EVIDENCE FROM GREENLAND AND THE SIERRAS 35 



land ; but very nearly the same conditions exist in those parts of the Greenland 

 coast, which were studied in detail. It is noticeable near Cumberland sound, as 

 well as in Turnavik, and in Hudson's strait, and indeed in Greenland, that there 

 are many basins of small size, surrounded entirely by rock. While some of these 

 have no doubt been scoured out by differential ice erosion, the position of many of 

 them, along the line of weaker rocks, indicates that they represent differential pre- 

 glacial weathering. The advance of the ice in these cases has served to remove the 

 decayed rock, and perhaps to deepen the depressions formed by this action, though 

 ice erosion would not in this case be the prime cause of the basin." (Ibid., 195.) 

 "In other words, the irregular surface (of rock) is made more regular by the 

 nearly stagnant bottom ice, which fills the depressions. . . . The ice arches 

 over the irregular land, making curves, which are plainly seen by the arch of the 

 debris layers, whose form is that of a generalized dome of a regular form. . . . 

 Some areas are scoured more than others, and there is a gradual reduction to a gen- 

 eralized surface because the depressions are protected by more nearly stagnant ice. 

 while the projections are worn down toward the curve of average outline of the 

 irregularity." 



If there is any reason why the ice should have less erosive power in 

 the Greenland region than elsewhere it has not been found. Possibly 

 there is some explanation in latitude ; greater rigidity of the ice, due to 

 low temperature, might facilitate shearing and reduce plastic flow at the 

 bottom. It is also possible that the Greenland ice cap is not very old 

 and has not been very active ; but, whatever explanation be forthcoming, 

 the Greenland phenomena give only decidedly negative evidence on the 

 question of deep ice erosion. 



Sierras. — It was formerly believed by a few geologists that the deep 

 valleys in the Sierras, including the Yosemite, had been excavated by 

 glaciers. At present probably no one holds such view ; but opinions 

 quite as radical and probably just as mistaken are still held for other 

 regions; hence it will be pertinent to review the Sierran phenomena for 

 comparison. Among many writings, we will note only a few which bear 

 specially on the glaciation. 



In 1891 Becker * published a paper on the structure of the high Sierras 

 between Truckee river and the south fork of the Stanislaus, in which 

 his argument and conclusion were most emphatically opposed to great 

 ice erosion. He says : 



" Some few geologists still believe that glaciers . . . vigorously erode solid 

 rock. In my opinion, this theory is maintained in opposition to overwhelming 

 evidence. Reference has already been made to some of the many facts indicating 

 a trifling amount of erosion since the preglacial date in the higher part of the 

 Sierra, and long before my examinations Professor Whitney reached the conclu- 

 sion that the solid rock had been scoured rather than eroded by glaciers." (Page 

 65.) 



*G. F. Becker: The structure of a portion of the Sierra Nevada of California. Bull. Geol. Soc. 

 Am., vol. 2, 1891, pp. 49-74. 



