202 THE TARIM RIVER.
point of view, lay claim to possess more than an ephemeral value. It says in effect only, »Thus it was the river appeared in the autumn of 1899 and early summer of I 900». But how long it will correspond to the actual state of things it is impossible to say. One thing however I do know for certain, and that is, that there are two powerful factors constantly at work modifying the topography of the river, namely (I) alterations in the river-bed for longer or shorter distances, and (2) local changes caused by the formation of loops (boldschemals). Hence a map of the Tarim so far resembles an edition of Baedeker or a statistical handbook, that it soon gets out of date and ought to be issued in a succession of new editions. A century hence only the broad topographical features of my map will admit of being identified with the then existing conditions. Perhaps the local nomenclature will to a large extent still remain, and so will be helpful as a guide for identification. This notwithstanding, the map is, I believe, possessed of considerable value for the physical geography of the regions traversed by the Tarim. For, disregarding what is surely an idle reproach, that it is not worth the trouble to map a river on such an extensive plan, and on so minute a scale, as I have adopted in the present instance, my map, when all is said and done, is, and will be, a document by means of which it will be possible twenty years hence to determine, on the basis of exact figures, in which direction and in what manner the stream has altered its course. Geography expects from modern explorers, that they shall construct accurate maps of the topography and relief of the earth's surface, and the expectation is one that may not be set aside. With the help of the material and the exact quantitative measurements which we collect, and shall hand down to them, the geographical inquirers of the future will be able to arrive at conclusions of the utmost exactitude, such as we can hardly conceive possible, because a hundred years ago scientific workers did not demand anything like the same exactitude and precision that we require at the present day. In view of these considerations I do not look upon the laborious work I have put into the mapping of the Tarim as efforts that have been wasted. There will come a day when it will be esteemed at its proper valuation, and then the results which I only perceive dimly will be established with mathematical precision.
But it is time to return to Arghan. We found that on 3rd June the arm of the river which came from the north — and which, for simplicity's sake, we will call by the name of its best known, though by no means its biggest, branch, the Jätim-tarim — carried a volume of 33.35 cub.m. in the second. The stream which we followed — here coming from the south-west — had a volume of only 21.89 cub.m. in the second; and yet on the very newest maps, e. g. my own in Pelermanns Mitleilungen, Ergänzungsheft, No. 131 and Stieler's Handatlas, map No. 62 (1902), it is represented as being the principal stream. This was unquestionably the case at the time of Prschevalskij's first visit, and this particular stream is even here actually known as the Jarkent-darja, an indication of its priority of existence. But it must now be deposed from the position of honour, and will in due time be mapped as an old dried up and forgotten bed.
The accompanying sketch-map (PI. 35) gives a faithful picture of the relief of the river-bottom at the confluence. It shows that the Jarkent-darja possesses at its termination a perfectly regularly formed channel. The greatest depth occurs nearest
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