Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/389

Rh m~:NUDA'r1oN.] degradation of the land by subaerial waste. GEOLOGY But most of the great tablelands of the globe seem to be platforms of little—disturbed strata which have been upraised bodily to a considerable elevation. N o sooner, however, are they placed in that position than they are attacked by running water, and begin to be hollowed out into systems of valleys. the valleys sink, the platforms between them grow into narrower and more deﬁnite ridges, until eventually the level tableland is converted into a complicated network of hills and valleys, wherein, nevertheless, the key to the whole arrangement is furnished by a knowledge of the disposition and effects of the ﬂow of water. The examples of this process brought to light in Colorado, Vyoming, Nevada, and the other western territories, by Newberry, King, II-ayden, Powell, and other explorers, are among the most striking monuments of geological operations in the world. The materials worn from the surface of the higher are spreacl out over the lower grounds. Ve have already traced how streams at once begin to drop their freight of sediment Acadian formatlon, 331. Air, movements of, 264; geological operations of, 264. .lps,structu1'eof,371,373. America, .'orth, geology of, 328, 339, 345, 350, 352, 354. 359, 364, 369. Andcsite, 235. Animals, geological oper- ations of, 2.99. Apntite, 225. _-lrclnean rocks, 327. Arcnig group, 331. .-ltmosphcre. 220, 265. Austria, geology of, 327, 364. .-ugite, 228. liagshot group. 361. llala group, 332. Basalt, 235. liath Oolitcs. Belgium. geology of, 341, 350, 358. Blown sand, 237. Bohemia, geology of, 330, 339. 1‘.ouldcr-clay, 367. llracklesham beds. 361. Bradford Clay, 354, 355. lireccia, 237. liritain, geology of, 327, 329, 331. 3-10, 342. 346, 351, 3-32, 351, 3-37, 369, 362, 364. liroolis, 272. Bunter group, 352, 3-53. Cainozoic formations, 360. Calcxfcrous Sandstoncs, 346. Calcite, 223. Cambrian System, 329. Canada. geology of, 323, 339, 345, 3.34, .35-.1. Caradoc group, 332. Carboniferous Limestone, 347. ,, Systcm,346. Carrara marble, 231, 232. Caverns, 271, 320, 369. Chalk, 358, 359, 360. Chlorite. 228. Clays, 237. Clay-slate, 238. Cleavage, 261, 306, 372. Cliff-debris, 237. Climate, affected by earth's movements, 219; by ocean, 285; by man, 291; indicated by fossils, 321. Coal, 235. Coal-measures, 349. Colonies, doctrine of, 323. Concretions in rock, 294. Conglomerate, 237. Contemporancity, goolo-‘ gical, 322. Contraction, effects of, 261, 26-1, 371. Coral islands, 2-37. Corallinc Oolite, 354, 356. Cornbrash, 354, 355. Cosmical aspects geology, 213. ‘ Crag deposits, 364. Cretaceous System, 357. Currents, marine, 283. Dclessite, 223. Deltas, 278, 319. Denudation, 372. Devonian System, 3-10. 1)iabasc, 235. I)iorite, 235, 309. Dip, 298. Dolomite, 2'28, 232. llust-showers, 266. Dykcs, 311. Dynarnical geology, 213, ":19. Earth, planetaryrelations of, 214; form of, 215; movements of, 216; stability of axis of, 216; changes in centre of gra':ityof,217; crust I of, 222, 227, 371; in- terior of, -2-23, 371; I internal heat of, 2213; age of, 226. I Earthquakes, 254. Ecliptic, change in ob- liquity of, 216. Eocene formations, 360. Eozoon,occurrcnee ef,328. I 1-Zpidote, 228. I I I I I I I of Epi gene or surface action, 263. Eqninoxes, precession of, 216. Europe, geology of, 327, 330, 338, 341, 350,351, 3:33, 3-56, 358, 362, 363, 364, 365. Excavation by rivers, 27-5. Expansion, effects of, 264. 1-'alse-bedding, 292. Faults, 261, 301, 372. Fjords, 257. Flint, 238. Fluor-spar, 22.9. Foliation, 315. 1'oraminiferal ooze, 290. Forest marble, 355. Formations, table of geo- logical, 327. Fossils, use of in geology. 296, 321, 324, 325; nature of, 319; how preserved, 319; r.-lativc value of, in geology, 320; relativcagcof,321. As‘ 375 when b the lessening of their declivit their carr inrv 7 y D Y) Y 5 power is diminished (p. 276-7). The great plains of the earth’s surface are due to this deposit of gravel, sand, and loam. They are thus monuments at once of the destructive and reproductive processes which have been in progress un- ceasingly since the ﬁrst land rose above the sea and the ﬁr-"t Every pebble and particle of their soil, once part of the distant mountains, has travelled slowly and Again and again have these materials been shifted, ever moving downward and sea-ward. For centuries, perhaps, they have taken their share in the fer- tility of the plains and have ministered to the necessities of ﬂower and tree, of the bird of the air, the beast of the ﬁeld, shower of rain fell. ﬁtfully down ward. and of man himself. OCBRII. But their destiny is still the great In that bourne alone can they ﬁnd undisturbed repose, and there, slowly accumulating in massive beds, they will remain until, in the course of ages, renewed upheaval shall raise them into future land, there once more to pass through the same cycle of change. INDEX. France, geology of, 350, 356, 358, 362, 363. Frost-, 265, 280. Gabbro, 235. Garnet, 228. Gas-spurts, 294. Gault, 357, 359. Geognosy, 213, 220. Geological record, 213, 323, 326. Geology, deﬁnition of.212; cosmical aspects of, 213; dynamical, 213, 239; structural, 213, 291; palzeontological, 213, 319; stratigra- phical, 13, 325; physio- graphical, 213, 370. Germany, geology of, 328, 338, 339, 341, 350, 351, 3-33, 357, 358, 363, 366. Glacial drift. 365. ,, periods, 219. Glaciation of Europe, 366; of America, 369. ' Glaciers, 281. Gneiss, 236. Granite. 230, 233, 308. Graphite, '.'2S. ' Greenland, 359, 363, 36-1. Grcensand, 357. Grcywacke, 231, 287. Gulf-stream, inﬂuence of, in climate, 219. llail, 250. llarlech group, 329. llaiiyne, 228. Heat, effects of, on rocks, 258, 262. llippuritc limestone. 3-58. Homotaxis, 322, 327. liornblendc, 228. Human period, 368. Huron, lake, 328, 37 0. Ilypogene action, 240. Ice, geological action of, 281, 366. Ice-cap, effects of polar, 217, 219. Igneous rocks, structures of, 307. Interbedded rocks, 313. lnterglacial periods, 220, 367. Intrusive rocks, 307, 310. Iron, oxides of, 228, Joints, 297. Jurassic System, 354. Kcllaways rock, 354, 356. Keuper group, 352, 3-53. liimeridgc Clay, 35-1, 3-36. Lakes, 27, 319, 374 ; frozen, 2S0. Lamina: of rocks, 293. Laurcntian rocks, 327. Lavas, 24 2, 246. Leucitc, 22S. Lias, 354. Life, geological effects of plant and animal, 289. Lignite, 238. Limcstones, 232-2-SS. Lingula Flags, 329. Liparite, 234. Llandeilo Flag group, 332. Llandovery group, lower, 332. Llandovery group, upper, 334. London Clay, 361. Longmynd group, 329. Ludlov group, 335. ‘Alan, antiquity of, 368. lllan as a geological agent, 291. lliangrovc swamps, 289. llarlstone, 354. .ay llill Sandstoncs, 33-1. Mcnevian group, 329. llctamorphic rocks, 314. _lctamorphism, 263, 315, 372. Miea, 2'28. .ica-schist, 231-236. Millstone Grit, 349. Mineral veins, 317. Miocene rocks, 362. Molasse, 363. Mountains, origin of, 2.19, 370, 371, 374. Ncocomian series, 359. Nephcline, 228. Nosean, 22S. Obsidian, 2130, 234. Oceanic circulation, 2S4. Oceans, 221, 282. Oil-shale, 238. Old Red Sandstone, 340, 342. Olivine, 228. Oolites, Lower or Bath, 355; Middle or Oxford, 356; Upper or Port- land, 356. Overlap, 295. Oxford Clay, 35-1, 356. Palzeontological geology, 213, 319. Palaeozoicformations,32S. Pearlstone, 23!. Peat, 238, 290, 319. Pemiian System, 351. Phonolite, 234. Physiographical geology, ‘213, 370. Pitchstone, 231, 23-4. Planets, relative densities of, 214. Plants, geological opera- tions of, 2S9, 319. Pleistocene deposits, 365. ..-— our, Plication, 261, 298. Pliocene deposits, 364. Porphyry, 234. Post - Tertiary deposits, 365. Prehistoric formations, 368, 369, 1370. Pressure. effects of, 261. 1‘rimordial zone, 329, 330. Prismatic structure, 249. Propylite, 23-5. 1’umice, 23-4. Purbeck group, 35-4, 356. Quartz, 227. Quartz-porphyry, 233. Quartz-rock, 237. Quaternary deposits, 365. Rain, 267. Rain-prints, 294. taiscd beaches, 256. ltcccnt period, 368. 370. lthtetie beds, 352, 353. Ripple-mark, 293. ltivers, 272, 373; geolo- gical action of, 273; frozen, 280. Rocks, characters of, 229; crystalline, 229, 230, 231, 307; f ragmental, 229, 231, 236, 292; microscopic structure. of, 220; schistose, 2335, 314: volcanic fragmen- tal, 239, 242; permea- bilit y of, 267; strat itied, 292, 370; joints of, 297; inclination of,298; curvature of, 298. llock-salt, 223. Rocky Mountains, struc- ture of, 372, 373. Russia, geology of, 338, 342, 367. Sandstone, 237. Scandinaﬁa, geology of , 331, 3:33, 355, 366, 367. Sea, geological operations of, 284; deposits in, 287, 290. Sea-water, composition of, 221. Secondary or systems, 352. Serpentine, 228, Sidcrite, 228. Silurian System, 331. Snow, 280. Soil, 265. Speeton Clay, 357. Springs, 270; hot, 22-}. Stoncsﬁeld slate, 354, 355. Strata, 293, 370; alterna- tions of, 295; persis- tence of, 295; groups of, 296, 327. Mesozoic 232. Stratiﬁcation, 292. (A. on.) Strike, 298. Structural geology, 2125, 291. Submerged forests, 2:16, 321. Subsidence, movements of, 256, 321, 367. Sulphates, 228, 232. Sulphides, 228. Sulphur, 228 Sun-cracks, 294. Superposition, order of, 295. 321, 325. Switzerland, geology of, 353, 359, 362, 363, 371. Sycnite, 234. Table-lands, 37-1. Talc, 22S. Tarannon Shale, 33-1. Tertiary systems, 360. Thanet Sand, 36]. Tides, 283. ’1'ill, 367. Tourmaline, 22S. Trachyie, 234. Trees, inﬂuence of, I11 I geology. 2:59. Trcmadoc Slates, 330. Triassic System, 352. Tuffs, 239. L'nconformability, 318. United States, geology of, 328, 331, 339, 345, 350, 352, 35-1, 357, 359. 364, 369, 372, 373. L’phca-al, movements of, 255, 321. Veins of intrusion, 311. Volcanic action, causes of, 253 Volcanoes, 223, 240; pro- ducts of, 241; action of, 243; ﬁssures at, 2-14; explosions of, 241; showers of stones from, 245; geological effects of, 249; mud from, 250; structure of, 251; submarine, 2.’-2; distribution of in space and time, 2-32; vapours from, 241. 251. agent, 267; subter- ranean, 269; inﬂuence of, in hypogene change, 262. Waves, 285. 'ealden series, 357, 359. 'eathering, 265, 268. Wenlocli group, 335. Woolwich and Reading beds, -161. Zeolites, 223. Zircon, 228. Water as a geological.