482 OSB-ORN AND REEDS PREHISTORY OF MAX IN EUROPE 



received with doubt chiefly because the assumption of uniform eustatic 

 movements, on which it is based, is not regarded as yet demonstrated.] 



DISCUSSION BY FRANK LEYERETT 



In a revised discussion, dated February 6, 1922, Leverett comments 

 as follows: (1) Deperet refers the changes in the (eustatic) altitude of 

 the marine shores to a rise and fall of the sea instead of a rise and fall 

 of the land or diastrophism ; he thus confidently correlates shorelines 

 of a given height, no matter where they occur in Europe and in Africa ; 

 by this method he makes a correlation without the essay of a continuous 

 tracing across the intervening space; with the exception of Scandinavia, 

 and certain local areas on the Mediterranean, he finds no occasion to 

 calculate differential uplift of the earth; also, where shorelines occur at 

 various other altitudes than those of the main ones of the type area (as 

 is sometimes the case), he rules them out as of minor rank. (2) Sim- 

 ilarly, the assumption is made by Deperet that if a stream has lowered 

 its bed a given amount, it is in response to a lowering of the sea, and 

 that, too, no matter how far from the sea the lowering may occur or what 

 the size of the stream. He assumes that a mature profile of equilibrium 

 is constantly maintained during the lowering. But a stream really acts 

 very differently when its mouth is lowered. The deepening begins at 

 the mouth and works back gTadually headward. This is well shown in 

 the Allegheny Eiver drainage of western Pennsylvania. Because of the 

 enlargement of its drainage area, in the Kansan (or Second) stage of 

 glaciation, the valley has been greatly deepened, but is still far from 

 being clown to a profile of equilibrium, its rate of fall being three times 

 as great as that of the Monongahela. The lowering of the main stream 

 has caused the tributaries to begin cutting down at their mouths, and 

 the deepening is gradually working headward. Yet even now, after the 

 lapse of perhaps a half million years, the deepening has had time to 

 reach scarcely two-thirds the way to their sources. See Chamberlin and 

 Leverett, American Journal of Science, April, 1894, pages 261, 262; 

 also I. C. White, American Journal of Science, volume 34, 1887, page 

 378. (3) Deperet also takes no account of the blocking of valleys by 

 drift accumulations in the glaciated regions, and the relatively small 

 amount of work required to remove some of these drift barriers, and 

 thus effect a notable lowering that is independent of any change in the 

 level of the sea into which the si ream discharges. In this way a stream 

 may lower its bed very materially in a sing; of glaciation. The 



terraces at 55-60 meters, and those at about 30 meters, on the Ehone in 

 the vicinity of Lyons, may thus be related to drift barriers, and if so 



