older rocks emerge, for instance Tamdi-Tau, Bukan-Tau, 

 Sultan Uis Dagh, now isolated mountainous masses consisting 

 of various slates and crystalline rocks which as a result of 

 greater denudation are now more cut up than the rocks of 

 Thianshan. 



The deposits from the Cretaceous and Tertiary periods 

 are of great thickness, attaining 5000 feet in Ferghana for 

 instance. They consist of diverse coloured strata of marl, 

 limestone, ferruginous sandstones, gypsum, clay &c. They are 

 not identical everywhere but change according to the near- 

 ness of the mountains: At the foot of the mountains, mar- 

 ginal deposits are found, such as shelly limestones, conglo- 

 merates, clay with gypsum and rock-salt, while, out on the 

 flat land, sand and clay are found deposited in deeper water 



(ROMANOWSKI, MUSHKETOW). 



The Tertiary deposits, however, are rarely visible, as they 

 are almost everywhere covered by newer deposits partly de- 

 rived from them. Of these the most important are: the moving 

 sands, the Aralo-Caspian deposits and the loess. 



Deserts of moving sand cover, according to Rodsewitch, 

 about 88 per ct. of the lowland. The sand is of varied origin. 

 In the northern part it is derived from old Aralian sea-coast 

 dunes and is white or grey. As this sand originates from the 

 old Aralo-Caspian Basin, it has much the same disti'ibution 

 as the Aralo-Caspian deposits mentioned below. 



Throughout the rest of the moving-sand territory, the 

 dunes ("Barchans") are genuine inland deposits which owe 

 their origin purely to the wind, The wind carries off every- 

 thing available, all that mechanical disintegration provides 

 for it. Thus the Aralian dunes, the Aralo-Caspian deposits 

 and the older rocks contribute to the formation of the "Bar- 

 chans". Illustrations of the effects of the levelling process 

 will be found in Berg. — The Barchans are of a dirty yellow 

 colour, they have the shape of a crescent, generally quite 

 regular. The convex part faces the wind, the inclination of 

 the surface is here 6 — 16", while on the lee side it is 30 — 38" 

 (MusHKETOw). The crest is a sharp and regular line, which 

 from the highest point curves downwards and away from 

 the wind. How the crescent shape is produced has been ex- 



