WIND AND WATER AS DISTRIBUTING AGENCIES 135 



Thus only can the main accumulations into extensive plains filling the 

 depressions between the mountain chains, with all their anomalies of 

 apparent terraces and interpolated beds of gravel and fragments of rock, 

 be accounted for. So limited is the subsequent erosion that this period 

 of depression must be brought down to some such moderately recent 

 date as that to which we are now compelled to assign the Glacial period. 

 In confirmation of this theory as applied to eastern China, it is in 

 place to point to the indubitable evidence of the recent existence of an 

 inland sea as large as the Mediterranean over the area of the desert of 

 Gobi, and connecting, probably, through the Sungarian depression be- 

 tween the Thian Shan and the Altai mountains, with a vast submerged 

 area in western Turkestan and Siberia. The existence of this internal 

 sea of central Asia is attested by the abundant sedimentary deposits 

 about its margin which have been studied, especially in the vicinity of 

 Kashgar, and also by the Chinese historical references to it as the ■' Great 

 Han Hai," or Interior sea. 



Confirmatory Facts from Turkestan 



Instead of following the Trans-Siberian railroad to its western terminus , 

 we left it at Omsk, and, turning up the Irtysh river, traversed by tarantass 

 the belt of country extending from Semipalatinsk to Tashkent, a distance 

 of 1,200 miles, along the northwestern base of the great mountain system 

 of central Asia. Here pretty uniformly, at an elevation from 2,000 to 

 3,000 feet above the sea, we found that the remarkably fertile belt, along 

 which Mongolian hordes have marched from century to century in their 

 westward migrations and expeditions for military conquest, consist of 

 broad expanses of loess very different from the desert sands of the north. 

 This also is spread out in such terrace-like extensions from the base of 

 the mountain as irresistibly to suggest deposition along the margin of a 

 standing body of water ; but there were no signs that glaciers had ever 

 extended out upon the plain. Here, too, the indications that they were 

 accumulated in their present position during a comparatively brief epoch, 

 and that they had not been subjected to present erosive agencies for an 

 indefinite period, is of the same character as that adduced for north- 

 western China. 



Other Evidences of recent geological Changes in the Region 



In confirmation of this theory of a short continental subsidence of 

 central Asia in post-Tertiary times we may point to the general evidences 

 of recent extensive changes of level throughout the region, indicating 



XX— Bull. Geol. Soc. Am., Vol. 13, 1901 



