INDEX 



473 



Plateau, lava, 47. 



origin of, 285. 

 Playas, 56. 

 Plesiosaur, 401. 

 Pliocene epoch, 433. 

 Plucking, 217. 

 Plugs, 53. 



Pocono sandstone, 370. 

 Polyps, 296. 

 Porphyritic texture, 24. 

 Porphyry, 28. 

 Porphyry dike, 50. 

 Pothole, 161. 

 Potomac series, 415. 

 Processes, geologic, 10. 

 Profile, interrupted, 153. 

 Proterozoic era, 322. 



fossils of, 329. 



Proterozoie group, unconformi- 

 ties in, 327. 

 Proterozoic rocks, 325. 

 Proterozoic strata in Arizona, 326. 



in Lake Superior region, 322. 

 Pteridospermse, 293, 

 Pteridophytes, 293, 383. 

 Pteropod, 337. 

 Pterosaur, 411. 

 Pumice, 31. 



Quaternary lakes, 458. 

 Quaternary period, 448. 

 Quaternary volcanoes, 460. 

 Quartz, 21. 

 Quartzite, 38, 79. 



Radiolarian ooze, 259. 

 Rainbow Falls, 158. 

 Range, mountain, 275. 

 Rapids, 157. 

 Ravine, 138. 

 Reef, barrier, 260. 



fringing, 259. 

 Reindeer, 462. 

 Rejuvenated area, 153. 

 Relief, 274. 

 Relief model of North America, 



62. 

 Reptiles, 301, 393, 400. 



Residual soil, 17. 

 Reversed faults, 71, 72, 73. 

 Ripple marks, 55. 

 River system, 142. 

 Rivers, braided, 178. 

 Rock structure, 46, 167. 

 Rock terraces, 166. 

 Rock texture, 24. 

 Rock waste, 17. 

 Rocks, 20. 



acidic, 24. 



basic, 24. 



classes of, 17. 



feldspathic, 29. 



fragmental, 39. 



glassy, 26, 31. 



granite, 130. 



igneous, 19, 23, 37, 42, 49. 



intermediate, 24. 



mantle, 17. 



metamorphic, 19, 41. 



neutral, 24. 



relation of, 44. 



secondary, 41. 



sedimentary, 19, 37, 40. 



stratified, 19. 

 Rodents, 442. 

 Run-off, 107. 



Salamander, 374. 

 Salina beds, 356. 

 Salt lakes, 268. 

 Sand dune, 92, 93, 

 Sandstone, 38. 



cross-bedded, 89. 



Eolian, 98. 

 Sapping, 160. 

 Scallop shell, 385. 

 Schist, 42, 82. 

 Scoria, 31. 



Scoriaceous texture, 32. 

 Sea, epicontinental, 339. 



movements of, 235. 

 Sea animals, Cretaceous, 424. 

 Sea cave, 243, 245. 

 Sea cliff, 241, 243. 

 Sea erosion, 239. 

 Sea expansion, Ordovician, 339. 



