366 THE LOP-NOR PROBLEM.
would be an error to suppose that the effect of the wind is solely restricted to deepening the gullies, for there exists a limit to which the depth can be carried, a limit determined by the collapse of the adjacent ridges. If the depression of the Lop-nor does not in the meantime become filled with water, all the remaining ridges that are held together by vegetation must infallibly fall, that is to say the whole of the area of the desert that is covered with vegetation will be destroyed. Even at the time of our visit, we found a relatively small number of poplar-trees still standing; most of them had already fallen. No year passes without many of them certainly giving way, and the time cannot be far distant when the last poplar will cease to offer resistance to the destructive power of the wind.
In the preceding chapters I have related the results of my investigation of the Desert of Lop, and I hope it will not be considered presumptuous if I now look upon the Lop-nor problem as having been definitively solved. Further detailed investigations in the future will of course extend our views and confirm the physicogeographical laws I have enunciated; but the materials we already possess are quite sufficient to prove that Richthofen's vindication of the accuracy of the Chinese maps is not only warranted, but perfectly correct. Nothing except a critical examination such as that I carried out can conduce to a clear understanding of the changes which have taken place; while in comparison with the information that can be gleaned by an actual study of the existing phenomena on the spot the Chinese maps lose a good deal of their value as proofs. But seeing that their testimony is in agreement with Nature herself, we are bound to render them the respect and recognition which are their due.
Before closing this chapter I should like to call attention briefly to an article entitled The Desiccation of Eur-Asia, which Prince Krapotkin has published in the Geographical ,journal (June i 904), and to the interesting discussion to which it has given rise. In so doing I find it impossible to resist quoting two or three passages from this remarkable article. Even the first few sentences indicate the main features of the writer's point of view with regard to this specially important, but little studied, question. He begins:
»Recent exploration in Central Asia has yielded a considerable body of evidence, all tending to prove that the whole of that wide region is now, and has been since the beginning of historic record, in a state of rapid desiccation. At the present time, evaporation over the whole .of Central Asia is very much in excess of precipitation, and the consequence is, that from year to year the limits of the deserts are extended, and it is only in the close neighbourhood of mountains, which condense vapours on their summits, that life and agriculture are possible with the aid of irrigation.»
Upon this Prof. Mackinder rightly observes, that according to my observations the wind is • the principal factor, and that it produces changes not only in the position of the rivers and lakes, at all events in the basin of the Tarim, but also compels the inhabitants to migrate, and, further, causes the deserts to expand and increase. I also am in full agreement with Dr H. R. Mill when he says:
»I think we may take it for granted, or take it as proved, that the amount of water-vapour in the atmosphere as a whole has remained the same during all historical time. So long as the existing ratio of lands and seas continues, I do not think there can be much room for any fluctuation in the actual amount of evaporation and condensation over the earth's surface as a whole, and any local desiccation
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