Nevertheless even there it is noticeable, that they are especially numerous around the loftiest mountain systems. According to this theory one would expect to find the greatest number of lakes in the extreme south, at the northern foot of the Himalaya, for it is precisely in that region that at the present day the rainfall is most abundant; but as a matter of fact, so far as our knowledge extends, the number of lakes in that part of the country would appear to be fairly small. But then we have to remember two other factors which come into play, and which we may fairly make answerable for this anomaly. The slope down from the northern foot of the Himalaya to the valley of the Tsangpo is so considerable that the surface is not per se adapted for the origination of lakes; and further, it may be assumed that the very presence of the river will have caused the disappearance of several of the neighbouring lakes through its filling them up itself either directly or indirectly with sediment.
In what I have just said, I purposed merely to point out certain of the problems associated with the "Tibetan lakes. For my own part, I am strongly persuaded that our knowledge of them is all too slight to warrant us in drawing any general conclusions with regard to their formation, and it is my intention to do what I can to fill up the gaps in that defective knowledge. With that end in view it is in the highest degree desirable to explore as many as possible of the lakes of southern Tibet and through numerous soundings endeavour to ascertain their morphology, and by making exact levellings in the environs of several of them to seek to measure not only their varying degrees of desiccation, but also the different heights to which the old beach-lines reach up in the different localities. And if any at all hopeful attempt is to be made to solve the glacial problem, southern Tibet is of course the part of the country in which there exists the greatest prospect of obtaining useful results, for it is there that under all circumstances the glaciation will have been most developed, as is indeed hinted by the number of Nain Singh's groups of lakes. Yet even now I hope that Dr. Nils Ekholm will be able, from my journal of meteorological observations, to deduce some important and salient conclusions. As to the distribution of the rainfall over Tibet at the present day little or nothing is known. Up on the plateau the precipitation is relatively insignificant. In that part of the country we encountered only a few rivers, and they are not large. The Pitelik-darja, Satschu-tsangpo, Jagju-rapga, the river emptying into the large salt lake (Camp XXXIII, 190o), and the Tsanger-schar are the greatest; but it is only during the melting of the snows in summer and during the rainy season of late summer that they swell to respectable dimensions. On the other hand the peripheral regions are incomparably richer in rainfall, and it is in them that the sources of several of the greatest rivers of Asia must be sought for, more especially in the east, south, and west. In the north, on the contrary, where we are too remote from the original fountain head of precipitation, namely the sea, the peripheral regions are relatively poorly supplied with rainfall, so that the rivers which originate there are rather small, pure »babies» as compared with those on the east, south, and west. The only large stream on the north is the Jarkent-darja, and it is so partly because its upper course runs through the highlands of Tibet where they contract to their narrowest, and partly because its sources lie so far south,
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