mediately opposite to each threshold in the chain of bajirs there is an expansion or swelling of the dune-range situated west of the threshold. An example of this is shown in the annexed sketch (fig. 301) of the threshold, not yet quite mature, which parts bajirs No. 9 and No. to. The same thing is true (see fig. 303) of each compound dune-length that has reached the stage in which the highest individual dunes trail the longest »tail», b, behind them. And even when we have several successive stages or »stories» represented, when the dunes have climbed up over each other, the relations remain exactly the same; that is, they are precisely such as we have found in the immense sand-accumulations. As the tongue of sand b must enjoy relatively greater shelter from the wind than any point (c) whatsoever, its advance westwards is obviously retarded, until eventually it becomes overwhelmed by the sand-wave a (fig. 301). If now several compound dune-lengths follow after one another, like the waves of the sea (fig. 303), there ensue sand-free spaces B in the parts which lie to the windward of the lowest dunes c; and these depressions are bordered by the »tails» of the highest dunes (b). When exemplified in its greatest conceivable degree, the arrangement becomes what we found it in the Desert of Tschertschen, amazing though it may at the same time be in its regularity.
As a rule in the districts nearest to the Tarim, we find that each sandy threshold corresponds to a westward bulging or swelling of the sand-wall that shuts it in on the east, as for example the threshold between bajirs Nos. I and 2 (see fig. 304). Here, too, I believe I am right in saying, that the swelling is higher than
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