444 NATURAL SCIENCE. ;,„^„,^. 



synclinal trougli in which the highly contorted and crushed sequence 

 of sedimentary rocks — great thicknesses of Palaeozoic, Mesozoic, and 

 even Tertiary strata have been upraised to stupendous altitudes. 

 Later Tertiary and Recent deposits have been laid down in areas 

 between the great lines of parallel flexure, and these help to form the 

 great tablelands of Tibet and the Gobi. 



Most of the great lines of flexure must have existed in Palaeozoic 

 times, " yet the great lateral compressions, which pushed up the 

 enormous masses of the Central Asian plateau, with its fringing rims 

 of mountains, were evidently formed after the Miocene beds were 

 deposited, for we see the latter contorted and crushed, under a cover 

 of almost horizontal young Tertiary deposits, which so far have 

 suffered little from the slow action of folding, which it may be 

 assumed is still going on." 



The oldest rocks consist of granitic gneiss, regarded as meta- 

 morphic granite ; they are apparently overlaid by a schistose series, 

 termed the " Vaikrita system " (from a Sanskrit word indicating 

 " metamorphism"). The rocks of this system comprise mica-schists, 

 talc-schists, and thin bands of gneiss ; and they are regarded as of 

 sedimentary origin. They seem to pass gradually into a newer series 

 of quartzites, phyllites, and slates, with coarse conglomerates, grouped 

 under the name " Haimanta system." 



This system (taking its name from a Sanskrit word signifying 

 "snow-covered") appears to be constant in lithological aspect, and 

 to have a thickness of from 3,000 to 4,000 feet ; but the beds are 

 extensively crushed and folded. The rocks underlie conformably 

 Lower Silurian strata, but as they may comprise not only the 

 Cambrian but still older groups, it was thought best to apply a 

 distinct name, even though it be a provisional one.^ The name itself 

 is meant to indicate the fact that the beds, with few exceptions, lie 

 within the area of perpetual snow. Hence they cannot reveal their 

 history very readily to the geological enquirer. The Haimanta 

 system has yielded only a doubtful Crinoid, a doubtful Bivalve, and 

 an undetermined species of Bellevophon. 



Conformably above the Haimanta system come beds grouped as 

 Lower and Upper Silurian. Limestone is the predominant rock of 

 the Lower Silurian, and quartzite of the Upper. They follow on 

 without break, passing gradually one into the other by alternating 

 beds. The Lower Silurian rocks are estimated to have a thickness 

 of from 200 to 300 feet only. The fossils, which include Encrinites 

 and Corals, await description, but the fauna of the " Coral-lime- 

 stone " is said to correspond with that of the Lower Silurian of 

 Europe. The Upper Silurian strata attain a thickness of 1,000 to 

 1,200 feet, but their fossils, which include Oythis and other Brachio- 



' It should be mentioned that somewhat different names were previously 

 adopted by Mr. R. Lydekker for the great groups of rocks in the adjoining area of 

 Kashmir, &c. See Mem. Geol. Sui'v. India, vol. xxii., 1883. 



