THE KURUK-DARJA AND THE COUNTRY SOUTH OF THE KURUK-TAGI-I. 47
usual tamarisk-mounds still continued to appear, though many of them were quite bare, their bushes having been destroyed by the wind and the abrasive action of the sand; though their roots probably in most cases remain, having been protected by the mounds themselves. A little way south of our course we observed a strip of standing toghraks, and beyond them we caught faint glimpses of a few low sand-dunes. These were the first we had seen that day, the nearest previous approach to dunes being slight accumulations of sand in two or three sheltered spots. Yet, owing to the haze which was now become general, we were unable to see to any great distance; . besides, under such conditions it is easy to deceive oneself as to both the distance and the size of objects. The blurring of their outlines leads you to think them farther away than they actually are, and this again deceives you as to their size.
Fig. 43. CLAY TERRACE AT THE SOUTH FOOT OF THE KURUK-TAGH.
About two o'clock a tempest burst upon us from the east-north-east, oc- casioning complete twilight, and preventing us from seeing farther than 20 or 3o m. away. After a while the wind changed to the north-east. Close to the earth it blew with a velocity of 18.E m. in the second; but when the anemometer was placed on the top of a mound only 2 m. high it registered a velocity of 26.6 m. in the second. The tempest continued all the evening and all night, and did not slacken until the following morning. It lowered the temperature to a minimum of — 7.1° C. If surprise was occasioned by the observation I made on this my first visit to the Lop Desert, that I failed to perceive any drift-sand, we have in this tempest a fairly natural explanation of the reason for it. The materials of which. the sandy desert is composed are obtained from the products of disintegration of the encircling mountains, and here we were exactly at the foot of one of the encircling ranges, the source and origin of the drift-sand. But the sand which is carried thence by the wind out into the desert does not get an opportunity to gather into dunes
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