Aa, lava, 241 Acadian coal field, 354 Accretion hypothesis, 304 Acidic rocks, 249 Adelsberg grotto, 47 Adirondacks, 309, 316 Africa, 357 Agassiz, Lake, 67, 111, 435 Agates, 251 Alabama, 317, 360 Alaska, 85, 138, 140, 378 Aletsch glacier, 121 Algæ, 51, 52 Algonkian era, 306, 310 Allegheny Mountains, 90, 224, 326, 403 Alluvial cones, 98 Alluvium, 62 Alps, 118, 121, 141, 210, 211, 212, 223, 229, 349, 427, 443 Amazon River, 175 Ammonites, 294, 367, 380, 382 Amphibians, 364, 383 Amphicyon, 413 Amygdules, 250 Andes, 236, 279 Angle of repose, 25 Antarctic continent, 294 Antecedent streams, 209 Antelope, 413 Anthracite, 281 Anticlinal folds, 203, 209 Ants, 20 Apennine Mountains, 399 Appalachia, 317, 351, 358 Appalachian coal field, 356 Appalachian deformation, 358 Appalachian Mountains, 211, 214, 218, 292 Aquifer, 44 Aragonite, 296 Archæopteryx, 393 Archean era, 305 Arenaceous rocks, 9 Argillaceous rocks, 9 Arizona, 32, 76, 140, 151, 164, 220, 229, 249, 257, 371, 390 Arkansas, 337, 356, 373 Arkose, 186, 282, 370 Artesian wells, 44 Arthropods, 322 Artiodactyls, 411 Assiniboine, Mount, 34 Atlas Mountains, 399 Atmosphere, 304, 305 Atolls, 191, 193 Augite, 274 Austin, Tex., 71 Australia, 190, 357 Avalanches, 26 Bad Lands, 397, 398 Baltic Sea, 170, 171, 199 Barite, 287 Barrier Reefs, 191, 192 Basal conglomerate, 173, 184 Basalt, 249 Baselevel, 80, 83 Basic rocks, 249 Basin deposits, 103 Bay bars, 164 Beaches, 162, 164 Bears, 413 Bedding planes, 5 Belemnites, 382 Belt Mountains, 309 Bergschrund, 121, 135, 137 Bermudas, 148 Birds, 392 Bison, 413 Bitter Root Mountains, 272 Black Hills, 309, 371 Blastoids, 339 Blastosphere, 311 Block mountains, 222, 226 Blowholes, 159 Blue Ridge, 309, 316 Bomb, volcanic, 256 Bonneville, Lake, 107, 488 Bosses, 270 Bowlders, erratic, 420 of weathering, 28 Brachiopods, 328, 383, 343, 364, 380 Brazil, 18, 286 Breccia, 218, 255, 264 British Columbia, 373, 378 Bronze stage, 443, 448 Bryozoans, 333 Bunker Hill, 422