264 THE LAKES BESIDE THE LOWER TARIM.
In the fig. (231) the alternate layers of mud and sand are, for the sake of clearness, greatly over-emphasized and shown with a regularity which they do not in fact possess, for they are of course deposited with great irregularity, and the total amount of deposit is excessively small. Yet for all that they are sufficient to act as one of the forces which co-operate to blot the lake out by to a certain extent filling it up with sedimentary matter.
The causes which contribute to make these alternate deposits uneven and dissimilar in different regions are the topographic projection of the lake, the arrangement and shape of the adjacent dunes, the direction of the wind, and the movement of the waves. Broadly speaking, the deposition of sediment takes place along the bottom of the lake, but the sedimentary layer is overlain transgressively by sand, and this takes place in all especially along the eastern shore where the dunes are advancing upon the lake. Nevertheless, as we have found to be the case in the Karaunelik-köl, it is the sand which predominates; at all events the bottom of the lake just mentioned is everywhere covered with sand. The conclusion, that the deposition of sand is greatest along the east side of the lake, is justified by the fact that, where Alga exist, as they do in the Jangi-köl, the Baschköl, and several others, they grow by preference near the western and northern shores, where they find suitable root-hold in the fine clay, whereas on the east side the reiterated sand-slides are clearly detrimental to their growth. On the 2oth May the presence of the river-mud, as indicated by the turbid condition of the water, could only be detected for about a hundred meters from the mouth of the feeding-canal. But at high-flood the mud is carried practically over the whole of the basin, the incoming water travelling in one unbroken wave to the very end of the lake. On the 2oth May the water in the southern basin was as clear as crystal, all the sediment having by that time settled down to the bottom. Hence it may be assumed, that in all these lakes the greatest loss by absorption takes place in their southern divisions, for the relatively greater part of the imported sediment settles in the northern basins. And an examination ad oculos of the southern basin of the Karaunelik-köl suggested at once that it contained less sediment than the northern basin. In both the bajir which comes next to the Tana-baghladi-köl and in that which forms the continuation of the Jangi-köl, we find that the salt-pools (daschis) lie towards the northern end. It is true, we always measured the greatest depths in the southern division of the lakes, though in the two bajirs just named, whatever the cause may be, there was water in their northern parts, whilst their southern basins were almost dry.
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