Trachyte (Gr. trachys, rough): a hemicrystalline volcanic rock. Travertine: another name for Calc-sinter (q. v.). Triassic (Gr. trias, three): one of the Mesozoic systems. Tufa, or calcareous tufa: same as Calc-sinter, Travertine (q. v.). Tuff: a volcanic fragmental rock; usually applied to the finer-grained ejecta of volcanic eruptions; may consist almost entirely of lapilli (q. v.) or of the finest sand and dust, or of a mixture of coarse and fine ingredients. Unconformable: not conforming in position, or not having the same inclination or dip with underlying rocks; applied to strata which rest upon an eroded surface of older rocks; unconformity or unconformability, the condition of not being conformable. Underclay the bed upon which a coal-seam rests. : Uniclinal (L. unus, one ; Gr. klino, to lean): applied to a series of strata dipping in one and the same direction. Upthrow, upcast: that side of a fault on which the strata lie at a higher level than their continuations on the other side of the fault. Normal faults are usually described as downthrows; reversed faults as upthrows. Wâdy (Ar.): a ravine or watercourse, dry except in the rainy season. wâdies are perennially dry. Some Weathering applied to the decomposition, disintegration, and breaking up of the superficial parts of rocks under the general action of changes of temperature, and of wind, rain, frost, etc. Zeolites (Gr. zeo, I boil; lithos, stone): a group of minerals, so called because they bubble up in the blowpipe flame; often met with filling up vesicular cavities, etc., in igneous rocks. Conglomerate, 3, 22 Connel Water, 138 Constance, lake, 293, 298 Constriction-basins, 299, 302 Constructional valleys, 347 Continental plateaux, 339 Coral reefs, 334 Cordilleras, 93, 119 Cornet, M., 127 Cornwall, sea-caves, 276 Corrie, see Cirque. Cotswold Hills, 83, 345 Coulmore, 71 Crag-and-tail, 242 Crater lakes, 281 Cree, river, 133 Crevasses in glaciers, 216, 218 Crustal deformation, 13, 47, 48, 179, 209, 280, 330 Early views as to origin of land-forms, I Earthquakes, 164, 267 East African lakes, 162 Elevation mountains, 102 Elk Mountains, 342 Engadine, 243, 284 English Channel, 317 Epigene agents, 4, 23 general results of their action, 332 Erosion of anticlines, 105 of arid regions, 206 of calcareous regions, 268 of Grand Cañon district, 57 of horizontal strata, 49 of inclined strata, 75 of mountains of uplift, 125 of volcanic accumulations, 187 glacial, 215, 287, 293, 300, 311 rate of, 38, 370 various processes of, 23 Escarpment mountains, 146 Escarpments, 73, 76, 79, 82, 84, 88, 120, 254, 304, 343 Escher, Von, 221 |