170 WESTWARDS TO LADAK.
And even with regard to the power of resistance possessed by the abrasion-lines and abrasion-terraces that do survive, the wind still continues to play a not unessential part. At the present time the slopes facing west are in a far higher degree exposed to the effects of deflation and corrasion than those that face east, because the latter lie sheltered against the predominant westerly wind. So far as this influence is concerned therefore, the latter are more likely to be able to defy the tooth of time than the former, which are incessantly subject to its attacks.
If wé were to follow one of the best marked of these beach-lines all round the lake, as well as we could, entering into the valleys, creeping along the mountainsides, and skirting round the rocky promontories, and so describing an extremely irregular figure, we should certainly find everywhere abundant and convincing proof, that the line is sharper and more distinct in the east than in the west; all the same we ought not to forget, that formerly the difference was probably much greater than it is now, because the mountains on the eastern side of the lake were then directly exposed to the filing of the wind, while the mountains in the west were sheltered from it. And if we confine our attention to the beach-lines which I have recently described on the slopes of the mountains that rise east of the gypsum area, and bear in mind that those same beach-lines decrease in size from above downwards, in consequence of the increasing acceleration in the desiccation of the lake, we are justified in concluding that the difference in size between the upper and the lower beach-lines was greater formerly than it is now; the reason being, that the upper beach-lines are in a higher degree than the lower directly exposed to the wind, which strikes them at a level at which its progress is less impeded by friction with the surface of the earth. The lower the lines lie, the greater is the protection they derive from the mountains in the west, which break the force of the westerly wind. Thus it is not only time per se, but also the varying power which the wind exercises at different altitudes, that tended to make the upper beach-lines formerly much more pronounced and much more developed than the lower ones, beyond what the different sizes of the several lines themselves suggest at the present day.
We have found that the uppermost beach-line is bigger than any of those below it, and have assumed that this points to the lake having maintained a constant level during a relatively long period. But there is yet one other factor which ought not to be entirely neglected when we proceed to compare the different abrasion-lines one with another. When the lake stood 133 m. higher than it does now, the relative altitudes of the surrounding mountains were of course 133 m. lower than they are now. The surface of the lake was consequently then in a far higher degree exposed to the wind, which had in this locality freer play and was less impeded by the relief of the mountains. Independently of the area of the lake, the beat of the waves was therefore both higher and more powerful than it is now, when the lake lies lower and better protected in its deeper basin. Then to this we must add the greater area of the lake, a matter of prime importance in determining the height to which the individual waves rise. When the lake was 133 m. higher, its area would be several times greater. The breadth of the valley outlet, in which stood our Camp CIX, was then at least twice as great as that of the southern bay of the existing lake. Let us say that this would double the abrasive power of the waves,
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