724 



F. E. WEIGHT EFFECTS OF GLACIAL ACTION IN ICELAND 



or other baselevel and deeply dissected by glaciated river valleys. A 

 cutting river tends to accentuate differences of elevation, while a water 

 surface, as the ocean, tends to reduce all land surfaces to its level; in 

 like manner, a valley glacier tends to cut deeper and to increase differ- 

 ences of altitude, while the ice-sheet tends to truncate the upland masses 



Figure 1. — Diagrammatic Section through a mountainous 

 Area at the 'beginning of the ice-flood Period 



Ice is indicated by the dotted lines 



Figure 2. — Diagrammatic Section through the same Area 



Showing physiographic effects of subglacial action on the 

 adjacent mountain mass, the level of the ice having been 

 held for a long period at that indicated by dotted line. 



to its general level. Such an aggregate of mountain tops may have 

 reached baselevel so far as the ice-sheet is concerned, but it would not 

 have been baseleveled in the ordinary sense of the word, although it 

 might resemble very closely an old uplifted, warped and dissected base- 

 level of erosion. 



THE UPLAND SURFACE IN ICELAND 



Ice-sheet beveling of this type has been a factor, I believe, in the de- 

 velopment of the old surface now marked on the uplands of northern 

 Iceland, especially of the area east of Akureyri. There the backs of the 

 mountains are gently arched, and present the appearance of an undulat- 

 ing, mature topography, approaching that of a peneplain, in which deep 

 canyon-like cuts have been made by the valleys, and above which occa- 

 sional sharp peaks project. But signs of glaciation are everj^where 

 visible, glacial rounding and glacial erratics and debris occur, and indi- 

 cate, at least, that the effect of the ice-cap should be regarded as a 

 possible factor in the modeling of this upland surface. 



The basalt formation, underlying this surface, dips gently to the north 

 and northeast, and must have been influential in determining the upper 

 limit of the ice-sheet. It is difficult, therefore^ to decide just how much 



