330 TO THE SU-LO-HO DELTA [Chap. IX
Glacis of I ascended the slope sufficiently far to make sure that rows of high clay terraces, just like those
gravel we had skirted, abutted on the foot of the Sai for a distance of at least four miles eastward. Above
this wide glacis of piedmont gravel there rose only a few scattered terraces of reddish clay of no great height, showing that the soil underlying the cover of coarse gravel was the same here as that from which the rows of Mesas had been carved out within the basin southward. No trace of vegetation, living or dead, could be seen anywhere on this desolate Sai ; nor could we, scanning its surface with our glasses, discover any signs of well-defined drainage channels across it. As seen from the Mesas that we ascended, the gravel slope to the north-east stretched away unbroken with an apparently very uniform gradient right up to the horizon. To the north only low isolated hills showed above it in the distance. It seemed clear that from those sides no drainage could reach the basin sufficient to account for all the moisture shown by its surface.
Length of After having thus reconnoitred the northern limit of the basin, we turned to the south-south-
Mesas. east and marched along the gravel-strewn trough between two rows of high Mesas. The longi-
tudinal extension of the Mesas is illustrated by the fact that, while thus moving for a distânce of over two miles, I noticed only one gap in the Mesa row on our left through which it might have been possible to take our camels. After that distance had been covered, vegetation appeared again in the shape of some thorny scrub growing on a few small hillocks of sand, and there we camped for the night. The attempt at a well was abandoned as the soil composed of mixed gravel and sand showed no signs of moisture after we had dug down a few feet.
Formation The night of March 14th to 15th brought a violent storm from the south-west, which cleared
of Mesas. the atmosphere completely. As a result, the view obtained when in the early morning we ascended a prominent Mesa, probably about a hundred and fifty feet in height, just south of our camp, was exceptionally comprehensive. All round us it showed serried lines of Mesas, built up of layers of reddish-brown clay with much thinner strata of yellow sandstone between. The panoramic view reproduced in Figs. 184-6 well illustrates the varied shapes of these Mesas, and also shows how wind-erosion attacking the softer sandstone strata undercuts the more solid clay and gradually breaks up the long ridges into smaller terraces and knolls.
Southern Besides the big area of Mesas in which we stood, two other belts of them, narrower but longer,
edge of could be made out eastwards. These, too, were obviously comprised within the limits of the ancient
basin. lacustrine basin extending between the foot of the gravel glacis northward and the line of high
sands on the south. From our elevated point of observation I could clearly see that this line of big dunes was continued on the south-east by a long flat plateau of Sai, and our mapping of 1907 left no doubt that behind this there lay the end of the Su-lo-ho course, as then surveyed.9 But of a gap in this plateau by which the waters of the dying Su-lo-ho might reach the basin, as then conjecturally assumed, no indication was to be discovered.
Snowy Far away to the south there stood up in glittering snowy whiteness the great range of mountains
mountains from above Tun-huang to Anambar-ula. It was a very imposing sight, which occasional clear sighted.
views obtained in the course of my explorations along the Tun-huang Limes had impressed on my memory. The night's storm had deposited a light sprinkling of snow, too, on some of the low desert hills rising above the dark gravel glacis to the north. But this soon disappeared as the sun rose higher. The panorama around me was on a vaster scale and, in spite of its utter desolation, more varied than any my eyes had rested upon in Central-Asian plains.
South- Satisfied as to the character and limits of the north-western portion of the basin, I now decided
eastern to reconnoitre it in the south-east. After moving for about two miles southward between rows of
basin. Mesas, we emerged on a level plain of sand fringed by clay terraces which wind-erosion had reduced
9 See Serindia, v. Map No. i4. A. 3, with the correction indicated, ibid., ii. p. 551, note io, .