752 



SCIENCE. 



[N. S. Vol. V. No. 124. 



ticable for observers to detect such signs of 

 glaciation. 



An additional source of confusion is in- 

 troduced by naming the promonotory of 

 the photograph 'The Devil's Thumb.' It 

 is stated in a foot-note that " This is the 

 Devil's Thumb as given on the Danish and 

 British Admii-alty charts. The real Devil's 

 Thumb of the Arctic explorers is some forty 

 or fifty miles to the north of this " (p. 254). 

 The true Devil's Thumb is, however, 

 sketched on the British Admiraltj^ chart. 

 The sketch as there given is herewith photo- 

 graphically reproduced (Fig. 3). It will 



'-«>l 



Fig 3 TheDe\il'a Tbumb, as givenon the Biitish 

 Admiralty Chart. 



be seen that it does not bear even a remote 

 resemblance to the promontory illustrated 

 in the paper. It is to be assumed without 

 question that the latter stands at the loca- 

 tion designated on the charts as The Devil's 

 Thumb, but this location is obviously an 

 error. It does not seem to us that it justi- 

 fies the transfer of the name Devil's Thumb 

 to a new promontory to which the name 

 has no fitness. It is especially unfortunate 

 to introduce a second Devil's Thumb in this 

 connection, because the true Devil's Thumb, 

 by reason of its slenderness and angularity, 

 has a significant bearing on the question of 

 glacial extension, and together with Mel- 

 ville Monument a similar pinnacle some- 

 what farther north has been so cited. Mis- 

 apprehension has already arisen on account 

 of this double use of the name. The slen- 

 derness and angularity of the Devil's 

 Thumb are exaggerated in the sketch of the 

 Admiralty chart — about as much as such 

 objects are usually exaggerated by the im- 

 pressions of the average observer. With 



some discount for this it gives a fair idea of 

 this singular landmark. 



If the true Devil's Thumb, Dalrymple 

 Rock, and similar instances of angularity 

 and asperity are taken as one type ; if the 

 contours illustrated by the paper under re- 

 view be taken as a second type ; if the con- 

 tours of the Carey Islands {Journal of Geol- 

 ogy, Vol. II., p. 662) be taken as a third 

 type, and if the plainer topography north of 

 Godhaab be taken as a fourth type, some- 

 thing of the degrees and gradations of 

 topographical modification which the coast 

 belt of Greenland suffered at the hands of 

 glaciation will be indicated. 



The view of the author that the peaks 

 would remain more angular than the val- 

 leys seems perfectly valid so long as the 

 conditions are limited to the border of the ice 

 cap. !N"ear the border the thickness of the 

 ice in the valleys is much greater than upon 

 the hills. The main flowage is through the 

 valleys, and subjugation of the heights is 

 relatively slight. On the other hand, this 

 reasoning entirely falls to the ground when 

 applied to profound glacial submersion, 

 such as is implied by an advance of the 100 

 or 200 miles necessary to reach the heart 

 of Baffin's Bay. Such an advance means a 

 depth of at least 5,000 feet of ice on the 

 peaks. In this case the difference be- 

 tween the depth on the heights and 

 in the valleys is relatively much less, 

 and three well established principles com- 

 bine to emphasize the erosion of the 

 peaks: (1) the upper portion of the ice 

 moves faster than the lower ; (2) ero- 

 sion is correlated with rapidity of motion 

 by some high power of the rate; (3) 

 peaks yield to erosion more than emboss- 

 ments of the valley, because (a) the surface 

 exposed to action is relatively greater, and 

 (b) the attachment, and hence the resist- 

 ance, of the exposed parts is relatively less. 

 The erosion, therefore, proceeds on the 

 crests with a facility superior to that in the 



