A Manual of Elementary Geology Part 3

CONTENTS.

CHAPTER I.

ON THE DIFFERENT CLa.s.sES OF ROCKS.

Geology defined--Successive formation of the earth's crust--Cla.s.sification of rocks according to their origin and age--Aqueous rocks--Their stratification and imbedded fossils--Volcanic rocks, with and without cones and craters--Plutonic rocks, and their relation to the volcanic--Metamorphic rocks and their probable origin--The term primitive, why erroneously applied to the crystalline formations--Leading division of the work Page 1

CHAPTER II.

AQUEOUS ROCKS--THEIR COMPOSITION AND FORMS OF STRATIFICATION.

Mineral composition of strata--Arenaceous rocks--Argillaceous--Calcareous--Gypsum--Forms of stratification--Original horizontality--Thinning out--Diagonal arrangement--Ripple mark 10

CHAPTER III.

ARRANGEMENT OF FOSSILS IN STRATA--FRESHWATER AND MARINE.

Successive deposition indicated by fossils--Limestones formed of corals and sh.e.l.ls--Proofs of gradual increase of strata derived from fossils--Serpula attached to spatangus--Wood bored by Teredina--Tripoli and semi-opal formed of infusoria--Chalk derived princ.i.p.ally from organic bodies--Distinction of freshwater from marine formations--Genera of freshwater and land sh.e.l.ls--Rules for recognizing marine testacea--Gyrogonite and chara--Freshwater fishes--Alternation of marine and freshwater deposits--Lym-Fiord 21

CHAPTER IV.

CONSOLIDATION OF STRATA AND PETRIFACTION OF FOSSILS.

Chemical and mechanical deposits--Cementing together of particles--Hardening by exposure to air--Concretionary nodules--Consolidating effects of pressure--Mineralization of organic remains--Impressions and casts how formed--Fossil wood--Goppert's experiments--Precipitation of stony matter most rapid where putrefaction is going on--Source of lime in solution--Silex derived from decomposition of felspar--Proofs of the lapidification of some fossils soon after burial, of others when much decayed 33

CHAPTER V.

ELEVATION OF STRATA ABOVE THE SEA--HORIZONTAL AND INCLINED STRATIFICATION.

Why the position of marine strata, above the level of the sea, should be referred to the rising up of the land, not to the going down of the sea--Upheaval of extensive ma.s.ses of horizontal strata--Inclined and vertical stratification--Anticlinal and synclinal lines--Bent strata in east of Scotland--Theory of folding by lateral movement--Creeps--Dip and strike--Structure of the Jura--Various forms of outcrop--Rocks broken by flexure--Inverted position of disturbed strata--Unconformable stratification--Hutton and Playfair on the same--Fractures of strata--Polished surfaces--Faults--Appearance of repeated alternations produced by them--Origin of great faults Page 44

CHAPTER VI.

DENUDATION.

Denudation defined--Its amount equal to the entire ma.s.s of stratified deposits in the earth's crust--Horizontal sandstone denuded in Ross-s.h.i.+re--Levelled surface of countries in which great faults occur--Coalbrook Dale--Denuding power of the ocean during the emergence of land--Origin of Valleys--Obliteration of sea-cliffs--Inland sea-cliffs and terraces in the Morea and Sicily--Limestone pillars at St. Mihiel, in France--in Canada--in the Bermudas 66

CHAPTER VII.

ALLUVIUM.

Alluvium described--Due to complicated causes--Of various ages, as shown in Auvergne--How distinguished from rocks _in situ_--River-terraces--Parallel roads of Glen Roy--Various theories respecting their origin 79

CHAPTER VIII.

CHRONOLOGICAL CLa.s.sIFICATION OF ROCKS.

Aqueous, plutonic, volcanic, and metamorphic rocks, considered chronologically--Lehman's division into primitive and secondary--Werner's addition of a transition cla.s.s--Neptunian theory--Hutton on igneous origin of granite--How the name of primary was still retained for granite--The term "transition," why faulty--The adherence to the old chronological nomenclature r.e.t.a.r.ded the progress of geology--New hypothesis invented to reconcile the igneous origin of granite to the notion of its high antiquity--Explanation of the chronological nomenclature adopted in this work, so far as regards primary, secondary, and tertiary periods 89

CHAPTER IX.

ON THE DIFFERENT AGES OF THE AQUEOUS ROCKS.

On the three princ.i.p.al tests of relative age--superposition, mineral character, and fossils--Change of mineral character and fossils in the same continuous formation--Proofs that distinct species of animals and plants have lived at successive periods--Distinct provinces of indigenous species--Great extent of single provinces--Similar laws prevailed at successive geological periods--Relative importance of mineral and palaeontological characters--Test of age by included fragments--Frequent absence of strata of intervening periods--Princ.i.p.al groups of strata in western Europe 96

CHAPTER X.

CLa.s.sIFICATION OF TERTIARY FORMATIONS.--POST-PLIOCENE GROUP.

General principles of cla.s.sification of tertiary strata--Detached formations scattered over Europe--Strata of Paris and London--More modern groups--Peculiar difficulties in determining the chronology of tertiary formations--Increasing proportion of living species of sh.e.l.ls in strata of newer origin--Terms Eocene, Miocene, and Pliocene--Post-Pliocene strata--Recent or human period--Older Post-Pliocene formations of Naples, Uddevalla, and Norway--Ancient upraised delta of the Mississippi--Loess of the Rhine Page 104

CHAPTER XI.

NEWER PLIOCENE PERIOD.--BOULDER FORMATION.

Drift of Scandinavia, northern Germany, and Russia--Its northern origin--Not all of the same age--Fundamental rocks polished, grooved, and scratched--Action of glaciers and icebergs--Fossil sh.e.l.ls of glacial period--Drift of eastern Norfolk--a.s.sociated freshwater deposit--Bent and folded strata lying on undisturbed beds--Sh.e.l.ls on Moel Tryfane--Ancient glaciers of North Wales--Irish drift 121

CHAPTER XII.

BOULDER FORMATION--_continued_.

Difficulty of interpreting the phenomena of drift before the glacial hypothesis was adopted--Effects of intense cold in augmenting the quant.i.ty of alluvium--a.n.a.logy of erratics and scored rocks in North America and Europe--Bayfield on sh.e.l.ls in drift of Canada--Great subsidence and re-elevation of land from the sea, required to account for glacial appearances--Why organic remains so rare in northern drift--Mastodon giganteus in United States--Many sh.e.l.ls and some quadrupeds survived the glacial cold--Alps an independent centre of dispersion of erratics--Alpine blocks on the Jura--Recent transportation of erratics from the Andes to Chiloe--Meteorite in Asiatic drift 131

CHAPTER XIII.

NEWER PLIOCENE STRATA AND CAVERN DEPOSITS.

Chronological cla.s.sification of Pleistocene formations, why difficult--Freshwater deposits in valley of Thames--In Norfolk cliffs--In Patagonia--Comparative longevity of species in the mammalia and testacea--Fluvio-marine crag of Norwich--Newer Pliocene strata of Sicily--Limestone of great thickness and elevation--Alternation of marine and volcanic formations--Proofs of slow acc.u.mulation--Great geographical changes in Sicily since the living fauna and flora began to exist--Osseous breccias and cavern deposits--Sicily--Kirkdale--Origin of stalact.i.te--Australian cave-breccias--Geographical relations.h.i.+p of the provinces of living vertebrata and those of the fossil species of the Pliocene periods--Extinct struthious birds of New Zealand--Teeth of fossil quadrupeds 146

CHAPTER XIV.

OLDER PLIOCENE AND MIOCENE FORMATIONS.

Strata of Suffolk termed Red and Coralline crag--Fossils, and proportion of recent species--Depth of sea and climate--Reference of Suffolk crag to the older Pliocene period--Migration of many species of sh.e.l.ls southwards during the glacial period--Fossil whales--Subapennine beds--Asti, Sienna, Rome--Miocene formations--Faluns of Touraine--Depth of sea and littoral character of fauna--Tropical climate implied by the testacea--Proportion of recent species of sh.e.l.ls--Faluns more ancient than the Suffolk crag--Miocene strata of Bordeaux and Piedmont--Mola.s.se of Switzerland--Tertiary strata of Lisbon--Older Pliocene and Miocene formations in the United States--Sewalik Hills in India 161