A Manual of Elementary Geology Part 4

CHAPTER XV.

UPPER EOCENE FORMATIONS.

Eocene areas in England and France--Tabular view of French Eocene strata--Upper Eocene group of the Paris basin--Same beds in Belgium and at Berlin--Mayence tertiary strata--Freshwater upper Eocene of Central France--Series of geographical changes since the land emerged in Auvergne--Mineral character an uncertain test of age--Marls containing Cypris--Oolite of Eocene period--Indusial limestone and its origin--Fossil mammalia of the upper Eocene strata in Auvergne--Freshwater strata of the Cantal, calcareous and siliceous--Its resemblance to chalk--Proofs of gradual deposition of strata 174

CHAPTER XVI.

EOCENE FORMATIONS--_continued_.

Subdivisions of the Eocene group in the Paris basin--Gypseous series--Extinct quadrupeds--Impulse given to geology by Cuvier's osteological discoveries--Sh.e.l.ly sands called sables moyens--Calcaire grossier--Miliolites--Calcaire siliceux--Lower Eocene in France--Lits coquilliers--Sands and plastic clay--English Eocene strata--Freshwater and fluvio-marine beds--Barton beds--Bagshot and Bracklesham division--Large ophidians and saurians--Lower Eocene and London Clay proper--Fossil plants and sh.e.l.ls--Strata of Kyson in Suffolk--Fossil monkey and opossum--Mottled clays and sand below London Clay--Nummulitic formation of Alps and Pyrenees--Its wide geographical extent--Eocene strata in the United States--Section at Claiborne, Alabama--Colossal cetacean--Orbitoid limestone--Burr stone 190

CHAPTER XVII.

CRETACEOUS GROUP.

Divisions of the cretaceous series in North-Western Europe--Upper cretaceous strata--Maestricht beds--Chalk of Faxoe--White chalk--Characteristic fossils--Extinct cephalopoda--Sponges and corals of the chalk--Signs of open and deep sea--White area of white chalk--Its origin from corals and sh.e.l.ls--Single pebbles in chalk--Siliceous sandstone in Germany contemporaneous with white chalk--Upper greensand and gault--Lower cretaceous strata--Atherfield section, Isle of Wight--Chalk of South of Europe--Hippurite limestone--Cretaceous Flora--Chalk of United States 209

CHAPTER XVIII.

WEALDEN GROUP.

The Wealden divisible into Weald Clay, Hastings Sand, and Purbeck Beds--Intercalated between two marine formations--Weald clay and Cypris-bearing strata--Iguanodon--Hastings sands--Fossil fish--Strata formed in shallow water--Brackish water-beds--Upper, middle, and lower Purbeck--Alternations of brackish water, freshwater, and land--Dirt-bed, or ancient soil--Distinct species of fossils in each subdivision of the Wealden--Lapse of time implied--Plants and insects of Wealden--Geographical extent of Wealden--Its relation to the cretaceous and oolitic periods--Movements in the earth's crust to which it owed its origin and submergence 225

CHAPTER XIX.

DENUDATION OF THE CHALK AND WEALDEN.

Physical geography of certain districts composed of Cretaceous and Wealden strata--Lines of inland chalk-cliffs on the Seine in Normandy--Outstanding pillars and needles of chalk--Denudation of the chalk and Wealden in Surrey, Kent, and Suss.e.x--Chalk once continuous from the North to the South Downs--Anticlinal axis and parallel ridges--Longitudinal and transverse valleys--Chalk escarpments--Rise and denudation of the strata gradual--Ridges formed by harder, valleys by softer beds--Why no alluvium, or wreck of the chalk, in the central district of the Weald--At what periods the Weald valley was denuded--Land has most prevailed where denudation has been greatest--Elephant bed, Brighton 238

CHAPTER XX.

OOLITE AND LIAS.

Subdivisions of the Oolitic or Jura.s.sic group--Physical geography of the Oolite in England and France--Upper Oolite--Portland stone and fossils--Lithographic stone of Solenhofen--Middle Oolite, coral rag--Zoophytes--Nerinaean limestone--Diceras limestone--Oxford clay, Ammonites and Belemnites--Lower Oolite, Crinoideans--Great Oolite and Bradford clay--Stonesfield slate--Fossil mammalia, placental and marsupial--Resemblance to an Australian fauna--Doctrine of progressive development--Collyweston slates--Yorks.h.i.+re Oolitic coal-field--Brora coal--Inferior Oolite and fossils 257

CHAPTER XXI.

OOLITE AND LIAS--_continued_.

Mineral character of Lias--Name of Gryphite limestone--Fossil sh.e.l.ls and fish--Ichthyodorulites--Reptiles of the Lias--Ichthyosaur and Plesiosaur--Marine Reptile of the Galapagos Islands--Sudden destruction and burial of fossil animals in Lias--Fluvio-marine beds in Gloucesters.h.i.+re and insect limestone--Origin of the Oolite and Lias, and of alternating calcareous and argillaceous formations--Oolitic coal-field of Virginia, in the United States 273

CHAPTER XXII.

TRIAS OR NEW RED SANDSTONE GROUP.

Distinction between New and Old Red Sandstone--Between Upper and Lower New Red--The Trias and its three divisions--Most largely developed in Germany--Keuper and its fossils--Muschelkalk--Fossil plants of Bunter--Tria.s.sic group in England--Bone-bed of Axmouth and Aust--Red Sandstone of Warwicks.h.i.+re and Ches.h.i.+re--Footsteps of _Chirotherium_ in England and Germany--Osteology of the _Labyrinthodon_--Identification of this Batrachian with the Chirotherium--Origin of Red Sandstone and rock-salt--Hypothesis of saline volcanic exhalations--Theory of the precipitation of salt from inland lakes or lagoons--Saltness of the Red Sea--New Red Sandstone in the United States--Fossil footprints of birds and reptiles in the Valley of the Connecticut--Antiquity of the Red Sandstone containing them 286

CHAPTER XXIII.

PERMIAN OR MAGNESIAN LIMESTONE GROUP.

Fossils of Magnesian Limestone and Lower New Red distinct from the Tria.s.sic--Term Permian--English and German equivalents--Marine sh.e.l.ls and corals of English Magnesian limestone--Palaeoniscus and other fish of the marl slate--Thecodont Saurians of dolomitic conglomerate of Bristol--Zechstein and Rothliegendes of Thuringia--Permian Flora--Its generic affinity to the carboniferous--Psaronites or tree-ferns 301

CHAPTER XXIV.

THE COAL OR CARBONIFEROUS GROUP.

Carboniferous strata in the south-west of England--Superposition of Coal-measures to Mountain limestone--Departure from this type in north of England and Scotland--Section in South Wales--Underclays with Stigmaria--Carboniferous Flora--Ferns, Lepidodendra, Calamites, Asterophyllites, Sigillariae, Stigmariae,--Coniferae--Endogens--Absence of Exogens--Coal, how formed--Erect fossil trees--Parkfield Colliery--St.

Etienne, Coal-field--Oblique trees or snags--Fossil forests in Nova Scotia--Brackish water and marine strata--Origin of Clay-iron-stone 308

CHAPTER XXV.

CARBONIFEROUS GROUP--_continued_.

Coal-fields of the United States--Section of the country between the Atlantic and Mississippi--Position of land in the carboniferous period eastward of the Alleghanies--Mechanically formed rocks thinning out westward, and limestones thickening--Uniting of many coal-seams into one thick one--Horizontal coal at Brownsville, Pennsylvania--Vast extent and continuity of single seams of coal--Ancient river-channel in Forest of Dean coal-field--Absence of earthy matter in coal--Climate of carboniferous period--Insects in coal--Rarity of air-breathing animals--Great number of fossil fish--First discovery of the skeletons of fossil reptiles--Footprints of reptilians--Mountain limestone--Its corals and marine sh.e.l.ls 326

CHAPTER XXVI.

OLD RED SANDSTONE, OR DEVONIAN GROUP.

Old Red Sandstone of Scotland, and borders of Wales--Fossils usually rare--"Old Red" in Forfars.h.i.+re--Ichthyolites of Caithness--Distinct lithological type of Old Red in Devon and Cornwall--Term "Devonian"--Organic remains of intermediate character between those of the Carboniferous and Silurian systems--Corals and sh.e.l.ls--Devonian strata of Westphalia, the Eifel, Russia, and the United States--Coral reef at Falls of the Ohio--Devonian Flora 342

CHAPTER XXVII.

SILURIAN GROUP.

Silurian strata formerly called transition--Term grauwacke--Subdivisions of Upper and Lower Silurian--Ludlow formation and fossils--Wenlock formation, corals and sh.e.l.ls--Caradoc and Llandeilo beds--Graptolites--Lingula--Trilobites--Cystideae--Vast thickness of Silurian strata in North Wales--Unconformability of Caradoc sandstone--Silurian strata of the United States--Amount of specific agreement of fossils with those of Europe--Great number of brachiopods--Deep-sea origin of Silurian strata--Absence of fluviatile formations--Mineral character of the most ancient fossiliferous rocks 350

CHAPTER XXVIII.

VOLCANIC ROCKS.

Trap rocks--Name, whence derived--Their igneous origin at first doubted--Their general appearance and character--Volcanic cones and craters, how formed--Mineral composition and texture of volcanic rocks--Varieties of felspar--Hornblende and augite--Isomorphism--Rocks, how to be studied--Basalt, greenstone, trachyte, porphyry, scoria, amygdaloid, lava, tuff--Alphabetical list, and explanation of names and synonyms, of volcanic rocks--Table of the a.n.a.lyses of minerals most abundant in the volcanic and hypogene rocks 366