720 F. E. WRIGHT EFFECTS OF GLACIAL ACTION IN ICELAND 



powers of the relatively stagnant glaciers of today. The present epoch 

 is one of ice drought, and the erosive action of the glaciers during the 

 two periods is, therefore, not comparable. This Mr. E. C. Andrews has 

 clearly demonstrated in his paper, "Ice-flood hypothesis of the New Zea- 

 land sound basins," ^ in which the effects of the two stages are strongly 

 contrasted and likened directly to those of water action during times of 

 flood and of drought, the flood period in the river bed or glacial valley 

 being one of intense corrasion and down-cutting, the drought period one 

 of stagnation and aggradation. 



The features which Mr. Andrews declares characteristic of intense ice 

 action in New Zealand occur also in Iceland, though in somewhat differ- 

 ent form, as might be expected from the differences in bedrock and 

 thickness of ice-cap in the two countries. In New Zealand, as in south- 

 eastern Alaska, the mountain uplands average from 1,500 to 2,000 

 meters in elevation, while in Iceland the plateau country rarely reaches 

 800 meters. As the upland areas in both cases were covered by an ice- 

 sheet, the depth of the ice currents in the valleys was far greater in New 

 Zealand and Alaska than in Iceland, and their cutting action conse- 

 quently much more profoimd. The double cliff slopes which occur fre- 

 quently in New Zealand and also in Alaska, and which evidently are 

 marks of the most intense glacial corrasion, were rarely seen in Iceland. 

 The "through" valleys of Professor Tarr, which are common in Alaska, 

 are seldom found in Iceland. Hanging valleys, vertical cliff bases and 

 truncation of spurs, on the other hand, physiographic forms which are 

 considered special marks of intense glacial action in New Zealand, are 

 abundant in Iceland, as well as other features, which may be noted briefly. 



FEATURES RESULTING FROM THE ACTION OF A SINGLE VALLEY GLACIER 



The master valleys in north Iceland, as Eyjaf jardardalur, Fnjoskada- 

 lur, Fljotsdalur, and others, exhibit: (a) U-shaped, troughlike cross-sec- 

 tions; (&) hanging side valleys; (c) sharp steepening of grade at the 

 valley head, due in part to cirque action, but also probably in part to ice 

 currents, which on the advance of the ice-sheet from the interior ocean- 

 wards were deflected by the directive influence of the existing valleys, 

 and, plunging into the valleys at their head, tended to abrade with 

 special severity there. During the period of maximum ice action, the 

 grade of the valley floor below the valley head was greatly decreased and 

 occasionally reversed for short distances, as indicated by the present hol- 

 lows at such points; (d) glacial grooves and markings along the valley 



3 Journal of Geology, xiv, 1906, pp. 22-54. 



