Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/868

Rh 828 HIMALAYA The outer parts of main chain. Probable age and relations. Lines of granite and other igneous rocks. The snowy moun tains. Great peaks. Fossil- iferous strata on Tibetan border. passing from these outer and lower ranges to those higher mountains which extend to the line of snowy peaks. On the west of the ch.iin the first of these ranges consists of argillaceous shales and schists, grits and limestones, inter sected by several lines of igneous action, and all devoid of fossil remains. True slates also occur. The stratification is everywhere well marked, the dip being usually towards the interior of the chain at an angle of from 10 to 2(T. Portions of the mountains are found in which the dip is quite reversed, or towards the plains, a result no doubt of absolute rupture and partial dislocation. The lines of igneous action follow generally the line of strike, the type of the rock being greenstone, and conglomerates or breccias being often associated with it. How far these beds extend to the eastward is somewhat in doubt. Suggestions have been made that they are the representatives of the Silurian or other fossiliferous beds found to the north of the great snowy mountains, but the evidence for this is hardly conclusive. The occurrence at the foot of the mountains in Sikim and Bhotan of a deposit containing fossil coal-plants, which are apparently identical with those of the Bengal coal-field, renders it probable that the rocks there are of the age of that coal, that is to say, of the lower Trias, a conclusion which somewhat serves to corroborate the speculation as to the age of the vesteru bids jiist referred to. In certain parts of this outer region of the mountains granite also occurs, accompanied by gneiss and mica-schist, the litter often abounding in garnets. In mineralogical character this granite and its accompanying schists differ greatly from those of the great peaks, which are also formed of granite and schists; this has suggested a possi ble difference of age, and it remains uncertain whether any or what connexion exists between them. As we approach the line of great peaks the rocks pass into highly crystalline gneiss or mica schist, and another more continuous line of granite intrusion occurs, divided into several branches, but distributed generally on the line of strike, that is, along the principal direction of the chain itself. It is chiefly in veins, though it expands at times into masses of considerable size, and more rarely into out bursts large enough to constitute whole mountains. The general dip of the strata continues throughout this area to be directed inwards, its angle being increased to as much as 45, though seldom to more than that. Beds of highly crystalline limestone, some pure, and some not easily dis tinguished from the gneiss or mica schist among which they occur, are common along a band following the direc tion of the strike. The vein granite is usually large-grained ; hornblende at times replaces the mica ; the felspar is invariably white, and crystals of schorl and kyanite are frequently seen in it. The great peaks are, with few exceptions, composed of schistose rock, though granite veins may be seen in the mountain faces to very great elevations ; one of these exceptions is the great peak of Kamet in Kuniaon, which rises to about 25,000 feet in what appears to be a mass of grey granite. Passing to the north of the line of great peaks the meta morphosed schists are suddenly- replaced by slates and lime stones, which are in many places highly fossiliferous, ex hibiting what appears to constitute in the aggregate a fairly continuous series from the Lower Silurian to the Cretaceous formations, though the complete sequence has not been observed in any one locality. The western region of the Himalaya alone has been sufficiently explored to admit of any positive statements, but the indications gathered from such imperfect accounts and other data as exist relative to the eastern parts of the mountains leave little doubt that the change observed in the west on approaching and enter ing Tibet holds good on the east also, and that the general physical features of the whole tract are much alike, though doubtless with many differences in detail. The fossiliferous strata of western Tibet are continued, Pkt&amp;lt; though perhaps with some breaks, to the Tertiary period Terti In certain localities nummulitic rocks, probably Eocene, have been observed, and from the great alluvial deposit which forms the plain of Guge, already noticed, the remains of mammals, apparently of Siwalik age, have also been obtained. Among these were bones of the elephant and the rhinoceros, the existence of which, in the present condition of these regions, would be wholly impossible ; so that there is no room to doubt that these deposits have been raised from a comparatively low level to their existing great elevation of upwards of 15,000 feet, since they were laid out. As in the case of the plain of India, we here, too, have no complete proof of the origin of these great nearly horizontal deposits, but it seems clear- from the materials of which they are formed, that they must have been laid out by water, either by the sea of some great inland lake. They are largely composed of boulder deposits, and large boulders are strewed over the surface imbedded in the ground in a manner that seems only explicable as the result of the action of a considerable body of water. Several lines of granitic and eruptive rock occur in Eruj western Tibet, of which all that need here be said is that r &amp;lt; x k they appear all to be older than the Tertiary alluvium, but e some of them are possibly contemporaneous with the num mulitic and older formations. The general conclusion that maybe drawn from the facts Epoi of structure thus briefly indicated is that the elevation of f el the Himalaya to its present great height is of compara- vatic lively recent occurrence. An area of land must have existed where the main line of snowy peaks now stands, which has not been submerged since the Palseozoic period, and which then had its northern boundary somewhere along what has been termed the Indian watershed. Evidence of a similar ancient sea on the south also exists, but in a less definite shape; and whether it was united with the northern sea or not is still a matter of conjecture, though the distinctive character of the fossils rather indicates that there was no direct union. The possible connexion of this ancient Himalayan land area with the pre-Tertiary land of the peninsula of India is also only a matter for speculation. There is further reason to infer that the existence of Anci the great line of peaks is rather due to some previous line F e - of elevation on the ancient land, which has continued to, el , , . . . i M i ii land, retain its relative superiority while the whole area has been raised, rather than to any special line of energy of upheaval of recent date ; and that the fundamental features of its former configuration of surface in mountain and valley have been preserved throughout. There is evidence for the con clusion that the chief rivers of the pre-Tertiary land issued from the mountains where the present main streams are found, and this embryo Himalaya may have been of such moderate height as to have permitted the passage across it of the Siwalik mammals, the remains of which appear both on the border of the Indian plain and in Tibet. It is after the middle Tertiary epoch that the principal elevation of these mountains must have taken place, and about the same time also took place the movements which raised the table-lands of Afghanistan and Persia, and gave southern Asia its existing outline?. The best answer that can be given to an inquiry as to Forc&amp;lt; how changes of level could have arisen, such as those to wl which are observed in the Himalaya, is that they should ? e y a be regarded as due rather to secondary actions conse- their quent on the general contraction of the cooling terrestrial mode sphere than to direct elevating forces, for which no actio1