Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/867

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necl. int of mil- ill itures. eology nper- ction data. of Mont Blanc, 15,750 feet, slightly exceeds the highest point of the Pir-panjal, which is but little over 15,500 feet, though, with this single exception, the Kashmir range certainly much exceeds in general mass- that of the por tion of the Alps compared with it. To obliterate these two ranges from the Himalaya would make no very sensible inroad on it, though they surpass in bulk the whole of the Swiss Alps ; and it is no exaggeration to say that, along the entire range of the Himalaya, valleys are to be found among the higher mountains into which the whole Alps might be cast without producing any result that would be discernible at a distance of ten or fifteen miles. And it is important to bear in mind these relations of magni tude, for the terms at our disposal in the description of mountains are so limited that it is necessary to employ the words chain, range, ridge, spur, &c., rather with refer ence to relative than to absolute importance, so that the scale of our nomenclature changes with the extent and altitude of the mountains of which we speak. An examination of the maps of the Himalaya indicates that throughout their whole extent a constant tendency is discernible for the rivers to flow either parallel to the general direction of the part of the chain through which they run, or perpendicular to it, many or perhaps most of them combining both tendencies, and running first in the one direction and then in the other. The conclusion is hence suggested that the system of surface drainage is determined by a series of longitudinal and transverse lines of rupture along and across the mountains. The study of the rivers and mountains themselves confirms this view. In many cases an apparent diagonal direction is found to be really due to a succession of short abrupt bends, though no doubt the rivers at times actually take an oblique course across the mountains. Frequently, too, where a river changes from a longitudinal to a transverse direction, another longitudinal stream meeting the first flows down from an exactly opposite direction. The same disposition is otherwise often exhibited by the occurrence of both transverse and longitudinal lines of drainage, or valleys, starting in opposite directions from the same point on the main ranges, while a depression occurs in the ridge at the point whence such valleys take their departure. As the rivers and ridges that separate them must be laid out on the same general plan, it is natural to find in these last the same tendency to follow lines perpendicular, or parallel, to the general direction of the chain. There is no part of the mountains in which these peculiarities may not be traced, the longitudinal character prevailing on the summit of the table-land, and the transverse being domi nant on the Himalayan slope. By the combination of these tendencies the rivers flow to the plains along a line generally oblique to the component parts of their actual course ; and the watershed ridges that separate them follow corresponding directions. But such watershed lines rarely have any true structural continuity, however strongly they may be marked on our maps, and great caution must be exercised in inferring physical relations among such features of the mountains without obtaining some know ledge of their geological structure. Considering the vast extent of these mountains, and the material and political difficulties in the way of the traveller who visits them, it is not surprising that the knowledge of their geological structure is still very imper fect. From causes which are not very obvious, important parts of the deposits of which they consist have till now not yielded any fossil remains by which their age can be determined : the visits of qualified geologists to the more remote parts of the chain have been very rare ; and it is only within the last few months that any connected memoir on the subject has been published. Much that has been written on it is of too speculative a nature to find place in such an account as the present, and all that can be attempted is a brief outline of the main conclusions that seem estab lished. Of the great Indian plain nothing very definite can be The said. It is an alluvial deposit of sandy clay, on the sur- great face of which nothing in the shape of a pebble can be found P lain - excepting in the immediate vicinity of the hills that rise from it. In one place alone, in the north-west, on the Jumna river, have fossil remains been found imbedded in it, at some depth below the surface. They belonged to terrestrial mammals, with fish and crocodiles, which seem to be of the post-Tertiary epoch. A few borings have been made to depths of some hundreds of feet, but they throw no great light on the subject of the origin of the plain. There is no direct evidence either for or against its having been laid out by the sea ; on the one side it seems difficult to understand how so even a surface could have been pro duced otherwise than under the sea, while on the other there is a complete want of marine remains both in the alluvium itself and in the most recent deposits which form the hills that rise from it. It seems to be admitted that some parts of the alluvial plain of the Indus have been submerged, and in any case, if it was produced by river action, it must have been by rivers having a very small inclination, and in a delta, or at a low elevation. The outermost ranges of the sub-Himalaya are also geolo- The gically the most recent. They are composed of grey outer micaceous sandstones, generally very soft and often quite Siwali unconsolidated, with beds of red and blue clays and marls interspersed, and boulder and gravel beds, at times hardly to be distinguished from those formed in the existing rivers, and often cemented by carbonate of lime into conglome rates. Though these formations are most strongly de veloped to the west, they have been observed in Nepal and also in Bhotan. It is from the ranges in the vicinity of the Jumna river that the characteristic Siwalik fossils have chiefly been obtained. They consist of numerous species of mammals and reptiles, with a few fish, birds, and mollusca, all, however, remains of land or fresh water animals, with no certain trace of marine creatures. Lignite occurs in thin isolated beds in small quantities. It had been commonly supposed that the Siwalik fauna was of Miocene age. The later views rather point to its j being Pliocene. Sixteen genera among the fossil remains have not been found in any beds older than Pliocene, and of the many genera which continue to the present time, some of the forms preserved in these fossils are remarkably similar to existing species, all of which indicates a closer relation to the more recent than to the older Tertiaries. In close juxtaposition with this external band, but con- The nected geologically in a manner that has not been very inner clearly established, is an older series of beds, the lowest of which is nummulitic and of the oldest Tertiary epoch. The fossils found in these beds are as markedly marine as those of the other series are terrestrial. The junction of the newer with this more ancient series is concealed by disturbances, and the former has not been found overlying the latter, but only abutting upon it. This older section of the Tertiary beds of the sub-Himalaya has only been properly made out to the west of the Jumna, though it is likely that it is also represented in the central and eastern parts of the chain by certain sandstones which occur there at the foot of the higher mountains. It may be surmised also that the nummulitic beds of these ranges are connected on the one side with those which are found to the west of the Indus extending to Sindh, and on the other with the nummulitic rocks of the hills south of Assam. A complete change of geological character occurs on