and that that power was again doubled by the level of the lake being 133 m. higher. Ceteris paribus therefore the abrasion-terrace, which the waves are now creating on the western shore of the promontory visible to the N. 49° E. (see the coloured plate) ought to be only about one-quarter as big as that situated at the 133 m. level.
All I desire to say is, that it would be wrong to make time and the constant position of the lake exclusively responsible for the circumstance that, e. g., the highest beach-line is the most developed; because the additional circumstances, that the wind was then stronger than it is now by reason of the smaller friction, and that the beat of the waves was higher by reason of the same cause, as also by reason of the greater area of the lake — these circumstances account to no slight extent for the greater development of the higher-lying terraces. In other words, apart from the disintegration and corrasion operative at a later period, the abrasion-terrace that is now being created at the western foot of the recently mentioned promontory would require at least four times as long a period to become as much developed as the 133 m. line, or in other words, the lake ought to remain at its present level at least four times as long a period as that in which the 133 m. line was formed.
To sum up. These old beach-lines offer incontrovertible proofs, that the Lakor-tso is shrinking and contracting, and is advancing to meet the same fate that has overtaken many of the lakes which we encountered subsequently, that is to say, it will dry up completely. In each and every one of these energetically marked beach-lines we have as it were a distant »fossilized» echo of the song which the waves once sang when they beat themselves against its rocky shores. With the help of the perspective that they open out, one can adumbrate a distant past in which the physical geography of Tibet was in essential particulars different from what it is now. Orographically the country has since then undergone no other change except that which has been occasioned by the still progressive disintegration. But the number of lakes was then greater, and each separate lake was of greater size ; the rivers carried down fuller volumes to this self-contained basin, the precipitation was more abundant, white-robed rocks commoner, glacier arms, which are now rare as well as rudimentary, were then general, and descended lower down into the valleys, and, as a consequence of all this, the erosive energy was as a rule more active than it is at the present day. In the levelling of the highlands water played a more important part than it does now, for at the present time it is the rending power of the frost, insolation, and wind which in combination continue to counteract the formation of mountain-ranges, while aqueous erosion plays but a secondary rôle. On the other hand, as I have already suggested above, the wind does not appear to have altered since then its characteristic properties ; for at that time also the prevailing wind blew from the west. But the sky was more frequently and more heavily clouded, hail and rain showers smote more often upon the bare mountainsides, and the earth was, I feel sure, not seldom covered with a connected sheet of snow, though snow is now an infrequent sight, at all events it was so during the autumn and winter of 1901.
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