THE WORK OF SNOW AND ICE. 



297 



carried to the surface by actual upward movement, and a terminal 

 moraine or a series of terminal moraines sometimes aggregated 

 where the upturned layers of ice outcrop at the surface (Fig. 271). That 

 the material of these moraines was originally basal is abundantly 

 demonstrated by the bruised and scratched condition of the bowlders 

 and pebbles, and sometimes by the 

 nature of the material itself. For 

 example, in two cases in North Green- 

 land w^here glaciers descend into the 

 heads of shallow bays and move 



forward on their bottoms, moraines 



Fig. 272. — Diagram illustrating the up- 

 turning of the layers of ice at the end of 

 an arctic glacier as seen in end-section. 

 The bottom line represent? sea level. 



formed by the upturning of the layers were seen to contain abundant 

 molluscan shells derived from the bottom of the bay. The upturning some- 

 times affects the side-edges of ice-tongues (Fig. 272) as well as their ends, 

 and the material thus brought to the surface gives origin to lateral 

 moraines altogether different in origin from the lateral moraines formed 

 by the falHng of debris upon the glaciers. Sometimes also there is an 

 upturning of the ice along a longitudinal zone well back from the lateral 



Fig. 273. 



-Diagram illustrating the same point as 272, where the structure is more 

 complex. The bottom line of the figure represents sea level. 



margins (Fig. 273), and the material so borne to the surface in such a 

 zone gives rise to a moraine resembling the medial moraine formed by 

 the union of lateral moraines, but of wholly different origin. 



The phenomenon of upturning here referred to has been observed 

 only at or near the terminus of the ice, and is perhaps due in most part 

 to the resistance of frozen morainic or other material beneath and in 

 front of the edge. To this should probably be added the effect of 

 the increased rigidity of the ice at its borders, due to the low 

 external temperature during the larger part of the year, while the 

 interior, T\ith its higher temperature, remains more fluent. But 

 even this probably leaves the explanation inadequate. In not a 

 few instances the upturning is associated with a notable thickening 

 of the layers toward their edges (Fig. 274). This suggests that per- 

 haps there is an exceptional gro\\i:h of the granular crystals of the ice 



