STR es 
Kum, and at Dshideli MusHkerow found Barchan-sand with 
grains not exceeding 0,1 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'Ss 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 Rappe “Hiigel- 
sand”, in SEMENOW ‘désert de sable mamelonnée’’). 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-, oder Streifen- 
sand” of RADDE, “déserts 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 
