range which runs north of the Tengri-nor and south of my route to Ladak, and in that part of western Tibet which has been explored by Deasy and others, and which is traversed by the range that I assume to link together the Tang-la and the Kara-korum. In so far as the country between the northern foot of the Himalaya and the Tsangpo is known, it too appears to be studded pretty thickly with lacustrine sheets of water. When you enter on a provisional map all the known lakes, as well as both all the known and all the still problematical mountain-ranges of the first rank, the impression is inevitably borne in upon you that the origin of these lakes is in some way or other dependent upon these lofty mountains. In a word the lakes appear to be concentrated in greatest number in the vicinity of the highest mountains. In consequence of this one is led to surmise, that in some far distant and now vanished past the Tibetan highlands, notwithstanding that it is now vain to seek for evidences of any wide extension of ice, were nevertheless subjected to a glacial period, which, while not comparable with that which was experienced by northern Europe, was yet sufficiently powerful to scoop out these lake-basins. We know that the Himalaya, the Tien-schan, and the Hindu-kusch possessed formerly a greater abundance of glaciers than they do now, and every probability points to the same thing having been the case in Tibet. The lakes now drying up prove that the climate in that country is changing from a moister to a more arid period. On the strength of this alone we may à priori presuppose that the glaciated areas which once existed in Tibet are shrinking and contracting, or in other words that they were formerly bigger than they are now. At the time when the lakes swelled out to the greater dimensions indicated by certain surviving strand-terraces, the precipitation will have been so copious that the glaciers would then receive incomparably greater nutriment than they do at the present time. And going back to a still earlier period, we may conceive that the glaciation was not merely local and restricted to certain culminating portions of the lofty ranges, but regional, embracing at least the greatest of the mountain-ranges in their entirety. If these lake-basins do not owe their existence to the excavating force of the ice-streams, it is difficult to understand why they should par ftréférence be accumulated around the loftiest mountain-ranges.
With regard to the distribution of the lakes over the surface of the plateau we may also apparently lay down the general law, that they grow more numerous from north to south, and this is especially true of the eastern half of the country. But how far towards the south they continue to increase thus in number it is difficult to say; but the law does seem to hold good all the way from the southern foot of the Arka-tagh to Nain Singh's group of crowded lakes. This circumstance is probably in some way connected with the passage of the monsoons across the Tibetan highlands and the varying amounts of their precipitation which fall to the lot of the different mountain-ranges. Thus, genetically considered, the lakes must be most numerous in the south, because it was in that quarter that the glaciation was most developed, and consequently the force which chiselled out the lake-basins must there have been most active and most effective. The farther you advance towards the north the less will have been the nutriment that the ice-bound ranges caught from the monsoons, and the smaller and fewer will have been the lakes.
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