CHAPTER XXXII.
ALONG THE SOUTHERN FOOT OF THE ARKA-TAGH.
Hitherto we had travelled through a series of large latitudinal valleys, broken up into a countless number of small self-contained basins with next to no vertical differences of altitude; now however we appeared to be approaching a region in which not only the basins, but also their lakes, are larger. In fact it may be laid down as a rule, that both the self-contained basins and their lakes increase in size from west to east; though this law is far less pronounced in the latitudinal valley down which Wellby and Malcolm travelled. On 7th September we marched over the flat threshold which separates the two lake-basins Nos. XV and XVI; the altitude of the threshold was 5116 m. We reached the threshold by following up the brook which empties itself into the first-mentioned lake, and which is embraced between distinctly marked terraced banks. The ground was soft, although it had a thin sprinkling of gravel resting upon a substratum of fine soil. The streams come from the south, from rather imposing mountain-masses, mantled with snow-covered glaciers. Upon reaching the threshold just mentioned they divide, some making their way into lake No. XV, others into lake No. XVI. The latter received about 2 I 2 cub.m. in the second from the mountain-mass I; this was the main stream, and on its bank we pitched Camp XXI at an altitude of 4988 m. To the east-northeast rose a vast snowy mass of the Arka-tagh, which now made its appearance again, though it was generally difficult to make out the positions of its peaks owing to their being enveloped in clouds.
On 8th September we followed the left bank of the main stream. Its eroded terraces are fairly distinct and bear evidence that sometimes a considerable volume must flow down that way, a circumstance easily accounted for by the propinquity of the snowy mountains on both north and south. It receives more particularly from the Arka-tagh several not inconsiderable streams of very muddy water, an indication that they have their origins in glaciers. Consequently the main stream gradually swells into a river of some magnitude, which finally empties itself into the extreme western end of lake No. XVI.
We kept along the foot of the range that rises on the northern side of the stream; the space intervening between our route and the existing river-bank is not
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