INDEX 
Aa, 334. 
Abyssal rocks, 66. 
Acadian, 402. 
Acid igneous rocks, 64. 
Adirondacks, early history of, 447, 449. 
Agassiz, Louis, glacial theory of, 486. 
Age, geological, 400, 401. 
Agents of weathering, 112, 128. 
Air, 14. 
Algonkian, 402. 
Alluvial cones, 176. 
Alluvial fans, 176, 187. 
Alluvial strata, 397. 
Alpine glaciers, 196. 
Alps, 315, 320. 
Alumina, 28. 
Aluminum, 24, 28. ; 
Amazon, absence of delta from, 185. 
Amorphous minerals, 34. 
Amphibia, Carboniferous, 423 ; descend- 
ants of, 481; Devonian, 423. 
Amphibole, 46. 
-Amygdaloidal rock, 68, 69. 
Amyegdules, 67. 
Andes, 315. 
Andesite, 66. 
Angle of hade, 290. 
Animal deposits in lakes, 189, 194. 
Animals, aid of, in weathering, 116, 128 ; 
destruction of, by volcanic eruption, 
345. 
Anthracite coal, 94, 99, 105, 462. 
Anticlinal mountains, 310, 311. 
Anticlines, 285, 287, 288, 304, 309, 311, 
313; symmetrical, 311, 313; unsym- 
metrical, 311, 313. 
Ants, aid of, in weathering, 116. 
Appalachian Mountains, 308, 309, 312, 
313, 315, 317, 323; formation of, 438, 
463 ; rocks of, 454. 
Aqueous rocks, 71. 
Archeopteryx, 431, 436. 
Archean, 372, 398, 402; condition in, 444; 
geography of, 447; life in, 405; rocks 
of, 371, 404. 
Archean mountains, 450. 
Arctic currents, 236. 
Arctic, former climate of, 393. 
Arenaceous clay, 80, 81. 
Argillaceous limestone, 90; sandstone, 
80. 
Argon, 14. 
Argonaut, 411. 
Arid Permian climate, 463. 
Arid regions, absence of vegetation in, 
124, 125; wind action in, 130, 136, 138. 
Arkansas River, sediment in, 174. 
Artesian wells, 147. 
Ash, eruptions of, 336; voleanic, 57, 97, 
329, 336, 344. . 
Atmosphere, 14. 
Atolls, 254, 255. 
Augite, 46, 47, 66.. 
Augite andesite, 66. 
Auk, 436. 
Australia, life of, 400. 
Avalanches, 143, 199, 356. 
Axis of fold, 285, 311. 
Azores, 330. 
B 
Bad Lands of South Dakota, 153, 154. 
Bahamas, origin of, 237. 
Banded structure in veins, 382. 
Barrier reefs, 254. 
Bars, 177, 179, 187; in lakes, 238; in 
ocean, 226, 231. 
489 
