Vol. 57.] CHANGES IX NORTHERN AND CENTRAL ASIA, 247 



of the lower Amur Valley south of the 53rd parallel. There are, how- 

 ever, abundant indications that the whole drainage of the lower 

 Amur basin has been obstructed by a recent diiferential subsidence, 

 reducing the gradient to a very low degree. The entire descent 

 from Blagovestshensk to the sea, a distance of about 1200 miles, 

 is less than 300 feet. Nevertheless, it has in this part of its 

 course cut a channel across the Bureya Mountains down to base- 

 level, while both above and below this range the bordering flood- 

 plains and low-level expanses of alluvium extend as far as the eye 

 can reach. We drove for 80 miles over these plains below the 

 mouth of the Zeya Eiver, but there was nothing anywhere to be 

 seen except rich, rolling, grassy (but nearly timberless) prairie-land. 

 In the vicinity of Kavarosk and Blagovestshensk extensive thin 

 gravel-deposits are spread over wide level areas 200 or 300 feet 

 above the river. 



From Blagovestshensk to Chita, a distance of 1200 miles, the 

 river-channel consists of a deep trench cut by the stream across 

 mountains and through broad tablelands. A very pronounced rock- 

 shelf or terrace, 300 or 400 feet above the present level, is almost 

 everywhere to be seen. Chita, in lat. 52° N., is between 2000 and 

 3000 feet above the sea, and lies at the mouth of a valley coming 

 down from the vast Vitim Plateau, which is about 5000 feet above 

 the sea. Here, if anywhere, we ex:pected to find marks of former 

 glaciation ; but we were disappointed. The whole aspect of the 

 country shows the effect of long-continued subaerial erosion. There 

 is no transported material away from the immediate vicinity of the 

 streams. The rocks are everywhere deeply disintegrated by sub- 

 aerial agencies, and the slopes of the sides of the valleys are very 

 gentle, showing the influence of long and uninterrupted subaerial 

 erosion. 



On the other side of the Vitim Plateau, about 500 miles farther 

 west, the lower part of the TJda Valley exhibits an equal absence 

 of glacial marks, though at one point about 3 miles above Verkne 

 Udinsk there were some granite-boulders in a clay-deposit which 

 had much the appearance of Glacial Till. But, as there were 

 outcrops of the granite within a few hundred yards of the place, 

 it would manifestly be unsafe to base any conclusions upon them. 

 There was an equal absence of glacial signs for the 200 miles 

 which we followed down the Kilok River, which, like the TJda, 

 has cut a wide, deep channel across nearly the whole width of the 

 Vitim Plateau. 



Lake Baikal presents some interesting problems in regard to 

 recent geological changes. It is completely surrounded by moun- 

 tains, rising from 3000 to 4000 feet above it, except at one narrow 

 depression through which the Angara lliver carries off its surplus 

 waters. Its surface is 1560 feet above the sea, but in its southern 

 portion it is 4500 feet deep. Its recent origin can be inferred from 

 the fact, that it is not filled with the sediment brought into it by the 

 Selenga and other rivers, all of which have in their long course 



