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0436 Scientific Results of a Journey in Central Asia, 1899-1902 : vol.1
Scientific Results of a Journey in Central Asia, 1899-1902 : vol.1 / Page 436 (Grayscale High Resolution Image)

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[Figure] Fig. 260. VERTICAL SECTION THROUGH A BAJIR, FROM NE. TO SW. THE DARK PARTS ARE THRESHOLDS; THE PARALLEL LINES MARK THE STEEP LEEWARD SIDE OF A DUNE-ACCUMULATION.

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doi: 10.20676/00000216
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316   THE TSCHERTSCHEN DESERT.

different directions, an opinion to which I have called attention in my popular description. But further reflection has led me to doubt the correctness of this view as an explanation of the arrangement of the masses of sand and of the desert relief in general, except indeed in part. The circumstance that the thresholds or isthmuses of separating sand are built up each of an agglomeration of dunes, which melt together and are connected at a thousand different angles and in a thousand different ways, and that, at any rate at the season when we visited them, they turn very steep faces towards the south-west, are proofs that their structure is especially influenced by the north-east wind. The winds which predominate in this part of the desert all come from the north-east quarter of the compass, though at the same time the violent storms issue rather from the east than from the north. If, however, these winds are the sole originating causes of the thresholds coming into existence, we should expect to find the distances between them shorter, whereas we have already had one such distance of over 6 km. I believe therefore that they are, as I have reasoned in Chap. XVII, parts of the original windward flanks of the great on-moving north-east and south-west dune-masses, which are lagging behind, and that the retardation is due to the sheltering influence of lofty summits in the great sand-wave which follows immediately after them; these overtopping summits prolonging and emphasising the shelter which their own leeward flanks afford, in such wise that the outer parts of the windward side of the next following »wave» become less exposed to the wind, and consequently travel more slowly towards the west. But, once one of these thresholds is formed, it becomes exposed, like every other part of the sandy desert, to the north-easterly and south-westerly winds, and thus the arrangement to which I have alluded, with their steep faces towards the south-west is produced. On the other hand these thresholds are virtually protected against the violent easterly tempests. But I shall return to this topic again when I come to sum up the results of this excursion.

Fig. 260. VERTICAL SECTION THROUGH A BAJIR, FROM NE. TO SW. THE DARK PARTS ARE THRESHOLDS; THE PARALLEL LINES MARK THE STEEP LEEWARD SIDE OF A DUNE-ACCUMULATION.

Meanwhile my astonishment increased with each fresh bajir that opened out before us. The first impression which these bajirs produce upon the beholder, as he gazes down upon them, at all events it is true of those nearest to the river, is that they too must be desiccated lakes; but upon penetrating farther into the desert, and finding that the same regular architectural laws still continue to govern their formation, he becomes convinced, that what he sees is due to the effect of the wind, and that the lakes are, so to speak, a mere chance occurrence, their existence depending solely upon their accidental propinquity to the river. But for travelling across a desert no more favourable formation could be wished for than that of these bajirs. What a difference as compared with the abominable surface I had to travel over in the Takla-makan Desert! Not more than one-quarter of the day's march was through