LACUSTRINE PROBLEMS. DESICCATION ETC. 607
that a relatively large percentage of the moisture of the Indian Ocean finds its way into them.
In Chapter XXVII to XXXIV of the present volume I have given a general view of the characteristics of the physical geography of the Tibetan plateau in so far as they can be gleaned from the pages of the various explorers and travellers, and my object in doing so was to confirm by the documentary evidence of eyewitnesses the statements which I myself make about it. All the journeys quoted from traversed the same geographical region as my own journeys do, and the leading features of that region, the northern and central portions of "ITibet restricted to internal drainage, are pretty well known. All these travellers are unanimous in representing that highland region as on the whole a level fundamental plateau or socle, traversed by relatively low, flat mountain-ranges disposed latitudinally, and greatly denuded and rounded. They agree likewise in their descriptions of the intervening broad and shallow latitudinal valleys, with their numerous undrained salt-lakes. They agree likewise in their descriptions of the usually soft and treacherous ground that fills those valleys, ground which refuses to bear the weight of a caravan. This phenomenon as it exists in other parts of the world, especially in the mountainous districts of Scandinavia and in the Falkland Islands, has been thoroughly and instructively studied by my countrymen, J. G. Andersson and R. Sernander. To their theories of »travelling ground» I shall hope to return again after I have myself studied the phenomenon more closely in southern Tibet. In the pages of all the travellers quoted above we read the same descriptions of a very dead and desolate country, a highland desert, where edible grass is a great rarity, so much so that even the Tibetan nomads do not think it worth while to drive their flocks and herds thither. It is a monotonous country, where the selfsame landscape scenes follow one another incessantly; the only diversities that present themselves as you travel from north to south are the successive mountain-ranges that continue to rise up in front of you between the latitudinal valleys, mountain-ranges which in their broad features all resemble one another, are all equally bare and barren, are all equally poorly equipped with hard rock. And when you travel from east to west or vice versa, the only diversities you encounter are the fresh lakes you successively meet with on the road; but even they resemble one another, and are equally hopeless, equally monotonous, equally lifeless. The whole of this lofty central region may therefore be regarded as belonging to one single type of regional landscape, where similar climatic conditions have given rise to similar results, where the active agencies of denudation and sedimentary deposition have produced everywhere the same uniform surface forms, a stereotyped morpho-
logy, cast . everywhere in the selfsame mould.
In the south the circumstances are different. The shape of Nain Singh's lakes alone suggests that the mountain-ranges are there built up with less regularity. They also lie closer together, are in general smaller, but at the same time much steeper, and abound in hard rock. Of this country we possess but the scantiest information, having no knowledge even of what its broad features are like. Within the very last year or two the extreme south of Tibet, 1. e. the valley of the Tsangpo, has been reconnoitred by the members of the English expedition; but the
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