boinf^ (lenticiilated. Lastly, in the Upper Trias, appear for 
 the tii'st time true Aminotiites (Fi^. l33), in wliidi the par- 
 til i(}ns bcjtween the chambers of the shell are wonderfully 
 folded and frilled at their edges. With these also are lidetn- 
 nites (Fig. 13^), which are really the internal shells or skele- 
 tons of cuttle-fishes. 
 
 The Vertebrates are represented by Fishes, Amphibians, 
 Reptiles, Birds, and Mammals, in fact by all the great sub- 
 divisions of the vertebrate sub-kingdotn. The fishes arc all 
 G((/ioiilSy but some of them for the lirst time exhibit the sym- 
 metrical or equally-lobed tails, which characterize the great 
 majority of living fishes. The Amphibians are represented by 
 Lahi/rinthodonts^ mostly of gigantic size ; but this order of 
 the class, which appeared first in the Carboniferous rocks, does 
 not appear to have survived the Triassic period. The true 
 lloptiles are represented by lizards, swirruning reptiles of vari- 
 ous kinds, and often of large size, crocodile-like species, and 
 others wholly unlike any thing that we know as existing at 
 the present time. The class of Birds is represented doubtful- 
 ly by the footprints of the American Trias (Fig. 129) ; but if 
 these are rightly determined, then the class has its conuuence- 
 nient in this period. Mammals are for the first time repre- 
 sented by two or three small quadrupeds, which are only 
 known to us by their teeth or lower jaws, but which appear to 
 belong to the Marsupials or pouched quadrupeds, the lowest 
 order of the class Mammalia. They appear to be most near- 
 ly allied to the living Banded Ant-eater and Kangaroo-rat of 
 Australia. 
 
 m 
 
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 IMAGE EVALUATION 
 TEST TARGET (MT-3) 
 
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 Photographic 
 
 Sdences 
 Corporation 
 
 23 WEST MAIN STREET 
 
 WEBSTER, NY. 14580 
 
 (716) 872-4503 
 

 C/i 
 
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 f 
 
CHAPTER XXI. 
 
 JURASSIC OR f OUnC SERIES. 
 
 ! -l! 
 
 
 
 m 
 
 l'\i 
 
 Succeeding to the Trias, we have a great series of rocks 
 whicli are known as the OcCdic liocksy from their commonly 
 containing oolitic limestones, or as the Jurassic Series, from 
 their being largely developed in the mountain range of the 
 Jura, on the western borders of Switzerland. The Jurassic 
 rocks are very extensively developed in Britain, where they 
 consist of the following members in ascending order (Fig. 
 130) : 
 
 I. Lias. 
 
 II. Lower Oolites (consisting of the Inferior Oohte, Ful- 
 
 ler's Earth, Great Oolite, Stonesficld Shite, etc.). 
 
 III. Middle Oolites (Oxford Clay and Coral Rag). 
 
 IV. UjDper Oolites (Kimmeridge Clay, Portland Stone, and 
 
 Purbeck beds). 
 
 Fio. 130. — Qenonilizpd section of tho Jurassic rocks. — n. Lias; h. Lower OoHtcs; c, Mlddlo 
 Oolites; </, Upper Oolites; e, Would Clay; f, lihaotic beds. 
 
 I. Tlie Z/ias (Fig. 130, a) succeeds the uppermost beds of 
 the Trias with perfect conformity, and passes upward, gener- 
 ally conformably, into the lowest beds of the Lower Oolites. 
 It consists essentially of a great series of bluish or grayish 
 laminated clay, alternating with thin bands of blue or gray 
 limestone, the whole assuming at a distance a characteristic- 
 ally striped and banded appearance. The total thickness of 
 
JURASSIC OR OOLITIC SERIES. 
 
 Hi 
 
 the Lias may be over 1,000 feet, and it teems with fossils, of 
 which only a few of the more characteristic can be meutioucd 
 here. 
 
 Brachiopoda are very abundant, and it is noticeable that 
 we have here the last appearance of the Palaeozoic genas Spir- 
 ifer. 
 
 Bivalve shell-fish are common, and one of the most charac- 
 ttTJstic species is a singular curved oyster, the Cryphcea incvrva 
 (Fig. 131). Of all the Liassic fossils, however, the most 
 
 abundant and characteristic are the re- 
 mains of Cephalopods^ allied on the one 
 hand to the living Cuttle-fishes, and on 
 the other to the Pearly Nautilus. Under 
 the first head come the Selemnites (Fig. 
 132), or, as they are commonly called, 
 " thunderbolts," from their conical form. 
 These really are the internal supports or 
 skeletons of animals like the living Cut- 
 tle-fishes or Squids ; and they consist of a long, tapering, fibrous 
 bjdy, enclosing above a hollow chambered portion, and termi- 
 
 Fio. 1ti\ .—Gruph<ea in- 
 curva. Lias. 
 
 FiQ. lSi2.—Beleinnitea elongatus. Lias, 
 
 n.iting in front in a horny plate, which is rarely preserved in 
 a fossil condition. Under the second head we have true iVaw- 
 tih\ and a vast abundance of difibrent species of AmnioiiiteSy 
 of which two characteristic forms are figured below (Figs. 133, 
 134). 
 
 Pia. A^.—AmmoniteH BiwJrldtuH, 
 }i nat. Bi2o.— u, Sido view ; ^, Fruut view. 
 
 Pio. IM.—Am monitea planorbis, 
 >i nat. 8i2u. 
 
 m 
 
t 
 
 i <: 
 
 I . ■ ;: 
 
 
 
 irc 
 
 GEOLOGY. 
 
 iLchinodcrms orour not iinoommonly in iho Lias, the com- 
 monest bcint^ (!ri/ioii7.% the form fi;rurf'<l bellow boiu^ espe- 
 cially cliaractcristic and abundant (Fiir. loo.) Besides these, 
 we iind true Soa-urchins, Brittle-stars, and Star-fishes. 
 
 Fio. 12SS.—E3iracrinuH Briareus. }4 nat. size. 
 
 Fishes are very largely represented, both by Ganoids and 
 by forms allied to the recent Port-Jaokson Shark, the teeth and 
 tiu-spines of the latter being especially abundant (Fig. 130). 
 
 Fm. \Z%,~ITyhodua reticulatits.—a, Fin-splnc; 6, Tooth. 
 
 Lastly, the Lias swarms with the bones, teeth, and" petrified 
 droppings or " coprolites" of large marine reptiles, which con- 
 stitute the genera Ichthyosaurus and Phsiosaurus^ and which 
 will be spoken of at greater length in treating of the life of 
 the Oolitic period. 
 
JURASSIC OR OOLITIC SERIES. 
 
 177 
 
 n. The* Xoxcer Oolifcs (Fi<jr. 130. h) consist of caloarpons 
 freestones (Inl'i'iiM' Oolite), sliiilcs, chivs, and marls (Fuller's- 
 eartli), iiue-grained Oolitic limestt)iies (Great Oolite), with cal- 
 careous llai;s at the base (StoneslieUl slati ), and shelly liino 
 stones and calcareous sandstones (Forest-marble and Corn- 
 brash), the whole liavinj^ a thickness of from 400 to 500 feet. 
 \i\ Yorkshire the Lower Oolites consist of limestones uith 
 carbonaceous shales and thin seams of coal, which are sulli- 
 cicntly extensive and constnnt to be worked for coal. Of this 
 a^e, also, is jjrobably the coal-field of Brora, in Sutherland- 
 shire, in the north of Scotland. 
 
 Fio. \Z1.—I'terophyllum comptum. Lower Oolites, Yorkshire. 
 
 Among the fossils of the Lower Oolites, plants are very 
 abundant in some places, the leading forms b(?ing Ferns and 
 Cycads. The specimen figurcjd above (Fig. 137) is a Cycad 
 belonging to the genus Pterophyllwn, 
 
 il 
 
 
 FiQ. 188.— ^7nm<w»«e« HumphrMianm. Inferior Oolite. 
 
178 
 
 GEOLOGY. 
 
 Molhisca are common in the Lower Oolites, Univalves 
 especially so, but thero are also Brachiopods and true Bivalves. 
 Cephalopods are not so common, but there are some charac- 
 teristic Ammonites (Fig. 138). The J^hinodermata are rep- 
 resented by Sea-urchins and Crinoids, the most characteristic 
 form among the latter being the Pear Encrinite {Apiocrinits 
 rotundus^ Fig. 139), which sometimes occurs in layers. Corals, 
 also, are abundant in some of the limestones. Among the 
 
 ■>^ 'V ■ 
 
 ■'':'-"■■ 
 
 —.- 
 
 6 
 
 isflB^-- 
 
 r— _— 
 
 
 ■^ 
 
 
 im.^ 
 
 
 " ' ' ~ "i 
 
 
 
 
 . i_ 
 
 
 Fio. 189. — ApiocHniu rotiindn«. — a. Stem and ono of the joints; b, Section showing the 
 Encrinitt'8 (frowingon limestone and enveloi»€<l above by clay (now shale); c, Three 
 perfect individuals represented as growing, but of reduced size ; d. Head, without the 
 
 arms. 
 
 most remarkable, however, of the organic remains of the Lower 
 Oolites are three small Mammals which are found in the Stones- 
 field slate, and which were long the oldest known representa- 
 tives of their class. Two of these have been described under 
 the names of Am,phUherium and Fhascolotherium^ and are 
 certainly Marsupial, the latter (Fig. 140) presenting a close 
 
 ^ 
 
 Fio. 140. — "Lovmivcft ot Phascototherium Burklandi.— 
 a, Natural size; b. Molar tooth magnified. 
 
 resemblance to the living opossums. The third forms the 
 genus Stereognathtte, and its exact affinities are still doubtful. 
 III. Tlje Middle Oolites are composed of a great mass of 
 dark-blue, tenacious clay (Oxford clay), with a maximum thick- 
 ness of 700 feet, surmounted by from 150 to 260 feet of lime- 
 stones known as the Coral-rag, from the number of corals 
 contained in them. The fossils of the Oxford clay are chiefly 
 
JURASSIC OR OOUTIC SERIES. 
 
 179 
 
 Ammonites and Belemnites^ the little Belemnites haatatua 
 (Fig. 141) being a characteristic species. The Coral-rag may 
 
 Fia. \4&.—T?iecosmilia annu 
 laHa. Corul-rag. 
 
 Fio. \4t\.—Belemnite$ hagtatm. Oxford Clay. 
 
 be regarded as an ancient coral-reef, and contains numcr- 
 ous corals, some of which attained a very large size. A 
 
 characteristic species is Thecosniilia 
 annularis (Fig. 142). Besides corals, 
 however, tlie Coral-rag contains nu- 
 merous bivalve and univalve Shell-fish, 
 with sea-urchins and other fossils. 
 
 IV. The Upper Oolites consist in 
 Britain of lammated, sometimes car- 
 bonaceous or bituminous clays (Kim- 
 meridge clay), forming the base of 
 the group, and having a thickness of 
 600 or 600 feet. These are succeeded 
 by sandstones and limestones (Port- 
 land stone) of about 120 feet in thick- 
 ness ; and the formation is capped by 
 a remarkable group of alternating 
 strata of fresh-water, brackish-water, 
 and marine beds, with old land-surfaces, the whole known as 
 the Purbeck beds, and having a united thickness of about 150 
 feet. Of the same age as the Upper Oolites in Britain is the 
 Solenhofen slate of Bavaria, an exceedingly fine-grained stone, 
 which is largely used in lithography, and is celebrated for the 
 number and beauty of its organic remains, especially those of 
 Vertebrates. The number of fossils in the Upper Oolites is so 
 great that it is impossible to give those characterizing the 
 minor subdivisions, and it will be suflBcient to indicate some 
 of the more striking forms. 
 
 Mbllusca are very nmnerous, and ta^ represented by ma- 
 rine forms in the marine beds, but by fresh-water forms in 
 
 many of the beds of the Purbeck group. 
 Oysters are especially abundant, and there 
 is one bed in the Purbecks 12 feet thick, 
 and composed entirely of the valves of a 
 singular oyster, Ostrea distorta (Fig. 143). 
 Corals occur in some of the beds, and 
 there are also Sea-urchins, and numerous 
 little bivalved Crustaceans allied to the 
 living Water-fleas. The Solenhofen slates 
 
 flo. \^.— Ostrea dUtoria. 
 MiddlA Purbeokt. 
 
! 
 
 \> 
 
 i 
 
 ! 
 
 i 
 
 I 
 
 I: 
 
 I 
 
 ! 
 
 180 
 
 GEOLOGY. 
 
 have yielded numerous Crustacea of higher types, along with 
 numerous insects, fishes, Tortoises, and other Reptiles, among 
 whieli the most singular are the Flying-lizards, known as Ptero- 
 dacUjles (Fig. 144). Besides these, the Solenhofcn slates have 
 yielded the lirst actual remains of birds 
 in the form of the bones and feathers of 
 the Arehceopteryx macrura (Fig. 150). 
 The characters of this extraordinary 
 bird will be spoken of later on. Lastr 
 ly, a thin bed of marl in the Middle 
 Furbeck beds has given up the bones 
 of no less ihfin fourteen distinct species 
 of small Mammals. These quadrupeds 
 are all of small size, and hardly any of 
 their bones have hitherto been discov- 
 ered, except separate branches of the 
 lower jaw ; so that it is very difficult ^°- 'SrirrS^'S). 
 to refer them to their proper place in 
 
 the class JIammalla. One genus, however, viz., Plagiaulax 
 (Fig. 145), appears to bo almost certainly Marsupial, and to be 
 most nearly allied to the living Kangaroo-rats. 
 
 erat- 
 
 Fio. 146.— Lower Jaw and teeth of Plagiauiaoa minor. Parbeck beds. 
 
 Jurassic Rocks vf North America. — Rocks belonging 
 to the Jurassic series, in the form of limestones and marls, have 
 been detected by their fossils in the Laramie Mountains and 
 in other portions of the Rocky Mountains, and also at various 
 points in Arctic America. The extent, however, of these beds 
 IS unknoAvn, and no subdivisions have hitherto been established 
 in them. 
 
 LiPB OF THE Oolitic Period. — The vegetation of the 
 Jurassic period is characterized by the abundance of ferns, 
 Couiferap, and Cycadaceous plants, and the rarity of Angio- 
 
JURASSIC OR OOLITIC SERIES. 
 
 181 
 
 spcrmous Exogens. The Cj-cads are especially abundant 
 throughout the whole Oolitic series, and the subjoined cuts 
 (Figs. 146, 147) exhibit the trunk of a fossil form side by side 
 with a living species, with its crown of feathery leaves. 
 
 Fio. 146. — Cycadeoidea megalophi/lia, a fossil Cycad. Pmbcck b<'<l8. 
 
 The Brachiopoda of the Jurassic series are decidedly less 
 numerous than in the older rocks, and they approximate more 
 t(j living forms. Bivalve and univalve Mollusks are numerous, 
 and upon the whole present a decided likeness to those of ex- 
 isting seas. Cejyhalopods are extraordinarily numerous, and 
 
 Fia. 147. — Zamia spiralis, a living Cycad. Australia. 
 
 Ammonites and Jielemnites may be said to be preeminently 
 the fossils of the Oolitic rocks. The Crinoids are now con- 
 siderably diminished in number, but the Echinoderiiuita are 
 represented by an increased number of Sea-urchins, Brittle- 
 stars, and Star-fishes. The Crustacea of the Oolitic rocks show 
 a very decided advance in structure, and we now meet with 
 forms resembling our living Crabs and Lobsters. Insects also 
 
 are numerous. 
 
 9 
 
182 
 
 GEOLOGY. 
 
 Fishes arc very abundant in parts of the Oolitic scries, the 
 majority being still Ganoids^ though most of these have the 
 symmetrical tail of most modern fisiiea. Besides these, there 
 are many fishes allied to the living Port-Jackson Shark ( Ces- 
 tracion)j and true Sharks and Rays. Reptiles are still more 
 numerous than in the Trias, their great abundance in these 
 formations and in tho Cretaceous epoch having led to the 
 naming the Mesozoic period the " Age of Reptiles." Tlie 
 Lahyrlnthodonts of the later Palax)zoic and earlier Mesozoic 
 formations have now disappeared, and we have no longer the 
 same forms of true reptiles as characterize the Trias. We 
 have, however, four reptiles of especial interest which are tlie 
 types of so many extinct orders. The first of these is the 
 Mbf/alosauruSy a gigantic terrestrial reptile, which belongs to 
 the order Deinosauria (Gr. cleinos, terrible; saura, lizard). 
 This order is better represented in the earlier portion of the 
 Cretaceous period. Secondly, we have a group of extraor- 
 dinary flying reptiles, Pterosauria (Gr. pterofi, wing ; saura^ 
 lizard), characterized by having one finger of the hand enor- 
 mously elongp.ted for the support of a leathery membrane by 
 which flight was effected. The best known genus of this 
 order is Pteroda(^tylus (Fig. 144), of which several species arc 
 known, varying in size from a crow, up to an expimse of wing 
 of 15 to 30 feet, or more. Tliirdly, we have two gigantic rci> 
 tiles, the types of two distinct orders, the remains of which 
 are very common in the Oolitic series. One of these is tlie 
 Ichthyosaurus (Gr. ichthus^ a fisli; saura^ lizard), of which 
 r ,ny species are known. The Ichthyosaurus (Fig. 148) was a 
 marine, swimming reptile, fully adapted to an aquatic life by 
 having a horizontal tail-fin, and by having all the limbs con- 
 verted into flippers or swimming-paddles. The jaws are very 
 long, and are furnished with numerous conical teeth, so that 
 the animal must have been highly predaceous. The Plesio- 
 saurus (Gr. plesios, near to ; saura^ lizard) was also a marine 
 animal, inhabiting the sea, and likewise had the limbs com- 
 pletely enveloped in the integuments, and thus converted into 
 powerful swimming-paddles. The Plesiosattrus, however, dif- 
 fers from the short-necked and voracious Ichthyosaurus in hav- 
 mg much shorter jaws and an enormously and disproportion- 
 ately elongated neck. Many species of both of these huge 
 reptiles are known, and they attained in some instances a 
 length of over 30 feet. 
 
 The class of Birds is represented by the tail, tail-feathers, 
 and some detached bones of a single bird, the Arcceopteryx 
 
JURASSIC OR OOLITIC SERIES. 
 
 188 
 
 macrura (Fig. 150), which was about as laro^o as a pigeon. 
 This extraordinary bird differed from all living birds in having 
 two free claws to the wing, and in having the tail long and 
 composed of separate vertebrae, each of which carried a single 
 feather on each side (Fig. 150, A). The tail, therefore, except 
 
184 
 
 GEOLOGY. 
 
 r 
 
 i ' 
 
 for the presence of feathers, was lonj^ and lizard-Iikc. In all 
 living birds, on the other hand, the tail-feathers aprinj^ in a 
 buncli from the last few vertebne of the tail, and the tail ter- 
 minates in a single upright, ploughshare-shaped bone, which 
 can be erected and depressed at will (Fig. 150, D, E). 
 
 Fig. 150.— a, Tnll of ArcTuropteryx macnira.—'R, Two of tho vertcbne of tho tail, nat. 
 size; C, A sinplo fcatJior. nat. size; 1), Tail of a livinjf vulture; E, Skeleton of the tail 
 of tlie sauie, the dotted linea showing tho altuchmeut of the tail-feathers. 
 
 The Mammals of the Oolitic period are all small, and show 
 no decided advance upon those of the Triassic rocks. They 
 aj)pear to have been for the most part insectivorous or flesh- 
 eating Marsupials, allied to the living Banded Ant-eater {Myr- 
 mecobius) and Opossums (Didelphys). 
 
CHAPTER XXII. 
 
 CRETACEOUS SERIES. 
 
 The next series of rocks in ascending order is tlie great 
 and important series of the Cretaceous Itocks^ ■, called frcM 
 the general occurrence in the system of cLalk (La< , creta^ 
 clialk). As aevcioped in Britain ard Europe gener.dly, the 
 followin T leading subdivisions may be recognizod in the Cre- 
 taceous series (Fig. 151) : 
 
 1. Wealden, ) , /^ . 
 
 2. Lower Greensand or Ncocomian, f ^^^^ Cretaceous. 
 
 3. Gault, 
 
 4. Upper Greensand, \ n r^ a. 
 
 5. Chalk, [►Upper Cretaceous. 
 
 6. MiBstricht beds, 
 
 Fio. 151. — Oencrallzod scrtion of tho Crctaopous rwks — n, TiOwor rrctftii'otis rwks; R, 
 Upper Cretacpous nx^ks; c, Wcnldon; </, Lowor (Jrecnsand ; ^. Onult;/. Upper Green- 
 sand ; j7, Chalk-marl ; A, White Chalk ; i, Eocene i-ucks ; o, Upper Oolites. 
 
 I. The Wealden formation, though of considerable impor- 
 tance, 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 Sur- 
 rey, Sussex, and Kent, where it is largely developed. Its 
 lower portion, for a thickness of from 500 to 1,000 feet, is 
 arenaceous, and is known as the Hastings Sands. Its upper 
 
 w 
 
186 
 
 GEOLOGY. 
 
 B! I' 
 
 W '■' 
 
 
 If 
 
 portion, for a thickness of 150 to nearly (j'OO feet, is chiefly 
 argillaceous, consisting of clays with sandy layers, and occa- 
 sionally courses of limestone. The geological thicknf'ss of 
 the Wealden formation is very great, and 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 calcu- 
 late 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 
 ( Unid)y river-snails {Paludina)^ and other fresii-water shells, 
 with numerous little bivalved Crustaceans, and some fishes. 
 
 Fio. 152.— Teeth of Iguanodon Mantdli. Wealden. 
 
 Besides these, however — the natural fossils of such a fresh- 
 water deposit — >"e find a number of remains of animals and 
 
CRETACEOUS SERIES. 
 
 187 
 
 is chiefly 
 and occa- 
 kin'ss of 
 )tediy the 
 ivholly of 
 n marine 
 •graphical 
 inudation 
 t, since it 
 in North 
 all these 
 a modern 
 Wealden 
 iccupying 
 ied in the 
 t, though 
 ely calcu- 
 li, mostly 
 nt day as 
 mussels 
 er shells, 
 le fishes. 
 
 plants which were brought down by the current of the ancient 
 stream. The animal remains consist of the bones of various 
 gigantic reptiles belonging to the order Dcinosauria^ of Pie- 
 siosaurtiSy of the flying l^terodactyles, and of the cases of river- 
 tortoises. Of the Deinosauria, the most remarkable is It/iia- 
 7iodo?i, which resembles the living Iguana% especially in the 
 form of its teeth (Fig. 152), but which is believed to have 
 reached the tremendous length of from 50 to 60 feet. There 
 is, also, good reason to suppose that Ignanodon^ in spite of its 
 vast bulk, walked, temporarily or permanently, upon two legs, 
 like a bird. 
 
 Plant-remains occur abundantly in the Wealden, and agree 
 with those of the Oolitic series and the Lower Greensand in 
 consisting of Fenis, Conifers, and Cycads, without any Angio- 
 sjiermous Exogens. 
 
 II. The Wealden beds pass upward, often by insensible 
 gradations, into the Lower Greetiscmd (Fig. 151, d). 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 Nccocomian^ derived 
 from the town of Neufchatel — anciently called Kcocomtmi — in 
 Switzerland. If this name were adopted, aa 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 color of the series is dark brown, sometimes red, 
 and the sands are occasionally green, from the presence of sili- 
 cate of iron. 
 
 The fossils of the Lower Greensand are purely marine, and 
 among the most characteristic are the shells of Cephalopods. 
 
 a fresh- 
 lals and 
 
 ^^1^' 
 
 Fio. 153. — Aneyloctra» gigoi. 
 
I 
 
 n 
 
 
 li 
 
 i<ti 
 
 IIm:i I 
 
 |M ' ; : 
 
 !l t. 
 
 i \, : 
 
 188 
 
 GEOLOGY. 
 
 Tlie frenus Nhutilus is representedhy the Nautiltis pUcafus 
 (Fig. 154), and there are a few Ammonites as well. Besides 
 these, we have the allied genus Anci/loceras (Fig. 153), which 
 is like an Ammonite partially unrolled, and having its larger 
 end bent inward. There are also Bivalve Shell-fish, Belemnites, 
 Sea-urchins, and Corals. 
 
 The most remarkable point, however, about the fossils of 
 tlie 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 [)hysi- 
 cal break as well, for the Gault is often, if not always, uncon- 
 formably superimposed on the Lower 
 Greensand. At the same time, the 
 Lower and Upper Cretaceous groups 
 form a closely-connected and insepa- 
 rable series, as shown by a comparison 
 of their fossils with those of the un- 
 derlying Jurassic rocks and the over- 
 lying Tertiary beds. Thus, in Britain 
 no marine fossil is known to be com- 
 mon to the marine beds of the Upper 
 Oolites and the Lower GrecJisand ; and of more than 500 spe- 
 cies of fossils in the Upper Cretaceous rocks, almost every 
 one died out before the formation of the lowest Tertiary 
 strata, the only survivors being one Brachiopod and a few 
 Foramuilfera. 
 
 III. The lowest member of the Upper Cretaceous series is 
 a stiff, dark-gray, blue, or brown clay, often worked for brick- 
 making, and known as the Gault^ from a provincial English 
 term. It occurs chiefl}'^ in the south-east of England, but can 
 be traced through France to the flanks of tlie Alps and Bavaria. 
 It never exceeds 100 feet in thickness ; but it contains many 
 fossils, usually in a state of beautiful preservation. Besides 
 Bivalves and Univalves, the Gault contains many Cephalopods, 
 such as Ammonites, Belenmites, Ancyloceras (Fig. 155), etc. 
 
 IV. The Gault is succeeded upward by the tipper Green- 
 sandy which varies in thickness from three up to 100 feet, and 
 which derives its name from the occasional occurrer>ce in it of 
 green sands. These, however, are local and sometimes want- 
 ing, 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 
 
 Fia, 154. — Na utUuti pHcatus, 
 
CRETACEOUS SERIES. 
 
 180 
 
 ipltcatus 
 Besides 
 J), which 
 its larger 
 lemnites, 
 
 fossils of 
 nee from 
 lecies of 
 ibout 18 
 break in 
 ?d l)hysi- 
 5, uncon- 
 
 pHcatua. 
 
 500 s}ie- 
 every 
 Fertiary 
 I a few 
 
 series is 
 )r brick- 
 English 
 but can 
 Bavaria, 
 many 
 Besides 
 ilopods, 
 ), etc. 
 Green- 
 tet, and 
 in it of 
 IS want- 
 ed as a 
 3ritain, 
 us grit 
 
 or siliceous limestone, and occasionally containing concretions 
 of phosphate of lime, which are largely worked for agricul- 
 tural purposes. 
 
 Fig. 155. — Ancylocerasspinigerum, Gault. 
 
 The fossils of the Upper Grr ^nsand are chiefly Sponges, 
 Brachiopods, Echinodernis, Cephalopods, Reptiles, and Birds. 
 V. The to]) of the Upper Greensand becomes argillaceous, 
 and passes up gradually into the base of the great formation 
 known as the true Chalky divided into the three subdivisions 
 of the chalk-marl, white chalk without flints, and white chalk 
 
 \v\i\\ flints. The first of these is simply 
 argillaceous chalk, and passes up into a 
 great mass of obscunjly-stratified white 
 chalk in which there arc no flints. This, 
 in turn, j>asses up into a great mass of 
 white chalk, in which the stratification is 
 marked by nodules of black flint arranged 
 in layers. The thickness of these three 
 subdivisions taken togetlier is sometimes 
 over 1,000 feet, and their geographical 
 extent is very great. Wiiite Chalk, with 
 its characteristic appearance, may be 
 traced from the north of Ireland to the 
 Crimea, a dl=tance of about 1,140 geo- 
 graphical mi; -., and, in an opposite direc- 
 tion, from the south of Sweden to Bor- 
 TiQ.\^.— Ventriculites ra- dcaux, a distance of about 840 geograph- 
 
 (fin(m,n sponge of the Ip^l rnilr>«: 
 
 White Chalk. ^ rr^i r' m <• , ^, „ 
 
 The fossils of the Chalk are extreme- 
 ly numerous, and consist chiefly of l^oraminifera^ Sponges, 
 Echinoderms, Bivalves, and Cephalopods. As regards the first 
 of these, almost the whole bulk of ordinary chalk is made up 
 of the microscoj)ic shells of I'oratninifera^ some of which are 
 
 •■'m 
 
100 
 
 GEOLOGY. 
 
 «-' ^* 
 
 specifically identical with forms now existing. Sponges are 
 very numerous, some being mushroom-shaped, others branch- 
 ing, and others funnel-shaped. Of the last, a good example is 
 to be found in Ventriculites (Fig. 15G). 
 
 Of the Mollusca^ the Chalk yields an enormous number of 
 forms allied to the plant-like Sea-mosses and Sea-mats, with a 
 good many Brachiopods. Bivalves are very numerous, and 
 characteristic, the commonest being Scallops (Pecteii) and 
 Oysters ( Ostrea). An exclusively Cretaceous genus of Bivalves 
 is Inoccramus (Fig. 157). Cephalopods arc very abundant, 
 
 Fig. 15S.— Portion of BacvUUs 
 Faujasii. 
 
 Fio. 157. — InocernmuK Lamarckii, 
 White Chalk. 
 
 Fiu. 15'J.— Portion of BacuUten 
 anceps. 
 
 and their forms are very varied. Helemnitcs and N^autili are 
 present, as well as true Ammonites^ but the most character- 
 istic forms are I^aciditcs, Scaphites, and Tur- 
 rilites. These all agree with i\\e Ammonites 
 in having chambered shells, the partitions 
 between the chambers of which are (iuriously 
 folded (Fig. 159), but they differ in the shape 
 of the shell. BacuUtes (Figs. 158, 159) 
 have a straight, staff-shaped shell, resembling 
 an Orthoceras in shape, but differing in the 
 form of the partitions. The shell of the 
 7\irrilite. again, is coiled into a spiral, the 
 convolutions of which do not lie in one plane 
 (as in the Ammonite)^ but are drawn out 
 into a cone or turret (Fig. 160). The Sca- 
 phite, lastly, resembles an Ammonite^ the 
 larger extremity of which has been unrolled, 
 and is finally bent inward toward the smaller, 
 
 .1-1 •' ,. /Tr«- i/>i\ Ftg. 160. — Tiirrtlite$ 
 
 coiled-up portion (1^ ig. 161). vo^tattn*. 
 
CRETACEOUS SERIES. 
 
 191 
 
 3 
 
 
 Of all the Chalk-fossils, however, none are more abundant or 
 more characteristic than Sea-urchins, which occur in very varied 
 
 forms and in a state of beautiful preserva- 
 tion. Two very characteristic species are 
 fi,2:ured below (Figs. 1G2, 1G3). llemains of 
 Fishes are tolerably abuntlant in the White 
 Chalk, and here for the first time we meet 
 with Bony Fishes, with flexible horny scales, 
 resembling the great majority of living 
 ^"'' ^^iwaiif"^'*"'" Fishes. Tliereare, however, also Shark-like 
 
 Fishes allied to the Port-Jackson Shark ( Ces- 
 tracion)^ and numerous true Sharks. 
 
 As the Chalk is certainly a deep-sea deposit, we naturally 
 find in it no remains of strictly terrestrial animals or of land- 
 plants. Remains, however, of Turtles and Pteroclactyles occur, 
 and the latter appear now to have finally died out, as they 
 have not been met with in any later deposit. 
 
 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 
 
 Fig. 1G2. — Micraster cor-anguinum. 
 
 Fia. ICS.—Galeritea albogalerua. 
 
 a scries of yellowish limestones, of about 100 feet in thick- 
 ness, and undoubtedly superior to the White Chalk. These 
 Mciefitricht beds contain a remarkable series of fossils, the 
 characters of which are partly Cretaceous, and partly Ter- 
 tiary. Thus, with the characteristic Chalk-fossils, J3eletnnites^ 
 Baculites^ Sea-urchins, etc., are numerous Univalve Mollusks, 
 such as Cowries and Volutes, which are otherwise exclusively 
 Tertiary or Recent. Another celebrated Maestricht fossil is 
 ' e skull of a gigantic marine Lizard, which has been described 
 under the name of Mosasaurus (Fig. 164). 
 
 ».sja 
 
 li 
 
i 
 
 i< 
 
 ^ 
 
 mi 
 
 
 rj 
 
 n 
 
 r 
 
 'I 
 
 192 
 
 GEOLOGY. 
 
 »' ■, '*( -/ 
 
 Fio. 1C4. — Skull of Moaasauriia C<i/nperi.—OT\g'ma,'i over three feet in length. 
 
 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, 
 ill Denmark, and which are known as the Faxoe Limestone. 
 
 Chalk of the South of Europe. — The great Chalk for- 
 mation of the south-west of England is continuous with a 
 similar series in the north of France, the two forming part of 
 one continuous mass, in which the Straits of Dover form mere- 
 Iv a shallow furrow. South of the Parisian basin, in the south 
 of France, there are again Cretaceous rocks, but the series 
 here diifers a good deal both in mineral characters and fossils 
 from the Chalk of the north of Eurojie. Ammonites^ for in- 
 stance, are very rare, and Tiovilltes^ Scaphites, and Selem- 
 nites^ appear to be wanting. The most characteristic member 
 of the Cretaceous series of the soutli of Europe consists of 
 certain compact marbles, known as Jlippurite limestones. This 
 name is derived from the abundance in these beds of a very 
 jioculiar family of Bivalve Mollusks known as Hippwrites (Fig. 
 165). All the members of this family were attached and lived 
 associated in beds, like Oysters. The two valves of the shell 
 are always altogether unlike in sculpturing, in appearance, 
 and in shape ; and the cast of the interior of the shell is often 
 extremely unlike the outer surface of the shell (compare a and 
 d. Fig. 165). About a hundred different species of the family 
 Ilippuritidiv are known, all of which, so far as is known, are 
 exclusively Cretaceous, occurring in Britain, Southern Europe, 
 the West Indies, Algeria, and the East. 
 
 Cretaceous Kocks op North America. — Tlie Lower 
 
CRETACEOUS SERIES. 
 
 193 
 
 Cretaceous rocks are represented not at all, or veir feebly, in 
 North America ; but there is a very oxtensive development of 
 rocks of Upper Cretaceous age in the United States. " The 
 
 Fio. lf)5. — TTippurites orqanisans.—a, A separate shell; (J, Cast of the interior of the 
 Bume ; c, Upper end of the lower conical valve ; b. Upper side of the upper valve. 
 
 Cretaceous rocks occur — 1. At intervals alon^ the Atlantic 
 hordeVy south of New York, from New Jersey lo South Carolina ; 
 2. Extensively over the States alon^ the Gulf border^ and 3. 
 Through a large part of the Western interior rcffion^ over the 
 slopes of the Rocky Mountains, from Texas northward, to the 
 h(>ad-waters of the Missouri on the cast of the summit of the 
 chain, and far into the Colorado region on the west. Still 
 farther north-west in British America, they appear on the 
 Saskatchewan and Assiniboine, and also on the Arctic Sea, 
 near the mouth of the Mackenzie " (Dana, " Manual of Geol- 
 ogy "). The rocks of these areas consist chiefly of sands, marls, 
 clays, and Hmestones ; but it is to be remembered that there 
 is no white Chalk. Green sands are often present, as in New 
 Jersey, where they are called " marls," and are largely worked 
 for agricultural purposes, their fertilizing properties being 
 due to the presence of a small percentage; of phosphate of 
 lime. The fossils of the Cretaceous rocks of North America 
 
 i 
 
 
 i« 
 
»' 
 
 li 
 
 . 
 
 :. 
 
 
 ¥ <" 'if' 
 
 iiiik 
 
 li 
 
 I' I IJ^ 
 4. <r 
 
 M«9 
 
 .1 Mli)?: 
 
 194 
 
 GEOLOGY. 
 
 aj^rce generally with those of the Upper Cretaceous rocks of 
 Europe, and some of them will be spoken of in treating of 
 the lite of the period. 
 
 Origin of Chalk and Flints. — As regards the origin 
 of the great masses of soft pulverulent White Chalk, it is now 
 generally admitted that it is a deep-water deposit, and is 
 formed chiefly of the shells of those minute Protozoa which 
 are termed i'oraminifera. Researches in the deep Atlantic 
 have shown that there is now in process of formation at great 
 Jepths in this ocean a deposit of white, chalky mud, which is 
 known as " ooze," and which, if consolidated, would form a 
 chalk-like rock. This ooze is composed almost entirely of the 
 microscopical shells of Foraminifera^ especially of tiie genus 
 Glohigerina (Fig. 166). Besides these, are the flinty cases of 
 
 Fio. 1C6. 
 
 Fio. ICL 
 
 Fig. 1C3. 
 
 Fio. ICa. Fig. 170. 
 
 • ••do*?"' 
 
 - -'•'•'•.'ir 
 
 
 Organic bodies In the oo?:e of the Atlantic bed at preat depths. 
 
 Fio. 166. — Gfohifferina huJloidfA, a Forainini/er. 
 Fi(is. 16T-169. — Siliceous jdants (Diatoms). 
 Fig. 170. — Spicule of a siliceous sponge. 
 
 certain of the lower plants {Diatoms, Figs. 167-169), also of 
 microscopic size; and, lastly, there are the needle-like spicules 
 of flint which are part of the skeleton of the siliceous sponges 
 (Fig. 170). 
 
 Chalk, similarly, has been shown to consist in great part 
 of the shells of Foraminifera, some of which are actually 
 identical with existing species ; so that there can no longer 
 be any doubt as to the chalk having originated as a deep-sea 
 deposit, much as we now see in the Atlantic ooze. Not only 
 so, but the ooze of the deep Atlantic is further found to be 
 peo})led with higher animals greatly resembling those now 
 found fossil in the Chalk, similar conditions of life favoring the 
 occurrence of representative forms. We do not, it is true, 
 meet with the characteristic Cephalopods of the Chalk ; but we 
 find Sea-urchins, Crinoids, and siliceous Sponges, sufficient to 
 establish a decided resemblance between two deposits so 
 widely removed in time. 
 
 As regards the origin of flints in Chalk, it is now generally 
 
CRETACEOUS SERIES. 
 
 105 
 
 now 
 
 admitted that these must be also ascribed to organic agencies. 
 The water of the sea contains a minute proportion of silica in 
 solution, and this is withdrawn by the living agency of ani- 
 mals or plants to form their shells or skeletons. Thus, certain 
 of the lower plants (Diatoms) secrete a siliceous shell (I'igs. 
 167-169), and these abound in the waters of tlie ocean, lakes, 
 and rivers. There are also certain animalcules, nearly allied 
 to the toramhiiferay which secrete a flinty shell ; and many 
 sponges produce a flinty skeleton. Remains of all these living 
 beings may be detected in sections of flint under the micro- 
 scope, and similar bodies have now been found in the nodules 
 of hornstone (impure flint), which are found in many of the 
 older rocks, from the Devonian upward. We may conclude, 
 then, that flints are chiefly due to the exertions of animals and 
 plants. Their occurrence in layers seems to be in some meas- 
 ure connected with " the periodic growth of large crops of 
 sponges " (Owen). 
 
 Life op the Cretaceous Period. — As regards the vege- 
 tation of the Cretaceous period, we have to mark a great ad- 
 vance over the plants of the preceding periods. The plants 
 of the Lower Cretaceous rocks agree with those of the earlier 
 Oolitic period, in consisting chiefly of Ferns, Cycads, and Coni- 
 fers, without any Angiospermous Exogens. In the Upper 
 Cretaceous rocks, however, we meet for the first time with an 
 abundance of forms allied to our ordinary trees and shrubs, 
 and belonging to the class of the Angiospermous Exogens. 
 Not only is this the case, but we meet with many familiar 
 genera, such as the Oak, Willow, Walnut, Fig, Beech, Poplar, 
 etc. It is singular, therefore, to reflect that trees, difl"ering little 
 from those of our own forests, should have coexisted with the 
 Ammonites and Belemnites^ and other extinct forms of marine 
 life which characterize the Upper Cretaceous period. Here, 
 also, we meet for the first time with true Palms. 
 
 The Protozoa are represented by numerous Foraminiferay 
 which are found chiefly in the Chalk, but also in other beds, 
 and by an abundance of Sponges of various forms. Tlie Coi- 
 lenterates are represented by Corals; the Echinodermata are 
 represented by a profusion of Sea-urchins; but the CrlnoidSy 
 so characteristic of the older periods, are now reduced to a 
 few forms, nearly resembling living species. Crustaceans are 
 not common, the most abundant being little bivalved forms 
 like the living Water-fleas ; but there are also a few Barnacles, 
 and some of the higher stalk-eyed species, like Crabs and Lob- 
 sters. The Mollusca are represented by an enormous number 
 
 III] 
 
^^ 
 
 ■ ^ '4 
 
 im 
 
 
 If- 1 
 
 I ^t 1 
 
 
 w 
 
 'if 
 
 
 
 . • 
 
 ' 1 
 
 106 
 
 GEOLOGY. 
 
 of forms, belonging to all the great subdivisions of tlic class. 
 The Urachiopods are proportionately much reduced in num- 
 bers, and their forms approximate more closely to living species. 
 The Jiivalves are represented by numerous types, of which 
 some are of existing genera, such as the Scallop and Oyster ; 
 while others are exclusively Cretaceous, such as Inoceraniu8 
 (Fig. 157), and the entire family of the Hijmnritldo' (Fig. 
 1G5). Univalves are pretty abundant, l)ut the greatest devel- 
 opment of the MoUuscan sub-kingdom is in the class Cephalo- 
 poda^ which is represented by a great number of complex and 
 beautiful forms. Ammonites and JSelemnites continue their 
 life from the uppermost beds of the Trias, but die out finally 
 here. The true Ammonites^ however, are to a great extent 
 su[)erseded by allied forms, such as the Bacidite (Fig. 159), 
 the 2'urrUite (Fig. IGO), and the Scaphite (Fig. IGl). All 
 these, also, disu|)pear with the close of the Cretaceous period. 
 The Vertebrate sub-kingdom is represented by Fishes, Rep- 
 tiles, and Birds, no Mammals having iiitherto been detected. 
 In this period we meet for the lirst time with representatives 
 of the liony Fishes, with thin, flexible, horny scales, such as 
 now predominate in existing waters. Here, also, we meet 
 with true Sharks, many of which were of large size. The 
 older groups of the Ganoids and the fishes allied to the Port- 
 Jackson Shark ( Cestracionts) are, however, still represented ; 
 and, indeed, both groups have survived to the present day, 
 though reduced in numbers. Reptiles are ver}- numerous, and 
 are represented by many orders. The Dcinosauria, which 
 commenced in the Oolitic period, are represented by the 
 gigantic Iguanodon of the Wealden, the Iladrosaiirus of 
 North America, and other forms, but died out during this 
 epoch. The marine Ichthyosaii7iis and PlesiosauruSy with the 
 flying Pterodactyles^ which also commenced in the Jurassic 
 period, are represented in the Cretaceous epoch, and also die 
 out at its close. The Lizards are represented by the 3fos(isau- 
 rtis of Europe, a gigantic marine reptile, by an equally gigantic 
 and nearly allied form from New Jersey, and by related spe- 
 cies of smaller size. Turtles are represented by several forms, 
 and there are also true Crocodiles in the Cretaceous beds of 
 New Jersey. 
 
be class, 
 in mmi- 
 
 species. 
 >f which 
 Oyster ; 
 ceramns 
 'm (Fig. 
 it dcvcl- 
 lephalo- 
 )lex and 
 le their 
 t finally 
 
 extent 
 
 ). All 
 
 period. 
 cs, Rep- 
 :;tectrd. 
 itatives 
 such as 
 e meet 
 The 
 ic Port- 
 sented ; 
 nt da}', 
 •us, and 
 
 wliich 
 by the 
 irus of 
 ig this 
 ith the 
 urassic 
 Iso die 
 )sasau- 
 igantic 
 d spe- 
 
 forms, 
 eds of 
 
 KAIN OZOIC EPUCir. 
 
 CHAPTER XXIII. 
 
 EOCENE FORMATION. 
 
 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 a complete and entire ph^^s- 
 ical break between the rocks of the Mesozoic and Kainozoic 
 ])cr!ods. In no instance are Tertiary strata to be found rest- 
 ing conformably upon any Secondary rock. The Chalk has in- 
 variably suffered much erosion and denudation l)efore 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 second place, there is a complete 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 Ammonitidce and IIippuritkl<v^ 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 in- 
 creasing number of living species as we pass from the bottom 
 of the Kainozoic series to the top. Upon this last fact, as we 
 
198 
 
 GEOLOGY. 
 
 ,i; 
 
 i 
 
 
 shall SCO, is foimdod tlio modorn classification of the Kainozoio 
 rocks, ])ropoim(Jed by Sir Clmrles L}cll. 
 
 It follows from the constant want of conformity between 
 the Cretaceous and Tertiary rocks, and still more from the en- 
 tire dillerence in life, that ike Cretaceous and Tertiary j)erioda 
 are separated by an enormous lapse of unn^presented time. 
 IIovv long this interval may have been, we have no means of 
 ju(lgin<r exa<;tly, 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 surfaqp, strata which were deposited 
 during this period, and which will contain fossils intermedi- 
 ate in character between the organic remains which respec- 
 tively characterize the Secondary and Tertiary periods. At 
 present, we have only slight traces of such deposits, such, for 
 instance, as the Maestricht beds. 
 
 Classification op the Tertiary Rocks. — The classifica- 
 tion of the Tertiary rocks is a matter of unusual difficulty, in 
 consequ(!nce of their occurring in disconnected basins, forming 
 a serit!s of detached areas, which hold no relations of super- 
 position to one another. Tlie order, therefore, of the Tertia- 
 ries in point of time can only be deterniined by an appeal to 
 fossils ; and in such determination Sir Charles Lyell proposed 
 to take as the basis of classificjition the proportion of living 
 or existinff species which occur in each sirdturn or group of 
 strata. Acting upon this principle. Sir Charles Lyell divided 
 the Tertiary scries into four groups : 
 
 I. The Eocene formation (Gr. eos, dawn ; Jcainos^ 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 Jf/oce«c formation (Gr. me2on, less ; .^ainos, 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 ; kainoft^ 
 new), with more than half the species of shells identical with 
 existing species; the proportion of these varying from 35 to 
 r>0 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 
 
EOCENE FORMATION. 
 
 190 
 
 belong to existing species. Tliis, in ttarn, is divided into two 
 minor frroiips — the Post-IHiocaie and lleccnt J'Wniations. la 
 tlio PoHt-1 1'ocenc formations, wiiiie all the JUollusca belonfir 
 to cxistinpf 8j)ecie8, most of tl»c Mammals belong- to extinct 
 species. In the liecent period, the quadrupeds, as well as the 
 shells, belong to living species. 
 
 The above, with some modifications, was the original 
 classiiicution proposed bv Sir Charles Lyell for the Tertiary 
 rocks, and now universally accepted. More recent researches, 
 it is true, have somewhat altered the proportions of existing 
 spc(;ies 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 dei)osits. 
 
 EOCENE FOEMATION. ; ' 
 
 Tlic 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 Jilolhtxca — from three and a 
 half to five per cent. The Eocene rocks occiu- in several basins 
 in Britain, France, the Netherlands, and other parts of Eurojie, 
 and in the United States. The subdivisions which have been 
 established are extremely numerous, and it is often inipossible 
 to parallel those of one basin with those of another. It will 
 be sufiicient, therefore, to accept the division of the Eocene 
 formation into three great groups — Low er, Middle, and Upper 
 Eocene — and to consider some of the more important beds 
 comprised under these heads in Europe and in North America 
 (Fig. Kl). 
 
 FlQ. 171. — ffoneralizod softion oftho Eocrno rocks. — rr, Lower Eoprno : h. Middle Eocene ; 
 c, UpiH-T liocc'iio; t/, Chalk; c, London Clay;/, Nuiiinmlitic Linustone. 
 
 I. Lower Eocene. — Tlie Lower Eocene rocks of Britain 
 consist of sands, mottled clays, lignites, and gravels, sur- 
 mounted by a great mass of dark-brown or blue clay, which 
 has a thickness of ivoin 200 to 500 feet, and is known as the 
 
200 
 
 GEOLOGY. 
 
 .11-1 
 
 Fio. 172.— Vofuta 
 nodoKd. (Lou- 
 don Clay.) 
 
 ill 
 
 London Clay. The London Clay is a marine deposit, and 
 contains many marine fossils, with the remains of terrestrial 
 animals and plants. All tiie remains indicate a high tempera- 
 ture of the sea and tropical or sub-tro[)ical con- 
 ditions. The Mollusca belong chiefly to well- 
 known tropical genera, such as Volutes, Cones, 
 and Cowries (Fig. 172), and there are also sev- 
 eral species of jVautilns and other Ccphalopods. 
 Crustaceans allied to the living Crabs and Lob- 
 sters are likewise abundant. Fish are numerous, 
 and are mostly related to the living Sharks, but 
 there are also remains of Sword-fishes and Saw- 
 fishes. Turtles, Sea-snakes [Paloiophis), and 
 Crocodiles, have been detected ; and the remains 
 of Birds and Quadrupeds also occur. Of the lat- 
 ter, the most important are Ilyracotherlum, belonging to the 
 Hog-family, and Goryphodon^ allied to, but larger than, the 
 living Tapirs. 
 
 In North America, Lower Eocene rocks are extensively 
 developed at Clail)orne, Alabama, and consist of clays, lig- 
 nites, marls, and impure limestones. The fossils of the Clai- 
 borne beds are very numerous, and belong to the me groups 
 as those of the London Clay, except that Mammals appear to 
 be wanting. The lignites (imperfect coals) contain numerous 
 plant-remains. 
 
 II. Middle Eocexe. — The Middle Eocene of Britain con- 
 sists chiefly of sands, clays, and gravels. In F' ranee, the Middle 
 Eocene consists chiefly of a compact limestone (the so-called 
 " Calcaire Grossier"), which contains an extraordinary number 
 of fossils. Among these are more than 130 species of a single 
 genus of Univalve Mollusks (Cer/^/< /?<;??), almost all the living 
 forms of which inhabit estuaries, where the water is brackish. 
 
 !l? 
 
 t.K\ 
 
 Fio. 1"S. — Calcarina rnri^fpinn. 
 ft, Nat. sizo; a, c, Same tuognilled. 
 
 Pm. 174. — Spirolina rteno/<toma. 
 fc, Natural size ; (/, c, </, Same inaguifled. 
 
iffin"" to the 
 
 I 
 
 
 EOCENE FORMATION. 
 
 201 
 
 Foraminifera are also wonderfully abundant, whole beds of 
 limestone being almost composed of their shells. Some of the 
 more characteristic species are figured above (jf^igs. 173, 174). 
 More important than the above minute forms of the Fo- 
 raminifera are certain large coin-shaped species called JVkim- 
 mulites (Lat. nummus, a coin), which occur in the Eocene 
 beds of almost all parts of the v/orld. The Nummulites (Fig. 
 175) are so abundant in one of the Middle Eocene rocks, that 
 
 Fig. 175. — yummnUtes Pmchi. — a. External surface of one of the Nummnlitcs, of which 
 longitudinal sections arc seen in the limestone ; b, Transverse section of the same. 
 
 it has been called the " Nummulitic Limestone." Tliis forma- 
 tion attains a thickness of sometimes thousands of feet, and is 
 largely developed in the Alps. It supplied the stone of which 
 the Pyramids were built, and it has been traced through India 
 to the frontiers of China. It is worthy of notice in this con- 
 nection that tlie Eocene rocks of the Alps have not the com- 
 paratively soft, incoherent, and unaltered (character of the Ter- 
 tiary rocks in general. They rival the older Palseozoic rocks 
 in thickness, and are as much contorted, faulted, indurated, 
 and cleaved ; while they rise in many instances to very lofty 
 elevations. 
 
 Fio. 176.— Tooth of Carcharodon heterodon. Fio. 177.— Tooth of Otodua obliquvt. 
 

 I i 
 
 w \ ■ 
 
 n 
 
 miLL 
 
 202 
 
 GEOLOGY. 
 
 The Middle Eocene rocks of Britain, besides Niimmulitcs, 
 contain many univalve and bivalve Mollusks, a large marine 
 serpent of the Constricting family {l\ikeophis)^ a Crocodile, 
 an ' -numerous Fishes. Among the remains of the last of these 
 are the pavement-like teeth of huge Kays [Myliohatis), and the 
 trenchant teeth of large Sharks ( Carcharodon, Otoclus, etc., 
 Figs. 176, 177). 
 
 The Middle Eocene group is represented in North America 
 by lignitic clays and marls which occur at Jackson, Mississippi. 
 Among the more remarkable fossils of the Jackson beds are 
 the teeth and bones of a gigantic Mammal belonging to the 
 order of the Whales, but diifering from all existing forms in 
 lijiving molar teeth with double roots (Fig. 178). It forms 
 the genus Zeuglodon, and attained a length of 70 feet. 
 
 ^^d 
 
 Fig. 178.— Molar tooth, nat. eizo. 
 
 Zeuglodo7i ceioidcs. 
 
 Fig. 179. — Vertebra, reduced. 
 
 III. Upper Eocene. — The Upper Eocene is poorly rep- 
 resented in Britain by alternations of fresh-water, brackish- 
 water, and purely marine beds, consisting of clays, sands, 
 marls, and limestones. The fresh- water beds are characterized 
 by the occurrence of Pond-snails, River-snails, and other shells 
 pt;culiar to fresh waters, along with I.iand-snails. There are 
 also fresh-water Tortoises, Snakes, Crocodiles, and Fishes, one 
 of the latter being closely allied to the Gar-pike of the United 
 States. Mammals are numerous and belong to several genera, 
 the two most Important being Anoplotherium ^ a hoofed quad- 
 ruped forming a kind of link between the Swine and the true 
 Ruminants, and Ilyoenodon^ a large carnivorous animal allied 
 to the living Hyoenas. Here, also, we have the genus Palcco- 
 therium^ which is represented by several species allied to the 
 living Tapirs (Fig. 180). 
 
EOCENE FORMATION. 
 
 203 
 
 :f!' i 
 
 ?i*S! 
 
 Fio. ISO. — Outline of Pulacotherium inagnuhi, as restored by Cuvier. Upper Eocene. 
 
 The most important member of the Upper Eocene of 
 France is the so-called "Gypseous series of Montmartre," 
 named from the hill of Montmartre in the vicinity of Paris. 
 This series consists of three masses of granular crystalline 
 gj'psum, largely quarried for plaster of Paris, with intervening 
 laminated marls. The most remarkable fossils of this series 
 are Mammals, of which about fifty species are known. Four- 
 fifths of these are hoofed quadrupeds, more or less closely 
 allied to the Rhinoceros, Tapirs, and Swine of the present day, 
 the two most important genera being Anoplotherium and 
 PalcBotherium. There are also Marsupials, Bats, Rodents, and 
 Carnivores, all belonging to extinct species. 
 
 Rocks of Upper Eocene age occur in North America at 
 Vicksburg, Mississip{)i, and consist of lignites, clays, marls, 
 and limestones. On the White River they are about 1,000 
 feet thick, and consist of (;lays, sandstones, and limestones, of 
 fresh-water origin. Among their most remarki^ble fossils are 
 the remains of Mammals, of which about forty species have 
 been already determined. Among these we have two Ithl- 
 noceroseSj several Carnivorous animals, some small animals 
 allied to the 3Iicey and a number of herbivorous animals 
 related to the Tapirs^ Peccary^ Gamely etc. 
 
 Life op toe Eocene Period. — Little need be added 
 here as to the life of the Eocene period, fossils being so abun- 
 dant as to render it impossible to do more than indicate some 
 general considerations. Upon the whole, the plants and ani- 
 mals of the Eocene period closely resemble those now in ex- 
 istence upon the globe j not, however, necessarily in the exact 
 
M 
 
 1 
 
 
 ii 
 
 H 
 
 i! 
 
 204 
 
 GEOLOGY. 
 
 localities in which they are now found. Thus, the modern 
 representatives of the plants and animals of the Eocene rocks 
 of Europe are not to be found in Europe itself, but in some 
 tropical or sub-tropical region. The climatic conditions of Eu- 
 rope in the Eocene period were very different to those at pres- 
 ent subsisting, and tlic animals and plants were correspond- 
 ingly different. Still, there are few Eocene fossils which have 
 not their modem representatives in warm countries. 
 
 Foraminifera are peculiarly abundant in the Eocene seas, 
 and sometimes attained a size rarely equalled by existing 
 forms, Nummulites being often as much as three inches in cir- 
 cumference. Corals are not abundant, but more closely re- 
 semble living types. JBrachiopods are much reduced in num- 
 bers, both individually and as regards the tj-pes represented. 
 Univalve and JBivalve 3follusJcs are exceedingly abundant, 
 and most recent genera are represented, though less than five 
 per cent, only are identifiable with existing species. The Arn- 
 moniteSf 2'urrilites^ Haculites, Jielemnites^ etc., of the Creta- 
 ceous rocks have now disappeared, and the Cephalopoda are 
 represented mainly by N^autlU. Fishes are abundant, the 
 leading types being true Sharks, some of which must have 
 reached a perfectly tremendous length. The large and won- 
 derfully-modified Reptiles of the Mesozoic scries are no longer 
 in existence, but their place is taken by other forms agreeing 
 more closely with existing types. Birds are tolerably abun- 
 dant, and all the living orders of the class find some ancient 
 representative here. Lastly, Mammals show an extraordinary 
 advance, both in point of numbers and development, as com- 
 pared with the Mesozoic period. In the latter epoch we have 
 no certain evidence of any quadrupeds higher in the scale than 
 Marsupials^ allied to living Kangaroos, Opossums, etc. In the 
 Eocene Tertiary, however, we meet with representatives of 
 the greater number of the chief mammalian orders. Besides 
 Marsupials, we have Eocene examples of the orders Sirenia 
 (Dugongs), Ce^acea (Whales), Ungulata (Hoofed Quadrupeds), 
 Carnivora (Lion, Tiger, Hynena, etc.), Rodentia (Mouse, Bea- 
 ver, etc.), Insectivora (Mole, Hedgehog, etc.), and Cheiroptera 
 (Bats). The orders of tlie Proboscidea (Elephants), and Quad- 
 rumana (Mon^^eys), are not known to be represented in this 
 period. 
 
e modem 
 ;ene rocks 
 t in some 
 )ns of Eu- 
 ie at pres- 
 )iTespond- 
 hich have 
 
 cene seas, 
 r existing 
 bes in cir- 
 3losely re- 
 el in num- 
 3resented. 
 abundant, 
 < tlian five 
 The Am- 
 he Creta- 
 }poda are 
 idant, the 
 lust have 
 and won- 
 [no longer 
 agreeing 
 ^ly abun- 
 ancieut 
 aordinary 
 as com- 
 \ve have 
 cale than 
 In the 
 atives of 
 Besides 
 Sirenia 
 drupeds), 
 •use, Bea- 
 eiroptera 
 nd Quad- 
 in this 
 
 0. 
 
 CHAPTER XXIV. 
 
 MIOCENE FORMATION. 
 
 The 3Tlocene formations comprise those Tertiary deposits 
 which contain less than about 35 ])er cent, of existing species 
 of Mollusca, and more than five per cent., or those deposits in 
 which the proportion of living shells is less than of extinct 
 species. The Miocene formations are divisible in Europe into 
 a Lower Miocene and Upper Miocene group. 
 
 I. Lower Miocene. — The Miocene formations are very 
 poorly represented in Britain, their leading development being 
 at Bovey Tracy, in Devonshire, where there occur sands, 
 clays, and beds of lignite or woody coal. These strata contain 
 numerous plants, among which are Vines, Figs, the Cinnamon- 
 tree, Palms, and a number of Coni ferae. Of the Conifers, the 
 most abundant is a gigantic Pine {ISequoia Couttsicc)^ which is 
 most nearly allied to the huge Sequoia gigantea of California. 
 Other plant-bearing strata in the Hebrides, on the west coast 
 of Scotland, have been referred to the Miocene age. 
 
 In France, the Lower Miocene is represented in Auvergne, 
 Cantal, and Vclay, by a great thickness of nearly horizontal 
 strata of sand, sandstone, clays, marls, and limestones, all of 
 fresh-water origin. Other Miocene deposits occur in Austria, 
 Germany, Switzerland, and the Siwalik hills in India, some of 
 which wnll be further alluded to hereafter. 
 
 II. Upper Miocene. — The typical European deposits of 
 Upper Miocene age occur in the valley of the Loire, in France, 
 and are known as the " Faluns," a provincial term given to 
 shelly sands employed to spread upon soils which are deficient 
 in lime. The Faluns occur iri 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 liind and fresh-water shells, and the remains of numerous 
 
 III 
 
i\ 
 
 
 206 
 
 GEOLOGY. 
 
 Mammals. Some of these last, such as the Walrus, Manatee, 
 and Dolphin, are aquatic ; while others are terrestrial, such as 
 the Hippopotamus^ Rhinoceros^ Mastodon^ and Deinotherium 
 (Fig. 181). Tlie Mastodons resembled the Elepiiants in most 
 respects, but dififer in the shape of the molar teeth. The Dei- 
 notherium was a gigantic Proboscidean^ allied to the Elephants, 
 but diflfering in possessing greatly-developed incisor teeth in 
 
 FiQ. 181. — Skull of Deinotherium giganteum. Fio. 182. — Valuta Lamberil. Faluns. 
 
 the lower jaw, which formed long, curved tusks, bent down- 
 ward in a most singular manner. The shells of the Faluns 
 belong to more than 300 species, of which only 45 are common 
 to the Pliocene. They indicate a tropical climate, and consist 
 chiefly of Cones, Volutes (Fig. 182), Cowries, and other well- 
 known tropical genera. About 25 per cent, of the shells be- 
 long to existing species. 
 
 In Switzerland, between the Alps and the Jura, there oc- 
 curs a great series of Miocene deposits, known collectively as 
 v^ "Molasse," from the soft nature of a greenish sandstone, 
 ]• junstitutes one of its chief members. It attains a thiok- 
 
 {* i many thousands of feet, and rises into lofty mountains, 
 9'^ ?. Ci which — as the Rigi — are more than 6,000 feet in 
 
 >« vr-iv The middle portion of the Molasse is of marine 
 origin, and is shown by its fossils to be of the age of the Fa- 
 luns ; but the lower and upper portions of the formation are 
 mainly or entirely of fresh-water origin. The Lower Molasse 
 
s, Manatee, 
 ial, such as 
 iinothenum 
 nts in most 
 I. TheDet- 
 ) Elephants, 
 sor teeth in 
 
 r 
 
 mberti. Falans. 
 
 bent do\vn- 
 the Faluns 
 ire common 
 and consist 
 other well- 
 e shells be- 
 
 a, there oc- 
 lectively as 
 
 sandstone, 
 ms a thick- 
 mountains, 
 )00 feet in 
 
 of marine 
 ! of the Fa- 
 rmation are 
 rer Molasse 
 
 MIOCENE F0RM4.TI0NS. 
 
 207 
 
 (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, etc. Of the characters 
 of the plants something will be said in speaking of the vege- 
 tation of the Miocene period. 
 
 Miocene op North America. — Miocene deposits are 
 found in the United States in New Jersey, Maryland, Virginia, 
 California, Oregon, etc., and they attain sometimes a thickness 
 of 1,500 feet. They consist chiefly of clays, sands, and sand- 
 stones ; and in Virginia there is a bed of what is wrongly 
 called " Infusorial Earth," which attains a thickness of many 
 feet, and consists almost wholly of the siliceous cases of cer- 
 tain low forms of plantsi (Diatoms). The strata of the White 
 River, with remains of numerous Mammals, formerly spoken 
 of as Upper Eocene, are sometimes referred to the Miocene 
 formation. The fossils of the Amerl. in Miocene are chiefly 
 Mollusks (of which 15 to 30 })er cent, are living species), 
 Sharks, Whales, Dolphins, and Seals. 
 
 Life op the Miocene Period. — As regards the animals 
 of the Miocene, only the Mollusks and Mammals need any 
 special notice. The Mollusca of the Miocene deposits (when 
 these are marine) are referable to genera now in existence, 
 but, for the most part, proper to warm climates. The per- 
 centage of living forms varies from 15 to 30 per cent. In the 
 European Miocene, however, though shells of existing species 
 are present, these do not belong to species now found in 
 European seas. Very few of the now existing European 
 shells are found in any Tertiary deposit older than the Plio- 
 cene. In America, however, shells now extinct, such as 
 Fmus quadricostatus (Fig. 184) are found side by side in the 
 Miocene Tertiaries with shells which still exist ^ American 
 waters, such as Fulgur canaliculatus (Fig. 183), 
 
 The Mammals of the Miocene period are very numerous, 
 and show an advance upon those of the Eocene period. Tlie 
 entire order of the Prohoscidea^ comprising only the recent 
 Elephants, appears to have first come into existence in the Mio- 
 cene period, where it is represented not only by true Elephants, 
 but by the nearly-allied Mastodons, and the singular Deinothe- 
 Hum. The order Quadrumana, comprising the Apes and the 
 Monkeys, likewise appears to date its existence from the Mio- 
 cene period, when it is represented by forms allied to the Mon- 
 keys of the Old World. True Deer first make their appearance 
 
 I 
 
\ 
 
 i\ 
 
 
 :;i 
 
 \m 
 
 hi 
 
 W^ 
 
 :i 
 
 m 
 
 
 208 
 
 .GEOLOGY. 
 
 in the Miocene, with Giraffes and Antelopes, some of the last 
 of gigantic size and furnished with four horns. The JLdentates 
 (such as the modern Sloths, Armadillos, and Ant-eaters) are 
 represented by a gigantic form somewhat allied to the Scaly 
 Ant-eaters or Pangolins of the Old World. Lastly, the great 
 order of the Carftivora was represented i.-i two of its leading 
 divisions by the bear-like Amphicyon and the great sabre- 
 toothed tiger, Machairodus. 
 
 Fig. 183. — Fulgvr cnnaliculatii^. Maryland, 
 Miocenu and recent. 
 
 Fia. 184. — Fum« quadrico8iatu». 
 Maryland, Miocene. 
 
 Vegetation op the Miocene Period. — Our chief sources 
 of information as to the vegetation of the Miocene period are 
 derived from the brown coals of Germany and Austria, the 
 Lower and Upper Molasse of Switzerland, and the Miocene 
 beds of Greenland. The brown coals, or lignites, of Germany 
 and Austria are simply vegetable matter in process of conver- 
 sion into ordinary coal, but still retaining a good deal of 
 its original structure. From marlstone associated with these 
 brown coals at Rad.aboj, in Croatia, have been obtained more 
 than 200 species of plants, most of which indicate tropical 
 conditions. Among these is the Sabal (Fig. 187), a genus of 
 Palms which is now found in America. Accompanying these 
 plant-remains are numerous insects, among which are Termites, 
 or White Ants, Dragon-flies, Grasshoppers, and even Butter- 
 flies (Fig. 185). 
 
 The plants of the Lower Miocene of Switzerland are 
 also mostly of a tropical character, but include several Ameri- 
 can forms, such as a Tulip-tree {Liriodendron) and a Cypress 
 ( Taxodium). Among the more remarkable forms from these 
 
MIOCENE FORMATION. 
 
 209 
 
 idricostatrtt. 
 
 lOCCDC. 
 
 Fio. 185. — Vanessa Pluto, nat. size. Lower Miocene, HodaboJ. 
 
 beds may be mentioned numerous tropical ferns, two species 
 of Cinnamon, and a Fan-palm ( Chammrops, Fig. 186). 
 
 The plant-remains of tiie Upper Molassc of Switzerland in- 
 dicate an extraordinarily rank and luxuriant vep^etation, com- 
 posed mainly of tropical fcrms. Among the commoner plants 
 
 Fio. 186. — Chamcerops Helvetica. Lower 
 Miocene. 
 
 Fio. 187. — Sahnl major. Lower Mio- 
 cene, France. 
 
 of tills formation are many species of Maple {Acer)., Plane- 
 treos (Platanus, Fig. 188), Cinnamon-trees (Fig. 189), with 
 other members of the Laurel order, numerous species of Sarsa- 
 parilla {Smilax)^ with Palms, Cypresses, etc. 
 
 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. Among these plants are many 
 
 .At 
 
 
210 
 
 GEOLOGY. 
 
 trees, such as Conifers, Beeches, Oaks, Maples, Walnuts, Mag- 
 nolias, etc., with numerous shrubs, ferns, and other smaller 
 plants. 
 
 m 
 
 i t tS 
 
 |*i ; 
 
 Fio. IBS.— Platanua aceroides.—a. Leaf; 
 ft, The core of a bundle of pericarps ; c, 
 Single fruit or pericarp, nutural size. 
 Upper Miocene. 
 
 Fio. 189. — Chnnamomum poly- 
 morphnm.—a. Leaf; b, Flower. 
 Upper Miocene. 
 
 Taking the Miocene flora as a whole. Dr. Heer concludes 
 from his study of about 3,000 plants contained in the European 
 Miocene alone, that the Miocene plants indicate tropical or 
 sub-tropical conditions, but that there is a striking intermixture 
 of forms which are at present found in countries widely re- 
 moved from one another. It is impossible to state with cer- 
 tainty 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 inhabit- 
 ing 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 Eu- 
 rope 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 de- 
 termined that the Miocene plants indicate a temperate climate 
 in that country, with a mean annual temperature at least 30° 
 wanner than it is at present. 
 
its, Mag- 
 • smaller 
 
 wjwwt poly- 
 if; b, Flower. 
 
 oncludes 
 Curopean 
 )pical or 
 rmixture 
 idely re- 
 with cer- 
 existing 
 extinct, 
 ire most 
 • Europe 
 Lustralia. 
 urope is 
 inhabit- 
 has led 
 ic Ocean 
 ts to Eu- 
 the fact 
 allied to 
 d of the 
 Miocene 
 has de- 
 climate 
 least 30° 
 
 CHAPTER XXV. 
 
 PLIOCENE FOBMATIONS. 
 
 The Pliocene formations contain from 40 to 95 per cent, 
 of existing species of Mollusca, the remainder 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 Suflblk, 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 Plio- 
 cene, viz., the Norwich Crag. The relative position of the older 
 Crags to the subjacent Eocene rocks is shown by the annexed 
 section (Fig. 190). 
 
 Crag. 
 
 London Clay. 
 
 Chalk. 
 
 Fia. 190. — Section BhowinR the position of the Coralline Crag, resting uncon- 
 formably upon the London Clay. 
 
 Tlie 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 hO 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 
 Mollusks^ related to the living Sea-mosses and Sea-mats, but 
 often of very singular forms. The Shells of the Coralline Crag 
 are mostly such as inhabit the seas of temperate regions ; 
 
 
 1 
 
 If, El 
 
 1 
 
 m 
 
 ■i 
 
 
 ■Hf 
 
 
 HUj 
 
 
 1 
 
212 
 
 GEOLOGY. 
 
 but there occur some forms usually looked upon ns indieat- 
 in<^ a warm climate, such as a Volute (Fi^. 191) and a Pyruhi 
 (Fi;;. 11)2). With these occurs a Sea-urchin ( 7}?m/<cc7A/y/«.v, 
 Fig. 103), the only living species of which is found in the In- 
 
 rio. \^\.— Vohita Lnmberti. 
 Young individual. 
 
 Pio. \^.—ryrula reti- 
 culata. 
 
 Fio. VM.— Temnechi- 
 nim excdvatiu. 
 
 dian Ocean. Altogether the Coralline Crag contains more 
 than 300 species of marine shells, of which 52 per cent, are 
 living forms. 
 
 The Upper or Hed 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 color, and charged with numerous fos- 
 sils. Most of the organic remains of the Red Crag are Mol- 
 lusca^ among which are Spindle-shells {Fusus), Purples (Pur- 
 pura), Dog- whelks (Nassa), Cowries [Cyprcea)^ etc. {see 
 Figs. 194-197). 
 
 Fossils chabacteeistic of the Red Cbag. 
 
 Fig. 196.— iVrtfl«a ffra- 
 nulaia. 
 
 TlQ, 194. — Fiunu contrarim. 
 (Bevcrsed variet7.) 
 
 Fig. 195.— Pwrpura te 
 tragona. 
 
 Fig. \Vl.—Oypraa 
 EuropoM. 
 
3 inrlicat- 
 a Pijriihi 
 nec/iinus^ 
 in the Iii- 
 
 lechi- 
 
 ins more 
 cent, are 
 
 line Crag 
 hickness, 
 3, usually 
 !rous fos- 
 are 3Iol- 
 !es {Pur- 
 etc. {see 
 
 ma ffra- 
 
 I, 
 
 'Typraa 
 
 Ota. 
 
 PLIOCENE FORMATIONS. 
 
 213 
 
 Altipfothcr more than 200spocios of shells are known from 
 the Ked Cnip^, of which GO per cent, arc referable to existin^jf 
 species. The shells indicate upon the whole a temperate or 
 even cold climate, decidedly less warm than that indicated by 
 the or<j^aiiic remains of the Coralline Craj^. It appears, there- 
 fore, that a gradual r< frig(!ration was going on during tho 
 Pliocene period, commencing in the Coralline Crag, becoming 
 intensified in the lied Crag, being still more severe in the 
 Norwich Crag, and finally culminating in the Ai'ctic cold of 
 the Glacial period. 
 
 Besides the Mollusca^ the Red Crag contains the ear-bones 
 of Whales, the teeth of Sharks and Hays, and remains of the 
 Mastodon, Rhinoceros, and Tapir. 
 
 The Newer Pliocene deposits are represented in Britain by 
 the JVoncich Crar/^ a local formation occurring near Norwich. 
 It consists of incoherent sands, loams, and gravels, resting in 
 detached patches, from two to 20 feet in thickness, upon an 
 eroded surface of chalk. The Norwich Crag contains a mix- 
 ture of marine, land, and fresh-water shells, with remains of 
 fishes and bones of mammals ; so that it must have been de- 
 posited as a local sea-deposit near tho mouth of an ancient 
 river. It contjiins altogether more than 100 marine shells, of 
 which 89 per cent, belong to existing species. Of the Mam- 
 mals, the two most important arc an Elephant {Elepfuts meri- 
 diotialis), and the characteristic Pliocene Mastodon (il/i Arver' 
 nensis. Fig. 198), which is hitherto the only Mastodon found 
 in Britain. 
 
 The following are the more important Pliocene deposits 
 which have been hitherto recognized out of Britain : 
 
 Fie. 108b— JTtMftKfon ArverTunHa.—T)ATA milk molar tooth, left side, upper Jaw ; ffrindtne 
 
 surflMo, nataral aim. Newer Pliocene. 
 
 ,ril 
 
i-- 
 
 214 
 
 GEOLOGY. 
 
 »» 
 
 ' *?. 
 
 1. In the neigliborhood 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 GO per cent, of existing species of shells, the remain- 
 der being extinct. 
 
 2. Bordering the chain of the Apennines, in Italy, on both 
 sides are a series of low hills made up of Tertiary strata, which 
 are known as the Sub-Apeniiine beds. Part of these is of 
 Miocene age, part is Older Pliocene, and a portion is Newer 
 Pliocene. The Older Pliocene portion of the Sui)-Apennines 
 consists of blue or brown marls, which sometimes attain a 
 thickness of 2,000 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 Car- 
 nivorous Mammals, Mastodon, Elephant, Rhinoceros, Hippo- 
 potamus, etc. 
 
 4. In Sicily, Newer Pliocene strata are probably more 
 largely developed than anywhere else in the world, rising 
 sometimes to a height of 3,000 feet above the sea. liie 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 foLsil^ in these beds are partly fresh- 
 water, partly marine, and partly intermediate in character, 
 and they are in great part identical with species now inhabit- 
 ing the Caspian. The entire formation appears to indicate 
 the former e ' <tence of a great sheet of brackish water, form- 
 ing 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 Mollusks and Echhw- 
 derms. 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 refer- 
 able 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, Rhi- 
 noceroses, Mastodons, Elephants, the Horse, Stag, etc. 
 
 
' crags," 
 in [)art. 
 
 and the 
 remain- 
 
 on both 
 a, which 
 se is of 
 3 Newer 
 )ennines 
 attain a 
 
 re both 
 : of bhi.e 
 e hitter 
 rge Car- 
 , Hippo- 
 
 \y more 
 I, rising 
 le series 
 pped by 
 11 700 to 
 tirely to 
 Scallcp 
 
 n, Aral, 
 " Aralo- 
 [y fresh- 
 laracter, 
 inhabit- 
 indicate 
 form- 
 larger 
 
 T, 
 
 found 
 ids and 
 Echhw- 
 3xisting 
 5 Upper 
 le refer- 
 ivision. 
 i shells 
 Is, Rhi- 
 
 PLIOCENE FORMATIONS. 
 
 215 
 
 Life op the Pliocexe Period, — as regards the life of 
 the Pliocene period, it is sufhcient to indicate two general 
 considerations. In the first place, we have to notice that the 
 introduction upon the globe of existing species of animals was 
 carried 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 existing species rises to as much as 80 to 95 per cent. The 
 Mammals still all belong to extinct species, but modern types 
 gradually supersede the more antique forms of the Eocene and 
 Miocene periods. In the second place, there is good evidence 
 to show that the Pliocene period was one in which the climate 
 of the northern hemisphere gradually became colder. In the 
 Miocene period, as we have seen, Europe possessed a climate 
 probably very similar to that now enjoyed by the Southern 
 States of the Union, and certainly very much warmer than its 
 present climate. In the Older Pliocene, northern forms, on 
 the other hand, predominate among the shells, though some 
 of the types of warmer regions still survive. In the Newer 
 Pliocene, the Mollusca are almost exclusively such as inhabit 
 the seas of temperate, or even cold regions. It might be 
 thought that the occurrence of Mammals such as the Elephant, 
 Rhinoceros, and Hippopotamus, would prove 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 quadru- 
 peds were more abundantly furnished with hair, and more 
 rdapted to withstand a cool temperature, than any of their 
 living congeners. 
 
 m\ 
 
!! 
 
 llli 
 
 ij 
 
 i 
 
 POST-TERTIARY PERIOD. 
 CHAPTER XXVL 
 
 . POST-PLIOCENE DEPOSITS. 
 
 Later than any of the Tertiary formations are a series of 
 deposits which are spoken of as Post-Tertiary or Quaternary^ 
 and which are characterized by the fact that all the contained 
 shells belong to existing species. The Post-Tertiary deposits 
 are divided by Sir Charles Lyell into Post-Pliocene, in which 
 the shells belong entirely to existing species, but some of the 
 Mammals are extinct^ and the Recent^ in which the shells and 
 the Mammals alike belong to existing siyecies. 
 
 The most iinportant of the Post-Pliocene deposits are the 
 Glacial formations ; but we have sometimes evidence of 
 Post-Pliocene beds of pre-glacial age. Thus, in the cliffs of 
 the Norfolk coast in Britain we find reposing upon the Newer 
 Pliocene Norwich Crag an ancient land-surface which is 
 known as the " Cromer Forest-bed." This consists of an an- 
 cient soil, having imbedded 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, Bison, Reindeer, Beaver, Walrus, etc., side by 
 side with three extinct Elephants, the Rhinoceros, and Hippo- 
 potamus, and a gigantic extinct Beaver. Among the Elephants 
 are two Pliocene species, viz., Elephas meridionalis (Fig. 
 199), and Mephas antiquud. The third species is the Mam- 
 
POST-PLIOCENE DEPOSlfS. 
 
 217 
 
 moth {Elephas primigennis\ which has as yet only been found 
 in Post-Pliocene deposits. 
 
 Fio. 199. — Molar tooth oi Elephas meridionalia, yi nat. size. Pliocene and Post-Pliocene. 
 
 series of 
 'Mernary^ 
 contained 
 T deposits 
 
 in which 
 me of the 
 shells and 
 
 ts are the 
 dence of 
 3 cliffs of 
 he Newer 
 which 
 of an 
 ny trees, 
 ants, and 
 erlaid by 
 belong to 
 
 " glacial 
 T Forest- 
 ecies, the 
 
 find the 
 , side by 
 
 1 Hippo- 
 Clephants 
 flis (Fig. 
 
 he Mam- 
 
 IS 
 
 an- 
 
 GLACIAL DEPOSITS. 
 
 We come now to speak of a great series of beds 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 specialized names of the 
 Drift, the Northern Drift, the Bowlder Clay, the Till, etc. 
 
 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 for- 
 mations 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. Uustratljiecl clays, or loams, containing numerous an- 
 gular 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 JBowlder-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 
 
 mi 
 
218 
 
 GEOLOGY. 
 
 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 mostly of an Arctic character, comprising 
 a majority 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 
 loom and rounded, and which have been produced by a rear- 
 rangement of ordinary glacial beds by the sea. These beds 
 are commonly known as " Drift-gravels," or " Regenerated 
 Drift" 
 
 The glacial deposits exhibit many phenomena of interest 
 which cannot be noticed here, and they have been produced 
 by the action of glaciers, continental ice, coast-ice, and ice- 
 bergs, after the manner described in the earlier portion of this 
 work. The general sequence of the phenomena of the Glacial 
 period, and the general nature of the resulting deposits, will 
 be best brought out by examining a single district, and no 
 better example can be found than Scotland. 
 
 In considering the glaciation of Scotland, we have evidence 
 of three periods : 1. The period of the Lower Bowlder Clay ; 
 2. Tlie period of the Upper Bowlder Clay ; and 3. Tlie period 
 of the recession and final disappearance of the glaciers, or the 
 period of the Moraines. 
 
 1. The lowest glacial deposit of Scotland is what is known 
 as the I'illy or Lower Bowlder Clay^ consisting of thorouglily 
 unstratified, stiff clay, containing numerous angular blocks or 
 " bowlders " of rock, which are generally more or less polished, 
 grooved, and striated. The surface of rock beneath the Till 
 is everywhere ice-worn, polished, smoothed, and furrowed, just 
 like the rock beneath a glacier. Tlie Lower Bowlder Clay 
 gives evidence of a time at the commencement of the Glacial 
 period, when Scotland was very much more elevated than it is 
 at present, and when all its mountains were covered by a con- 
 tinuous ice-sheet, constantly moving seaward, as we now see 
 in Greenland. By the abrasion of this ice-sheet upon the 
 rocks beneath was produced the Lower Bowlder Clay. That 
 this theory as to the origin of the Till is correct — namely, that 
 it was produced by land-ice, and not by icebergs — is shown 
 by the absence in it of marine shells, the generally not per- 
 fectly angular condition of the included blocks, the fact that 
 the blocks are never far transported, and the universally stri- 
 ated, furrowed, and polished condition of the fundamental 
 rocks on which it rests. 
 
)eds it is 
 lough of 
 inprising 
 d in the 
 1 spoken 
 
 )bles are 
 y a rear- 
 3se beds 
 enerated 
 
 interest 
 )roduced 
 and ice- 
 n of this 
 3 Glacial 
 sits, will 
 , and no 
 
 evidence 
 er Clay ; 
 e period 
 s, or the 
 
 s known 
 
 )rou|^hly 
 
 (locks or 
 
 )olished, 
 
 the Till 
 
 ^ed, just 
 
 ler Clay 
 
 Glacial 
 
 lian it is 
 
 y a con- 
 
 low see 
 
 3on the 
 
 That 
 
 ely, that 
 
 shown 
 
 not per- 
 
 ict that 
 
 lly stri- 
 
 amental 
 
 POST-PLIOCENE DEPOSITS. 
 
 219 
 
 During the formation of tlje Lower Bowlder Clay, the land 
 must have been slowly sinking beneath the sea, till ultimately 
 the greater part of it must have been submerged, nothing re- 
 maining above water except the highest and most mountainous 
 districts. 
 
 2. At the commencement, therefore, of the period of the 
 Upper Bojvlder Clay, Scotland must have been an archipelago, 
 its highest mountains forming islands projecting above the 
 waters of an icy ocean. Every peak which still remained 
 above water would be the seat of glaciers, which would grind 
 their way down to the sea, and would finally break off as huge 
 icebergs, laden with sand, clay, and stones, derived from the 
 moraines. Drifting before the wind, or hurried along by 
 oceanic currents, the rock-laden bergs would ultimately melt 
 and deposit their burden at the bottom of tlie sea, by the 
 waves and currents of which it would be more or less sorted 
 and stratified, and the shells of which it might come to contain 
 as fossils. 
 
 In this way, then, was produced the Upper Bowlder Clay^ 
 a deposit of sands and clays, generally more or less distinctly 
 stratified, including more or fewer erratic blocks, which have 
 usually been transported to great distances from their parent 
 rock, and often containing marine shells of Arctic species. 
 
 In this period, also, were formed masses of reasserted 
 drift, or " Drift-gravels," by the action of the sea upon the 
 older drift. These drift-gravels resemble stratified drift in 
 most respects, but the blocks which they contain are more or 
 less completely rounded and water-worn, and all their striae 
 and grooves ?ire obliterated. 
 
 3. The land now commenced again to rise from beneath the 
 soa, and it must have reached its present level, or one a little 
 higher. The cold of the Glacial period still continuing, the 
 higher regions were occupied by great glaciers, filling their 
 valleys. These have left behind them, in many places, traces 
 of their presence in the form of terminal moraines. These 
 appear as transverse ridges, or rows of mounds crossing val- 
 l(»ys from side to side. Sections of them show that they con- 
 sist of unstratifjed materials, with many angular blocks, some 
 of which are striated and polished. They mark the ancient 
 limit of the glacier, and there may be several in the same val- 
 ley, indicating pauses in the recession and ultimate disappear- 
 ance of the glacier. In some cases, also, these ancient mo- 
 raines have served to dam up the stream of the valley, and thus 
 to give rise to a larger or smaller lake. Finally, under the in- 
 
 ['1 
 
 
 %' 
 
 V*-'>S 
 
I'i 
 
 I'! ■ 
 
 !' J 
 
 j: 1 
 
 SI. 1. 
 
 220 
 
 GEOLOGY. 
 
 fluence of a gi'adually-increasing temperature, the glaciers dis- 
 appeared altogether, and their place was taken hy the present 
 mountain-torrents. 
 
 As before remarked, the Bowlder Clay occasionally con- 
 tains the remains of marine shells. The greatest height to 
 which marine shells have been traced in the Drift of Britain is 
 about 1,400 feet, indicating that the country was submerged 
 to at least this amount below its present level beneath the 
 waters of the glacial sea. All the glacial shells belong to 
 living species, but they comprise many forms which belong 
 exclusively to Arctic seas. During the Glacial period these 
 Arctic shells were enabled to migrate southward, in conse- 
 quence of the extension of the Arctic conditions necessary for 
 their existence. When the Glacial period again finally ended, 
 they were either ;^es /ed by the uncongenial warmth, or 
 gradually receded back again to the north. Some of the shells 
 characteristic of t'lO Scotch Drift are figured below. 
 
 Shells of the Drift of Scotland. 
 
 Fio. 2m.- I.cda 
 oblonga. 
 
 Fig. 203— /'it/t'/i island- Y\g. 204— 3'a<- Fig. 205-- rro/)/io» 
 'FiQ.2Q2.Saxicavarugoaa. icm- ica clausa. clathratum. 
 
 Similar evirl once of a like sequence of phenomena can 
 be detected in Wales and the north of England. That is to 
 sav, there was first an intensely cold period, in which the land 
 was probably much more elevated than it is at present, and all 
 the higher regions were covered with gigantic glaciers, or a 
 continuous ice-sheet; secondly, a submergence took place to a 
 depth of at least 1,400 feet below the present sea-level, all the 
 higher mountains standing out in the icy sea fis the sources of 
 glaciers and icebergs ; thirdly, the land wa^j re-elevated, and 
 there was a second period of glaciers, in which the cold was 
 not so intense, and the glaciers consequently smaller than in 
 the first period. 
 
aciers dis- 
 le present 
 
 nally con- 
 height to 
 Britain is 
 ubmerged 
 neath the 
 belong to 
 ch belong 
 riod these 
 in conse- 
 ■essarv for 
 illy ended, 
 varmth, or 
 the shells 
 
 20!>- Trophon 
 laihratum. 
 
 mena can 
 .That is to 
 1 the land 
 it, and all 
 ciers, or a 
 place to a 
 el, all tlic 
 sources of 
 /ated, and 
 cold was 
 jr than in 
 
 POST-PLIOCENE DEPOSITS. 
 
 221 
 
 Evidence of an essentially similar state of affairs exists 
 over the whole of Northern Europe, in the Alps, in the Hima- 
 layas, and elsewhere. In the United States, as far south as 
 the 39 th parallel, the surface of the fundamental rocks is stri- 
 ated, grooved, and polished. Unstratified sands and clays, 
 with large erratic bowlders, cover a great portion of the coun- 
 try, and, whenever these deposits contain fossil shells, a consid- 
 erable proportion are such as only exist at the present day in 
 the Arctic seas. As in the case of Europe, a large portion of 
 the North American drift has been produced by floating bergs, 
 during a period of submergence, but glaciers and continental 
 ice likewise existed over large areas. As in the case of Eu- 
 rope, also, the Post-Pliocene Mammals lived through the cold 
 of the Glacial period, remains of some of the larger forms 
 having been found in both pre-glacial and post-glacial de- 
 posits. 
 
)i' 
 
 liii 
 
 CHAPTER XXVIL 
 
 VALLEY-GEAVELS AND CAVE-DEPOSITS. 
 
 The remaining Post-Pliocene deposits which require no- 
 tice are valley-gravels and cave-deposits. In the first place, 
 however, it may be as well to define a rather vague term, 
 which is commonly used in connection with the Post-Tertiary 
 deposits, namely, the term alluvium. Between the ordinary 
 soil of every country and the subjacent fundamental rocks 
 may be found, in places, interv*. ^ing deposits of incoherent 
 sands, gravels, or mud. All these deposits are loosely called 
 by the general name of alluvium (Lat. alluvio^ an inundation), 
 because they resemble the kinds of deposits which are formed 
 by the overflowing of rivers. Much of this so-called alluvium 
 is now known to be really of glacial origin, and to belong to 
 the Glacial period. There are, however, other alluvial deposits 
 of Post-Tertiary age which really have been produced by riv- 
 ers, and are known properly as alluvium. 
 
 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 coun- 
 tries in various localities, and at various heights above the 
 present channels of our rivers. Many of these fluviatile (Lat. 
 JiuviuSy a river) deposits consist of f^ne loam, worked for 
 brick-making, and known as "Brick-eirths;" and they have 
 yielded the remains of numerous extinct Mammals, of which 
 the Mammoth {Cephas pritnigenius) is the most abundant. 
 In the valley of the Rhine these fluviatile loams (known as 
 " Loess") attain a thickness of several hundred feet, and con- 
 tain land and fresh-water shells of existing species. With 
 these occur the remains of Mammals, such as the Mammoth 
 
VALLEY-GRAVELS AND CAVE-DEPOSITS. 
 
 223 
 
 ill' 
 
 jquire no 
 rst place, 
 ^ue term, 
 >Tertiary 
 
 ordinary 
 ital rocks 
 icoherent 
 3ly called 
 mdation), 
 re formed 
 
 alluvium 
 belong to 
 I deposits 
 id by riv- 
 
 fine mud 
 jposits at 
 )ying the 
 »g above. 
 i03t coun- 
 bove the 
 tile (Lat. 
 rked for 
 hey have 
 of which 
 bundant. 
 nown as 
 and con- 
 i. With 
 [ammoth 
 
 and Woolly Rhinoceros ; and in one locality a human lower 
 jaw has been disinterred from the same beds, the authenticity 
 of which appears to be free from doubt. According to Sir 
 ('harles Lyell, these fluviatile loams in the Rhine Valley are 
 the result of the impalpable mud and sand produced by the 
 grinding action of the great Swiss glaciers, and then conveyed 
 by the rivers to lower levels. 
 
 High-level and Low-level Valley Gravels. — It is 
 very common to meet in the valley of any river with two or 
 more sets of gravels and loams, formed by the river itself, but 
 formed at times when the river ran at different levels. A 
 reference to the accompanying diagram will explain the origin 
 and nature of these deposits (Fig. 206). When a river first 
 
 Fig. 206.— Recent and Post-Pliocene alluvial deposits.— 1. Peat of the recent period; 
 2. Gravel of the modern river; 2'. Loam of the modern river; 8. 1-ower-level valley- 
 pravel with bones of extinct Mammals (Post- Pliocene ) ; 8'. Loam of the same age as 8 : 
 4. Higher-level valley-gravel (Post- Pliocene) ; 4'. Loam of the same ape as 4; 5. ITpland 
 gravels of various kinds (often glacial drift) ; 6. Older rocks. (After Sir Charles Lyell.) 
 
 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 modem 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. 206, 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. 206, 3, 3') are the so-called 
 ^^ low-level gravels" of a river. At a still higher level, and 
 
wa. 
 
 224 
 
 GEOLOGY. 
 
 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. 206, 4, 4') are the so-called " hiffh-level f^-ravels " 
 of a river, and there may be one or more terraces of these. 
 
 The important fact to remember about these fiuviatile 
 deposits is this : that here the ordinary geological rule is re- 
 versed. 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 grav- 
 els. 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, the -efore, 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 de- 
 termine accurately, but, if we are to calculate from the observed 
 rate of erosion of the actually existing rivers, the period be- 
 tween the different valley-gravels must be a very long one. 
 
 The lowest or recent fiuviatile deposits (Fig. 206, 2, 2') 
 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 
 (Fig. 207), the Mammoth {Elephas primigenius)^ the Woolly 
 Rhinoceros {R. tichorhinns)^ the Hippopotamus, the Cave-lion, 
 and the Cave-bear. 
 
 Fig. 207. — Molar of Elephas antiquus, }i natural size. Pliocene and Post-Pliocene. 
 
 Mixed in these Post-Pliocene gravels with the bones of ex- 
 tinct Mammals occur unquestionable remains of man, in the 
 
VAL^ EY-GRAVELS AND CAVE-DEPOSITS. 
 
 225 
 
 T, WG may 
 iterials as 
 when the 
 ss extent. 
 
 gravels " 
 these. 
 
 fluviatile 
 rule is re- 
 ighest, so 
 ;rned, but 
 uch older 
 ent grav- 
 ; than the 
 It heights 
 ■channels, 
 3ls by the 
 his depth. 
 
 us to do- 
 i observed 
 leriod be- 
 ig one. 
 P6, 2, 2') 
 
 referable 
 
 none but 
 ire Post- 
 ils, mixed 
 Among 
 and high- 
 
 antiqxms 
 B Woolly 
 ^ave-lion, 
 
 Pliocene. 
 
 es of ex- 
 3, in the 
 
 form of worked flints or flint implements. These, though 
 very roughly executed, are of suoh a nature as to leave no 
 doubt, on the mind of any who have examined them, as to their 
 being truly of human workmanship. They ditt'er nnich in 
 shape, being commonly like a cat's tongue, or like the head 
 of a spear ; and they have been laboriously chipped with a 
 stone to their present shape. 
 
 As regards the antiquity of tliese flint implements and of 
 the races of men who employed them, it will be sufiicieut to 
 indicate the following general considerations : 
 
 1. Man must have coexisted in Western Europe with a 
 number of large Mammals which are now wholly extinct. Wo 
 do not know either the causes of such extinction, or how long 
 a period is required to consummate the destruction of a group 
 of species; but we know of no mammalian species that has 
 become extinct during the historical ])criod. 
 
 2. The extinct Mammals with which man coexisted are 
 referable to species which require a very difl'erent climate to 
 that now prevailing in Western Europe. Most of them, in 
 fact, are referable to genera, the living representatives of 
 which are exclusively found in tropical or sub-tropical regions. 
 How long a period, however, has been consumed in the bring- 
 ing about the climatic changes thus indicated, we have no 
 means of calculating accurately. 
 
 3. The position of some of the gravels with flint imple- 
 ments is many feet (in one instance 100 feet) above the 
 present river-bed. As before remarked, however, we cannot 
 accurately judge of the period required for the river to cut 
 its channel to its present depth, at any rate until we are 
 certain that the river in past time has not exceeded its pres- 
 ent velocity and volume of water. 
 
 4. The implements themselves bear evidence of an ex- 
 ceedingly barbarous condition of human life. The makers of 
 the flint implements were clearly without any knowledge 
 of the metals. Not only so, but their workmanship v^ ;. k- 
 traordinarily inferior to that of the later tribes who were like- 
 wise unacquainted with metals and who also used nothing but 
 tools of stone. For this reason the period of the makers of 
 the flint implements has been called the Palceolithic age (Gr. 
 palaios, ancient ; lithos, stone) ; while the later and more ad- 
 vanced age of stone has been termed the Neolithic period 
 (Gr. neos, new ; lithos, stone). 
 
 Caveen-deporits. — We come now to consider a class of 
 deposits essentially similar to the older valley-gravels, but 
 
 :4 
 
M 
 
 226 
 
 GEOLOGY. 
 
 h ♦;' 
 
 \\ 
 
 Si 
 
 
 occurring in caves. Caves, in the great majority of instances, 
 occur in limestone. When this is not the case, it will general- 
 ly be found that they occur along lines of sea-coast, or along 
 lines which can be shown to liave 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 th 
 origin to the solvent action upon lime of water holding c 
 bonic acid in solution. Tlie 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, gen- 
 erally along the lines of jointing so characteristic of lime- 
 stones, 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 continu- 
 ance 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 sprinr 
 issuing from the limestone rock — sometimes as large rivers 
 the waters of which are charged with carbonate of lime, oo- 
 tained 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 r'ltural 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 eaves were formed in consequence of 
 the then existing drainage taking the line of some fissure. 
 
 Secondl}', there must have been a period in which various 
 deposits were accumulated in the caves thus formed, ^^hese 
 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, etc., may be washed by 
 rains or by floods from some neighboring river. Sometimes 
 the cave has been the bed of an ancient stream, and the de- 
 posits 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 
 
VALLEY GRAVELS AND CAVE-DEPOSITS. 
 
 227 
 
 f instanrrs, 
 
 ill gencral- 
 st, or al()ii<r 
 I tiic coast- 
 
 g of which 
 I these arp 
 
 owe th 
 olding c 
 a limestone 
 'om the air, 
 
 rock, pen- 
 io of limc- 
 >fF a certain 
 tural joints 
 seen at the 
 ' a continu- 
 caves may 
 noner in a 
 to take the 
 ie; In this 
 ith sprinr 
 ^e rivers 
 'f lime, OL»- 
 )ugh which 
 ions, every 
 ped will be 
 or fissures, 
 ve-deposits 
 rocks were 
 ■quence of 
 fissure. 
 ich various 
 id. Chese 
 ig of mud, 
 ases, these 
 )me period 
 tion of the 
 surface by 
 vashed by 
 Sometimes 
 nd the de- 
 lie surface. 
 • elevation 
 filled with 
 
 fluviatllc de|X)sits by the river at a time prior to the excava- 
 tion of its bed to the present depth (Fig. 208). In this last 
 case, the cave-deposits obviously bear exactly the same rela- 
 tion in point of antiquity to recent deposits, as do the low- 
 level and high-level valley-gravels to recent river-gravels. In 
 
 Fio. i'tN. — Section of Hmestono valley and cavo. — a. Cavern, partly filled with cave-earth; 
 I', lii^h-levcl (gravels ; c, I'ccent gravels of prcscut river (e); d, Fissure tlllvd with high- 
 Ic'vul gravel ; e, Bed of present river. 
 
 any case, it is necessary for the physical geography of the dis- 
 trict to change to some extent, in order that the cave-deposits 
 should be preserved. If the materials ^ave 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 configura- 
 tion 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. 208, 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. 
 
 If the cave be entirely filled, the included deposits gener- 
 ally 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 subse- 
 quent evaporation, would lead to the formation over the de- 
 posits 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 pre- 
 served without injury, for an altogether indefinite period of 
 time. 
 
 The great interest of cavern-deposits is to be found in the 
 fact that they in very many cases contain the bones of extinct 
 as well as living Mammals, associated with the implements, 
 and in some cases even the bones, of man. The number of 
 instances in which this association of the works or bones of 
 man with remains of extinct Mammals in cave-deposits is 
 
 I 
 
 il 
 
228 
 
 GEOLOGY. 
 
 I 
 
 i 
 
 ! 
 
 !i 
 
 t! - 
 ill 
 
 y -■ 
 
 •r' 
 
 ti 
 
 known to occur, is now so great that it is unnecessary to dwell 
 upon any particular case, and it will be sufficient shortly to 
 summarize the more important facts under this head. 
 
 The human implements which have been found in cave- 
 deposits are in the great majority of instances referable to the 
 age of stone ; and, when associated with extinct Mammals, 
 they are not only always of stone, but are referable to the Pa- 
 laeolithic period. They consist chiefly of stone hatchets or 
 other tools, with occasional implements worked out of bone. 
 In some of the caves, however, the stone implements, though 
 of a very rude construction, nevertheless show a decided ad- 
 vance on the flint tools of the older valley-gravels. 
 
 In some cases, with implements of human workmanship 
 have been found the bones of man, associated with the bones 
 of extinct Mammals. 
 
 The human implements are so mixed with the bones of 
 extinct quadrupeds as to render it unquestionable that man 
 existed contemporaneously with these extinct animals. 
 
 The more important extinct Mammals which hav^e been 
 found in cave-deposits in Europe, along with the remains of 
 man, are the Mammoth {Elepfias j^flmigenius^ Fig. 209), the 
 
 Fio. 209.— Molar of the Mammoth, upper jaw, ripht side, »< nat size. Post-Pliocene.— a, 
 
 Grinding surface ; i, Side view. 
 
 Woolly Rhinoceros {li. tichorhums), other species of Elephant 
 and Rhinoceros, the Cave-lion {Felis sjiclma)^ the Cave-bear 
 ( Ursus spelceus), and the Cave-hyaena {Ilyoena spelcea^ Fig. 
 
y^ to dwell 
 ihortly to 
 
 in cave- 
 ble to the 
 Vlammals, 
 o the Pa- 
 tcliets or 
 
 of bone. 
 s, though 
 cided ad- 
 
 kmanship 
 the bones 
 
 bones of 
 that man 
 Is. 
 
 ave been 
 jmains of 
 209), the 
 
 ?llocene.— a, 
 
 lephant 
 ave-bear 
 pa, Fig. 
 
 VALLEY-GRAVELS AND CAVE-DEPOSITS. 
 
 229 
 
 210). Many more might be added to these, but the above 
 are sufficient to show that the Mammals of the caves are 
 
 Pig. 210.— Lower jaw of the Cave-hyocna, >i nat. size. Post-PHocene. 
 
 the same as those which occur in the ancient valley-gravels 
 along with the implements of man. 
 
 In certain of the caves of the south of France the remains 
 indicate a transition between the PalaH)lithic and Neolithic 
 periods. The implements are somewhat improved in woik- 
 manship, and some of the bones are artistically carved so as 
 to represent animals, a recognizable portrait of the 3lammofh 
 in its living condition having been in one instance discovered. 
 The Mammals of these caves, with one or two doubtful excej)- 
 tions, are of living species, but they are mostly such as re- 
 quire a colder climate than the south of France, and are only 
 found at the present day in much more northern latitudes. 
 Of these the most abundant is the Reindeer, and this would 
 imply that man coexisted with these animals at a time when 
 the climate of the south of France approximated moie or less 
 closely to what we see at the present day in Laj)land. 
 
 In Australia, cave-deposits have been found which have 
 yielded the bones of numerous extinct Mammals, more or less 
 closely allied to the living quadrupeds of that region, but of 
 gigantic size, comparatively speaking. Thus we find ginantie 
 Kangaroos, Wombats, and Carnivorous Marsupials, and others 
 also Marsupial, but not represented at the present day. 
 
 In like manner the cave-deposits and other Post-Pliocene 
 formations of South America have yielded the remains of nu- 
 merous Mammals, mostly allied to the living quadrujjcds of 
 that continent, but generally of much greater size. Thus, we 
 have gigantic Sloths and huge Armadillos, together with ani- 
 mals allied to the living Llamas, and Monkeys belonging to 
 the same group of the Quadrumana as is now characteristic 
 of South America. 
 11 
 
Illlj 
 
 CHAPTER XXVIII. 
 
 RECENT PERIOD. 
 
 Wi 
 
 
 i\ 
 
 
 III 
 
 The last geological period is the Recent period, character- 
 ized by the fact that all the Mammals, as well as all the Mol- 
 lusks, are referable to existing species. This being the case, 
 we have chiefly to deal with tlie Recent period in connection 
 with the remains of man. So far as man is concerned, the 
 Recent period admits of subdivision into three ages — the Age 
 of Stone, or Neolithic period, the Age of Bronze, and the Age 
 of Iron. 
 
 I. In the Affe of Stone the implements which are found 
 are always of stone, bone, or wood, showing that the metals 
 must have been unknown. The bones of Mammals accom- 
 panying the implements are all of living species, and this dis- 
 tinguishes this, the Neolithic period, from the older JPalceo- 
 I'tthic period in which some of the Mammals were extinct. 
 The implements, also, of this period are more artistically 
 fashioned than those of the earlier period. Another fact to be 
 remembered is, that the bones of animals which occur asso- 
 ciated with the human remains of the later Stone Age are 
 those of wild animals, showing that the men of this period 
 were hunters and not agriculturists. Thus we have numerous 
 remains of the Deer, Wild-boar, and Wild-ox, but none of any 
 domestic animal, such as the Pig, Goat, or Sheep. 
 
 II. In the Age of Bronze metals had been discovered, and 
 the use of stone in making implements was gradually dis- 
 carded. Stone, however, must have been only very slowly 
 given up, for some of the implements of this age are generally 
 of stone, though these are certainly more artistically worked 
 than those of the Neolithic period. The curious thing, how- 
 ever, about the discovery of metals is, that bronze should have 
 been found out at such an early stage, seeing that it is an 
 
 ti 
 
iharacter- 
 the Mol- 
 the case, 
 mnection 
 rned, the 
 -the Age 
 I the Age 
 
 ire found 
 le metals 
 s accom- 
 
 I this dis- 
 
 II Palceo- 
 I extinct, 
 rtistically 
 "act to be 
 cur asso- 
 Age are 
 is period 
 [lumerous 
 ne of any 
 
 ered, and 
 Lially dis- 
 y slowly 
 generally 
 y worked 
 ing, how- 
 julci have 
 , it is an 
 
 RECENT PERIOD. 
 
 231 
 
 alloy of the two metals copper and tin. Copper is a moderate- 
 ly abundant metal, and its discovery might have been looked 
 for ; but tin is not only difficult to recognize in its ores, but is 
 very limited in its occurrence. In fact, we do not know of any 
 locality from which tin could at that period have been ob- 
 tained in Europe except Cornwall ; so that the Age of Bronze 
 must have been one in which commerce had developed itself 
 to a considerable extent. It is to be remembered, however, 
 that in some places, as in Hungary and Transylvania, there 
 appears to have been an intermediate age — the Age of Copper 
 — in which copper alone was in use. The civilization of the 
 Age of Bronze was also much further advanced than that of the 
 Neolithic period. The implements are often very beautifully 
 made and are of various shapes. Agriculture had begun to 
 be practised, as shown by the occurrence of sickles, with car- 
 bonized grains of wheat and barley, and even pieces of bread. 
 And, the bones of animals associated with the implements are 
 those of domesticated varieties, such as the domestic Ox, the 
 Pig, and the Goat. 
 
 III. Lastly, we have the Age oflron^ in which iron was dis- 
 covered and gradually supplanted bronze in the manufacture 
 of all instruments requiring a cutting edge. All other articles 
 continued to be made of bronze up to a late period, in fact, 
 until the discovery of steel; for even the Greeks and the 
 Romans used bronze largely for all ordinary purposes. 
 
 As regards the localities in which the records of these 
 three periods of human civilization are found, the following 
 more celebrated ones may just be mentioned : 
 
 1. Kitchen-Middens of Denmark. Tiiese are refuse-heaps 
 found on the coast of the Danish inlands of tiie Baltic, and 
 consisting of the accumulated leavings of the meals of an 
 aboriginal race during a long period. Tliey are composed 
 almost entirely of the castaway shells of the Oyster, Mussel, 
 Cockle, and other eatable shell-fish, with the bones of ani- 
 mals, all wild except the Dog. They contain implements of 
 stone, bone, or wood only, and are, therefore, referable to the 
 Age of Stone. 
 
 2. The Danish Peat-mosses. The lower portions of the 
 peat-mosses of Denmark cont-ain stone implements, with 
 trunks of the Scotch fir, a tree which has not existed in Den- 
 mark within the historical period. Higher portions of the 
 Danish peat contain implements of bronze mixed with those 
 of stone, and associated with the oak, a tree now very scarce 
 in Denmark, and almost supplanted by the beech. 
 
 i 
 
 t 
 
232 
 
 GEOLOGY. 
 
 3. The Lake-dwellings of Switzerland. ' The Swiss lakes 
 have been found in many cases to contain the remains of 
 ancient habitations, which are called Lake-dwellings, because 
 they consisted of villages built upon platforms supported 
 upon piles driven into the bottom of the lake. Some of the 
 lake-dwellings are much older than the others, and are refer- 
 able to the Neolithic period, as they yield nothing but im- 
 plements of stone. Some, however, are referable to the Age 
 of Bronze, having yielded numerous bronze implements (axes, 
 lances, bracelets, fish-hooks, sickles, etc.), with tolerably ar- 
 tistic pottery. Lastly, some few of the lake-dwellings have 
 yielded tools of iron, and must, therefore, be referred to the 
 Age of Iron. 
 
 Scarcity of Human Bones. — As regards the scarcity of 
 human bones in all these recent deposits, it is difficult to 
 give a universal or adequate explanation. In the Danish peat 
 and Swiss lake-dwellings exceedingly few bones of man have 
 been detected, and this has been ascribed, probably with 
 truth, to the fact that these early races of man must have 
 been in the habit of burning their dead. 
 
 In the Neolithic period the custom seems to have pre- 
 vailed, in some places at any rate, of burying the dead in 
 vaults constructed of large undressed blocks of stone. Many 
 skulls, therefore, have been obtained from these, and they 
 show that the men of the Neolithic period had what is called 
 
 
 Fxa. 211.— Short-headed skixll of the 
 Ago of Btoue. 
 
 Fio. 212.— Long-headed ekull of the Age of Iron. 
 
 
 the "short-headed" type of skull. Tliat is to say, the skull 
 (Fig. 211) was more or less approximately spherical, rounded 
 in every direction, like the skull of the modern Laplander. 
 
TisB lakes 
 mains of 
 I, because 
 mpported 
 Tie of the 
 are refer- 
 g but im- 
 > the Age 
 nts (axes, 
 jrably ar- 
 ings have 
 3(1 to the 
 
 sarcitv of 
 
 • 
 
 ifficult to 
 nish pent 
 man have 
 ibly with 
 lust have 
 
 have pre- 
 j dead in 
 e. Many 
 and they 
 b is called 
 
 le Age of Iron. 
 
 the skull 
 I, rounded 
 ander. 
 
 RECENT PERIOD. 
 
 233 
 
 The skulls of the Bronze Age are not known in sufficient 
 numbers for us to be able to determine tlieir general type. 
 Tlie skulls, however, of the Age of Iron are well known, and 
 tliese belong to the so-called "long-headed" type (Fig. 212), 
 which prevails at the present day in Europe. In this type the 
 greatest diameter of the skull is from before backward, and its 
 s!iortest diameter is from side to side. The skull, therefore, 
 when viewed from above is decidedly oval, and the forehead 
 retreats more than in the short-headed type. 
 

 ml 
 
 i- 
 
 n- if 
 
 fi:': 
 
 it 
 
 '„ J. 
 
 CHAPTER XXIX. 
 
 VOLCAJSIC AND TEAPPEAN ROCKS. 
 
 The volcanic and trappean rocks are found — as might be 
 expected from their having been originally fluid — in very- 
 different forms: 
 
 1. They occur as overlying masses (P'ig. 213) ; that is to 
 say, they are found as masses which have been poured forth in 
 
 Fia. 213.— Trap dividing and covering sandstone in the Isle of Skye. (MacCulloch.) 
 
 a molten state from some volcanic focus, and now rest upon or 
 overlie other rocks. It is obvious, however, that every such 
 overlying mass (as c c, in Fig. 214) must originally have com- 
 municated with the interior of the earth, whence its materials 
 were in the first place derived. Hence to each overlj'ing mass 
 of lava or trap there must be a pipe or vein of igneous matter 
 comnumicating with another underlying mass, and cutting 
 through the rocks between. In many cases it is now iippos- 
 
 Fio. 214.— T)laprram representing tlie relations of the granitic, stratified, and trappean forma 
 tions to one another.— a, Granitic and Metamorphic rocks; h, Stratified rocks; c, Vol- 
 canic or Trappean rocks. 
 
 sible to demonstrate the existence of such a communication, 
 though there can be no question as to its necessarily being 
 
night be 
 
 -in 
 
 very 
 
 bat is to 
 . forth in 
 
 illoch.) 
 
 upon or 
 ry such 
 ve com- 
 laterials 
 ng mass 
 5 matter 
 cuttino: 
 ' irrDOS- 
 
 o 
 
 »ean forma 
 ks ; c, Vol" 
 
 ication, 
 y being 
 
 VOLCANIC AND TRAPPEAN ROCKS. 
 
 235 
 
 "^ A 
 
 
 <'■.. ■ ||, m\U\0 
 
 
 "^^ "" ^--^ 
 
 
 , r'.ln , \,r., 1,, "Ml 
 
 °°:r?c 
 
 i;^^ ~~~~ 
 
 ^v^ 
 
 Fig. 215, 
 
 horizontal maases of trap. 
 
 Step-like appearance of 
 1 1 
 
 present. In other cases, again, the whole overlying mass has 
 been removed by denudation, and little or nothing has been 
 left except the original pipe by which the melted matter reached 
 the surface. 
 
 2. The Volcanic and Trappean rocks occur as masses or 
 tabular sheets intercalated among other rocks (Fig. 215). 
 
 As we shall see immediately, such 
 masses may either conform to the 
 stratification of the rocks above and 
 below, or may cut across these at 
 any angle. In any case, the pres- 
 ence of such horizontal or nearly 
 horizontal masses generally leads 
 to a peculiar step-like or terraced 
 appearance, owing to the greater 
 hardness of traps, and their superior 
 power of resisting denudation. Hence the name " trap," from 
 the Swedish trappa^ a flight of steps (Fig. 215). 
 
 3. The volcanic and trappean 
 rocks have been injected while in 
 a fluid state into fissures, and now 
 constitute more or less nearly ver- 
 tical, wall-like masses, which cut 
 through the other rocks, and are 
 known as dikes or veins (Fig. 216). 
 
 Age op the Volcanic and 
 Trappean Rocks. — As regards the 
 
 relative and absolute ages of the f,o. 2I6.— v<?tmta intercepted by a 
 
 volcanic and trappean rocks, there ^^^^^^""^ '^^ '°^*'"'^ ^'^ '^''' 
 are four principal tests: 1. Super- 
 position ; 2. Organic remains ; 3. Mineral composition ; 4. In- 
 cluded fragments. 
 
 Firstly^ as to superposition, the following rules may be 
 laid down : 
 
 If a volcanic or trappean rock rest upon a stratified rock, 
 
 c^ „ 
 
 ^0 „ 
 
 U 
 
 ? n ..VV 
 
 ^^ 
 
 
 -^xr 
 
 
 i 
 
 \j- 
 
 
 
 
 
 ■ 
 
 
 >^ ' '7^^?7^~!nZIlLlILLL 
 
 rio. 217. — Section flhowinp nn intrusive sheet of tmp (h\ at first simply included between 
 two foBsllifurouB beds (a and c), but ultimately cutting through a, and coining to over- 
 Ueit. 
 
 1 
 
 I 
 
 iiiiiil'l 
 
* I 
 
 
 236 
 
 GEOLOGY. 
 
 the igneous mass must be the newest, and the stratified rock 
 tlie oldest. Thus, in Fig. 217, the igneous sheet b reposes upon 
 a fossiliferous bed c at D, and we may be quite certain that c 
 was formed at the time when b was poured forth, and that it 
 is, therefore, the oldest. The reverse of this, however, by no 
 means holds good. When a stratified rock rests upon an 
 igneous rock, as a upon i, in Fig. 217, it may perhaps be that 
 the stratified rock is the youngest, but it by no means neces- 
 sarily is so. If the igneous rock has been originally forced or 
 injected between two sets of beds (as is actually the case with 
 J, for it is seen to cut across a at the point E), then the igne- 
 ous rock is younger than the beds between which it lies ; the 
 beds which rest upon it are older in spite of their being the 
 highest. The test of age, therefore, by mere superposition, is 
 not a certain one as api)lied to lavas and traps, but it applies 
 with certainty to all stratified volcanic and trappean deposits, 
 such as ashes, tuffs, and breccias. As we shall see, however, 
 in explaining the distinction between " contemporaneous " and 
 *' intrusive " lavas and traps, the test of age by superposition 
 becomes a very reliable one, even in the case of these, when 
 combined with the metamorphism or alteration of the rocks 
 above and below. 
 
 Secondly, the test of age bv organic remains is in the na- 
 ture of the case only very rarely applicable. It is only appli- 
 cable Jn the case of ash-beds which have been produced by a 
 sub-aerial volcano, and which have fallen on land ; or in the 
 case of ashes or tuffs which have been sorted by water, and 
 which may contain marine or fresh-water fossils — as the former 
 may include the remains of terrestrial animals. The laws here 
 are exactly the same as in the case of ordinary sedimentary 
 deposits, and need no further notice. 
 
 Thirdly, the test of age by mineral characters is even 
 more uncertain in the case of volcanic rocks than in that of 
 the aqueous formations. In some cases, no doubt, the mineral 
 characters of a particular bed of trap or lava are sufficiently 
 well marked and constant to allow of its being identified at 
 distant points ; but this is not very common, and of itself gives 
 no clew as to the age of the rock. 
 
 Fourthly, the test of age by included fragments, when 
 available, is a very certain one. If an aqueous rock be found 
 to contain pebbles of a given igneous rock, then obviously tlie 
 former is the youngest. Again, if an igneous rock contain 
 determinable fragments of some aqueous rock, as sometimes oc- 
 curs, then the igneous rock has been the last formed of the two. 
 
VOLCANIC AND TRAPPEAN ROCKS. 
 
 237 
 
 led rock 
 ses upon 
 in that c 
 d that it 
 jr, by no 
 upon an 
 3 be that 
 IS necos- 
 forced or 
 !ase with 
 the igne- 
 iies; the 
 sing the 
 sition, is 
 t applies 
 deposits, 
 lowever, 
 lus " and 
 [•position 
 5e, when 
 lie rocks 
 
 the na- 
 ly appli- 
 2ed by a 
 >r in the 
 iter, and 
 e former 
 iws here 
 mentary 
 
 is even 
 that of 
 mineral 
 ficiently 
 tified at 
 If gives 
 
 s, when 
 )e found 
 usly tlie 
 contain 
 nnes oc- 
 ;he two. 
 
 Contemporaneous and Intrusite Traps. — There are 
 two terms constantly employed in speaking of the volcanic 
 and trappean rocks, which it is absolutely necessary to under- 
 stand, viz. : the terms " contemporaneous " and " intrusive." 
 
 When a bed of lava or trap has been deposited as part of 
 a stratified series — that is to say, when the lava or trap has 
 been poured out so as to rest upon one set of beds, and then 
 a second set of beds has been formed upon its cooled surface, 
 so that the whole forms one continuous series — then the ig- 
 neous rock is said to be contemporaneous or interbedded. 
 
 When, on the other hand, the igneous rock has been forced 
 violently among the other rocks at some time subsequent to 
 the formation and deposition of the latter, then the igneous 
 rock is said to be intrusive (Fig. 218). 
 
 Fia. 218. — Trap intruded between displaced beds of limestono and shale, High Teesdale, 
 
 Durham. (Sedgwick.) 
 
 A contemporaneous or interbedded trap belongs to the 
 same geological period as the rocks among which it is situated. 
 Thus, a Carboniferous trap, if interbedded, has been formed 
 by a Carboniferous volcano, and belongs to the Carboniferous 
 period. 
 
 An intrusive trap always belongs to a later period than 
 the rocks through which it breaks. Thus, a Carboniferous 
 trap, if intrusive, does not belong to the Carboniferous period, 
 but to some later epoch — possibly to some very greatly later 
 date. An intrusive trap in Carboniferous strata might, for in- 
 stance, have been formed by a Tertiary volcano, and thus be- 
 long to the Tertiary period. 
 
 It is to be remembered, also, that as every trap or lava, 
 even if contemporaneous, has come jip through the crust of 
 the earth through some conduit or fissure, so it must be intru- 
 sive as regards the rocks upon which it rests, not everywhere, 
 but at some particular point or other. 
 
238 
 
 GEOLOGY. 
 
 As regards tlie distinction in practice between those lavns 
 and traps which are contemporaneous or interbedded, and 
 those which are intrusive, the following rules may be laid down : 
 
 a. If the igneous rock can be shown to cut across tlie 
 stratified rocks at any point, so as to come into relation at dif- 
 ferent times with different beds, then it is almost certainly in- 
 trusive. Thus, the bed of trap h^ in Fig. 217, would seem to 
 be contemporaneous if only examined at the point D; but, 
 when examined at E, it is seen to cut across the bed a, so that 
 it is shown to be really intrusive. 
 
 h. If the igneous rock keep invariably at the same horizon, 
 coming always into relation with the same beds both above 
 and below, tlien it is interbedded. 
 
 c. If the beds which rest upon the igneous rock are in any 
 way metamorphosed or altered by the heat of the originally 
 iKcUod mass, then the igneous rock is intrusive. 
 
 d. If only the beds below the igneous rock are metamor- 
 phosed or burnt, and those above it are unaffected, then the 
 igneous mass is contemporaneous, since this shows that its 
 upper surface had cooled before the higher beds were deposited 
 upon it. 
 
 e. If the beds above the igneous rock contain fragments 
 clearly derived from that rock, then we are dealing with a con- 
 temporaneous trap. 
 
 f. Lastly, if beds of trap or lava are clearly interstratified 
 with beds of ash or tuff, then the igneous rock is in all proba- 
 bility contemporaneous. 
 
 Trap-dikes. — Little need be said here as to Trap-dikes. 
 As has been already explained, they are vertical or nearly ver- 
 tical wall-like masses of originally melted rock, forced during 
 a paroxysm of volcanic activaty into fissures in the crust of the 
 earth. This being their mode of formation, they generally 
 run tolerably straight — often for many miles — cutting across 
 all the rocks in their course, whether these be aqueous or ig- 
 neous. Hence, it is not at all uncommon to find dikes of trap 
 traversing other trap-rocks, whether these be contemporaneous 
 or intrusive. 
 
 It is hardly necessary to remark that every trap-dike is of 
 necessity 3'ounger than all the rocks through which it cuts. 
 This is obviously the case, though we may not be able in any 
 given case to decide how much younger the dike may be than 
 the walls of rock on either side. 
 
 As regards the metamorphism produced by traps, and 
 especially by trap-dikes, it is easy to understand what occurs. 
 
 ■•! -i 
 
lose lavns 
 (Ifd, and 
 lid down : 
 cross tlic 
 on at dif- 
 tainly in- 
 1 seem to 
 tD; but, 
 </, so that 
 
 3 horizon, 
 )th above 
 
 re in any 
 jriginally 
 
 metamor- 
 
 then the 
 
 that its 
 
 leposited 
 
 ragments 
 th a con- 
 stratified 
 11 proba- 
 
 ap-dikes. 
 arly ver- 
 during- 
 st of the 
 enerally 
 \g across 
 us or ig- 
 } of trap 
 )raneous 
 
 VOLCANIC AND TRAPPEAN ROCKS. 
 
 239 
 
 As the entire mass of the dike was originally fluid with heat, 
 it would, of course, part most readily and ra])idly with its heat 
 at its sides, where the melted rock came into contact with the 
 cold walls of the fissure. Tiiis produces a twofold effect — 
 partly upon the dike itself, and partly u})on the rocks forming 
 the sides of the fissure. As regards the dike itself, as the 
 process of cooling has gone on most slowly in the centre, it is 
 here that the rock is most coarsely crystalline, and it becomes 
 gradually more and more fine-grained as we approach tiio 
 sides, where the cooling was most rapid. If the dike is por- 
 phyritic, containing distinct crystals — these will be found to 
 become gradually smaller, and ultimately to disappear alto- 
 gether toward the sides of the dike. As to the effect pro- 
 duced upon the rocks through which the dike cuts, tlu^se are 
 always burnt and metamorphosed on both sides for a greater 
 or less distance, the amount of metamorphism depending 
 partly on the nature of the rock itself, and partly upon the 
 size of the dike. The metamorphism presents nothing very 
 special. The rocks are all indurated, their fossils are partly or 
 wholly obliterated, their bedding is often destroyed, and fre- 
 quently they have a reddened or burnt appearance. Their 
 mineral characters, too, are changed ; sandstones becoming 
 quartzites, shales being converted into hornstone, limestones 
 and chalk becoming saccharoid marbles, and so on. 
 
 With respect to the different ages of the different volcanic 
 and trappean rocks, it would lead us too far to enter into any 
 consideration of the characters of the igneous rocks of the 
 great geological periods, and of the areas in which these are 
 found. It is sufficient to say that the stratified rocks of every 
 period are accompanied by contemporaneous igneous rocks, 
 not in every country, but somewhere or other. Thus we have 
 Palaeozoic, Mesozoic, and Kainozoic traps ; Silurian, Devonian, 
 and Carboniferous traps, and so on. 
 
 ke is of 
 
 it cuts. 
 
 e in any 
 
 be than 
 
 ps, and 
 ; occurs. 
 
CHAPTER XXX. 
 
 it .•'» t 
 
 m 
 
 n 
 
 III 
 
 GEANinC AXD METAMORPniC ROCKS. 
 
 Granitic Rocks, — Granites, and the granitic rocks gen- 
 erally, make their appearance at the surface in large masses, 
 which usually occupy considerable areas, and which send 
 veins into the rocks with which they come in contact. With 
 one or two exceptions, however, and these on a small scale, 
 no granitic rock has been shown to rest upon any stratified 
 rock ; so that granite is said to be an " underlying " rock, and 
 thus differs wholly from the overlying trappean rocks, which 
 commonly repose upon stratified rocks {see Fig. 214, a). 
 
 Though granite never rests upon any otlier rock, it may 
 and does break through the other rocks, altering those with 
 which it comes in contact. Granite, therefore, would appear 
 to be commonly an intrusive rock ; and as such it is, of course, 
 of later age than all the rocks through which it breaks. This 
 would hold good, even if we suppose granite to have a purely 
 metamorphic origin. 
 
 This fact has led to the very important generalization that 
 granites are of all ages. When, for instance, we find a granite 
 intruded among Tertiary strata, dnd altering them on its way 
 to the surface, we know that it is of later age than the T i-- 
 tiary rocks through which it breaks. The older rr< ts 
 
 believed that the first rock which was formed w .nite, 
 
 and that the first step in the production of the cr of the 
 earth was the formation of a continuous envelope oi ^tani<c. 
 Upon this coat of so-called '' primeval " or " fundament; " 
 granite they believed all the stratified formations to have been 
 subsequently deposited. This may be so, but we are unable 
 to point with certainty to any of this primeval granite. All 
 we know is the undoubted fact that the aqueous rocks are 
 always seen to rest upon granite. That is to say, if in any 
 
 -m 
 
cks gen- 
 i masses, 
 ich send 
 t. With 
 all scale, 
 stratified 
 rock, and 
 cs, which 
 a). 
 
 :, it may 
 ose with 
 d appear 
 f course, 
 s. This 
 a purely 
 
 tion that 
 I granite 
 I its way 
 
 the T ;. 
 
 ' • >t8 
 
 .nite, 
 of the 
 ^ rani It', 
 mentii I " 
 ave been 
 e unable 
 ite. All 
 ocks are 
 i in any 
 
 GRANITIC AND METAMORPniC ROCES. 
 
 241 
 
 particular region, or country, you can find out which was tho 
 oldest stratified rock ever deposited in that area, and if you 
 can see what that rests upon, you will find it to repose upon 
 granite. This is a very different thing, however, to the belief 
 that all the granites which we see at the present day, at tho 
 surface of the earth, belong to a primeval crust of granite, 
 and are, therefore, older than all the stratified rocks. In all 
 probability 7wne of the granites which we see at the present 
 day belong to any such primeval crust ; and we now know 
 for certain that granitic formations have been produced during 
 every great geological period, and are probably being formed 
 at the present moment at great depths below the surface. 
 
 The chief tests by which the age of any given mass of 
 granite may be determined are these : 
 
 1. Whenever sedimentary rocks are found reposing upon 
 a mass of granitic rock, without showing any alteration near 
 the line of junction, then the granite is the older of the two. 
 
 2. When, on the other hand, sedimentary rocks come into 
 contact with granitic rocks, and are found to be metamor- 
 phosed near the line of contact, then it is clear that the gran- 
 ite, if not intrusive, is, at any rate, newer than the strata 
 which it alters. 
 
 Fio. 219.— Granitic veins in hornblende slate. CorL»vaIl. 
 
 Exactly the same thing is proved in a still more striking 
 ir nner by the phenomena of granitic veins. Many granites, 
 namely, agree with the intrusive trap-rocks, not only in alter- 
 ing the strata with which they come in contact, but also in 
 sending veins into them (Fig. 219). And, these veins meta- 
 morphose all the rocks in their immediate vicinity, just as 
 
242 
 
 GEOLOGY. 
 
 i'^ 
 
 trap-veins do ; thus affording convincing proof that the granite 
 is younger than the rock thus penetrated. 
 
 As regards the metamorphism produced by granitic veins, 
 exactly the same phenomena are observable as in trap-veins, 
 but generally upon a smaller scale, as the granite-veins are 
 mostly smaller. Thus, the granite of the vein itself is more 
 fme grained and less coarsely crystalline tjian that of the main 
 mass, being, in fact, sometimes hardly distinguishable from 
 trap ; while the rocks in contact with the vein are baked, in- 
 durated, and altered in various ways. The metamorphism pro- 
 duced by granitic masses, also, does not differ in kind from 
 that produced by traps, but it is usually much more extensive. 
 Thus, the metamorphism produced by a mass of trap rarely 
 extends more than a few feet or yards from the igneous rock 
 itself. In the case of large masses of granite, however, the 
 metamorphism may be traced for half a mile to a mile, or 
 more, from the granitic mass. The metamorphism is also 
 usually more intense than in the case of trap, the strata being 
 converted for a great distance into sucii genuine metamorphic 
 rooks as gneiss, mica-sohist, or hornblende-schist. 
 
 With respect to the different ages of the granitic rocks, it 
 is sufficient to say that tliere are Palaeozoic, Mesozoic, and 
 even Kainozoic granites ; in fact, that there are granites be- 
 longing to most of the great geological periods except the 
 latest. And, even in the case of these, there are doubtless con- 
 temporaneous granites also, but we do not see them, because 
 granite is a rock formed at a great depth beneath the surface 
 of the earth, and denudation has nf)t yet been at work for a 
 period of time sufficient to expose to our view the granites of 
 the later Tertiary and Post-Tertiary epochs. 
 
 Metamorphic Rocks. — The chief regions in w^hich Meta- 
 morphic rocks are developed over large areas, are North 
 America, South America, the Alps, Norway and Sweden, the 
 Highlands of Scotland and Wales ; and in all these districts 
 they are associated with lofty mountain-chains, and exhibit 
 their most typical characters. 
 
 As to the age of the Metamorphic rocks, it is clear that 
 they may be regarded as having a twofold age. In the first 
 place, they must obviously belong to the geological period in 
 which they were first deposited as unaltered sediments ; and 
 this, whether we can determine the date of this period or not. 
 In the second place, every Metamorphic rock is secondarily 
 referable to the period in which it was metamorphosed. The 
 two periods in no way coincide with one another, the period 
 
GRANITIC AND METAMORPHIC ROCKS. 
 
 243 
 
 H 
 
 le granite 
 
 tic veins, 
 rap-veins, 
 veins are 
 f is more 
 the main 
 ble from 
 laked, in- 
 hism pro 
 :ind from 
 xtensive. 
 ip rarely 
 20US rock 
 ever, the 
 mile, or 
 1 is also 
 ita being: 
 amorphic 
 
 rocks, it 
 zoic, and 
 nites be- 
 cept the 
 less con- 
 because 
 3 surface 
 3rk for a 
 inites of 
 
 3h Meta- 
 
 North 
 
 den, the 
 
 districts 
 
 exhibit 
 
 ear that 
 the first 
 )eriod in 
 its; and 
 or not. 
 mdarily 
 d. The 
 3 period 
 
 of metamorphism being always later — sometimes enormously 
 so— than the period of original deposition. If, for example, 
 we met with a group of Metamorphic rocks which we could 
 prove to have been originally Liassic, and to have been meta- 
 morphosed in the Eocene period, then we should have to re- 
 gard them as Liassic, looking to the time of their deposition, 
 but as Eocene, if we regard them merely as Metamorphic rocks. 
 
 In determining the age of any given series of Metamorphic 
 rocks, great difficulties are met with. The ordinary test of 
 superposition, when available at all, only gives us the original 
 age of the deposit, but gives no clew as to when the meta- 
 morphism took place. Mineral characters are altogether use- 
 less in determining the age of Metamorphic rocks, except as 
 regards particular districts, and even then upon only a very 
 limited scale. Fossils, as a matter of course, very rarely occur 
 in the metamorphic rocks ; and when they do, they can only 
 tell us the original age of the deposit. Thus, it is now known 
 that the Metamorphic rocks of the Highlands of Scotland are 
 really of Lower Silurian age, as they have been shown to con- 
 tain in some places fossils characteristic of this period. 
 
 As regards the actual ages of the diflfercnt Metamorphic 
 rocks, it is sufficient to say of them, as of the Granitic rocks, 
 that they are of all ages. They commence in the Laurentiau 
 period, they are found in all the great geological periods 
 which follow, and they are doubtless in process of formation 
 at the present day. It is not meant by this, that we can 
 point to tlie Metamorphic rocks of each formation ; but no 
 doubt there are such, and in many instances we can satisfac- 
 torily prove this. 
 
 H; 
 
 III 
 if 
 
 I 
 
 n 
 
 I 
 
 m 
 
 m 
 
CHAPTER XXXI. 
 
 MINERAL VEINS. 
 
 Deposits of minerals of different kinds are found in rocks 
 of all ages, and principally in three different ways: 1. In 
 beds ; 2. In superficial detritus ; 3. In veins. 
 
 1. Metallic ores not uncommonly occur in beds in other 
 stratified deposits. This is the case, for instance, with the 
 beds ot clay-ironstone which occur in the Coal-measures. 
 These deposits, however, differ in no way from the ordinary 
 stratified or sedimentary formations, the ore having been de- 
 posited in the same way as the other materials in the bed or 
 beds in which it is now found. 
 
 3. Metallic ores often occur in superficial detritus or allu- 
 vium. This is the case with the platinum of the Ural Moun- 
 tains, with much of the gold of Australia and California, and 
 with some of the tin in Cornwall. This case, also, needs no 
 special consideration, because the metal has simply been de- 
 rived from the denudation of rocks containing metalliferous 
 veins, and in other respects these deposits resemble ordinary 
 superficial accumulations. 
 
 3. Most of the metallic ores occur, solely or chiefly, in 
 what are called vei7is or lodes, A vein or lode may be defined 
 as being a more or less highly-inclined fissure in the crust of 
 the earth, which has been subsequently filled with foreign 
 matter, this usually consisting of various spars or crystalline 
 substances, more or less impregnated with metals in a native 
 state, or in the condition of ore. 
 
 That mineral veins or lodes are in resMty faults, filled up 
 subsequently by extraneous material, can be proved, in the 
 great majority of instances, by the fact that the beds on the 
 two sides of the lode do not correspond with one another, by 
 
MINERAL VEINS. 
 
 245 
 
 [ in rocks 
 s: 1. In 
 
 in other 
 with the 
 neasures. 
 ordinary 
 been de- 
 e bed or 
 
 s or allu- 
 al Moun- 
 rnia, and 
 leeds no 
 been de- 
 illiferous 
 ordinary 
 
 liefly, in 
 ! defined 
 crust of 
 foreign 
 ystalliiie 
 a native 
 
 filled up 
 , in the 
 8 on the 
 )ther, by 
 
 the frequent occurrence of " slickensides," and by the fact that, 
 when veins cross one another, one very generally displaces 
 the other (Fig. 330), or produces an apparent lateral shift at 
 the surface. 
 
 The materials con- 
 tained in veins differ 
 immensely in different 
 veins, and often in dif- 
 ferent parts of the 
 same vein. As a rule, 
 the bulk of the vein is 
 made up of some gen- 
 erally useless, crj'stal- 
 line matters, such as 
 quartz, calc-spar, heavy 
 spar, etc., these consti- 
 tuting what miners 
 call the " vein-stuff " or 
 " gangue." The me- 
 tallic substances are 
 mostly disseminated 
 through the vein-stuff 
 as small grains or crys- 
 tals, or as little nests 
 or strings, or some- 
 times in considerable 
 masses. 
 
 As to the mode of 
 deposition of metals 
 in veins, several theo- 
 ries are held, and per- 
 haps no one of them 
 will apply to all cases. 
 As a general rule, it 
 would appear that the 
 contents of veins have 
 been deposited in the 
 primitive fissure by pre- 
 cipitation from a wa- 
 tery solution. This is 
 certainly the case with 
 the crystalline vein- 
 stuff, and would seem also to be the case with the metals, 
 whether these are native or in the state of ore. , lu judging 
 
 Fio. 220. — Vortical sertion. Rhowinp a copper lode (h, ft.) 
 intiTSoctinp a tin l()<i(('r. </). ami producing a vertical 
 displacoment or " shift" of tlic vein. 
 
 
 
 r 
 
 I 
 
 i- I 
 
 i.A 
 
 lit 
 
246 
 
 GEOLOGY. 
 
 i^i 
 
 w$ 
 
 t9( 
 •f 
 
 of this question we must not, of course, consider the solvent 
 power of water as we see it at the surface. When under 
 enormous pressure, and charged with various chemical ingre- 
 dients, water may be raised to a very high temperature, and 
 might then be capable of dissolving any of the metals. This 
 view is further strongly supported by the phenomena of hot 
 springs. These can generally be proved to break out along 
 lines of fault or fissures in the crust of the earth. They con- 
 tain most of the materials which are found in veins, especially 
 flint, carbonate of lime, fluor-spar (fluoride of calcium), and 
 heavy-spar (sulphate of barytes), all of which are found com- 
 monly in vein-stufi^, either alone or associated with one an- 
 other. Any fissure, therefore, occupied by a hot spring, 
 would doubtless be converted in the course of time into a 
 mineral vein ; and there is reason to believe that this has not 
 uncommonly been the case. 
 
 With regard to the age of veins, since they are undoubt- 
 edly in most cases connected with faults and fissures in the 
 crust of the earth, it is pretty certain that they must be of all 
 ages, and arc doubtless in process of formation at the present 
 day. It is very difficult, however, to point to the age of any 
 particular lode, except under special circumstances, such as 
 the occurrence of organic remains in the vein-stuff. In all 
 cases, however, if the lode has been a line of fault, it must be 
 of later age than the strata which it traverses, though it may 
 be impossible to say how much later. 
 
 i 
 
ii 
 
 he solvent 
 len under 
 ical ingre- 
 ature, and 
 als. This 
 sna of hot 
 out along 
 They con- 
 especially 
 lum), and 
 und com- 
 1 one an- 
 t spring, 
 rie into a 
 is has not 
 
 undoubt- 
 Bs in the 
 be of all 
 e present 
 je of any 
 , such as 
 P. In all 
 ; must be 
 h it may 
 
 QUESTIONS. 
 
 1. Objects and scope of physical geography, of palaeontology, of min- 
 eralogy, of geology proper ? 
 
 2. What is the figure of the earth, and what conclusion may be deduced 
 from this ? 
 
 8. Length of the polar and equatorial diameters of the earth ? 
 
 4. Most generally accepted hypothesis as to the origuial condition of 
 the globe ? 
 
 6. What facts support the view that the interior of the earth is liighly 
 heated ? 
 
 6. What is the general rate of increased temperature in mines and 
 Artesian wells in descending below the surface ? 
 
 7. What is meant by •' mean density," and what is the mean density of 
 the earth ? 
 
 8. What is the mean density of rock ? 
 
 9. W^hat conclusion seems deducible from the difference in the mean 
 density of the earth as compared with that of rock in general ? 
 
 10. What is the ordinary belief as to the condition of the interior of the 
 earth ? 
 
 11. What is the origin of dry land ? 
 
 12. Mention instances in which it has been shown that portions of the 
 earth are at present sinking or rising. 
 
 13. What is the difference between the northern and southern hemi- 
 spheres as regards the distribution of dry land ? 
 
 14. What is the general difference between the Old World and the New, 
 as regards their great mountain-cliains ? 
 
 15. Chief kinds of mountains ? 
 
 16. Mountains of circumdenudation, how produced ? 
 
 17. Mountains of uptilting, how produced ? 
 
 18. What mountains come under the head of " mountains of ejection? " 
 
 19. Define a volcano. 
 
 20. Difference between submarine and subaerial volcanoes ? 
 
 21. What is the general appearance of a quiescent volcano? 
 
 22. What are the conditions of volcanic activity ? 
 
 23. Why do earthquake-shocks usually precede an eruption ? 
 
 24. General phenomena of a volcanic eruption ? 
 
 25. Nature of volcanic ashes, of scoria?, of lava ? 
 
 26. What is the consistence of lava, and its general rate of movement ? 
 
 27. Chief theatres of volcanic activity at the present day ? 
 
 iPll'l 
 
 11 Ii 
 
 Ii 
 
 i 
 
 11 
 
 1' 
 
248 
 
 QUESTIONS. 
 
 tin 
 
 If 
 
 41. 
 42. 
 43. 
 44. 
 45. 
 
 28. What two great laws arc deducible from the present distribution of 
 volcanoes ? 
 
 2U. What is indicated by the arrangement of volcanoes in lines ? 
 
 30. General structure of a volcanic cone ? 
 
 31. Arrangement of the beds of ash and lava round the crater ? 
 
 32. Dikes, their nature and mode of production? 
 
 33. What is the generally-accepted theory as to the causes of volcanic 
 activity ? 
 
 34. General phenomena of earthquakes ? 
 
 35. Wliere are earthquakes most common ? 
 
 3G. What are earthquake-waves, and how are they caused ? 
 
 37. How are valleys produced ? 
 
 38. Define "denudation." 
 
 39. What are the chief denuding agents ? 
 
 40. Double action of rain as a denuding agent ? 
 What rocks are chiefly affected by rain, and why? 
 How do rivers act as denuding agents? 
 
 On what conditions does the denuding power of a river chiefly depend ? 
 Proofs that rivers really wear away the rocks over which tliey flow ? 
 What is shown by the occurrence of rounded blocks, gravel, and 
 
 sand, in a river-bed ? 
 
 46. Mention approximately the amount of solid matter brought down by 
 Borne of the great rivers of the earth ? 
 
 47. What is a delta ? 
 
 48. Mention some of the largest and most important river-deltas ? 
 
 49. What does the existence of a delta prove ? 
 
 50. Why sliould some large rivers not produce deltas? 
 
 51. General action of the sea as a denuding agent? 
 
 62. Mention some proofs that the sea wears away the coast ? 
 
 53. What is the essential difference between the action of the sea as a 
 denuding agent and that of rivers ? 
 
 54. What conclusion may be drawn as to many inland cliffs and preci- 
 pices ? 
 
 65. Show, from the phenomena of rivers and the sea, that denudation is 
 a process of rearrangement, and not of destruction. 
 
 56. What is the " line of perpetual snow ? " 
 
 57. What is the height of this line in Britain, in the Alps, in the Andes, 
 in Greenland ? 
 
 58. What is a "glacier," and how is it formed ? 
 
 59. Rate of movement of a glacier ? 
 
 60. Why does a glacier ultimately cease to advance ? 
 
 61. What are the "lateral moraines" of a glacier? 
 How is a "median moraine" formed? 
 What is a " terminal moraine ? " 
 
 What is the structure and appearance of a terminal moraine? 
 How would you recognize the terminal moraine of a glacier, suppos- 
 ing tlie glacier to have disappeared ? 
 
 66. What are " striated " blocks, and how are they produced ? 
 
 67. What phenomena would be presented by the bed of a glacier, sup- 
 posing the glacier to have disappeared ? 
 
 68. What are crevasses? 
 
 69. What are " roches moutonnees?" 
 
 70. What are " perched blocks ? " 
 
 71. What are " erratics ? " 
 
 62. 
 63. 
 64. 
 65. 
 
itributlon of 
 
 ics? 
 
 er? 
 
 } of volcanic 
 
 efly depend ? 
 1 they flow ? 
 , gi-avel, and 
 
 ^ht down by 
 
 Itas ? 
 
 the sea as a 
 s and preci- 
 enudation is 
 
 I the Andes, 
 
 ine? 
 
 ier, suppos- 
 
 ? 
 
 ;lacier, sup- 
 
 QUESTIONS. 
 
 249 
 
 72. Whence are the erratics of a gla'iier derived ? ■ 
 
 73. What is the present condition of Jreenland ? . 
 
 74. How are icebergs produced ? 
 
 75. What is " continental ice ? " 
 
 76. How do icebergs come to transport rocks and soil? 
 
 77. How may the erratics carried by icebergs be generally distinguished 
 from those transported by glaciers ? 
 
 78. What may be the size of a large iceberg? * 
 
 79. What is "weathering?" 
 
 80. What rocks weather most readily ? 
 
 81. What are " subaerial " rocks ? Mention examples. 
 
 82. What are organically-formed rocks ? Mention examples. 
 
 83. What are coral-reefs ? 
 
 84. What are the chief forms of coral-reefs, and how are they produced ? 
 86. What is " coral-rock ? " 
 
 86. What is " peat ? " 
 
 87. Explain the doctrines of the " catastrophists " and " uniformita- 
 rians ? " 
 
 88. What is meant by the doctrine of the " adequacy of existing causes ? " 
 
 89. What is meant by the " crust of the earth ? " 
 
 90. Has the earth's crust been formed at once, as we now find it, or at 
 successive periods and gradually ? 
 
 91. How is " rock " defined"? 
 
 92. What are the four great classes of rocks ? 
 
 93. By what other terms are aqueous rocks known? 
 
 94. How are the aqueous rocks distinguished ? 
 
 95. What is meant by the term " stratified ? " 
 
 96. What may be inferred as to th'.; origin of the stratified roc';s ' 
 
 97. How could you distinguish between beds deposited ir. fiesh water, 
 and those laid down in the sea ? 
 
 98. Define the term " fossil." 
 
 99. Do fossiliferous beds contain fossils throughout ? 
 
 100. Define the term "formation." 
 
 101. What is meant by the term " laminated ? " 
 
 102. Mention cases in which rocks are laminated, and may contain fossils, 
 and yet not be of aqueous origin. 
 
 103. What rocks are included under the head of volcanic rocks ? 
 
 104. How are the volcanic rocks distinguished ? 
 
 105. What are the Trappean rocks? 
 
 106. How would you prove that the Trappean rocks are of volcanic 
 origin ? 
 
 107. Why should we not be surprised at not being able to point to the 
 cones and craters of the Trappean rocks ? 
 
 108. What are the Platonic rocks? 
 
 109. How are they distinguished from the aqueous rocks ? from' the vol- 
 canic rocks ? 
 
 110. How is crystallization affected by rapid or slow cooling? 
 
 111. How does this bear on the question of the origin of the Plutonic 
 rocks ? 
 
 112. Why are the Plutonic rocks called "underlying rock'*?" 
 
 113. How can it be shown that the Plutonic rocks must have been at one 
 time melted ? 
 
 114. What general conclusions may be drawn as to the origin of the 
 Plutonic rocks ? 
 
 m 
 
 1 
 
250 
 
 QUESTIONS. 
 
 «' ■■1 
 
 U" 
 
 I' ' 
 
 rocks ? 
 119, 
 120, 
 121. 
 
 IIB. What are the Metamorphic rocks ? 
 
 116. How do they agree with the Plutonic rocks ? 
 
 117. In what do they differ from the Plutonic rocks ? 
 
 118. What is the ordinary theory as to the nature of the Metamorphic 
 
 What is understood by the term " hypogcne ? " 
 
 What are the main subdivisions of the aqueous rocks ? 
 
 What is meant by " derivative" rocks ? 
 
 122. Compof'ition of the arenaceous rocks? 
 
 123. What is a " grit ? '» 
 
 124. How are siliceous rocks recognized in the field? 
 
 125. What is a conglomerate ? 
 
 126. What caution must be observed in determining the age of a con- 
 glomerate from its fossils ? 
 
 127. What is a "breccia?" 
 Composition of the argillaceous rocks ? 
 What is clay ? 
 
 How are argillaceous rocks recognized in the field ? 
 Mention the chief varieties of the argillaceous rocks f 
 What is loam ? 
 What is " marl ? " 
 
 What rocks may be said to be chemically formed ? 
 Composition and characters of chalk ? 
 Characters of limestone ? 
 
 Various modes in which limestone may be produced f 
 Chief varieties of limestone ? 
 What is marble ? 
 What is an " oolitic " limestone ? 
 
 Characters of magnesian limestone and its chemical composition ? 
 How may limestone be recognized in the field ? 
 What is gypsum, and how does it generally occur ? 
 What is alabaster ? 
 How does rock-salt usually occur ? 
 Chemical composition of coal, and its chief varieties ? 
 In what two forms do volcanic and Trappean formations occur? 
 Is there any chemical difference between the melted products of 
 
 volcanoes and their mechanical accompaniments? 
 
 149. Of what two families of minerals are the volcanic and Trappean 
 rocks essentially composed ? 
 
 150. Chemical composition of felspar? 
 Leading varieties of felspar ? 
 Chemical composition of hornblende ? 
 What relations subsist between hornblende and augite ? 
 Chief varieties of lavas ? 
 What is a " trachyte ? " 
 What is obsidian ? 
 Chief mechanical accompaniments of modem volcanoes ? 
 
 158. Chief divisions of the Trappean rocks ? 
 
 159. What is basalt? 
 
 160. What are the mechanical accompaniments of traps? 
 
 161. Define the term " porphyritic." 
 
 162. What is an " amygdaloid," and how is it produced ? 
 
 163. Chief varieties of the Plutonic rocks ? 
 
 164. Chemical composition of granite ? 
 
 128. 
 129. 
 130. 
 131. 
 132. 
 183. 
 134. 
 135. 
 136. 
 137. 
 138. 
 139. 
 140. 
 141. 
 142. 
 143. 
 144. 
 145. 
 146. 
 147. 
 148. 
 
 151. 
 152. 
 153. 
 154. 
 155. 
 156. 
 157. 
 
QUESTIONS. 
 
 251 
 
 ::.!! 
 
 kletamorphio 
 
 ge of a cou- 
 
 iposition ? 
 
 occur? 
 roducts of 
 
 Trappean 
 
 165. How docs the quartz of granite ordinarily occur? 
 
 166. Chemical composition of mica ? 
 
 167. What peculiarity is there in the crystallization of granite? 
 
 168. To what couclusion as to the origin of granite does this peculiarity 
 point ? 
 
 169. What is the composition of syenite, of protogine? 
 110. What is euiite ? 
 
 171. What are the chief varieties of the Metamorphic rocks ? 
 
 172. Composition and structure of gneiss? 
 
 173. Composition of hornblende-8chist> of mica-schist? 
 
 174. Nature of quartzite ? 
 
 175. What are the " divisional planes" of rocks? 
 
 176. Define " planes of deposition." 
 
 177. What are the differences between "strata" and "laminae?" 
 
 178. What are "joints?" 
 
 179. Can any regular arrangement be traced in joints? 
 
 180. What are the causes of joints ? 
 
 181. In what rocks is columnar jointing seen? 
 
 182. What is the structure of "articulated" columnar basalt? 
 
 183. What law do the columns of an igneous rock always obey? 
 
 184. What is columnar jointing due to ? 
 
 185. Define cleavage, and distinguish it from lamination and jointing. 
 
 186. What is meant by the expression that cleavage is a "superinduced " 
 structure ? 
 
 187. How may the lines of bedding be detected in cleaved rocks? 
 
 188. Define "slate," and distinguish it from " shale? " 
 
 189. What relation do cleavage-planes hold to the original lines of lami- 
 nation ? 
 
 190. How is the texture of cleaved rocks affected by the cleavage ? 
 
 191. What is the effect of cleavage upon fossils? 
 
 192. What is the generally-accepted theory as to the origin of cleavage? 
 
 193. Mention the experiments of Sorby and Tyndall? 
 
 194. Define "foHation." 
 
 195. Define "schist," and distinguish it from slate and shale. 
 
 196. Mention any theory as to the cause of foliation. 
 
 197. Is there any necessary relation between the planes of foliation and 
 those of deposition ? 
 
 198. In what position were the stratified rocks originally deposited ? 
 
 199. In what position are stratified rocks now usually found ? 
 
 200. What is the cause of " inclined " strata ? 
 
 201. What is meant by " thinning out ? " • 
 
 202. What is meant by " false bedding? " 
 
 203. What does this indicate ? 
 
 204. Explain the fortnation of ripple-mark. 
 
 "205. What are " desiccation-cracks," and how are they formed ? 
 
 206. What do " rain-prints " indicate ? 
 
 207. What is meant by the " dip " of inclined beds ? 
 
 208. Define " outcrop." 
 
 209. What is the " line of strike ? " 
 
 210. What necessary relation subsists between the strike and dip of in- 
 clined beds ? 
 
 211. What beds have no "line of strike ? " 
 
 212. What inclined beds have no "point of dip ?'* 
 
 213. What is understood by " contorted " strata ? 
 
 'fill 
 
252 
 
 QUESTIONS. 
 
 214. IIow are contortions produced ? 
 
 215. What is an anticlinul curve? 
 
 21t). What position is held by the oldest beds in an anticline? 
 
 217. What is meant by a " (lUtl-quA-versal " dip':* 
 
 218. What is a synclinal curve V 
 
 2U). What position is held by the oldest beds in a synclinal curve? 
 
 220. When do beds form a " basin V " 
 
 221. When are strata said to be " conformable?" 
 
 222. Define uneonf'orniabiiity. 
 
 2215. Does unconformability necessarily indicate a discordance in dip? 
 
 224. What is the commonest ease of unconformability in practice; ? 
 
 225. What scfiuence of phenomena is indicated by unconformability? 
 
 226. What is " overlap ? " 
 
 227. Is overlap always a Bign of unconformability ? 
 
 228. What is a fault? 
 
 229. What is meant by the " throw " of a fault ? 
 
 230. Explain the terms " up-thiow side," " down-throw side." 
 2:31. What is the " hade " of a fault ? 
 
 232. In what direction docs a fault necessarily hade, and why? 
 
 233. WHiat is " slickensides ? " 
 
 234. WHiat is the ordinary condition of the up-throw side of a fault? 
 
 235. IIow are faults ordinarily detected in practice? 
 
 236. What is meant by the " lateral shift " of faulted and inclined strata ? 
 
 237. IIow does the repetition of the same beds as produced by iaults 
 differ from that produced by anticlinal and synclinal curves respectively ? 
 
 238. What are the chief tests of the age of any parlieular bed or set of 
 beds ? 
 
 2:59. In what way and to what extent do fossils enable us to pronounce 
 as to the age of any given bed or set of beds ? 
 
 210. Mention some reasons why no country exhibits a complete and regu- 
 lar succession of the aqueous rocks ? 
 
 241. Into what three great periods is the entire series of fossiliferous 
 rocks divided ? 
 
 242. What are the great divisions of the animal kingdom ? 
 
 243. Give the characters of the Frotozoa^ and their chief fossil represent- 
 atives. 
 
 244. Characters and chief fossil groups of the Codeniernta? 
 
 245. Characters and more important extinct forms of the EeJiinodermata ? 
 
 246. Characters and chief fossil forms of the Annulosa .^ 
 
 247. Characters of the Mollusca ? Leading groups of the same ? 
 
 248. Characters (?f the Vertcbrata? 
 
 249. Leading groups of the Vertebrates ? 
 
 250. Main divisions of the vegetable kingdom? 
 
 251. Name " Laurentian," how derived ? 
 
 252. Where are the Laurentian rocks chiefly developed ? 
 
 253. Mineral characters of the Laurentian rocks ? 
 
 254. Life of the Laurentian period ? 
 
 255. Relation of Lower to Upper Laurentian? 
 
 256. Where are the Huronian rocks found ? 
 
 257. Mineral characters and age of the Huronian rocks ? 
 
 258. Their relations with the Laurentian rocks ? 
 
 259. Name " Cambrian," how derived ? 
 
 260. Mention the chief members of the Cambrian series in Britain. 
 
 261. Give the chief fossils of the Lingulu flags. 
 
T^^l 
 
 QUESTIONS. 
 
 263 
 
 urvc? 
 
 I in (lip? 
 L'tico ? 
 lability? 
 
 a fault? 
 
 nod strata? 
 mI by iaultd 
 actively ? 
 ed or sot of 
 
 pronounce 
 
 ;e and regu- 
 
 fossiliferous 
 
 rcpresent- 
 
 nodermata? 
 tnc? 
 
 ntaia. 
 
 262. "What arc Trilobitca ? 
 
 26.'}. Chief Cambrian rocks of North America ? 
 
 261. What fossils spofially i-haracterize tlieSkiddawand Quebec proupa ? 
 
 265. Mention s'ome of the Cambrian rocks of the continent of Eurojjc. 
 
 266. What clas.ses of animals chiefly abounded in the Cambrian period ? 
 
 267. Name " Silurian," how derived V 
 
 268. Main divisions of tlic Silurian series and chief localities in which it 
 is developed ? 
 
 269. Chief subdivisions of the Lower Silurian scries in Britain ? 
 
 270. Mineral characters, thickness, and fossils, of the Hala group? 
 
 271. Cliief subdivisions of the Upper Silurians in IJrilain? 
 
 272. At what horizon are the earliest tish-reniains found in Britain ? 
 
 273. Chief subdivisicms of the Lower Silurians in North America? 
 
 274. Chief subdivisions of the Upper Silurians in North America ? 
 
 275. Chief classes of animals which flourished in the Silurian period ? 
 
 276. Origin of the name " Devonian ? " 
 
 277. How far can the name " Devonian " be regarded as equivalent to 
 ♦•Old Ued Sandstone?" 
 
 278. Divisions of the Old Red Sandstone in Scotland ? 
 270. Chief fossils of the Old Red Sandstone ? 
 
 280. Characters of the Devonian rocks of Devonshire ? 
 28L Chief fossils of the Devonian rocks ? 
 
 282. Chief subdivisions of the Devonian series in North America ? 
 
 283. At what horizon do fish first make their appearance in North America ? 
 
 284. Chief fossils of the Devonian rocks of Noith America ? 
 
 285. Characters of the vegetation of the Devonian jjoriod ? 
 
 286. Chief classes of animals which flourished in the Devonian period ? 
 
 287. Origin of the name " Corniferous ? " 
 
 288. Origin of the name "Carboniferous?" 
 
 289. Leading division of the Carboniferous series ? 
 
 290. Characters of the Mountain-Limestone ? 
 
 291. Chief fossils of the Mountain-Limestone? 
 
 292. What Brachiopods are most characteristic of the Carboniferous 
 rocks ? 
 
 293. Mineral characters of the Millstone Grit ? 
 29t. Mineral characters of the Coal-measures ? 
 
 295. Tliickncss of the Coal-measures in South Wales and Nova Scotia ? 
 
 296. What is the " underclay " of a coal-seam, and what fossils does it 
 contain ? 
 
 297. What classes of plants abounded especially in the Carboniferous 
 period ? 
 
 298. What living plants does Lcpidoclenihon chiefly resemble ? 
 
 299. What are the characters of Calatniks, and to what living plants arc 
 they most nearly allied ? 
 
 300. What connection is there between Sigillaria and Sfif/maria ? 
 
 301. To what group is SigVlaria believed to be referable ? 
 
 302. Give the generally-received theory as to the origin of coal. 
 
 303. Show how this is borne out by the fossil remains of the Coal- 
 measures. 
 
 304. What air-breathing animals are specially noticeable as occurring in 
 the Coal-measures ? 
 
 305. Mention some other fossils which characterize the Coal-measures. 
 
 306. What points of interest are noticeable as regards the hfe of the 
 Carboniferous period 'i 
 
 12 
 

 i 
 
 254 
 
 QUESTIONS. 
 
 807. Origin of the name '* Porniian ? " 
 
 308. Origin of the name "New Red Smdstono?" 
 
 '.W.). What groups of rock.s uro comprised under the old term "New Red 
 Sandstone ? " 
 
 811). In what case is the term "New Rod Sandstone" still useful ' 
 
 811. What relations do tho rerniian rocks usually bear to the Carbonif- 
 erous rocks ? 
 
 312. Into what three groups may the Permian scrie.'? be usually divided ? 
 
 813. 
 814. 
 '315. 
 810. 
 817. 
 318. 
 819. 
 
 Gancral ch:iracters of the Permian rocks in Britain? 
 
 0;>neral charaettirs of tiu; Permians in (Jermany ? 
 
 Mineral eliaractera of the Middle Pel mians? 
 
 (Tiiief fossils of il>c Permian scries ? 
 
 Why should tho Permians be j)laeed in the Palicozoic series ? 
 
 Characters of the Permians of North America ? 
 
 Contrast the vegetation of tho Permian with that of the Carbonifer- 
 ous period. 
 
 320. What are the three divisions of the Trias recognizable in Germany? 
 
 Mineral characters and chief fossils of the Hunter y 
 
 Mineral characters and chief fossils of the Musehdkalk ? 
 
 Mineral characters and chief fossils of the Kenpcr ? 
 
 What member of the Trias is wanting in liritain ? 
 
 Origin of the name " Rhaitic ? " 
 
 Wliat fossils characterize the Avicula contorta beds ? 
 
 What Pahozoic fossils appear for the last time in the Uhajtic beds ? 
 
 What Mosozoic fossils appear for the first time in the Rluctic beds? 
 329. What class of Vertebrates appears for the first time in the European 
 Trias ? 
 
 Name of the earliest known Mammal ? 
 
 To what group of living Mammals is Microlestrn supposed to belong? 
 
 How is CeratUes distinguished from Ammonites? 
 
 Chief localities of Triassic rocks in North America ? 
 
 Supposed nature of the footprints of the American Trias ? 
 
 What is the fossil called "Cheirotherium? " 
 
 To what class of Vertebrates do the Labiirinthodonh belong? 
 
 What classes of animals eliiefly abounded in the Triassic period ? 
 
 With what rocks is rock-salt often associated ? 
 339. What is the ordinary theory as to the origin of beds of rock-salt? 
 8 10. Origin of the name " Jurassic ? " 
 
 321. 
 322. 
 323. 
 321 
 325. 
 326. 
 327. 
 328. 
 
 330. 
 331. 
 332. 
 833. 
 334. 
 835. 
 3315. 
 337. 
 338. 
 
 311, 
 812 
 343 
 814 
 845, 
 316 
 
 Origin of the name " Oolitic V " 
 
 Chief subdivisions of the Jurassic rocks in Britain? 
 
 Characters and thickness of the Lias ? 
 
 Chief fossils of the Lias ? 
 
 Characters of the Great Oolite ? ' 
 
 What fossils render the Stonesfiold Slate remarkable ? 
 317. What plants chiefly characterize the Lower Oolites? 
 818. Divisions of the Middle Oolite.s in Britain ? 
 349. Characters, thickness, and fossils, of the Oxford Clay ? 
 
 850. Chief fossils of the Coral Rig? 
 
 851. Divisions of the Upper Oolites in Britain ? 
 
 852. Characters of the Kimmeridge Clay ? 
 353. Characters of the Portland beds ? 
 
 854. Characters of the Purbeck beds? ' . 
 
 855. What plants characterize the Purbeck beds? 
 
 856. Mention some of the Mammals of the Purbeck series ? 
 
m '* New Red 
 
 seful ? 
 
 the Cirbonif- 
 
 ally divided ? 
 
 icries ? 
 
 L' Carbonifer- 
 in Germany ? 
 : ? 
 
 1ia3tic bods ? 
 Llifctic beds? 
 he European 
 
 i to belong ? 
 
 i3? 
 
 (long ? 
 ic period ? 
 
 rock-salt ? 
 
 HP 
 
 QUESTIONS. 
 
 255 
 
 3{)U. 
 801. 
 802. 
 303. 
 
 307. 
 308. 
 309. 
 370. 
 371. 
 
 357. Characters and chief localities for the Jurasslo rocks In North 
 America y 
 
 358. What is the horizon of the Solenhoi'cn Slate, and what more remark- 
 able forisils has it yielded f 
 
 35'.). What characters distinguish Ammonitcn from NaulHua! 
 
 Mention some characteristic Liaiidic Ammonites. 
 
 What are lidcmnitesi 
 
 Mention a characteristic Lia.ssic Oyster. , 
 
 What ralseozoic genua of Urachiopods appears for the last time in 
 the Lias ? 
 
 30t. What groups of fushes specially characterize the Lias ? 
 
 805. What is the zoological position of J'^htfnpsaut'us and Plcaiosatirtu* f 
 
 300. What are the leading characters of Icht/n/osaiiriisi^ 
 
 IIow does l'lesiofiaurii,H difler from LUthi^osaurusf 
 
 What class do FUrodcwhffiH belong to ? 
 
 What characters distinguish the I'torodactyles ? 
 
 Mention a characteristic Crinoid of the Middle Oolites. 
 
 By what characters is Arcluxoptcryx distinguished from all living 
 birds, and in what formation docs it occur? 
 
 372. What peculiarity in Arefueoptcri/x is of a Kcptilian character? 
 
 373. To what order of living Mammals do the Oolitic MammaLi show 
 most resemblance ? 
 
 374. Derivation of the name " Cretaceous ? " 
 Ls chalk necessarily present in tlic Cretaceous rocks? 
 Chief divisions of the Cretaceous series in Europe ? 
 Chief subdivisions of the Lower Cretaceous series ? 
 Origin of the name " Wealdeii ?" 
 Geographical distribution of the Wealden beds ? 
 Mineral characters of the Wealden beds ? 
 Fossils of the Wealden ? 
 Origin of the Wealden beds ? 
 
 383. Mention some of the Reptiles of the Wealden. 
 
 384. To what living forms is Jguanodon comparable, as regards its teeth ? 
 Origin of the name " Greensand " — is it appropriate ? 
 Origin of the name " Neocomian V " 
 Mineral characters and origin of the Lower Greensand ? 
 Fossils of the Lower Greensand ? 
 Palajontological break between the Lower and Upper Cretaceous 
 
 375. 
 370. 
 377. 
 378. 
 879. 
 380. 
 381. 
 882. 
 
 385. 
 380. 
 387. 
 388. 
 389. 
 
 groups ? 
 
 390. Physical break between the same in Britain ? 
 
 391. Chief subdivisions of the Upper Cretaceous series? 
 
 392. Mineral characters and geographical distribution of the Gault? 
 
 393. Fossils of the Gault ? 
 
 394. Mineral characters of the Upper Greensand ? 
 
 395. Divisions of the Chalk proper ? 
 . 390, Nature of the Chalk-marl ? 
 
 397. Mineral characters of the Wliite Chalk ? 
 
 398. Geographical extent of tlie White Chalk ? 
 
 399. General belief as to the origin of Clialk ? 
 
 400. What microscopical shells have been shown to occur extensively in 
 chalk ? 
 
 401. What recent deposit is nearly allied to Chalk ? 
 
 402. How do flints occur in Chalk ? 
 
 403. To what are the chalk-llints supposed to owe their origin ? 
 
 m\ 
 
 i:| 
 
 ^' 
 
 m 
 

 
 
 
 1! r- 
 
 256 
 
 QUESTIONS. 
 
 404. What groups of the Protozoa abound especially in the Cretaceous 
 rocks ? 
 
 405. Mention a characteristic Chalk bivalve. 
 
 406. What Cephalopoda are espo'^ially characteristic of the Crctaceo"3 
 rocks ? 
 
 407. Mention some genera, allied to the Ammonites, which are exclusive- 
 ly Crotaceods. 
 
 • 408. How does a Baculite difior from an Ammonite? 
 How does a Turriiitc ditfer fiom an Ammonite ? 
 What group of Echinoderms is chiefly represented in the Cretaceous 
 
 40'), 
 410, 
 rocks ? 
 411, 
 412, 
 413, 
 414, 
 415, 
 
 Mention one or two characteristic Chalk Sea-urchins. 
 What group of lishes appears for the first time in the Chalk? 
 What Reptiles appear here for the last time? 
 What is the Maestricht ("halk ? 
 
 In what way does it indicate a transition between the Chalk and 
 the Tertiary beds ? 
 
 416. Mention a celebrated Reptile of tho Maestricht Chalk. 
 
 417. How does the Chalk of the south of Europe dift'er from that of 
 Britain ? 
 
 418. What is the chief member of the Chalk of Southern Europe? 
 
 419. What class do Ilippurites belong do? 
 
 420. Mention some of the peculiarities of Ilippurites. 
 
 421. What is the remarkable feature in the vegetation of the Cretaceous 
 period ? 
 
 422. Characters and geographical distribution of the Cretaceous rocks 
 of North America ? 
 
 423. What are the physical relations between the Kainozoic and Mcso- 
 zoic rocks? 
 
 424. How are the Tertiary rocks shown to be unconformable to the Cre- 
 taceous rocks? 
 
 425. What are the palajontological relations between the Tertiary and 
 Cretaceous rocks? 
 
 426. Why is there special difliculty in classifying the Tertiary rocks? 
 
 427. What is the basis of classification proposed by Sir Charles Lyell ? 
 
 428. Give the names of the divisions of the Tertiary series proposed by 
 Sir Charles Lyoll. 
 
 429. Derivation of the name " Eocene ? " 
 
 430. Proportion of existing species of shells in the Eocene? 
 
 431. Divisions of the Eocene in Britain? 
 
 432. Characters and thickness of the London clay? 
 
 433. Chief fossils of the London Clay ? 
 
 434. Characters and fossils of the Middle Eocene ? 
 
 435. Position and mineral characters of the Calcaire grossier? 
 
 436. Fossils of the Cakaire grossier? 
 
 437. Characters and position of the gypseous series of Montmartre. 
 
 438. Fossils of the same ? 
 
 439. Distribution of the Nunimulitic limestone? 
 
 440. Characters and position of KummulitcH ? 
 
 441. Characters and geographical distribution of the Eocene rocks of 
 the United States ? 
 
 442. Mention some of the more characteristic genera of Eocene Mammals. 
 
 443. What order of Reptiles, so far as known, first appeared in the 
 Eocene rocks ? 
 
Cretaceous 
 
 Crctaceo"3 
 e exclusive- 
 Cretaceous 
 ^alk? 
 Chalk and 
 
 m that of 
 3po? 
 
 Cretaceous 
 
 J0U9 rocks 
 
 and Mcso- 
 
 the Crc- 
 
 rtiary and 
 
 rocks ? 
 s Lyell ? 
 jposed by 
 
 :tre. 
 
 rocks of 
 
 Jammals. 
 d in the 
 
 444 
 445. 
 446. 
 447. 
 448. 
 449. 
 450. 
 451. 
 452. 
 453. 
 454. 
 
 QUESTIONS. 
 
 Derivation of the name " Miocene ? " 
 
 Proportion of existing species of shells in the Miocene? 
 
 Miocene rocks of Britain ? 
 
 Lower Miocene strata of France ? 
 
 Origin of the name " Faluns ? " 
 
 257 
 
 li 
 
 Cl)ief fossils of the Faluns ? 
 Afhiiilies of Diiuothcriwn? 
 Fossils of the Austrian Brown-coals ? 
 Characters of the Miocene strata of Switzerland ? 
 Fossils of the Swiss Miocene ? 
 
 Characters and geographical distribution of the Miocene rocks of 
 North America? 
 
 455. General characters of the Miocene plants ? 
 
 456. Miocene plants of Europe, what <'liniate do they indicate? 
 
 457. To the plants of what country are the plants of the European Mio- 
 cene most nearly allied ? 
 
 458. What theory is this supposed to support ? 
 
 459. Miocene plants of Greenland, climate indicated by? 
 
 460. Mention some of the more important Mammals of the Miocene period ? 
 
 461. What types of the order Proboscidm are now represented? 
 
 462. Derivation of the name " Pliocene ? " 
 
 463. Proportion of existing species of shells in the Pliocene? 
 
 464. Origin of the name " Crag ? " 
 
 465. Divisions of the Pliocene in Britain ? 
 
 466. Characters of the Coralline Crag ? 
 
 467. Fossils of the Coralline Crag ? 
 
 408. Climate indicated by the shells of the Coralline Crag? 
 
 469. Characters and distribution of the Red Crag? 
 
 470. Fossils of the Red Crag ? 
 
 471. Climate indicated hy the shells of the Red Crag? 
 
 472. Characters of the Norwich Crag? 
 
 473. Fossils of the Norwich Crag? 
 
 474. Characters and distribution of the Pliocene deposits of the United 
 States ? 
 
 475. Characters of the sub-Apennine deposits ? 
 
 476. Characters of the Newer Pliocene of Sicily ? 
 
 477. Characters of the Aralo-Caspian beds ? 
 
 478. Post-Tertiary deposits, how distingui.shed from Tertiary ? 
 
 479. Divisions of the Post-Tertiary, how distinguished? 
 
 480. Characters and fossils of the Cromer forest-bed ? 
 
 481. Glacial period, why so called ? 
 
 482. Names applied to the Glacial deposits ? 
 
 483. General nature of Gliu'ial deposits ? 
 
 484. Characters of true Bowldor-clay ? 
 
 485. General sequence of phenomena indicated by the Glacial deposits 
 of Scotland ? 
 
 486. Character of shells in Scotch Glacial deposits? 
 
 487. General phenomena of tlie glaciation of North America? 
 
 488. Moaning of the term "alluvium?" 
 
 489. Origin of fluviatile de[)osits ? 
 
 490. Nature and origin of the Rliine "loess? " 
 
 491. Distinction between high-level and low-level valley-gravels? 
 
 492. Show that the high-level gravels are older than the low-level gravels. 
 
 493. Extinct Mammals of the high-level gravels ? 
 
 
 I 1^ " 
 
 : iiiii^ 
 
 
 
258 
 
 QUESTIONS. 
 
 II*' 
 
 iii: 
 
 494. Nature and charact,,rs of the remains of man found in the high-level 
 gravels ? 
 
 41)5. Conclusions dcducible from the remains of these gravels as to the 
 auticjuity of the human race ? 
 
 4!)6. Mode in which caverns in limestone are produced ? 
 
 497. Mode in which various deposits have been introduced into caverns? 
 
 498. Mode in which cave-deposits have been preserved ? 
 
 499. Chief extinct Mammals of European caves ? 
 
 500. Remains of man in cave-deposits ? 
 DOl. Mammals of tlie Australian caves ? 
 
 502. Extinct Mammals of Brazilian caves ? 
 
 503. Jiecent period, how characterized ? 
 
 504. Age of Stone, liow characterized ? 
 
 505. How are the Paleolithic and Neolithic periods distinguished ? 
 
 506. VViiat animals accompany the reniaiiis of man in the Later Stone age ? 
 
 507. Age of Bronze, how characterized ? 
 
 508. Are there any traces of an age intermediate between the Age of 
 Stone and that of Bronze ? 
 
 509. Age of Iron, how characterized ? 
 
 510. Kitchen-middens ot Dciuuark ; what arc they, and to what age do 
 they belong ? 
 
 511. Age of the Danish peat? 
 
 612. Nature and age of the Swir-g Lake-dwellings? 
 518. How may the scarcity of human bones in Recent deposits be partly 
 accounted for ? 
 
 514. What two types of skull are recognizable in the earlier races of man? 
 
 515. What type of skull characterizes the men of the Later Stone age? 
 610. Mode of occurrence of volcanic and trappean rocks. 
 
 517. What are the principal tests of the age of a volcanic or trappean 
 rock? 
 
 618. ^Vliat is meant by a "contemporaneous " trap? 
 
 619. What is meant by an "intrnsive" trap? 
 
 620. ITow would j'ou distinguish a contemporaneous trap in practice ? 
 521. How would you distinguisli .in intrusive trap in practice? 
 
 622. What eflects are produced by a trap-dike upon the rocks through 
 which it cuts ? 
 
 623. How is the dike itself affocted ? 
 
 624. Are traps of one or many ages ? 
 
 625. How do the granitic rocks usually present themselves in the field ? 
 526. How can it be shown that granite is often intrusive ? 
 
 627. Have we any reason to believe in a "primeval" granite? 
 
 628. Can we point to any sucli " primeval " granite ? 
 
 629. What i)'.variable relation subsists between granite and the stratified 
 rocks of any given region ? 
 
 630. Can granite be shown to be ever an " overlying" rock ? 
 
 631. Principal Jests as to the ago of any given mass of granite? 
 
 632. General phenomena of granitic veins ? 
 
 533. General phenomena of the metamorphism produced by granitic 
 masses ? 
 
 634. Are granitic rocks of one or of many ages? 
 
 635. Chief regions in which Metamorphic rocks present themselves? 
 
 636. How have the Metamorphic rock.^ a twofold age ? 
 
 637. By what tests may the age of a Metamorphic rock be detected ? 
 538. Are Metamorphic rocks of one or of many ages? 
 
QUESTIONS. 259 
 
 639. In what chief \vay3 do rnln* al deposits occur? 
 
 540. Define a mineral vein or "lode." 
 
 541. What connection obtains between lodes and faults? 
 
 542. How can it bo shown that most lodes are really lines of fault? 
 
 643. What is meant by " vein-stulV" or "f:an;;uo? " 
 
 644. What materials occur most commonly in mineral veins? 
 
 645. IIow do the metals usually occur in veins ? 
 
 54('). What is the most generally accepted theory as to the mode in which 
 veins have been produced ? 
 
 547. IIow do the phenomena of hot-springs bear on the formation of 
 mineral veins ? 
 
 548. How can it be shown that veins are of all ages ? 
 
 •i 
 
 
 ;!■'! 
 
1 f 
 
INDEX. 
 
 mi 
 
 Acrogons, 120. 
 
 AdiantifcH Jlibernicus, 144 
 
 Age of Kroi)Z.\ 230, 23'i, 233. 
 
 Age of Iron, 231-233. 
 
 Age of 8tone. 230. 232. 
 
 Air-breathers in Coal, 159. 
 
 Alabaster, 67. 
 
 Albite, 71. 
 
 Alluvial deposits. 222; Pwecent, 223; Post- 
 Pliocene, 216, 222. 
 
 AUuviuin. (lotlned, 222. 
 
 Alpine erratics, 33. 
 
 Alps, glaciers o^ 38 ; Nummulitic Limestone 
 of, 201. 
 
 Alteration of Metamorpliic liocks, 57, 78. 
 
 Alternation of ditferent rocks, 4S. 81). 
 
 Alum Schists, of Sweden, 127, 130. 
 
 America, Laurentian Rocks of, 124; Iluro- 
 nian Rocks of, 126; Cambrian Hocks of, 
 127; Silurian Itocks of, 136; Devonian 
 Kocks of, 145; Carboniferous liocks of, 
 150; Permian Eocks of, KB; Triassic 
 Kocks of, 170; Jurassic IJocks of, 180; 
 Cretaceous Kocks of. 102 ; Kocene Rocks 
 of. 200 ; Miocene Kocks of, 207 ; Pliocene 
 Kocks of. 214; Glacial deposits of, 221. 
 
 American forms in Swiss Miocene Flora, 210. 
 
 Ann)toniten. 118, 173. 
 
 liuckliindi, 175. 
 
 j)lanorbi«,\1b. 
 
 IfumphreMunus,!'!'!. 
 
 Amphibia, 118. 
 
 Amphiojon, 203. 
 
 Amphitherium, 178. 
 
 Amygdaloid, defined, 74 
 
 Ancyloceras, 188. 
 
 Oiff<t'^, 187. 
 
 spinigerum, 189. 
 
 Angiosperms, 120. 
 
 Animal Kingdom, classiflcation of, 112-120. 
 
 Annuloida, sub-kingdom of, 114 
 
 Annulosa, sub-kingdom of, 115. 
 
 Anodonta Jukesi, 144 
 
 Anogeus, 120. 
 
 Anop/otherium,2(^2. 
 
 Anorlhite, 71. 
 
 Anthracite, 1.55. ' 
 
 Anticlinal curves. 96, 108. 
 
 Antwerp Crags, 214 
 
 Apioi'Hnifeg rotnndus, 178. 
 
 Aqueous Kocks, 49, 00; origin of, 50, 51 ; flu- 
 viatile, 62; lacustrine, 52; marine, 52; 
 
 classes of, 60-63; different ages of, 109; 
 chronological succession of; 121 ; mala sub- 
 divisions of, 122. 
 
 Ardchnidii^ 11.5. 
 
 Aralo-Caspian Post-Tertiary deposits. 214 
 
 Archaoptenjx nutcrura, 180, 182, 184. 
 
 A rdi e gom n run lu in or. lOO. 
 
 Arenaceous 'It^cks, characters of, 61, 62. 
 
 Argilia<;eous Kocks, characters and varieties 
 of, 6;i, ()4. 
 
 Artesian wells, 4. 
 
 Articulate animals, 115. 
 
 AmiphuH ii/ntnrniM. 1.3.3. 
 
 Ashes, fel.spathic, 73; trappean, 70,73; vol- 
 canic, 1.5. 19, 70. 
 
 Axtarte borenlis, 220. 
 
 Asteroids, 114. 
 
 Atlantic ooze, nature of, 43; organic bodies 
 of, 43, 194 
 
 Atolls, 45. 
 
 Augite, 71, 72. 
 
 Augitic lavas, 78. 
 
 Australia, cave-deposits o^ 229. 
 
 AveK 119. 
 
 Arivuld contoi'ta. 169, 170. 
 
 " Avicula contorta " beds, 169, 170. 
 
 Azoic Series, 125. 
 
 Baculitea, 190, 196. 
 
 ancepx, 190. 
 
 FavjoKii. 190. 
 
 Bala Beds of Britain, tliickness and fossils of, 
 
 133; American equivalents ot; 137. 
 Bala Limestone. 1:33. 
 Barrier-reefs, 45. 
 Basalt, 72, 73 ; columnar. 82, 88. 
 Basst't edges of strata, 94. 
 i?<'/f»in?7M, 117. 173. 175. 
 
 elongatun, 175. 
 
 hantittuH, 179. 
 
 Binrs-eye T^imestono, 138. 
 
 Bituminous Coal. 15.5. 
 
 Bivalve Shell-fish, 117. 
 
 Black-River Limestone, 138. 
 
 Bombs, volcanic, 1.5, 
 
 Bone-bed, of Ludlow Rocks, 136 ; of Khsetlc 
 
 beds. 169. 
 Bovey Tnicy, lignites of. 205. 
 BowIderclaV, 217, 219, 220; of Scotland, 218, 
 Bowlders, erratic. 37, 88, 40, 217-219. 
 Brachiopodn, 116. 
 Brazil, cave-dejiosits of, 229. 
 
 ill 
 
262 
 
 INDEX. 
 
 M 
 
 Broroia, dpfinldcm of, C2. 
 
 Iirick-o;irth, 22'J. 
 
 ISritJiin, I^iurentian Rocks of, 125; Cnmbrlan 
 Ko<-ks(»e m>, Silurian Hocks of, 13'2; De- 
 vonian lio<'ks of. U'i, 145; Carbon Ifurous 
 liocks of, 150; Pcrniiau iio(!ks of Wy; 
 Triassic Hocks of, ICs, 109 ; Jurassic l!ock» 
 of, 174; ('retaceous Hocks c.f, 185; Eocene 
 Hocks of, 199; Miocene Hocks of, 205; 
 Pliocene Hocks of, 211 ; Post-Tertiary de- 
 posits of, 21G, 217. 
 
 Brown-Coal, 208. 
 
 BunttT-Sandstein, of Britain, 1G3; of Eu- 
 rope, 1C7 ; fossils of, 163. 
 
 Calamite^, 156. 
 
 C(inn<rformi.% 156. 
 
 Sucoini, 15(i. 
 
 C'alcalro Grossicr, 200. 
 
 Calcareous Hocks. 64-06; Tarietics of, 64-66. 
 
 Caharina rarMpina, 200. 
 
 Calceola HarulaHna, 145. 
 
 Calciferous Sand-rock. 127, l-W. 
 
 Cambrian Hocks, 126; of Britain, 126.127; 
 
 of Nortlj America, 127; of Sweden, 127; 
 
 of Bohemia. 127 ; fossils of, 128-130. 
 Cnradoc Hocks, 1.32. 
 Carboniferous Limestone, 150, 151; fofisils 
 
 of, 151, 1.52. 
 Carboniferous Rocks, 150; of Britnin. 151, 
 
 154; vef,'etation of; 155-157: animal life of 
 
 151, 160, 101. 
 Carboniferous Slates, 1.51, 
 Carchcrodon futerodon, 201. 
 Cardium li/ucticiiTn, 109, 170. 
 Catistrophists, doctrine of, 46. 
 Catskill Sandstone, 146, 147. 
 Cave -bear, 228. 
 Cave-hyena, 228, 229. 
 Cave-lion, 228. 
 Caverns, origin of, 226; deposits In, 226, 227 ; 
 
 fossil Mammals of, 228, 229. 
 Centipedes, 115. 
 Cephalaspis Lyellii, 143. 
 Cephalopoda, 117, 118. 
 Ceratltes, 168, 172. 
 C'eratites nodoau«, 109. 
 Cerithium, 200. 
 Chalk, 64. 
 Chalk-marL 189. 
 Clialk, White, 189; of Britain, 189; origin 
 
 of, 194; fossils of, 189, 19u; of Southern 
 
 Europe, 192. 
 Chumocrops JTelrefica, 209. 
 Ch-izy Limestone, 137, 138. 
 Cheirotheriiwi, 168. » 
 
 Chemically-formed i-ocks, 64. 
 Chemung Group, 146, 147. 
 Chert, 66. 
 
 Cherty Limestone, 66. 
 Cularw j/apill(itii. 115. 
 Chinamommn poli/uiorphum, 210. 
 Clay, chemical composition ofi 63; definition 
 
 of. 63. 
 Clay-slato, 64. 79. 
 
 Cleavage, definition of 84 ; distortion of fos- 
 sils bv, 86; artificial production of; 87; 
 
 origin' of 86. S7. 
 Clinton (iroun. 137, 13S. 
 Club-niOK8e8.'l20, 1.56. 
 Clymenia linearis, 149. 
 
 Coal, 43; composftion of; C7: origin of, 
 
 158; plants oi; 155; underclays ot; 154, 
 
 l.'i.s. 
 Coal-measures, general characters of, 154; 
 
 of Wales, 154; production of, 15S; foasils 
 
 of 1.%, 160. 
 CoMioduH eov tortus, 153. 
 Cu'lenterate Animals. 113. 
 ' Columnar Jointing. 82, 83, 
 Columnar Trap, 82, &3. 
 Conformabiiity. 99. 
 Conglomerate', 62. 
 Coniston Group, 132, 183. 
 Continental ice. 39. 
 
 Contortions of strata, 95; causes oi; 97. 
 Corallijie Crag, 211, 212, 
 Coral Hag 178. 
 Coral-reel's, 44, 45. 
 Coral-rock, 45. 
 Corals, 44, 113. 
 
 Corniferous Limestone, 146, 147. 
 Coryphoilon, 200. 
 Crater, of volcano. 12. 
 Cix>taceou8 Hocks, 185; 8ubdi^^sio^^ of; 185; 
 
 of Britain, 185, 1S6; of Europe, 192; of 
 
 North America. 193; fossils of, 195. 
 Crevasses, of glacier, 35. 
 Crinoids, 114. , • , 
 
 Cromer Forest-bed, 216. 
 Cross-stratification, 91. 
 Crust, of earth, definition o^ 48; successive 
 
 formation of, 49. 
 CruHtaced, 115. 
 Cryptogamlc plants, 120. 
 Crystalline Schists, 56. 
 Curved strata, 95. 
 
 Cycads, 120, 172, 181. 
 (yproea Europoaa, 212. 
 Cystid.ans, 1,38, 139. ■ 
 
 Vytliere iiiflata, 161. 
 
 Deinmauria, 182, 187, 196. 
 
 DeinotheHum giganteum, 206. 
 
 Deltas, how formed, 27; of Ganges, 28; of 
 
 Mississippi, 23; of Nile, 28. 
 Density, mean, of earth, 5. 
 Denudation, definition of, 23; agents of, 23; 
 
 by rain, 24; bv rivers, 24-28; by the sea, 
 
 28-30; byi?e, 31-4L 
 Derivative Hocks, 61. 
 Desiccatioii-cracks, 93. 
 Devonian Rocks, 142; of Britain, 146; of 
 
 North .\merica, 146; fossils o^ 145, 147. 
 Diagonal stratification, 91. 
 Dicotyledonous plants. 121. 
 Didymorjrapmti* patuht«. 132. 
 DikelocephaliiH MinnenotenMs, 12S. 
 Dikes, volcanic, 20, 69; trappean, 54; mota- 
 
 morphism produced by, ^8, 239. 
 Diorite. "3. 
 
 Dip, of inclined strata, 94. 
 Dislocations (we Faults). 
 Di\ isional planes, of roclcB, 80. 
 Dolerite. 72. 
 Doleritie lavas, 72. 
 Dolomite. 66. 
 Drift, 217, 218. 
 Drlft-gravela, 2ia 219. 
 
 ' 
 
INDEX. 
 
 263 
 
 Drv land, oripln of, 7, 9 ; distribution oi; 9 ; 
 
 fi'atuiTii of, 10. 
 Duues, 4{>. 
 
 Earth, flpuro and dinnpnslons of, 2, 3 ; plane- 
 tary niations of, 2; mean density of, 5; 
 fluidity of interior of, G ; primitive condition 
 of, 3, 4; internal temperature of, 4; sur- 
 face-conjuration of, 6,7; movements of 
 crust of, S, 9. 
 
 Eartliqual<e>i, general phenomena of, 21, 22; 
 causes of. 21. 
 
 Eartliquaiie-wavcs, 22. 
 
 /•MiiKxierTnata, character and types of, 114. 
 
 Ecliinoids, 114. 
 
 JCchiiio(iph(X7-ite« Balticus, 13!). 
 
 Elephants, fossil, 207, 210. 224, 228. 
 
 Elephaa antiquus, 216, 224. 
 
 meridioruilw, 216, 217. 
 
 primiffenius, 217. 224, 228. 
 
 EncrinuH UHiYormui, 16'J. 
 
 Endogenous plants. 120. 
 
 Eocene Uocks, 193. 199; of Britain, 199-201'; 
 of North America, 200, 202, 203 ; fossils of, 
 203, 204. 
 
 Eoeodn Canaden-He. 126. 
 
 Equisetacea. 120. 156. 
 
 Erratic bowlders. 37, 38. 
 
 Eruptions, volcanic, general phenomena o^ 
 14; causes o^ 20. 
 
 Eurite, 77. 
 
 Eury})teHda, 115, 140, 148. 
 
 Exogenous plants, 120. 
 
 Extracrinus Briareua, 176. 
 
 False-bedding, 91. 
 
 Faluns (Miocene), 205. 
 
 Faults, definition of, 103 ; general phenomena 
 
 o^ 104, 105; displacement of strata by, 103; 
 
 throw of, 104; hade of 104; origin oi, 103; 
 
 denudation oC 105; connection of, with 
 
 mineral veins, 105, 244 ; repetition of strata 
 
 by, 107. 
 Fa'roHites Gothlandica, 135. 
 FaxOe Limestone, 192. 
 Felspar, composition o^ 71 ; varieties o^ 71. 
 Felspathic ashes, 73. 
 Felspathic lavas, 72. 
 
 Felspathic traps, 73. , 
 
 Felstones, 78, 
 Fire-clay. 63. 
 Flag, definition of, 64. 
 Flag-stone, 64. 
 Flint implements. 225. 
 Flints, origin of, 194. 195. 
 Foliation, structure of, 78, 87 ; origin o^ 88. 
 Foraminifera, 112. 
 Formation, definition of, 52. 
 Fos.sil, definition of, 52. 
 Fossiliforous Kocks, 49, 62. 
 ]<Yinging-reefs, 4^. 
 Frost, as a denuding agent, 41. 
 FtUgur canaliculntus, 207, 208. 
 Fuller's Earth, 167. 
 Fumarolas, 16. 
 
 Fundamental Gneiss, of Hebrides, 126. 
 Fundamental Granite, theory of, 240, 241. 
 FuHiM guadficostatiM, 207, 208. 
 - ■■ contrarius, 212. 
 
 Galeritea albogalerm, 191. 
 
 Oangnc, 245. 
 
 GdKieropoda, 117, 
 
 Gault, IbH. 
 
 Geology, definition of, 1, 48. 
 
 Glaciiil'Deposits, 39, 216, 217. 
 
 Glaciation, of Scotland, 218; of 'Walos, 220; 
 of Greenland, 39. 
 
 GLiciers, formation of. 81, 32; movement of, 
 32, 33; nioraini'S of. 3i^. !M; crevasses of, 
 35: ctl'ect oJ, on the surfaces over which 
 they move, 85, 86 ; in high latitudes, 89. 
 
 Glacier streams, 83, 39. 
 
 Gneiss, 78. 
 
 Goniatites, 149, 153. 
 
 creniittria. 158. 
 
 Granite, composition ot 75; crystallization 
 of, 75, 76; metaniorphism produced by, 
 242; veins of, 24l; p.issago into trap, 7«; 
 difforcnt .iges of, 242. 
 
 Granitic Uocks, characters of, 64. 75; varie- 
 ties of, 77 ; origin of, 50, 70 ; different ages 
 of, 242. 
 
 Graphite, in T^urentian Rocks, 124. 
 
 Gr<tptolite.% 113, 129, 132, 133, 14S. 
 
 Gravola, high-level, and low-level, 223, 224. 
 
 Great Ooliti', 177. 
 
 Greenland, glaciation of, 39, 40. 
 
 Greensand, 185; Lower, 187; Upper, 188. 
 
 Greenstone. 73. 
 
 Greenstone ashes, 73. 
 
 Grit, 61. 
 
 Gritstone, 61. 
 
 Gri/phcea inottrra, 175. 
 
 Gymnosperms. 120. 
 
 Gypseous marls. 67. 
 
 Gypseous Series, of Montmartre, 203. 
 
 Gyi)sum. 07. 
 
 Gi/rolepin (eiiuistriat'i«, 170. 
 
 Hade (of vein or fault), 104. 
 
 Ihidronaurufi, 196. 
 
 Ildlj/mteH catennUiriuK, 136. 
 
 Hamilton Group, 140, 147. 
 
 Hariech Grit.s. 127, 180. 
 
 Helderberg Group. Lower, 138; Upper, 146. 
 
 J/ippopotamna, 210, 224. 
 
 JlippuriteH. 192. 
 
 organimmn. 193. 
 
 Hippuritic Limestone, 192, 
 
 IIoloptijchiuH, 144, 147. 
 
 Hornblende, composition ot, 71 ; relations of 
 
 to aiigite, 71. 72. 
 Hornblende-schist, 78. 
 Hornblendlc gneiss, 78. 
 
 trap.s, 73. 
 
 Hornstone, 147. 
 Horse-tails. 120, 156. 
 Iludson-IIivcr Grou^), 187. 
 lluronian Kocks, 12b. 
 Ilyanodon. 202. 
 HyboduH pHadilis, 170. 
 
 reticuhtius, 176. 
 
 Hydraulic Limestone, 66. 
 IlymenocaviH rerwicauda, 129. 
 Hypogene Rocks. 58. 
 I/i/racotherium, 200 
 
 Ice, as a denuding agent, 31-41. 
 Ice, continental. 89. 
 
 Icebergs, 8S, 89; origin of, 89, 40; size o^ 
 41 ; transport of rocks by, 40, 41. 
 
264 
 
 INDEX. 
 
 I I 
 
 E'! 
 
 IchthyoHnuruK, 182, 196. 
 
 eom7nunin, 18;). 
 
 Iffuanofton, 186, 187, 196. 
 
 M<tntellii, 187. 
 
 Incliniitlon of beds, 93, 94. 
 Inferior Oolito, 177. 
 Inoceramu/i Lamarckii, 190. 
 Itmectay 116. 
 
 Joints, 81, 82 ; nnturo of, 81 ; causes o^ 82 ; 
 
 columnar, 82, N). 
 Jurassic Koclts, 174; divisions of, 174; of 
 
 Europe, 174; of North America, ISO; fos- 
 
 bUs of, 180-184. 
 
 Kalnozoic Period, 123, 197. 
 Kaolin, 63. 
 
 Keuper, 107, 169; fossils of, 169. 
 Kiiniiioridfre Clay, 170. 
 Kitchen-middens, 231. 
 
 Labrador Felspar, 71. , 
 
 Labradorite, 71. 
 
 Labrador Hocks, 126. 
 
 jAibi/riiithodontH, 159, 162, 163. 
 
 Lalce-dwellings, 282. 
 
 Lamellibrandiiatd, 117. 
 
 Ijaminu) of deposition, 50, 80. 
 
 Lateral shift, of faulted beds, 106, 107. 
 
 Laurontian Kocks, 124; of North America, 
 124; of Britain, 125; life of, 125. 
 
 Lava, 15, 16, 72; moveuionts ot; 16; dikes 
 of, 20. 
 
 Leda oblonga, 220. 
 
 Lepkioi/eiy/roii, 1.55. 
 
 Sternberai. 155. 
 
 LenidmtrobiiH, 156. 
 
 Lias, 174; fossils of, 175, 176. 
 
 Lijfhtiiinff, volcanic, 15. 
 
 Lif,'nit<s 205, 208. 
 
 Lime-felspar, 71. 
 
 Limestone, 64; weathering of, 24,42; varie- 
 ties of, 65; oripin of, 64, 68; how recog- 
 nized in the field, 66. 
 
 JAinuluH rotuvdatxui, 161. 
 
 Lingula ana Una, 116. 
 
 Orednerii, 165. 
 
 DavMi, 129. 
 
 LlnguIa Flags, 126, 131 ; fossils of, 129. 
 
 Lithodrotioii baJtalti/orme, 152. 
 
 Llanberis slates, 127. 
 
 Llandeilo Kocks, 132; Lower, 132; Upper, 
 132. 
 
 Llandovery Rocks, 182; Lower, 133; Upper, 
 134. 
 
 Loam, 63. 
 
 Lodes (nee Mineral Veins). 
 
 Loess, of Rhino Valley, 222. 
 
 London Clay, 200; fossils of, 200. 
 
 Longmynd Rocks, 126. 
 
 LotMda/eia florifonnis, 162. 
 
 liOwer Helderberg Group, 138. 
 
 Ludlow Rocks, 132; of Britahi, 184; of North 
 America, 138. 
 
 Zycopodiacece, 120, 155. 
 
 Maehairodu«, 208. 
 
 Maestrlcht Chalk, 191 ; fossils of. 191. 
 
 Magnesiun Ihnestone, 66 ; liow distinguished, 
 
 66, 67; of the Permian series, 164. 
 Mammals, 120. 
 
 Mammoth, 216, 222, 228. 
 MarbUt, 05. 
 Marl, m. 
 Marl-slate, 63. 
 Mimtodon. 21 16, 207. 
 
 ttrvetiienxiit, 213. 
 
 Meehaniciilly-fonned rocks, 60. 
 
 3fc(/ii/(Hlon c.ucullatus, 148. 
 
 MeyitUiHaurnH, 182. 
 
 Melaphyre, 73. 
 
 Mesozoic Perioil, 12.3, 167. 
 
 Metallic ores, modes of oc(!urrenco of, 244. 
 
 Metjmiorpliic Limestone, 79. 
 
 Metamorphic Rocks, 56, 78; structure of, 
 
 57, 78 ; origin of, 57, 78 ; varieties of, 78, 
 
 79 ; su('cessive formation of, 243 ; different 
 
 ages of, 242. 
 Metamorphism, theory of 78; produced by 
 
 trap, 23!» ; by granite, 242. 
 Mica, 76. 
 Mica-schist, 79. 
 
 MicrtiHter cor-anffuinum, 191. 
 Microle-ate-n antiqum, 170. 
 Millstone (Jrit, 153. 
 Minoralog}', delluition of 1. 
 Mineral veins, 244; origin of, 246; contents, 
 
 245 ; connection with faults, 105, 244 ; ages 
 
 of, 246. 
 Miocene Rocks, 198; of Britain, 205; of 
 
 France, 205; of Switzerland, 206; of North 
 
 America. 207 ; life of, 207. 208. 
 Molas.se, 206; fossils of, 207-209. 
 JfoUiuica, sub-kingdom of, 116. 
 Monocotylcdouous plants, 120. 
 Moraines, 33-85; lateral, 33; medLin, 33; 
 
 terminal, 84 ; structure of, 34, 85 ; striated 
 
 blocks of, 38. 
 Moftaminrus Camperi, 192. 
 Moulins, 38. 
 Mountain Limestone, 150, 151 ; fossils of, 
 
 151-153. 
 Mountains, of Old World, 10 ; of New World, 
 
 10; kinds of, 10-12. 
 Muschclkalk, 167, 168 ; fossils of, 168. 
 Jlyriapoda, 115. , 
 
 Nasna granulata, 212. 
 
 Xiitica clcuma, 220. 
 
 Nautilus, Pearly, 118, 149, 175. 
 
 KautUu« plicattis, 183. 
 
 Neocomian group. 187. 
 
 Neolithic period. 280. - ' 
 
 New Red Sandstone, 163. 
 
 Niagara Falls, 25. 
 
 Niagara group, 137, 188 ; fossils of, 13T. 
 
 Northern Drift, 217. 
 
 Norwich Crag, 218 ; fossils of, 213. 
 
 Nummulites, 201. 
 
 Pmchi, 201. 
 
 Nummulitic Limestone, 201. 
 
 Oblique lamination, 91. 
 
 Obsidian, 72. 
 
 Ocean, distribution of, 9 ; denudation effected 
 
 by, 28-30. 
 ^ffl/ffin BxicMi, 1-33. 
 Old Red Sandstone, 142 ; of Scotland, 143 ; 
 
 divisions o^ 143 ; fossils oi; 143, 144 ; of 
 
 Irt'land, 144. 
 Oldhamia aniiqua, 123. 
 Olenwa micrurw), 129. 
 
mmm 
 
 INDEX. 
 
 265 
 
 of, 244. 
 
 uctxirc of, 
 ;lcs of, 78, 
 ; different 
 
 xluccd by- 
 
 contents, 
 244; uges 
 
 205; of 
 of North 
 
 (lian, 33; 
 ; striated 
 
 bssils of, 
 jr World, 
 
 *- 
 
 J7. 
 
 effected 
 
 d. 143; 
 44; of 
 
 OHpoclnflP, Tl. 
 
 (hnphi/inii turfdnatum, 135. 
 
 Onchm fennhtriiifiiM, 136. 
 
 Oneida eon^'loimrate, 137. 
 
 Oolite, ()(5; (Jrcat 177; Inferior, 17T. 
 
 Oolitic- liocks (wf Jurassic Kocks). 
 
 Ooze of Atlantic hed. 194. 
 
 Orfranieally-f'orined rocks, 64. 
 
 Oriskany Sandstone, 146. 
 
 OrihtH e/c(/<iiitii/(i, 135. 
 
 tricerxtria, VVi. 
 
 peHjierfilio, 133. 
 
 OrthoceniH, 140. 
 
 Ludense, 141. 
 
 Ortlioclase, 71. 
 Ontrea dintorta, 179. 
 Otodns ohliguu«, 201. 
 Outcroj) of bo<ls, 94. 
 Overlap, 100. 102. 
 Overivinpr liocks, 234. 
 Oxfonl Clay, 178. 
 
 Pahrolitliic period, 225. 
 
 PalifoinHciiH, IOC). 
 
 Palaoiitolofjy. (ieilnition of, 1. 
 
 7'rt/(rrv>/iw, 200, 202. 
 
 I'alwotherium magniitn, 203, 
 
 Paltt'ozoic epocli, 123. 
 
 J'aradoxideH Bohemiciifi, 128. 
 
 Peat, 43 ; of Denmark. 231 . 
 
 Pevten Valouien^i^, 169, 170. 
 
 Jacohce.us, 214. 
 
 Mandiout, 220. 
 
 PentameniM, 184, 138. 
 
 Iceina, 134. 
 
 Pentremitett. 152. 
 
 I'erclied block.s, 37. 
 
 Permian Kocks, 163; of Britain, 161; of Ger- 
 many, 104; of Nortli America, 164; name, 
 how derived, 163. 
 
 Perpetual snow, line of, 31, 89. 
 
 Phacops latifrons, 145. 
 
 Pliancrogamic plants, 120. 
 
 Phoacolotheriitm Bucklandi, 17S. 
 
 Physical Geography, deflnition of, 2. 
 
 Pipe-clay, 63. 
 
 Pisces, 118. 
 
 Pisolitic Limestone, 66. 
 
 Plagiaulax 7)iin&r, 180. 
 
 Planes, of deposition, 80 ; of jointinp, 81 ; oi 
 cleavape, 84-86; of foliation, 87, 88. 
 
 Plaster of Paris, 203. 
 
 Platitnim aceroideJt, 210. 
 
 J 'isiomuriiK 182, 196. 
 
 dolichodeiruti, 183. 
 
 Pliocene Kocks, 198; of Britain, 211; of 
 North America, 214; fossils of. 215. 
 
 Plutonic Rocks, characters of, 54, 75; origin 
 of, .56, 59 ; varieties of, 75 ; successive for- 
 mation of, 242. 
 
 Porcelain Clay, 63. 
 
 Porphyritic lav.i.s, 72. 
 
 Porphvrv. deflnition o^ 74. 
 
 Portland' beds. 179. 
 
 Post- Pliocene beds, how characterized, 216; 
 in Kritjiin, 216, 222. 
 
 Post-Tertiarv Kocks, how characterized, 216; 
 
 Potash-felspar, 71 
 
 Pothole.H, 27. 
 
 Potsdam .Sandstone, 127; fossils o^ 127. 
 
 Primary Limestone, 79. 
 
 Primary Rocks, 123. 
 Primitive Kocks, 58. 
 Primordial zone, of Bohemia, 127; fossils of 
 
 127. 
 Producttt, 152, 165. 
 
 /torridd, 165. 
 
 net/ii reticulata, 153. 
 
 Protichniten. 129. 
 Protojfine, 77 ; stratified, 78. 
 Pr<itr>roH(iHrUH. 168. 
 Protozoa, 8ub-kin>,'(lom oi, 112. 
 Pteranpi/i, 135, 14;^. 
 
 Bankdii. 130. 
 
 Pterodactyle, 182, 196. 
 Iterodactijlun cramirontriA, 180. 
 Iterophi/ilum comptiini, 177. 
 Iterosnuria, 182. 
 I^eri/dotiiH Angiicus, 116. 
 Pumice, 73. 
 
 Purbeck beds. 179 ; fossils of, 179, 180. 
 Purpura fetragona, 212. 
 Pyrula reticulata, 212. 
 
 Qna-qiKl-versal inclination of beds, 96, 97. 
 
 (Quartz, 75, 79. 
 
 (iuartzite, 79. 
 
 (iuartz-rock, 79. 
 
 (Quaternary perio<l, 216. 
 
 Quebec group, 127, 130 ; fossils of, 129. 
 
 R.iin, ns a denuding agent, 23, 24. 
 
 Uain-i»rints, 93. 
 
 Recent deposits, how characterized, 199, 280. 
 
 Red Crag. 211, 212; fossils of, 212, 213. 
 
 Reindeer period, 229. 
 
 Jleptilia, 119. 
 
 Rha-tlc beds, 169 ; fossils of, 169, 171. 
 
 Iihinoceru« tichorhinu/*, 223, 228. 
 
 IthisocrinuN Lofotomis, 114. 
 
 Jihynchonella haricula, 135. 
 
 WilHoni, 135. 
 
 Rlpple-mark. 92. 
 
 Rivers, as denuding agents, 24-28. 
 
 Kivcr-vjiUeys, characters of, 26, 27. 
 
 Roches mo'utonnce.s, 87. 
 
 Rock, definition of, 49. 
 
 Rocks, classiflcation of, 49 ; Aqnoous, 49, 60, 
 89; Sub-aerial, 43; Volcanic; 53, 69; 
 Trappean. 54, 69; Plutonic, 5i. 75; Gra- 
 nitic, 54, 75; Metamorphic, 66, 78 ; Hypo- 
 gene, 58. 
 
 Rock-salt, 67 ; origin of, 172. 
 
 Roollng-slate, 64, 79. 
 
 Sabal major, 209. 
 
 Saccharoid limestone, 65. 
 
 Salina period, 137, 138. 
 
 Salt, 67. 
 
 Sand. 61. 
 
 Sand-dunes, 43. 
 
 Sandstone, 61. 
 
 SuurichthyH apicalin, 170. 
 
 fildxicara rugoNd. '220. 
 
 Scap/iitfn cetjiiali)!, 101, 
 
 Schist, H8. 
 
 ScoriiP. 15. 73. 
 
 Scorpions. 11.5. 
 
 Sea, as a denuding agent, 28-30. 
 
 Sea-cliffs, 29. 
 
 Se.a-urchin.s 1 14. 
 
 Secondary Rocks, 123, 107. 
 
 :i! 
 
 Jit' 
 
266 
 
 INDEX. 
 
 Scdlmrntary Rooks (we AqncouB Hocks), 
 
 Ke/puna ( '<ruttni(B, 205. 
 
 8hule, 6!i, W). 
 
 8hi'll-»HMl8. Ai\. 
 
 Shcll-tlsh, U(i; Bivnlvo. 117, Univalve, 117. 
 
 fiiiiUlariM, 147, Ms, mO. 
 
 SiyiUarui <7iemu7igen«i«, 148. 
 
 ieriffatii, ir)7. 
 
 SlliiilanlJocks, 131; of Britain. 132 ; of North 
 America, 186, IMS; life of, 138-141. 
 
 Bklddaw .Slates, 127, 180; fossils of; 129. 
 
 Slate, S.5, 88. 
 
 Slaty ckuivaffo (see Cleavage). 
 
 SllckcnsidcH, 105. 
 
 Soda-felspnr, 71. 
 
 8i)lders, ll.^. 
 
 tSpirifer, 145. 
 
 (ihjimctu.R, 145. 
 
 ql(ihei\ 161. 
 
 (riflonah'jt, 161. 
 
 Spirolina itenoatoma, 200. 
 
 Sponpoa, 113. 
 
 Stalactites. 05. 
 
 Stalaffinltes. Ki. 
 
 Statuary niai-Me, e,"), 79. • 
 
 StereogniithuH, 178. 
 
 Siifftnarid, 156. 
 
 ficokfes, 157. 
 
 Stone-lily, 114, 169. 
 
 BtraLi, orlj^lnal horlzontality ot, 90; lateral 
 extent of, 89 ; alternation of, 49, 89 ; dip of, 
 93, 94; strike of, 94; outcrop of, 94; con- 
 tortions of, 95. 
 
 Stratification, 49, 50, 80. 
 
 Stratified protoffin(>, 78. 
 
 Stratified IJwks, 49; origin of, 50-52. 
 
 Strike, of beds, 94. 
 
 Stripe, of slate, 85. 
 
 Strophomena grandis^ 133. 
 
 Bub-aorial IJocks, 43. 
 
 Sub-Apennine beds, 214. 
 
 Sub ( larbonlferous Limestone, 150. 
 
 Syenite, 77. 
 
 Syenitic pnelss, 78. 
 
 Synclinal curves, 96, 97, 108. 
 
 Talc, 77. 
 
 Talcoso pneiss, 73. 
 
 Talcose pranito, 77. 
 
 Temnechintts excnratn^, 212. 
 
 Temperature, internal, of earth, 4. 
 
 Tertiary period, 128, 197. 
 
 Tertiary Kocks, classification of, 198. 
 
 Tetragrapsun hryonoides, 129. 
 
 Thallopons, 120. 
 
 Thecoftmilia annularis, 179. 
 
 The/odm (shapreen scales of), 186. 
 
 Thinninp out, of beds, 89, 90. 
 
 Throw, of faults, 104. 
 
 Till, 217, 218. 
 
 Trachvtic lavas, 72. 
 
 Trap, '69, 73 ; weathering of, 42. 
 
 Trappean ashes. M. 
 
 Triippean breccias, 70, 73. 
 
 Trappean dikes, 238. 
 
 Trappean Rocks. .%% 54, 73; origin of, N3, 
 54; ajfcs of, 239; contomiM)nineous. 237: 
 Intrusive, 287; metomorphlsui produced 
 by, 238, 239. . 
 
 Trap-tulf, 70. 
 
 Travertine. 65. 
 
 Tn inadoc Slates, 127. 
 
 Trenton Limestone. 137 ; fossils of; 137. 
 
 Trenton period, 136, 188. 
 
 Triassic Kocks. 167; of BriUIn, 168, 169; of 
 Kurope, 167-169; of North America, 170; 
 fossils of, 172. 173. 
 
 Trilobltes, 115, 139, 158. 
 
 TtinndeuH conceutricus, 140. 
 
 Trocfioceras gigovteui^. 141, 
 
 Trophon clathratum, 220. 
 
 Tufa, 65. 
 
 Tuir, volcanic 73. 
 
 Tnrriliffn, 190, 196. 
 
 cmtdtus, 190. • 
 
 TTnconformability, 99-101. 
 Tlnderlyin),' rocks, 56. 240. 
 Ilniforinitarians, doctHnes of, 46. 
 Univalve Shell-fish, 117. 
 Utlca Slate, 187. 
 
 Valley -deposits, high-level and low-level, 223. 
 
 Valleys, 28. 
 
 Vanema J'liito, 209. 
 
 Vegetable Kingdom, classification of; 120. 
 
 Veins, of granite, 241. 
 
 I'eniriculitoi radiutus, 189. 
 
 VerteWata, 118. 
 
 Vesuvius, eruption of, 16, 17. 
 
 Volcanic activity, genenil phenomena of, 14, 
 15 ; exciting causes of; 20. 
 
 Volcanic ashes, 15, 73. 
 
 Volciinic bombs, 15. 
 
 Volcanic cone, general structure of, 19, 20. 
 
 Volcanic glass, (2. 
 
 Volcanic Kocks, 53, 69 ; origin of, 60 ; varieties 
 of, 72. 
 
 Volcanoes, definition of, 12; active and ex- 
 tinct, 12; submarine and sub-aCrial, 12.13; 
 appcanmce when quiescent, 13, 14; geo- 
 graphical distribution of; 17, 18; linear ar- 
 rangement of; 18, 20. 
 
 Volteia heterophylla, 1(J8. 
 
 Voluta Lamberti, 206, 212. 
 
 nodosa, 200. 
 
 Walchia pini/ormis, 165. 
 Waves of translation, 22. 
 Wealden, 185; fossils of, 186. 
 "Weathering, 42. 
 Wenlock beds, 182, 138; of Britain, 184; of 
 
 America, 137 ; fossils of, 184. 
 White Crag (fiee Coralline Crag). 
 Woolly Rhinoceros, 228, 224, 228. 
 
 Zainia ftptntlis, a recent Cycad, 181. 
 Z€Ch«Uin, 164. 
 Zeuglodon cMoide«, 202. 
 
 THE END. 
 
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 George lilpley says '* 8pc!icer is ae keen an analysist as is known in the history of Phi- 
 losophy . I do not except either Aristotle or Kant, whom he greatly resembles." 
 
 NIGEL BARTRAM'S IDEAL. A Novel. By Flor- 
 
 ENCE WiLPORP. 1 vol., 8vo. Paper covers. Price, .50 cents. 
 
 This is a novel of marked originality and high literary merit The heroine is one of 
 the loveliest and ])urest characters of recent fiction, and the detail of her adventures in 
 the arduous Umk of overcoming lier husband's ifri'judices and jealousies forms an exceed- 
 ingly interesting plot The Iraok is high ip. tone and excellent in style. 
 
 GOOD FOR NOTHING. A Novel. By Whyte 
 
 Melville. Author of " Digby Grand," " The Interpreter," etc. 1 
 vol., 8vo, 210 pages. Price, 60 cents. 
 
 " The Interest of the reader in the story, which for the most part is laid in England, 
 IB enthralling from the beginning to the end. The moral tone is altogether unexception- 
 able."— r^ie Chronicle. 
 
 A HAND-BOOK OF LAW, for Business Men ; con- 
 
 taining an Epitome of the Law of Contracts, Bills and Notes, inter- 
 est. Guaranty and Suretyship, Assignments for Creditors, Agents, 
 Factors, and Brokers, Sales, Mortgages, and Liens, Patents and 
 Copyrights, Trade-Marks, the Good-Will of a Business, Carriers, In- 
 surance, Shipping, Arbitrations, Statutes of Limitation, Partnership, 
 with an Appendix, containing Forms of Instruments used in the 
 Transaction of Business. By William Tracy, LL. D. 1 vol., Svo, 
 679 pages. Half basil, $5.50 ; library leather, $6.50. 
 
 This work is an epitome of those branches of law which aflect the ordinary transactions 
 of BUSINESS MKN. It U vot propoM(l hi/ it to make frery man a lawi/er, but to give 
 a man of business a convenient and reliable hook of reference, to assist him in the solu- 
 tion of questions relating to his rights and duties, which are constantly arising, and to 
 guide him in conducting his negotiations. 
 
 In pre|>ari.ig it the aim has been to set forth, in plain langitaoe, the rules 
 which constitute the doctrines of law which are examined, and to illuntr<ite the name 
 hy ileei*<ionn of the <\>urt^> in irhich they ore recognised, WiTU haruimal Bkfek- 
 
 ENCES TO THE VOLUMES WIIEKB THE CASES MAY BE rOUND. 
 
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 " There has never been published so beantiftil a guide-book to New York as this is. 
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649 & 551 Broadwat, New York. 
 
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 THE NOVELS AND NOVELISTS OF THE 
 
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 Morals of the Age. 
 
 I'irao. Cloth. Price, $1.50. 
 
 Mr. Forsyth, In his Instructive and pntortalnlnjr vohime, has Buero«><lwl In showinif 
 that inu(;h real Information cuncerninif the inonils us well as tlio niaunors of our nn«>s- 
 toi-s may be puthered from the novelists of the last century. With jmlicinl Impartiality 
 ho cxaniines and cross-examines the witnesses, laving nil the evidence ht^fore the reader. 
 Kssayists as well ns novelists are called up. I'he Hpcctator, The Tatler, The World, 
 i'lu! Connoisseur, aild confirmation stroni,' to the testimony of Parson Adams, TruUiber, 
 Trunnion. iSijuire Westi'rn, the " Kool of tiuality," " Ik-tsey Thouirhtless." and the like. 
 \ chanter on dress is susf^estive of comparison. Costume la a subject on which novol- 
 uts, like careful artists, are studiously precise. 
 
 REMINISCENCES OF FIFTY TEAKS. By Mark 
 
 Boyd. 1 vol., 12ino, 390 pp. Price, $1.75. 
 
 Mr. Boyd has seen much of life at homo and abroad. Tie has enjoyed the acquaint- 
 ance or fl-iendship of many Illustrious men, an 1 he has the additional advantage of ro- 
 momberin^ a number of anecdotes told by hU father, who |)osses!»tHl a retentive memory 
 and a wide circle of dist'nifuished friends. The book, as the writer acknowliKlges, is a 
 perfect o/la poiirilu. i^h -re is considiir.ible variety in the anecdotes. Home relate to 
 great generals, like the Duke of Wellinsfton and I^ord C'lyde ; some to artists and men 
 of kftters, and these include the names of Cainpboll, Uogers, Tha(;kenty, and David 
 Itoberts ; some to stati's nun, and, aujonif others, to Pitt, who was a friend of Mr. Boyd's 
 father, to I^ionls Palinuistin, Brougham, and Derby ; some to discoverers, like rtlr John 
 Franklin and Sir John Uoss : and othurs — am^ns? which may be reckoned, pi^haps, tho 
 most amusia'.^ in the vol mii! — to persons wholly uukuowa to luiuc, or to munuurs and 
 customs now happily obsalote. 
 
 FRAGMENTS OF SCIENCE* FOR ITNSCIEN- 
 
 TIKIC PEOPLE. A Series of Detached Essays, Lectures, an<l Re- 
 views. By Jonv Tynoall, LL. D., F. R. S. 1 vol., 12mo. Cloth. 
 422 pages. Price, $2.00. 
 
 Prof. Tyndall is the Poet op Modern Science. 
 
 This is a book of prenlus — one of those rare productions that come but once In a 
 penenition. Prof. Tyndall is not only a bold, broad, and original thinker, but one of the 
 most eloquent and attractive of writers. In this volume he goes over a large ran;,'-,', of 
 Bcientirtc (luestions. giving us tho latest views in the most lucid and graphic laniriiage, 
 so that the subtlest order of invisible changes .stand out ^^-ith all tho vivldri'-is of stereo- 
 scopic perspective. Though a disciplined S(^ien< ttc thinker. Prof. Tyndall is also a poet, 
 alive to all beauty, ond kindles into a glow of enthusiasm at the harmonies and wonders 
 of Nature which" he sees on every side. To htm science is no mere dry Inventory of 
 
 Erosaic facts, but a disclosure of tho Dlvhio order of the world, and fitted to stir the 
 ighest feelings of our nature. 
 
 GxVBRIELLE ANDRfi. An nistorical Novel. By 
 
 S. Barino-Gould, author of " Myths of the Middle Ages." 1 vol., 
 8vo. Paper covers. Price, 60 cents. 
 
 Those who take an Interest in comparing the effects of tho present French devolu- 
 tion on the Church with that of 17^9 will find in this work a g-eat deal of Information 
 lllustRitlng tho feeling in the Stjito and ('hurch of France at that pi-riod. The Literary 
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 tremely beautiful writing and description,^ 
 
 i 
 
 t A 
 
549 & 651 Broadway, New York. 
 
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 MUSINGS OVER THE CHRISTIAN YEAR AND 
 
 LYRA INNOCENTIUM. By Charlottk Mary Yonob, together 
 
 with a few Gleanings of Recollection, gathered by Severa] Frisnda. 
 
 1 vol. Thick 12mo, 431 pages. Price, $2.00. 
 
 Miss Yonge has hero produced a volume which will possess great Interest in the 
 eyes of Churehinen, who have for so manv years enjoyed tlie privilege of reading the 
 exquisite iKXJtry of the " Christian Year " oy Rev. John Ki'ble. Miss Yonge gives her 
 own exi)erience of the uninterrupted intercourse of thirty years ; then then' are the 
 " Recollections," l)y Francis M. Wlli>rahan> ; a few words of " I'ersonal Description." l)y 
 Rev. T. Miuipson Kvans ; tlien follow the " Musings," one each of the poew" illusti-ativfl 
 of the "Christian Year anU Lyra liinocentium." 
 
 THE HEIR OF REDCLYFFE. By Charlotte M. 
 
 YoNOE. A New Illustrated Edition. 2 vols., 12mo. Cloth. Price, 
 $2.00. 
 To be followed by HEARTSEASE. 
 
 " The first of her writings which made a sensation here was the ' ITclr, and wliat a 
 sensation it was! Referring to the remains of the tear-washed covers of tlii' copy afore- 
 said, we find it belonged to the 'eighth thousand.^ How uuiny thousands have been 
 issued since by the publishers, to supply the demand for new. and the places of di-owned, 
 dissolved, or swept away old copies, we do not attempt to conjectuic. Not individuals 
 merely, but households-consisting in great part of tender-hearted voung damsels — were 
 plunged into mourning. With a toiorjble acquaintance with fictitious heroes (not to 
 spcnk of real ones), from Sir Charles Grandison down to the nursery Idol, Carlton, we 
 have little hesitation in pronouncing Sir Guy Morvillo, or Re<lclyffe, Baronet, the most 
 admirable one wo ever met with, in story or out. The glorious, joyous l)oy. the brilliants 
 •rdcnt child of genius and of fortune, crowned with the beauty of his earlv holiness, and 
 Ivershadowed with the darkness of his her«>ditary gloom, and the soft and touching sad- 
 ness of his early death — what a ("hution is there I What a vision ! " — Extract from a re- 
 view of " The Ueir of Redclylfe," and " Heartsease," In the North American Jievieit 
 for April. 
 
 A COMPREHENSIVE DICTIONARY OF THE 
 
 BIBLE ; mainly abridged from Dr. William Smith's " Dictionary of 
 the Bible," but comprising important Additions and Improvements 
 from the Works of Robinson, Gesenius, Furst, Pape, Pott, Winer, 
 Keil, Lange, Kitto, Fairbaim, Alexander, Barnes, Bush, Thomson, 
 Stanley, Porter, Tristram, King, Ayre, and many other eminent 
 scholars, commentators, travellers, and authors in various depart- 
 ments. Designed to be a Complete Guide in regard to the Pronun- 
 ciation and Signification of Scriptural Names ; the Solution of Dif- 
 ficulties respecting the Interpretation, Authority, and Harmony of 
 the Old and New Testaments ; the History and Description of Bib- 
 lical Customs, Events, Places, Persons, Animals, Plants, Minerals, 
 and other things concerning which information is needed for an in- 
 telligent and thorough study of the Holy Scriptures, and of the 
 Books of the Apocrypha. Illustrated with Five Hundred Maps and 
 Engravings. Edited by Rev. Samuel W. Barnhm. Complete in 
 one large royal octavo volume of 1,234 pages. Price, in cloth bind- 
 ing, $5.00 ; in library sheep, $6.00 ; in half tuorocco, $7.60. 
 
iw York. 
 
 RKS. 
 RAND 
 
 1, togetlicr 
 il Frisndd. 
 
 erest in tho 
 rt'odintf the 
 ire (fives her 
 lere are tlie 
 LTiption." hy 
 " iliusti'utivo 
 
 OTTE M. 
 Ih. Price, 
 
 and what a 
 ' copy alore- 
 I have l)een 
 of <lrowucd, 
 
 individuals 
 iisels — were 
 •oes (not to 
 Carlton, we 
 et, the most 
 ;ho ln-illiant, 
 oliness, and 
 iictiin? Had- 
 
 from a re- 
 uin Jteview 
 
 THE 
 
 ionary of 
 'ovements 
 t, Winer, 
 Fhomson, 
 eminent 
 8 depart- 
 ! Pronun- 
 n of Dif- 
 rmony of 
 n of Bib- 
 Minerals, 
 or an in- 
 d of the 
 Haps and 
 nplete in 
 oth bind- 
 0. 
 
 649 & 551 Broadway, New York. 
 
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 LIGHT AND ELECTRICITY. Notes of Two 
 
 Courses of Lectures before the Royal Institution of Great Britain. 
 By John Tyndall, LL. D., F. R. S. 1 vol., 12mo. Cloth. Price, 
 
 $l.'.i5. 
 
 " For the benefit of tho»e who attended his Lectures on Lijfht and Electricity at tha 
 Eoyal Institution, l»rof. Tyndall prepared with much care a series of notes, suuiuiiu*; up 
 brielly and clearly the IcauliiK f^ts and principles of these sciences. The notes proved 
 so serviceatilo to those for whom they were desijnied that they were widely sought by 
 students aud teachers, and I^f. Tyndall hud them reprinted in two small t>ooks. Under 
 tlie conviction that they Mrill bo equally appreciated by instructors and learners in this 
 country, they uro here combined aud republished in a single volume." — Extract from 
 Prtjace. 
 
 THE DESCENT OF MAN AND SELECTION 
 
 IN RELATION TO SEX. By Charles Dakwis, M. A. With 
 Illustrations. 2 vols., l'2mo. Cloth. Price, $4.00. 
 
 "We can find no fiiult with Mr. Dar>vin'8 fhcta, or tho application of them." — Utiea 
 Ihrahi. 
 
 " The theory Is now indorsed by many eminent scientists, who ot first combated It, 
 including tiir Oliarles Lyell, probably the must learned of living geologists.^' — Emning 
 JiuJletin. 
 
 OF SPECIES. By St. 
 
 vol., 12ino. Cloth, with Illustrations. 
 
 ON THE GENESIS 
 
 George Mivart, F. R. S. 1 
 
 Price, $1.75. 
 
 " Mr. Mivart has snceeeded in producing a work which will clear the ideas of blolo 
 prists and tiieoloL'lans, and which treats the most dellc<it» questions In a manner which 
 throws light u[>on most of them, and tears away the barriers of intolerance on each 
 side." — Brituh Medical Journal. 
 
 MAKQITIS AND MERCHANT. A Novel. By 
 
 Mortimer Collins. 1 vol., 8vo. Paper covers. Price, 60 cents. 
 
 " Wo will not compare Mr. Collins, as a novelist, with Mr. Disraeli, btit nevertheless, 
 the qualities which have nuide Mr. DisraelPs fictions so widelv popular are to Im; found 
 in no small degree hi tho pages of the author of ' Marquis and Merctiant.^ "' — Times. 
 
 HEARTSEASE. A Novel. By the author of the 
 
 " Heir of Redclyffe." An Illu.strated Edition. 2 vols., 12mo. Price, 
 $2.00. 
 
 This Is the second of the series of Miss Yonpe's novels, now beincr issncd In a new 
 and l)eautiful stylo wi:h illustmtions. Since this novel was first puhliahe<l a new genera- 
 tion of readers have appeared. Nothing In the English language can equal tho delinea- 
 tion of character which she so beautifully portrays. 
 
 WHAT TO READ, AND HOW TO READ, 
 
 being Classified Lists of Choice Readinj:^, with appropriate hints 
 and remarks, adapted to the general reader, to sul)3C'ribers, to li- 
 braries, and to persons intending to form collections of books. 
 Brought down to September, 1870. By Charles H. Moork, M. D. 
 1 vol, 12nio. Paper Covers, 50 cents. Cloth. Price, >J6 cents. 
 
D. APPLETON ib CO:S PUBLICATIONS. 
 
 A Natural PhiloSOpliy : Jievmd Edition. 
 
 Embracing the most Recent Discoveries in the various Branches of 
 Physics, and Exhibiting the Application of Scientific Principles in 
 Every-day Life. Accompanied with full descriptions of Expori- 
 ments, Practical Exercises, and numerous Illustrations, liy G. P. 
 QUACKENBOS, LL. D. 12mo, 4 SO pages. 
 
 Thia standard text-book has just been carefully revised, and 
 may now be regarded as in all respects an accurate exponent ol 
 the present state of science. It is distinguished, 
 
 1. For ita remarkable clearness. 
 
 2. For ita ftilnoas of illuBtration. 
 
 8. For its ori^nal method of dealing with difficulties. 
 
 4. For its correction of numerous errors heretofore unfortunately stereotyped In 
 School Philosophies. 
 
 fi. For its explanation of scientific principles as exhibited in evcry-day life. 
 
 6. For the practical application of these principles in questions presented for the 
 pupiTs p^iution. 
 
 T. For a signal perspicuity of arrangement One thing being presented at a time, and 
 every thing in its proper place, the whole is impressed without ditliculty on the mind. 
 
 8. For the interest with which it invests the subject. From the outset, the student 
 is fascinated and tilled with a desire to fathom the wonders of the material world. 
 
 9. For the embodiment of all recent discoveries in the various departments of Philos- 
 ophy. Instead of relying on the obsolete authorities that have fUrnished the matter for 
 many of our popular School Philosophies, the author has made it his business to acquaint 
 himself with the present state of science, and thus produced such a work as is demanded 
 by the progressive spirit of the age. 
 
 Those who use this work commend it in the strongest terms. 
 
 "Whether we regard mutter or stylo, the selection of topics or the mode of develop- 
 ing the subject, clearness of illustnitioii or practical treatment, accuracy, ft-cshness, inter- 
 est, or general availability in the recitation-room, it gtwnds wit/iout an equal."-— ^ . Sv. 
 BuLKLEY, A. M., City Supt. of iSchook, Brooklytu 
 
 "I find that the author has maintained bis excellent reputation nf> an editor of school- 
 books. The style is clear and precise, yet simple and attractive. The fhmiliarity of the 
 illustrations constitutes a peculiar feature of the book. Altojrpther. I believe that it han 
 no eqxMl for the great moss of pupils in our common schools and acadomies." — A. J. 
 SiCKOFF, late Supt. of Schools, Cincinnati. 
 
 ^'■yfe are UJ^Ing your Natural Philosophy in our School, and wo find it miperior to 
 any itork ire hnre f'Ver imed. We have a class of forty yotm? ladies, and we find it a 
 plejwure to teach them ^^ith the aid of your admh^blo" book."— Prof. J. W. Stbwabt, 
 State Female College, Mempfm, Tenn. 
 
 *^It in juft my ideal of a nchonl-hook. Mr. Q. has not only loft out all the irrele- 
 vant matter and fhlso philosophy which iibound in most of the popular school-books on 
 this subject, but he has clearly state<l in the most systematic and natural manner every 
 important principle, and given the siibject a miicli ftillor development than has ever 
 been done before in any work of like grade. The book bears the impress of the nro- 
 foimd philosopher and the apt teacher."— J. G. Websteb, Prino. of Academy, SM^- 
 fMU.fnd 
 
 I I 
 
vs. 
 
 n. 
 
 13 Branches of 
 c Principles in 
 )n8 of Expori- 
 ona. liy G. P. 
 
 revised, and 
 ', exponent ot 
 
 Y stereotyped In 
 
 ay life. 
 >i-usuntod for the 
 
 ted at a time, and 
 y on the mind, 
 itsct, the Htudunt 
 rial world, 
 tments of Phiios- 
 ed the uuittcr Ibr 
 iiness to acquaint 
 k as is demanded 
 
 igest terms. 
 
 modeofdevelop- 
 , fri'shness, intor- 
 t equaV—J. W. 
 
 leditorof school- 
 fhmiliarity of the 
 flieve that it tian 
 adomies." — A. J. 
 
 id it tnipfHor to 
 and wo find it a 
 J. "W. Stewabt, 
 
 ont all the irrele- 
 ■ sphool-hooks on 
 ■nl manner every 
 it than has ever 
 [»re88 of the pro- 
 yadeniy, SMlky-