1844.] MR. HOPKINS' DIFFICULTIES CONSIDERED. 63 



cal explanation of the fact. This he does by assuming the 

 existence of vertical fissures, parallel to the sides of the glacier, 

 dividing it into a series of longitudinal stripes, whose adjacent 

 surfaces, according to him, slide over one another, arid, in the 

 case of a glacier forcing its way through a gorge, the lateral 

 portions are altogether arrested, whilst the central parts slip 

 down between them.* 



These parallel stripes of ice are supposed by Mr. Hopkins 

 to be of considerable breadth, and to have no sort of analogy 

 with the ribboned structure, to which the readers of my earlier 

 letters will recollect that I have ascribed a similar origin, being 

 lines of discontinuity arising from the crushing of one portion 

 of the semirigid glacier past another. This Mr. Hopkins 

 regards as "no more possible than that a mass should per- 

 manently maintain a position of unstable equilibrium." The 

 veined structure of glaciers he considers to be unexplained, and, 

 in the present state of science, inexplicable. 



Although the general absence of such a system of longitu- 

 dinal fissures as Mr. Hopkins has figured in page 14 of his First 

 Memoir, and the regularity and continuity of motion of the 

 glacier and of its parts, wholly inconsistent with the jostling of 

 huge masses of dislocated ice, might be considered as a sufficient 

 answer to this modification of the theory of De Saussure, 

 the consideration of this demand for a direct proof of the flexi- 

 bility of glacier ice led me to think of its practicability ; and I 

 shall now state what I have succeeded in doing, towards the 

 solution of this practical question in the only way in which it 

 admits of being treated, namely, by the assiduous observation of 

 the motion and change of form of a small compact space of ice 

 on a glacier. The Mer de Glace of Chamouni offers fewer fit 

 points for such an experiment than many other glaciers, since in 

 all its middle and lower portions the ice is excessively crevassed 

 near the sides. There is one spot, however, between the 

 " Angle " and Trelaporte, below the little glacier of Charmoz, 



* [Mr. Hopkins' figures are reproduced in Plate II., figs. 1, 2, and are referred 

 to again, later in this volume.] 



