346 Professor Forbes' Account of Ids recent 



is equally singular that it should net have been sooner noticed, 

 or if noticed, never once alluded to by the eminent and inge- 

 nious authors who have treated of existing glaciers and their 

 effects. 



With respect to the general type or form of this structure, 

 I am happy to say, that I have found not the slightest reason 

 to modify the description which I have given in the paper 

 above 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 1 

 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 im- 

 perfectly, 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 appear- 

 ance of horizontal stratification 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 fol- 

 low 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 sup- 

 ports them, gradually becoming more vertical as the centre of 

 the glacier is approached, 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. 



