Mono Lake in Quaternary period, 



394. 



Monotremes (one vent : the lowest 

 order of mammals, including 

 ornithorhynchus and echid- 

 na), 328. 



Monticles (little mountains), 136. 

 Moraines, 57. 



Mosasaur (Meuse lizard), 357. 

 Mound-builders, 415. 

 Mountain life, different stages of, 



245. 



sculpture, 246. 

 sculpture forms of, 247. 

 strata, thickness of, 244. 

 Mountains, denned, 238. 



structure and origin of, 238. 

 Murray's theory of atolls, 105. 

 Myrmecobius (ant-liver), 340. 



Nautilus, 281. 



Neolithic (new stone), 412. 



Niagara Falls, recession of, 21. 



gorge, origin of, 21. 

 Nodules, forms of, 198. 



how formed, 199. 



Obsidian, 214. 

 Ocean, agency of, 41. 



mean depth of, 176. 



why is it salt ? 79. 

 Oceanic currents. 47. 

 Organic agencies, 83. 



agencies, subdivisions of, 83. 

 Orohippus (mountain-horse), 377. 

 Orthoceratite (straight stone 



horn), 282. 

 Orthoclase (right cleavage), 212, 



215. 



Osteolepis (bony scale), 294. 

 Otozoum (giant animal), 342. 

 Outcrop, 186. 

 Overflows, 217. 



Pacificbottom, subsiding area,106. 

 Paleolithic (old stone), 409. 

 Paleotherium (old beast), 380. 

 Paleozoic (pertaining to old or 



ancient animal life), 259. 

 era, general observations on, 



321. 



era, progressive changes during, 

 321. 



Paleozoic era, subdivisions of, 



271. 



rocks, 268. 

 rocks and era, 267. 

 rocks, area of, in the United 



States, 269. 

 system, unconformity of, with 



Archaean, 267. 

 times, growth of the continent 



in, 271. 

 times, physical geography of, 



269. 



Peat, antiseptic property of, 85. 

 bogs, 84. 



bogs, rate of growth of, 87. 

 bogs, structure of, 87. 

 composition of, 84. 

 mode of accumulation of, 85. 

 swamps, 84. 

 Pegmatite, 212. 

 Peneplain, 28. 



Period, geological, defined, 204. 

 Periods arid epochs, 262. 

 Permian period, 323. 

 Petroleum (rock-oil), 313. 

 age of strata of, 314. 

 origin of, 315. 



Phonolite (ringing-stone), 214. 

 Pithecanthropus, 416. 

 Placoderm (plate-skin), 293. 

 Placoganoid (plate-ganoid), 293. 

 Plagioclase (oblique cleavage), 



212, 215. 

 Plesiosaur (near to a lizard), 



334. 



Pliocene (more recent), 365. 

 Pliohippus (more horse-like), 379. 

 Plumularia (plume-like), 276. 

 Plutonic rocks, composition of, 



212. 



Polypterus (many-fumed), 296. 

 Porphyry, 213. 

 Potholes, 26, 63. 

 Primordial beach, 269. 

 Protohippus (first horse), 379. 

 Protozoa (first and lowest living 



things), 266, 352. 

 Psychozoic (pertaining to rational 



life), 260. 

 era, 407. 

 Pteranodon (winged-toothless), 



356. 

 Pterichthys (winged fish), 292. 



