30 W. UPHAM — DKUMLINS AND MARGINAL MORAINES. 



channels. Advancing toward the interior, the explorer soon comes upon 

 higher clear ice and neve, having risen above the plane of the englacial 

 debris, excepting along the course of belts of medial surface morainic 

 drift, swept outward from spurs of the mountains. This ice-sheet par- 

 tially suggests the conditions of the moraine-forming southern portion 

 of the North American and European ice-sheets during the Champlain 

 epoch ; but these had a climate much warmer than that of Alaska, with 

 consequent far more rapid ablation and stronger glacial currents. 



In Greenland, on the other hand, the mean temperature has probably 

 been gradually lowered during several centuries past, since the prosper- 

 ous times of the Norse colonies 9U0 to 500 years ago. A great ice-sheet, 

 1,500 miles long with a maximum width of 700 miles, covers all the in- 

 terior of Greenland; and, although now its extent is less than during the 

 Glacial period, it has doubtless held its own or mainly somewhat increased 

 duiing several hundred years. While the snow and ice accumulation is 

 predominant, no englacial drift becomes superglacial ; but in the region of 

 Inglefield gulf Chamberlin finds the frontal ice-cliffs well charged with 

 englacial debris to a third or half of their total heights of 100 to 200 feet 

 or more. The same ratio of the lower part of the ice-sheet containing 

 drift would quite certainly give it a thickness of 1,000 to 2,000 feet in the 

 dee[)ly ice-covered central portion of Greenland. Other features espe- 

 cially noted are the very distinct stratification of the ice and its differ- 

 ential forward motion, producing not only this stratification, but also 

 sigmoid folds and overthrust faults, where the upper layers move faster 

 than the lower, and these in turn faster than the friction-hindered base. 

 In just the same way, as shown in the foregoing pages, the accelerated 

 currents of the waning ice-sheet during the temperate Champlain epoch 

 overrode each other in succession from the highest to the lowest on the 

 moraine-forming border, bearing a great amount of su})erglacial drift to 

 the margin, and under certain favorable conditions heaping massive 

 drumlin hills beneath the marginal part of the ice. 



If a mild, temperate climate could bring to Greenland the conditions 

 of the Champlain e])och, its thick ice-sheet in the interior under rapid 

 ablation would fully illustrate, as the Malaspina glacier even now does 

 in a considerable degree, the formation of the great series of morainic 

 drift hills and the diversely grouped drumlins which mark stages in the 

 retreat of the continental ice-sheets. 



