ACROSS THE JARDANG DESERT TO ALTMISCH-BULAK. 65
shrivelled tamarisk or two. It is therefore not rash to suppose, that at these poplars we quitted the lake-side, and that the sterile ground belonged to the bottom of the former lake. Here again the surface was plentifully littered with Limnœa shells, some whole, others fragmentary, generally lying loose upon the soil, though sometimes they were fixed fast in the clay faces of the jardangs, whence they are chiselled out by the wind. The ground consisted here of the same fine yellow clay as before. Its several layers, of varying degrees of hardness, were extraordinarily distinct, and had in general a dip of 2° to 3° to the SW. and W. Sometimes however they dipped as much as 20° towards every point of the compass. In other words, they bulged upwards, the bulging having taken place whilst the clay was still wet, so that there was no break in it. The mollusc-shells embedded in it prove that it was originally deposited in the basin of a fresh-water lake. The slight fall may be more apparent, the sediment having been deposited more abundantly in some parts than in others, for instance around the embouchure of the river. Each successive high-water period has added a fresh layer of silt; each successive storm has added a thin layer of sand.
Fig. 6o. IN A GULLY BETWEEN TWO JARDANGS.
With amazing regularity and without the slightest interruption, this dry clay soil is furrowed throughout by pretty deep gullies, which separate the jardangs one from another. The only variety they present arises out of the consistency of the surface, that is to say, out of the varying resistance which it has offered to the corrosive, abrading force of the wind. Over a considerable area the jardangs lay as depicted in the accompanying schematic sketch (fig. 6o). Each ridge was broken off pretty abruptly on the north-east, but had a gentle slope towards the south-west. But an even commoner conformation is that shown in fig. 61, which represents a vertical section from north-west to south-east across a number of jardangs. These ridges are often hundreds of meters long, and run uniformly from north-east to south-west,
fledin, 7onrney in Central Asia. H. 9
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