THE EVIDENCE OPPOSING GENERAL GLACIATION. 253 



quently it may be expected that peaks rising two or three thousand feet 

 above the valley bottoms were more rugged before the ice came and have 

 been more denuded since the ice left than has been the neighboring low- 

 land. That the latter is true is abundantly proved on every hand. 

 High areas bearing glacially transported materials have been attacked 

 by the frost and gullied extensively by the action of the snow water of 

 spring,* while the rocks of the lowland are still distinct roches moutonnees 

 forms, sometimes still grooved and polished. 



The high peak rising above the valley, especially if this is broad, is not 

 so readily worn by the glacier as the lower land. This is due partly to 

 the fact that the ice-currents, deflected by the land topography, are more 

 powerful and persistent in the valleys. That this is true is perfectly 

 apparent, and we may see proof of it on the surface of the present 

 glaciers of Greenland. In the valleys the ice projects beyond the aver- 

 age margin, entering the sea and there floating away in the form of ice- 

 bergs. There is evidence of rapid movement in these valley portions 

 and very slight motion over the ridges and peaks. The divide between 

 two valley glaciers near the margin of the ice-cap is usually smooth and 

 relatively unbroken, while the valley portion is intricately crevassed ; 

 but even over these divides there is some movement, as is shown by the 

 stratification at the base of the land margin and by the debris in the ice. 



Not only is there less rapidity of movement, but the peaks rising into 

 the ice reach above the level of the debris zone, and thus have a rela- 

 tively slight attack upon them. As this ice is mainly clear and moraine - 

 free, the destruction must be mainly done by the ice itself, not by tools 

 held in its grasp. 



Granting for the moment that all the land was ice-covered, and that 

 the present margin of the glacier is only one stage in the general retreat, 

 there must have been a time when the peaks rose above the ice as nuna- 

 taks, while the valleys were still occupied by glaciers. This condition 

 must have lasted for a long time, and the same was true when the glacier 

 began to encroach upon the land. First the valleys were occupied, then 

 the hilltops were enwrapped, and finally all land was buried beneath the 

 advancing ice-cap ; hence the valleys were actually occupied very much 

 longer than the mountains, and this necessitates not only a difference in 

 ice erosion, but also a much greater preglacial and postglacial exposure 

 to denudation for the mountain tops than for the valley bottoms. 



For these reasons we may naturally expect the topography of the 

 higher peaks to be very much more angular than that of the lower land, 

 and there would be a marked difference in the ruggedness of peaks, ac- 

 cording to even slight variations in rock structure and position as well 



* See Tarr : American Geologist, vol. xix, 1897, p. 131. 



