CHAP. xi.] DÉBRIS-STREWN ' TATIS ' 189
invariably displayed on their bare sides the natural soil without any trace of ancient deposits.
In the formation of these banks, as in all other features of such sites, it was impossible to mistake most striking evidence of the erosive action of the winds and sandstorms which sweep the great desert and its outskirts for long periods of the spring and summer. Only the fragments above described could, by the Hardness and weight of their material, survive, sinking lower and lower as the ground beneath gets more and more eroded, while everything in the shape of mud walls, timber, &c., as ordinarily used in the construction of Turkestan houses, has long ago decayed and been swept away. Even the potsherds which have withstood destruction bear plain evidence of the slow but continuous onset to which they have been exposed, in their small size and in their peculiarly rough surface, that looks as if it had been subjected to " grounding."
It is evident that such a process of erosion at sites of ancient habitations could not have gone on during the long centuries since their abandonment without also considerably lowering the ground level. But the erosion has not proceeded uniformly over an entire area, as shown by the banks of loess already referred to, which are now seen rising like small plateaus or islands above the more disintegrated parts of a ` Tati.' Whether they derived comparative protection from the greater abundance of liard débris with which they are ordinarily covered, or from some other special feature, it is certain that they are most useful to the archæologist as evidence of the original ground level. Coins, much corroded metal ornaments, stone seals and similar small objects which can withstand the force of the winds, are occasionally picked up from Tatis. A few of the latter situated beyond Giulia were found to be named in the list of places where Islam Akhun alleged he had made his discoveries of paper manuscripts or "block-prints." But the examination of the very first sites passed
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