SECTION I. TRANSCASPIA AND ITS 
NATURAL CONDITIONS 
CHAPTER I 
Situation and Boundaries of the Region examined. 
HE great tract of lowlands, a southern extension of the 
West-Siberian plain, stretching from the Caspian Sea to 
the country round Lake Balchash, and having as its southern 
boundary the mountains of northern Persia, the Thianshan 
and Ala-tau and which is in open communication with the 
south of Russia, to the north-west, through the plains north 
of the Caspian Sea, cannot strictly be designated as belonging 
to those portions of the continent which are without drainage 
to the sea. The »Duab« or »country with two streams« tra- 
versed by the two great rivers Amu and Syr, both flowing 
into the Aral Sea, is of the type designated by RICHTHOFEN 
as a peripheral region, that is a region whose waters are car- 
ried by rivers to the sea, or to remnants of sea which are 
now lakes. RICHTHOFEN’s Central Asia, on the contrary, in- 
cludes the areas in the interior of Asia which are devoid of 
any drainage to the sea. Here the wind is the principal 
geological agent, and all the products of chemical or mech- 
anical disintegration remain in the country; they are only 
moved from one place to another, filling up the hollows 
and thus imparting a monotonous aspect to the country. 
While, as RICHTHOFEN remarks, the movement in Central 
Asia is centripetal, it is centrifugal in the peripheral regions, 
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