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Across Coveted Lands by Arnold Henry Savage Landor

They are within the same zone of volcanic formation


To

the east-south-east of the lakes the sand-hills rise to a great height and eventually form a high ridge, which for some reason or other is cut perpendicularly on its western side, possibly as the result of a volcanic commotion. Of similar origin probably was the gigantic crack caused by an earthquake which we shall examine later on near Nushki. In fact, both the crack at Nushki and the collapse of the west side of this hill range, as well as a great portion of that deep crack in the earth's crest in which the Shela flows, have very likely been formed by the same cause. They are within the same zone of volcanic formation. In the particular case of this hill range in Afghanistan the collapse did not appear to me to be due to the action of water, but to a sudden crumbling which had caused a very sharp vertical cut.

[Illustration: Sand Hills.]

To the north of the salt wastes was another long belt of yellow sand extending for some 40 miles, upon which there was absolutely no vegetation, while intervening between the salt and this sand flat were numerous sand barchans, like horseshoes, with a gradual slope on the windward side (north) and a crescent hollow with a steep but not quite vertical bank on the lee side.

I noticed all over Persia, and in Beluchistan as well as here, that these sand barchans, or barchanes, will only form on level ground--generally on extensive plains. All

single sand hills, however, whether barchans, conical, semi-spherical, or of more irregular shapes, are invariably caused by a primary obstacle, however small, arresting the sand. Various are the theories with regard to the formation of these barchans, and especially with regard to the formation of the hollow on the lee side.

[Illustration]

The explanation from my own observation has--if no other--at least the merit of simplicity. The wind, on meeting the semi-circular back of the barchan, is diverted on the two sides of it; these two currents come into violent collision again on the lee-side, where, the air being more or less still, a considerable portion of the wind is forcibly driven back towards the barchan, corroding its side in a double rotatory way, each such circle having for a diameter the radius of the barchan crescent containing them. In fact in many barchans the sand ripples on the windward slopes cross the direction of the wind at right angles. A line of sand formed in the centre of the barchan crescent in the opposite direction to the wind is often to be seen during wind storms or soon after. I have also seen barchans, the inner crescent of which showed beyond doubt that when there is a prevalent wind from one side only, the above explanation, although less scientifically obscure and elaborate than most, applies, and, I think, it may eventually be found quite the most probable.

The diagram here given will illustrate and, I hope, make quite clear the meaning of my words. In the centre of the crescent can be noticed the action of the parting wind currents.


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