two mounds of clay rising before us separated by a distance of about two miles. I was at once struck with the idea that they might mark ruined watch-towers of the ancient frontier line, such as we had previously failed to trace east of An-hsi, and as we passed between them this was strikingly confirmed. When near, it was easy to notice the low but continuous mound, the old agger, which connected the towers. Its line ran parallel to the river, as elsewhere. There was no time then to visit the badly decayed towers ; but of their character there could be no doubt, and I was glad to have ocular proof of remains of the old wall surviving so far eastward.
Close to a large deserted road-side station, ruined apparently as so many others during the havoc of the Tungan rebellion, we crossed a narrow belt of grass and jungle watered by a channel coming from the river, but now swollen to unusual size by surface drainage. The vivid green formed a pleasing contrast to the dark grey gravel of the glacis and the red and brown tinted hills in the background. The grey-haired old ` Ya-i ' who was supposed to guide us knew no name for either stream or station. The ground now rose quickly, and within a mile or so the well-marked cart track brought us among the denuded cliffs and detritus slopes of a regular Wadi. The fantastically eroded hill-sides were so steep, and the winding gorge between them so narrow, that I was constantly wondering how the lumbering carts of this region could ever find a passage through them. But the gorge, in spite of the rock coulisses, never closed completely, and, if it did, a conveniently low ridge at the end of a side branch gave access to another passage.
As is so often observed among desert hills, which wind erosion even more than that of water has scoured and fissured, the eye could not always make out whether the particular bit of gorge was rising or falling. It was getting quite cool when we crossed a somewhat wider depression which I thought might be the watershed, at an approximate elevation of about 5700 feet, to plunge once more into a maze of small serrated ridges and gorges. Their cliffs, apparently coarse sandstone and shale, were
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