Tarim, its lower course would to a dead certainty incline successively towards the north, north-north-east, and north-east, and would consequently form an arc of approximately the same shape as that described by my itinerary through the Desert of Tschertschen (Pl. 38).
The circumstance that, during the scanty thirty years in which the Karakoschun has been known to Europeans, it has been constantly shrinking, an omen, as some opine, of its speedy total disappearance — this circumstance in no way proves that the terminal basin of the Tarim has been uninterruptedly growing less and less right down from the earliest times of which the Chinese annals speak. No inference can be drawn from the nomenclature of the Chinese records; for, while some of the names terminate in the equivalent for »sea», others indicate a »marsh», e. g. Lôu-lan-hai (the Lôu-lan Sea) and Jen-tsö (the Salt Marsh). The dimensions, 200 li long and I oo li broad, suggest on the other hand a very small lake. All the lakes of Central Asia are undergoing a process of desiccation, although the process has of course reached different stages in different types of lake. While, for instance, the Baghrasch-köl and the Issik-köl are hardly likely, for a long time to come, to undergo any appreciable alteration in either form or extent, it is quite easy to trace the amount of shrinkage which the Sea of Aral or the Lake of Balkasch has undergone within a pretty recent period. But the Lop-nor-and-Kara-koschun forms such a peculiar exception both in regard to geographical situation and hydrographical relations, that no comparison can be instituted between this migratory lake and any of its neighbours. For one thing, its sources are distributed over such a vast area and occur in such widely diversified regions as northern and western Tibet, the eastern Pamirs, and the southern Tien-schan, and for another thing the terminal basin is situated at such an immense distance from all its headwaters. I have already alluded to the stupendous changes which took place during the later geological epochs in connection with the Central Asian Mediterranean, and its.final complete disappearance; but within historical times, with which alone we are here concerned, that is at the most a period of 2,000 years, we can hardly suppose that any very great climatic changes have taken place within the basin of the Tarim or its catchment area. Dr. Nils Ekholm has personally suggested to me, that the encroachment of the peripheral regions upon the central territory, or in other words the forward movement of the water-partings towards the central parts of the continent, may be at any rate one of the causes of the desiccation of the Tibetan lakes. If this theory is sound, the continued erosion of the head-feeders of the Tarim would tend to push back the water-partings outwards towards the periphery, and consequently to enlarge the drainage-area of the Tarim system, the effect of which would be the direct opposite of that which actually takes place, that is to say the terminal lake would increase in area. In any case however a change that is dependent upon the displacement of the water-parting is a geological phenomenon, and consequently lies entirely beyond the control of historical criteria.
If we except the Kerija-darja, it cannot be said that the rivers of East Turkestan carry any smaller volumes now than they did 2,000 years ago. According to Stein, the river I have mentioned reached the Tarim as late as the 16th century. But, one cannot help asking, can such great climatic changes have taken place
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