Part 4 (2/2)

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

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