HYDROGRAPHIC RELATIONS OF THE JARKENT-DARJA AND TIIE AK-SU-DARJA. 79
Lake of Kara-koschun would probably disappear. Heavy contributions are levied upon all the rivers of East Turkestan the moment they emerge from the mountains, in that the oases, which girdle the outer periphery of the lowland parts of their basin, deprive them of very considerable quantities of water, so that, as they radiate across the arid regions towards their point of convergence in the Lop marshes, they shrink in a more than proportional degree. The stream which suffers least from these antagonistic influences is the Ak-su-darja. On the assumption that this river is the main trunk of the hydrographic system, and the Jarkent-darja, Chotandarja, Kerija-darja, and Nija-darja are its chief branches, it is interesting to note how these streams become severally smaller the farther they lie to the east; and this applies to the area of their drainage no less than to their length and their volume. The Jarkent-darja, when it joins with the Ak-su-darja, is, in spite of its losses on the way, a really imposing stream; the Chotan-darja, however, only flows into the Jarkent-darja during forty days throughout the year; while the Kerija-darja perishes in the sand fully 132 km. before reaching the Atschik-darja, a branch of the Tarim, * and the Nija-darja disappears at a distance of no less than 28o km. from the Tarim. The only exception to this rule is the Tschertschen-darja, which carries water all the year round. The causes of this are, however, the great extent of its drainage area in Northern Tibet, its own geographical position, and the climatic conditions which prevail within its basin.
If a stranger, ignorant of the hydrographic peculiarities of the region, were to arrive at the Jarkent-darjaning-kujluschi, no matter what the season of the year, he would not hesitate for a single instant as to which of the two rivers that meet there is the mother stream and which the tributary; and a glance at the accompanying sketch-map (p. 77) is equally conclusive. However for the future we shall continue to treat the Jarkent-darja as the principal stream of the Tarim system.
Returning now to the Jarkent-darjaning-kujluschi — a short distance above the actual confluence the Jarkent-darja contracts to a very narrow canal-like stream, with quite insignificant alluvial deposits. At the apex between the two converging rivers there is a crescentic deposit of sedimentary matter. During the last few hundred metres or so of its course the current comes to a complete standstill, and
* This was the measurement I ascertained when in 1895 I traversed the Kerija-darja from Kotschkar-aghil to its termination, though from the point where the water ceased to flow it was possible to follow its sanded-up bed for another 1 V. days. After that it disappeared under sand-dunes 3o m. high, and its further course could only be surmised from the poplars and tamarisks which survived at intervals along a pretty straight line towards the north. Dr. M. A. Stein, when describing his visit to the ruins of Kara-dung, which I discovered in 1895, makes the following interesting statements: 0A remark of Mirza Hajdar, the Moghul leader and historian, makes it very probable, that the Kerija River reached the Tarim as late as the t6th century. Its old course across the desert can be followed even now without serious difficulty, and certainly forms the most direct route between Khotan and the ancient settlements of Kucha and further north-east. Kara-dong lies about half-way between the Tarim and the line of oases stretching to the east of Khotan, and a small post established here would have answered the purpose of guarding the route and protecting the approaches from the northern region» (Sand-buried Ruins of Khotan, p. 432).
The Kerija was cut off from the Tarim by a gradual process, receding from it step by step; indeed, the process is still going on, for the distance between the northernmost tentacle of the former and the great river is constantly increasing, though at a slow rate. And although the old channel of the Kerija-darja is now obliterated or filled in with sand, it is not only possible, it is indeed quite probable, judging from the still living poplars, that it did reach the Tarim as late as the 16th century.
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