1842.] FORMS OF SURFACES OF STRUCTURE. 19 



alluded to, of the conformation of the glacier of the Rhone. 

 The description is characteristic, not of that glacier only, but of 

 every other, with certain modifications similar to the variation 

 of the parameter of a curve ; variations, therefore, not in kind 

 but in degree. The most beautiful structure I have ever met 

 with is in the glacier of La Brenva, in the Allee Blanche, which 

 was one of the earliest I examined this season, and in which I 

 found all that I had seen, though imperfectly, on the glacier of 

 the Rhone (which it resembles in the circumstances of being 

 derived from an icy cascade, and in having a considerable 

 breadth in proportion to its length), developed in a manner so 

 clear and so geometrically precise, as gave me the most lively 

 satisfaction. I refer to my former paper for the figure and 

 description of that structure ; I have found the same conoidal 

 surfaces, and the same false appearance of horizontal stratifica- 

 tion on the terminal face of the glacier, arising from the veins 

 dipping inwards at first at an angle of only 5, rising to 10, 

 20, up to 60 and 70, if we follow the medial line of the 

 glacier, or axis parallel to its length. The sides of the glacier, 

 in like manner, have their cleavage planes or veins dipping 

 inwards towards the centre at an angle determined by the 

 declivity of the rock or moraine which supports them, gradually 

 becoming more vertical as the centre of the glacier is ap- 

 proached, where they twist round by degrees, so as to become 

 transverse to its length, and to form part of the system of planes 

 dipping inwards first described. Fig. 1 exhibits a section parallel 

 to the length. Fig. 2, a transverse section. 



Fig. 1. Fig. 2. 



You are already aware that this structure consists in the 

 alternation of more or less perfectly crystallized ice in parallel 

 layers, often thinning out altogether like veins in marble, not 



