100 Professor Forbes' s Twelfth Letter on Glaciers, 



direction of the lines E D, not close to the foot of the rock 

 at B> but at a little distance, the veins E D running in the 



direction of the declivity of the glacier, and beginning to be 

 developed at E, becoming more and more so towards I>y 

 where they form a tangent to a swelling surface of rock,, 

 whose resistance evidently gives rise to them. It seems, 

 clear that all the ice within the line F E D, or between it 

 and the shore 2 C B D is embayedy as it were, and has but 

 little motion, in consequence of the intense pressure with 

 which the whole mass of the glacier is urged against the side 

 of the valley ; but as the glacier is finally compelled to move 

 in the direction of the declivity from E towards B, a longi- 

 tudinal tearing force arises parallel to E D, and the motion 

 is facilitated by the formation of the veined structure already 

 mentioned, for of longitudinal crevasses there are absolutely 

 none. Such crevasses as there are, are transverse to the bliie 

 bands, shewing the usual direction of the tearing force due to 

 the lateral friction. But they are small and isolated. 



Now, in this case, the development of the structure is evi« 

 dently due to the projection at D in contact with which it 

 terminates, and though the whole glacier is more or less 

 structured in the manner described and figured in my former 

 work, this remarkable development gradually ceases about 

 E, where the rush of the ice-current past the promontory B 

 has ceased to exert so palpable an efiect. I can positively 

 state that no such unusual development of the structure oc- 

 curred opposite to B in 1842, and, for this reason, that the 



