EVIDENCES OF RECENT GEOLOGICAL CHANGES 137 



not great. The whole area occupied by this delta above the water is 

 not over one-twentieth that of the portion under consideration, while if 

 we estimate the amount which has been carried into the lake beyond 

 the shoreline as four times this amount, that would only result in one- 

 fifth of the work required to fill the whole basin, thus bringing the actual 

 time down to 100,000 years, while, on account of our probable overesti- 

 mate of the thickness of the deposit in the delta, the total amount of 

 work done is doubtless much overestimated, bringing the elate down to 

 still lower limits; but however much one should lengthen this esti- 

 mate, it must remain the clearest and most definite evidence yet brought 

 to notice of the recency of some of the extensive changes connected with 

 and following the close of the Tertiary period. 



3. Other evidence concerning the recency of these great changes in 

 northern and central Asia appears in the more definite witness of recent 

 shoreline deposits of gravel at an elevation of 600 or 700 feet in widely 

 separated regions. One of these is reported by J. Stadling* near the 

 mouth of the Lena river and 10 miles back from it, where he found, 600 

 feet above the sea, " in a layer of soil composed of turf and mud mixed 

 with sand, resting on a foundation of solid ice as clean and blue as steel 

 and of unknown depth, large quantities of driftwood, evidently brought 

 down by the river at the remote period when it had its course here." 

 Another is one, which I have elsewhere described,f at Trebizond, on 

 the Black sea, where a large amount of fresh-looking beach gravel is 

 found clinging to the precipitous side of the volcanic rocky mass back 

 of the city at an elevation of 750 feet above the sea. Still anothor in- 

 stance, w r hich I have described in the same paper, is in the lower part of 

 the Dariel pass, on the north side of the Caucasus mountains, w T here 

 there are extensive fluviatile deposits of such character as to indicate a 

 great change in the relative level of the gorge in correspondingly recent 

 times. In conformity with this, Professor Charles W. Keyes tells me 

 that he has observed extensive raised beaches of corresponding height 

 to those of Trebizond at Soudak, on the north shore of the Crimea.' 



All these things point to the fact that in those epeirogeniclmovements 

 which characterized the latter part of the Tertiary and the whole of the 

 Glacial period, there, was a brief subsidence of the Asiatic continent — 

 central Asia, perhaps, playing see-saw with northwestern Europe and 

 America, the one going down w r hile the other went up. But, however 

 that might be, at some stage during this late period of geological insta- 

 bility, a general depression of central Asia must have occurred to account 

 for the phenomena we have presented, distributing the loess in the pecu- 



*See J. Stadl.ing : Through Siberia, p. 161. New York, 1901. 

 fSee Quarterly Journal, Geol. Society, toI. 57, 1901, p. -249, 



