398 IN SEARCH OF THE LIMES TO SU-CHOU [Chap. XI
to fifteen feet. This comparatively plentiful vegetation is probably supported by subsoil moisture brought down into this part of the depression by the flood-bed of the Po-yang-ho, which debouches from the transverse hill range farther south. When this zone was passed, bare patches of clay increased and gradually gave way to a surface of gravel or very coarse sand, and here the well of Ko-ta-ch`üan-tzti was reached after a total march of seventeen and a half miles (Map No. 42. A. 4). Aneroid readings showed for our camp at this place an elevation of 3,370 feet, fully three hundred feet lower than that of Ying-p`an-p`u-tzti (3,67o feet). This, together with the direction of the dry shallow beds met with in the course of our reconnaissances to the north-east and north, justifies the conclusion that the lowest portion of the Hua-hai-tztl basin lies in this direction.
These reconnaissances were carried out on April 29th by R. B. Lai Singh and myself independently under weather conditions unusual for this desert region. Clouds hung over the basin, hiding from view both the gravel glacis of the Pei-shan northward and the steep and rugged hill chain to the south, and we actually started in the morning under light drizzling rain. Both reconnaissances were rewarded by interesting discoveries. The Limes wall was struck by Lai Singh at a distance of over eight miles to the north, while I myself, to the east and north-east, traced a line of ancient watch-towers stretching towards the wall but quite distinct from it. In describing these remains, the survey and exploration of which kept us busy for a second day, I may conveniently start from the northernmost of the watch-towers mentioned.
We reached this tower, T. xLly. a, after covering a distance of close on five miles from Camp 129, across clayey ground dotted with sparse tamarisk-cones. Numerous shallow beds coming from the north-west showed surfaces of cracked mud on their banks, and suggested that flooding had occurred during recent years. To the north of T. XLIV. a we crossed for about four miles an area covered by low dunes and holding in its centre a narrow belt of small Yardangs. We then entered a zone of tamarisk-cones gradually growing in height, and at a point about five miles from the tower, where these rose to about 3o to 4o feet, we came upon the line of the wall skirting their foot.
As seen in Fig. 219, it presented itself here as a low mound half-smothered by drift-sand, but unmistakably disclosing its character by a thick layer of flat tamarisk branches covering its top. Where we cleared the agger of sand, it showed a width of 9 feet and still reached a height of about 4 feet. It was found to consist entirely of closely packed faggots of tamarisk wood, with plenty of sand between them but no layers of stamped earth. The thickness of the tamarisk branches employed indicated that old tamarisk growth must already have been plentiful near by when the wall was constructed ; while from the absence of stamped clay layers anywhere along this section of the Limes it may safely be concluded that water for forming pisé layers was difficult to obtain.
Line of The agger, at a distance of about a furlong, disappeared eastwards among the tamarisk-cones ;
agger hidden but Lai Singh, when returning here under my instructions, succeeded in tracing its line at intervals by dunes.
for about two miles farther east to a point where it became completely hidden under ridges of high dunes. Westwards, too, the agger was lost, about 300 yards away, among tamarisk-cones. Going half a mile farther, we reached the north-eastern end of a regular ` Dawân' of drift-sand which with its dunes, 20 to 3o feet high, completely smothered the Limes line. Continuing, however, for another mile westwards we got clear of these high dunes and then without difficulty picked up the dark line of the agger again on open bare ground overrun by light sand only.
It could be seen from the last high sandy ridge running for over two miles westwards with one or two slight bends. At the spot where the photograph reproduced in Fig. 218 was taken, about half a mile on, the agger stood to a height of about io feet and was 61 feet wide at the top. Here and
Reconnaissances towards Limes line.
Limes line struck north of T. 'ctn.. a.
Agger formed of tamarisk faggots.
Continuation of line traced westwards.