INDEX 



475 



Tertiary deposits, 433, 435. 

 Tertiary mountains, 439. 

 Tertiary period, 433. 

 Tertiary volcanoes, 440. 

 Texture, porphyritic, 24. 



rock, 24. 



scoriaceous, 32. 



vesicular, 31. 

 Thallophytes, 293. 

 Throw, 71. 

 Tides, 236. 

 Tools of a river, 133. 

 Topographic divisions of North 



America, 63. 

 Topography, karst, 118. 



mature, 146. 



old, 146. 



serrate mountain, 102. 

 Transportation, 86, 125. 



by glaciers, 208. 



by streams, 130. 

 Transported soil, 17. 

 Triassic invertebrates, 399. 

 Triassic period, 397. 



Appalachian Mountains in, 398. 



deserts in, 397. 



marine strata in, 397. 



volcanic eruptions in, 398. 

 Trilobite, 336, 343, 352, 365, 373. 

 Tropics, glacial condition, 394. 

 Trough, glacial, 221. 

 Tuff, 33, 120. 

 Type, generalized, 393, 443. 



Unconformities, in Proterozoic 

 group, 327. 



value of, 304. 

 Unconformity, 75, 76. 



basal, 322. 



of Comanchean period, 415. 

 Undercut cliff, 265. 

 Undertow, 235. 

 Unglaciated regions, 457. 

 Ungulates, 442. 

 United States coal fields, 381. 

 Upthrow, 71. 



Valley deepening, 139. 



Valley flat, 140. 



Valley glaciers, 194, 211, 458. 



surface of, 199. 

 Valley lengthening, 141. 

 Valley system, 142. 

 Valley trains, 227. 

 Valleys, 137. 



hanging, 222, 225. 



mature, 143. 



old, 143. 



structural, 138. 



tributary, 142. 



young, 143. 

 Vein, mineral, 79. 

 Velocity of stream, 134. 

 Vertebrates, 300. 

 Vesicular texture, 31. 

 Volcanic ash, 33. 

 Volcanic breccia, 33. 

 Volcanic cones, 46. 

 Volcanic dust, 33. 

 Volcanic eruptions, Triassic, 398. 

 Volcanic glass, 31. 

 Volcanic mountain, 52, 280. 

 Volcanic necks, 52, 53. 

 Volcanoes, Quaternary, 460. 



Tertiary, 440. 

 Vulcanism, 11, 77. 



Warping, 64. 



Waterfall, 160. 



Water gaps, 162. 



Water table, 107. 



Waters, ground, work of, 107-123. 



Weathering, 125. 



belt of, 80. 



exfoliate, 101. 



processes of, 126. 



rate of, 127. 

 Wells, artesian, 112. 

 Worms, 297. 



Zinc, 120. 



Zinc deposits, Ordovician, 342. 



Zone, of flowage, 78. 



of fracture, 78. 



of greatest cementation, 119. 



of greatest solution, 117. 



