﻿502 M. A. Heim on Glaciers. 



an oblique angle, or disappear beneath the lateral moraines — 

 which gives lengths of 800 metres and more. There are never two 

 very near together, but they are at nearly uniform distances (per- 

 haps from 10 to 20 feet), like the displacement-fissures in the 

 gypsum stream. We found by many excavations that the ice 

 is perfectly divided in these fissures, while it is easy to cut a 

 piece of white glacier-ice through which blue bands run trans- 

 versely, and the structure does not destroy the cohesion. 



Where the structure cuts these fine fissures, many displace- 

 ments which have taken place along them are directly demon- 

 strable ; and in those which we have found, the fragment nearest 

 the middle was always in advance of that nearer the bank. See 

 fig. 9 : the structure-bands a and a, b and b, on the two sides 

 of the displacement-fissure x, correspond to each other. From 

 different points of the valley-slopes we viewed the glacier under 

 different lights, in order to see the course of these fissures over 

 the whole glacier ; but at a little distance they cease to be vi- 

 sible, even under oblique illumination. How difficult it is, on 

 the surface of a glacier, to take the bearings of these and similar 

 objects, he only knows who has experienced it. The enormous 

 dimensions of the surface, the excessive number of great eleva- 

 tions and depressions all resembling one another, the large open 

 fissures one must go round, the attention he must pay to his 

 footsteps — all this renders the survey incredibly difficult. On 

 this account I was obliged to content myself with ascertaining 

 the course of the displacement-fissures on the eastern side of the 

 Upper Rhone Glacier. I afterwards found on other glaciers, 

 especially near irregular banks, similarly situated fine fissures 

 with quite the same character, but could not accurately follow 

 their course. They are met with chiefly where the motion is 

 retarded at the margins more considerably than in a regular 

 valley, as behind projections. Pig. 10 shows their course in 

 the Upper Rhone Glacier : a denotes the displacement-fissures, 

 b the direction of the structure, c the usual open fissures. Figs. 

 10A and 10B represent on a larger scale, with the correct 

 angles, the parts at A and B in fig. 10. Fig. 9 is also to be 

 supposed in the region of B, fig. 10. The large bay between 

 D and E must occasion great retardation of motion in these 

 parts of the Rhone Glacier. 



In the gypsum stream the displacement-fissures, when nu- 

 merous, may altogether replace the ordinary gaping fissures ; 

 in glaciers they appear rather to be a local phenomenon, while 

 the gaping fissures are universal. Whether the system of fine 

 fissures found on the Rhone Glacier is really the analogue of 

 the displacement-fissures in the gypsum stream can only be de- 

 cided by subsequent observation of the stone lines which we 



