262 



SCIENCE. 



[N. S. Vol. XVI. No. 398. 



mountains of British Columbia and Alas- 

 ka. The term Pacific Mountains, which 

 was used by Powell as a designation for 

 the westernmost ranges of the United 

 States, was extended to apply to the moun- 

 tain ranges contiguous to the Pacific Ocean 

 from Lower California to the Alaskan 

 peninsula. 



North of the United States the moun- 

 tains are generally flat-topped and their 

 uniform summits are considered to repre- 

 sent uplifted peneplains. Back of them 

 the plateaus of the interior are of similar 

 origin. Reasoning from the antecedent 

 character of the rivers which head in the 

 inland plateau, and cross the coastal 

 mountain belts, and also from local mer- 

 ging of interior and mountain plateaus, it 

 was shown that the peneplains of the vari- 

 ous regions can be correlated. A great sea- 

 ward-sloping surface of erosion was pro- 

 duced in Eocene time, and upon it the pre- 

 cursors of the present drainage systems 

 were developed. Since the completion of 

 this peneplain, all of the existing moun- 

 tains have been formed, mainly by differ- 

 ential uplift attendant upon the general 

 elevation of northwestern North America. 



Development of the Southeastern Missouri 

 Lowlands: C. F. Marbut. (Abstract 

 read by W. M. Davis.) 

 The lowland region of southeastern Mis- 

 souri consists of two broad belts of flat 

 lowland with a discontinuous ridge between 

 them. One of the lowland belts is an aban- 

 doned valley of the Mississippi river, the 

 other is the valley of the Ohio. The Mis- 

 sissippi river has gained its existing valley 

 by two successive changes, abandoning 

 first about 200 miles of its original valley, 

 and later about twenty more. It was led 

 to abandon its valley because of a shorter 

 and steeper course having been offered it 

 by the Ohio. The Ohio drainage first cap- 



tured some of the small tributaries of the 

 Mississipf)i and later the Mississippi turned 

 itself into these valleys in succession by 

 sapping the ridge between. Since the cap- 

 ture of the Mississippi, several of the small- 

 er rivers of the region have abandoned their 

 older valleys. 



Note. — The above papers were presented 

 through the Geological Society of America, and 

 for more complete accounts of the same see Bul- 

 letin G. 8. A., Vol. XIII., 1902. 



The following papers were offered di- 

 rectly to Section B : 



The International Geographic Congress of 

 1904 under the Auspices of the National 

 Geographic Society: Gilbert H. Gros- 

 VENOR. (Read by title.) 



Possible Effects of the Glacial Period upon 

 the Land Levels of Central Asia: G. 

 Frederick Wright. 



That northern and central Asia has ex- 

 perienced an extensive subsidence in recent 

 geological time is proved by a variety of 

 evidence : 



1. Stadling reports gravel terraces con- 

 taining fresh pieces of wood several miles 

 back from the lower part of the Lena river, 

 650 feet above it. In some cases these ter- 

 races contain the bones of the mastodon 

 and are resting upon solid ice. 



2. On the south shore of the Black sea 

 at Trebizond and Samsun, and upon the 

 north shore around the Crimea, there are 

 fresh gravels which are evidently beach de- 

 posits, hanging upon the sides of cliffs, 

 indicating a recent subsidence of that whole 

 region to the extent certainly of 750 feet. 



3. In the Dariel pass, on the north side 

 of the Caucasus mountains, a few miles 

 above Vladikavkas, there are extensive re- 

 cent water deposits, with the finer material 

 at the bottom and the coarser material at 

 the top, which could have accumulated only 

 when the gradient of the incline was very 



