INDEX 
Tides, 16; action of, 251, 239. 
Till, 209, 210, 219, 484. 
Time-scale, geological, 397, 402. 
Titanium, 31. — 
Trachyte, 66, 342. 
Transition strata, 397 
’ Trap, 66; Triassic, 466. 
Travertine, 84. 
Trees, aid of, in weathering, 115, 116, 
117, 128; submerged, 298, 300. 
Trenton, 402. 
Triassic, 402, 464; life of, 426. 
Trilobites, Cambrian, 408, 409; Carbo- 
niferous, 419; Devonian, 413, 414, 415 ; 
Mesozoic, 426; Ordovician, 408, 409; 
Silurian, 410. 
Tufa, 84, 86, 87, 97. 
Tuff, 81. 
iy 
Uintah Mountains, 319. 
Unconformity, 320, 394, 399, 452. 
Underground rivers, 141, 145, 150. 
Underground water, 139-150, 173, 241; 
supply of, for rivers, 155. 
Undertow, 223, 227, 239. 
Unstratified glacial deposits, 211, 219. 
Unsymmetrical folds, 285, 288, 311, 313. 
Upthrow side of fault, 290. 
V 
Valley deepening by rivers, 163. 
Valley glaciers, 195, 196, 218; former 
extent of, 211. 
Veins, mineral, 362, 380. 
Vesuvius, 330, 332, 336, 340-343, 345, 346. 
Voleanie ash, 57, 97, 329, 336, 344; dis- 
tribution of, by wind, 130. 
Volcanic cones, 306; formation of, 54; 
history of, 350. 
499 
Volcanic neck, 346, 350. 
Volcanic rocks, 56, 66. 
Volcanoes, 322; ancient, 450; associa- 
tion of earthquakes with, 358, 360; 
association with mountains, 352 ; cause 
of, 351; definition, 329; difference in 
eruptions, 342; effects of, 345; history 
of, 350; location of, 329; materials 
erupted by, 332; nature of eruption 
of, 338; supply of sediment from, 74; 
Triassic, 466; of the West, 469, 471. 
Vuleano, 339. 
WwW 
Water, aid of, in rock .ormation, 74; 
deposit of ore by, 580; importance of, 
in the earth, 31, 51, 53, 110, 117, 128, 
139, 273; importance of, in metamor- 
phism, 368, 374; solution of minerals 
by, 82, 275. 
Water vapor, 15, 51. 
Waterfalls, 167; caused by glacial inter- 
ference, 484. 
Waterlime strata, 457. 
Waves, 16; attack of, on coast, 224; 
earthquake, 349, 354, 357; erosion by, 
221, 228, 239; nature of, 221. 
Weathering, 72, 109, 241; agents of, 112, 
128; aid in river erosion, 165, 173; 
difference in rate of, 124; of feldspar, 
41; importance of, 127, 172. 
Wind, action of, in arid lands, 124, 125; 
aid of, in rock formation, 73; erosion 
by, 129, 135, 138, 241; currents in 
ocean, 223, 225; waves, 16, 221. 
hg 
Yellow River, delta in, 183, 184. 
Yellowstone Park, geysers of, 83, 84, 
362, 363, 
