LACUSTRINE PROBLEMS. DESICCATION ETC.
several successive stages one above another; beside yet others the beach-lines reach up to no less than 133 m. above the existing level. Some lakes are as much as 48 m. deep, others quite shallow. In some we found only little pools of water surviving amid an expanse of nothing but salt and gypsum; while others are ternporary, and others again completely dried up. The varying extent to which the desiccation has proceeded does not seem to have anything to do with the absolute altitude, but appears on the contrary to be intimately connected with the positions which the several lakes ocupy on the highland plateau. The desiccation advances, for instance, more rapidly in the south than in the north, and, at an even more enhanced rate, more rapidly in the west than in the east. But what are the climatic
Fig. 375. VIEWS OF THE NAKTSONG-TSO.
or other agencies which give rise to this desiccation throughout the whole of Tibet, and that with varying degrees of energy ? Probably the amount of moisture and of precipitation which is carried up from the Indian Ocean is smaller than formerly; but what is the cause of that ? I leave the solution of this question to Dr. Ekholm, who has been digesting the materials of the meteorological observations. Can it be that it is dependent upon a still active elevation of the geologically recent ranges of the Himalaya, or, as Dr. Ekholm suggests, upon the encroachments which the peripheral regions are making upon the central regions ? That the Himalayan water-divide is advancing from the Indian side towards the Tibetan is certain ; but considering the amount of the precipitation, this change can hardly produce any other effect except that of diminishing to some extent the supplies yielded up to the Indus and the Tsangpo, without on the other hand influencing the amount of the precipitation in the interior, self-contained drainage-basins. It is more probable that the desiccation of the Tibetan lakes is dependent upon more comprehensive climatic alterations, possibly of a periodic character and affecting perhaps the whole of the
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