XIV CONTENTS. 



Chapter XXV. — Carhoniferous Group — continued. 



Coal-fields of the United States — Section of the country between the Atlantic 

 and Mississippi — Uniting of many coal-seams into one thick bed — A^ast extent 

 and continuity of single seams of coal — Ancient river-channel in Forest of Dean 

 coal-field — Climate of Carboniferous period — Insects in coal — Great number of 

 fossil fish — First discovery of the skeletons of fossil reptiles — First land-shell of 

 the coal found — Rarity of air-breathe-rs, whether vertebrate or invertebrate, in 

 Coal-measures — Mountain limestone — Its corals and marine shells Page 387 



Chapter XXVI. — Old Red Sandstone or Devonian Group. 



Old Red Sandstone of the borders of "Wales — Scotland and the South of Ireland 

 —-Fossil reptile of Elgin- — Fossil Devonian plants at Kilkenny— Ichthyolites of 

 Clashbinnie — Fossil fish, &c., crustaceans, of Caithness and Forfarshire — Dis- 

 tinct lithological type of Old Red in Devon and Cornwall— Term "Devonian" 

 — Devonian series of England and the Continent — Old Red Sandstone of Russia 

 —Devonian strata of the United States - - - - - 411 



Chapter XXVII. — Silurian and Cambrian Groi^ps. 



Silurian strata formerly called "Transition" — Subdivisions — Ludlow formation 

 and fossils — Ludlow "bone-bed, and oldest known remains of fossil fish — Wen- 

 lock formation, corals, cystideans, trilobites — Caradoc sandstone — Pentameri 

 and Tentaculites— Lower Silurian rocks — Llandeilo flags — Cystidefe — Trilo- 

 bites — Graptolites — 'Vast thickness of Lower Silurian strata in Wales — -Foreign 

 Silurian equivalents in Europe — Ungulite grit of Russia — Silurian strata oi 

 the United States — Canadian equivalents — Deep-sea origin of Silurian strata 

 — Fossiliferous rocks below the Llandeilo beds — Cambrian group — Lingula 

 flags — Lower Cambrian — Oldest known fossil remains — " Primordial group" of 

 Bohemia — Metamorphosis of trilobites — Alum schists of Sweden and Norway 

 —Potsdam sandstone of United States and Canada — Trilobites on the Upper 

 Mississippi — Supposed period of invertebrate animals — 'Absence of fish in 

 Lower Silurian — Progressive discovery of vertebrata in older rocks — Doctrine 

 of the non-existence of vertebrata in the older fossiliferous periods prema 

 ture -...--.-= 429 



Chapter XXVIII. — Volcanic Rocks. 



Trap rocks — Name, whence derived — Their igneous origin at first doubted — • 

 Their general appearance and character — Mineral composition and texture — ■ 

 Varieties of felspar — Hornblende and augite — Isomorphism — Rocks, how to be 

 studied — Basalt, trachyte, greenstone, porphyry, scoria., amygdaloid, lava, tuf! 

 — Agglomerate — Laterite — Alphabetical list, and explanation of names and 

 synonyms of volcanic rocks — Table of analyses of minerals most abundant in 

 the volcanic and hypogene rocks ------ 460 



Chapter XXIX. — Volcanic Rocks — continued. 



Trap dikes— Strata altered at or near the contact— Conversion of chalk into 

 marble — Trap interposed between strata — Columnar and globular structure — 

 Relation of trappean rocks to the products of active volcanoes— Form, exter- 

 nal structure, and origin of volcanic mountains — Craters and Calderas — Sand 

 wich Islands — Lava "flowing underground — Truncation of cones — Javanese 

 Calderas — Canary Islands — Structure and origin of the ealdera of Palma — 

 Aqueous conglomerate in Palma — Hypothesis of upheaval considered — Slope 

 on which stony lavas may form— Island of St. Paul in the Indian Ocean — Peak 

 of TenerifFe, and ruins of older cone — Madeira — Its volcanic rocks, partly of 

 marine and partly of subaerial origin — Central axis of eruptions — Varying dip 

 of solid lavas near the axis, and further from it — Leaf-bed and fossil land- 

 plants — Central valleys of Madeira how formed - - » - 476 



