DEBRIS-LAYERS. z05 



Drygalski has remarked, they closely simulate the foliation and contor- 

 tion of gneiss. Indeed, the whole structure is perhaps as well described by 

 the term '' foliation " as l)y any other in common use. (Figure 6, plate 5.) 



The debris belts are essentially parallel to the base of the glacier. They 

 are chiefly confined to the lower 50 or 75 feet ; sometimes they prevail 

 up to 100 feet and rarely beyond. I think 150 feet might be named as 

 a rather extreme limit. They are more abundant at the sides of the 

 lobes than in the center, a fact that is significant in indicating the intro- 

 duction of a notable part of the debris after the lobes were formed. In 

 consonance with this, the debris appears to be most abundant in the 

 glacier-lobes which descend as cataracts or crowd between closely hugging 

 clifts. If, standing in front of a glacial lobe, the dirt bands are traced, 

 many will be found disappearing toward the axis of the lobe. If, stand- 

 ing on the side, they are traced upward, many will be found disappearing 

 at the cataracts or at the embossments of the bottom or at s])urs on the 

 sides. 



In meeting obstacles in front, the basal beds have the habit of curving 

 upward, carrying their debris with them. Terminal moraines are some- 

 times thus made, resting on the edges of the ice-layers which formed 

 them. 



In front of obstacles the layers are sometimes simply curved upward 

 and pass over the prominence; but if the frontal slope be steep, much 

 crumpling of the lamimi^ may take place. (Figure 13, plate 9.) 



Faulting. — Not only are the foliations twisted in gneissic fashion, but 

 they are fractured and faulted, and along the fault-line the laminae are 

 effected by drag precisely analogous to that found in faulted rocks. 

 (Figure 5, plate 5.) 



Origin of the Stratification. — Two classes of phenomena are obviously 

 embraced in the stratification, the one relating to the bedding of the ice 

 irrespective of the debris-layers, the other relating to the introduction of 

 them. The first is a general phenomenon ; the second is superinduced. 



Beyond serious question, the general stratification had its initial stages 

 in the original snowfalls. Whenever encrustment intervened between 

 one fall and another, a layer of more or less definiteness resulted. When- 

 ever a succession of falls was followed by a period of encrustment, a more 

 complex and massive layer was formed. The seasons doubtless devel- 

 oped annual suljdi visions, and possibly, at intervals of a few years, un- 

 usual summer effects bound the deposits of a succession of years into a 

 great stratum. It is the testimony of Tiieutenant Peary and his associ- 

 ates tliat the surface of the ice-ca}), under the action of the great wind- 

 storms, becomes marble-like in solidity and texture, as well as in color. 

 At the same time the erosicHi of the wind develops sastrugi, which furtlier 



