﻿M. A. Heim on Glaciers. 501 



down into cavities produced by melting, but only treats it as 

 the effect of the extension of the glacier into a wide valley (Essai } 

 § 21, 1841). 



Fissures of Displacement. — If across the surface of a stream 

 of killed gypsum a straight line be drawn of another colour, one 

 might have expected that, in consequence of the greater velocity in 

 the centre, it would be drawn out into a continuous curve with 

 its convexity turned towards the lower end of the valley, instead 

 of which we obtain a form like fig. 8. There appear displace- 

 ment-fissures approximately parallel to the margin, especially 

 numerous near the bank ; and on these our line is broken, pro- 

 ducing a broken curve. A row of stakes driven into the ice, in 

 a line across the glacier, will not suffice to enlighten us concern- 

 ing the corresponding condition there ; we must have a distinct 

 continuous line. Such a one can easily be made by gathering 

 small dark-coloured stones and laying them close together in a 

 straight line. They form a line which cannot be disturbed by 

 the most violent shower of rain, because, through greater absorp- 

 tion of heat, they immediately sink into the ice. At the end of 

 August, 1869, I, with the aid of my friend Alfred Kleiner, 

 Stud. Med., and Joseph Maria Trosch, chamois-hunter of Ma- 

 deran, placed such lines in two different places on the Upper 

 Rhone Glacier, and at the beginning of September across the 

 Hun Glacier. When, three weeks later, I again visited the lo- 

 calities, all the lines had remained quite entire ; but the interval 

 was too short for a perceptible change in the form of the lines to 

 have been produced. Hoping that our lines would last through 

 the winter, and in the summer of 1870 more change of form 

 would be visible, I descended the valley again. 



Although I have not yet demonstrated the displacements, yet 

 I believe I have discovered displacement-fissures of the most defi- 

 nite character, especially on the Upper Rhone Glacier. When 

 the bed of a glacier is regular, we know that the principal fis- 

 sures proceed from the margin obliquely upwards towards the 

 middle. These may often have considerable breadth. They 

 are perpendicular, or nearly perpendicular, to the ice-structure 

 (the blue bands) in the lateral parts. Now, in the Upper 

 Rhone Glacier, there is also a system of fissures which are partly 

 parallel to the structure, and partly cut it at slight angles. This 

 system has hitherto remained unnoticed, because these fissures 

 do not gape ; mostly they only offer space sufficient to insert 

 the blade of a pocket-knife, and at first sight may be confounded 

 with the structure. They penetrate the mass of the glacier, and 

 can be traced downward in the deepest principal fissures. They 

 are very regular in their course — as far as we could trace them, 

 always rectilinear — and are continued till they cut the bank at 



Phil. Mag. S. 4. No. 276. Suppl. Vol. 41. 2 L 



