510 THE DASH FOR LHASA.
rainfall, be remarkably great. The flow of the stream and the transport of water take place in the Tarim throughout the whole of the year; but in the case of the Satschu-tsangpo, it may safely be assumed, that the river only flows during the rainy season, and even then only intermittently, according as the rain falls, whereas during the winter the river will be virtually to all intents and purposes moribund, except for the spring-water which at that period finds its way down its bed, though that will soon freeze. Most of these dissimilarities which I have alluded to are of course to be ascribed to the different lengths of the two rivers, and to their positions with regard to the higher grounds which collect the precipitation for them both. "I'he winter temperature plays a less conspicuous part, for in general the cold will probably be as great in the basin of the Tarim as in high Tibet. The real sources of the Satschu-tsangpo would no doubt be found on the southern slopes of the Tang-la, the same immense mountain-system that gives birth to the Jang-tse-kiang, the Mekong, and the Salwen, the first on the northern, the last two on the southern versant respectively. It is probable that there are localities along the outermost border of the drainage-area of the Satchu-tsangpo which are separated by only one ridge or range from these great streams that flow down to the ocean. At all events the sources of all these rivers are to be sought for within a relatively not very extensive area in the eastern part of high Tibet. Seeing now how great are the effects of the copious rainfall during the rainy season in the relatively short and insignificant Satchu-tsangpo, it is no straining of probability to suppose that they will be incomparably greater in the big rivers that run down to the sea. It would be a task, as grand as it would be pleasing, for one who had the necessary time and inclination, to investigate and clear up the relations within the source region of these great Chinese and Indo-Chinese rivers. One is amazed, even after casting a fugitive glance upon the map, to see that within the relatively narrow space of 200 km. four large rivers are thus pressed together as it were into a sheaf. If this unusual hycirographical arrangement is intimately connected with the little known orographical structure, it is at all events strange that these rivers, flowing so close together and having issue from a common source region, which in point of area can scarcely be bigger than the source region of the Jarkent-darja and the Kaschgar-darja, and in any case is incomparably smaller than the united source-areas of the whole of the Tarim system, — it is strange that they should nevertheless carry so much the greater volumes, so that each of them singly in this respect pretty certainly excels greatly the Tarim. This dissimilarity depends no doubt upon the different amounts of precipitation. While the border-ranges of the Tarim basin, by reason of their more central position, arrest a smaller amount of precipitation, the amount which falls within the source region of the Chinese and Indo-Chinese rivers must clearly be much more abundant. But beyond doubt the same difference obtains in the oscillations of volume between these last-named rivers and the Tarim that obtains between the Tarim and the Satschu-tsangpo, and the difference is intimately connected with the capability of the respective mountains to magazine the precipitation. This capability would seem to be greater in the case of the border-ranges of the Tarim basin than in those of Eastern Tibet. Hence it is that the oscillations of volume in the Tarim are relatively so insignificant, while the Indo-Chinese rivers
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