674 THE JOURNAL OF GEOLOGY. 
from this surface to the vertical face, as illustrated in Fig. 45. 
The lines which represent the outcropping of the layers on the 
surface form sweeping curves more or less concentric with the 
frontal edge of the glacier. By differential melting of these 
layers little steps or terraces are formed, which sometimes 
become somewhat pronounced. This phenomenon was observed 
on other glaciers. 
As in the preceding glaciers—indeed in all the glaciers of 
Greenland that were seen—the upper part was found essentially 
free from débris, while the basal part was well inset with rock 
rubbish of various kinds. Along almost the whole face there 
was a layer twelve or fifteen feet thick at the upper edge of the 
talus slope that was so thickly inset as to be almost black with 
débris (Fig. 46). A part of this blackness, however, is attrib- 
utable to the illusive effects of the surface wash. Much of the 
débris of this layer was coarse. Large bowlders were abundant, 
but all grades were present down to fine clay. When freed by 
melting it constituted a very coarse, stony till. Many of the 
fragments were rubbed, bruised, scratched or polished in typical 
glacial fashion. The assemblage of rock species was unusually 
interesting, embracing gneissic and igneous rocks and the gray and 
red sandstones. The walls of the valley and doubtless its bed 
were formed of the gneissic series into which had been intruded 
igneous dikes. Among these were some of a markedly green 
rock of diabasic aspect that was capable of receiving and exhib- 
iting glacial markings with unusual facility. The sandstone 
series capped the plateau and formed the nunatakes at the head 
of the valley in the main. The distribution of the formations 
seemed to favor the view that the débris of the very bowldery 
layer above described was introduced at the cataract at the head 
of the valley. 
The melting out of the débris of this bowldery layer at the 
frontal edge of the glacier was the chief cause of the formation 
of the pronounced talus slope shown best in Fig. 46. Its height 
varied from thirty or forty feet downwards. It gave the glacier 
the appearance of resting ona pedestal. This appearance was, 
