— 78 — 



Kum, and at Dshideli Mushketow found Barchan-sand with 

 grains not exceeding 0,i millimetre. 



The sand always, in the Barchans and elsewhere, consists 

 of quartz. A little mica is found in it, also varying quantities 

 of clay (up to 30 — 40 per ct. on barchans in dry river- 

 valleys), and frequently iron, small quantities of gypsum, cal- 

 cite, etc. (Radde 1899 p. 16). 



The form of the Barchans has already been described 

 (p. 7). Radde's comparison of a barchan-landscape to a frozen 

 stormy sea is a good simile except that waves are not regularly 

 crescent-shaped. Standing on one of the summits and looking 

 towards the north so that the concave sides of the barchans 

 are turned towards one, this imposing waste is most awe-in- 

 spiring. As far as the eye can reach vawe rises behind wave, 

 crest behind crest. The barchans arise irregularly, often se- 

 veral in a group, their flanks blending so that the sharp crest- 

 lines undulate up and down, in and out. Even a gentle breeze 

 raises the fine sand from every crest, and the brownish sand- 

 smoke from the bare dune -summits adds an additional 

 weirdness to the waste landscape. 



As the prevailing winds are northern or north-easterly 

 the sand migrates towards the south and west and crosses 

 the Amu Darya. This will be further dealt with in chap. 11. 



2. Hummock-Desert, Hummock-Sand (in Radde "Hiigel- 

 sand", in Semenow "desert de sable mamelonnee"). Rounded 

 hills, quite low or fairly high, up to about 10 metres, with 

 basin-shaped hollows between them, and with no windward 

 and lee side. They are stationary dunes with a compara- 

 tively rich vegetation. 



3. Desert of the sand-plains ("Sand -steppe", "steppes 

 sablonneuses"), flat or somewhat undulating areas of sedentary 

 sand. 



4. Dune-chain sands ("Ketten-,Reihen-, Wall-, oderStreifen- 

 sand" of Radde, "deserts de sables en sillons" of Semenow). 

 Parallel sand-hills formed by the grey or white sand of pre- 

 sent or past times. Between the chains are valleys, ab. 45 — 200 

 metres (150—700 feet) wide, the soil of which is bare clay 

 (Takyr). The valleys are crossed by lower dunes which 

 run transversely to the main dune-chains. Dune-chain sands 



