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 shells [326]

Old Red Sandstone of Scotland, and borders of Wales — Fossils usually rare — "Old Red" in Forfarshire — 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 shells — Devonian strata of Westphalia, the Eifel, Russia, and the United States — Coral reef at Falls of the Ohio — Devonian Flora [342]

Silurian strata formerly called transition — Term grauwacké — Subdivisions of Upper and Lower Silurian — Ludlow formation and fossils — Wenlock formation, corals and shells — Caradoc and Llandeilo beds — Graptolites — Lingula — Trilobites — Cystideæ — 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]

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 analyses of minerals most abundant in the volcanic and hypogene rocks [366]

Trap dike — sometimes project — sometimes leave fissures vacant by decomposition — Branches and veins of trap — Dikes more crystalline in the centre — Foreign fragments of rock imbedded — Strata altered at or near the contact — Obliteration of organic remains — Conversion of chalk into marble — and of coal into coke — Inequality in the modifying influence of dikes — Trap interposed between strata — Columnar and globular structure — Relation of trappean rocks to the products of active volcanos — Submarine lava and ejected matter correspond generally to ancient trap — Structure and physical features of Palma and some other extinct volcanos [378]