Prof. Tyndall on the Conformation of the Alps. 267 



The crack, I submit, had at least as much reason to prolong 

 itself in a straight line as the glacier had. A statement of Sir 

 John Herschel with reference to another matter is perfectly ap- 

 plicable here : — "A crack once produced has a tendency to run — 

 for this plain reason, that at its momentary limit, at the point 

 on which it has just arrived, the divellent force on the molecules 

 there situated is counteracted only by half the cohesive force 

 which acted when there was no crack, viz. the cohesion of the 

 uncracked portion alone " (Proc. Roy. Soc. vol. xii. p. 678). To 

 account for the bend, the adherent of the fracture theory must 

 assume the existence of some accident which turned the crack at 

 right angles to itself; and he surely will permit the adherent of 

 the erosion theory to make a similar assumption. The influence 

 of small accidents on the direction of rivers is beautifully illus- 

 trated in glacier streams, which, on slopes of equal inclination, cut 

 either straight or sinuous channels, the determining causes being 

 apparently of the most trivial character. In his interesting paper 

 " On the Lakes of Switzerland," M. Studer refers to the bend of 

 the Rhine at Sargans in proof that the river must there follow a 

 pre-existing fissure. I made a special expedition to the place this 

 year ; and though I felt that M. Studer had good grounds for the 

 selection of this spot, I was unable to arrive at his conclusion 

 as to the necessity of a fissure. 



In the interesting volume recently published by the Swiss 

 Alpine Club, M. Desor informs us that the Swiss naturalists 

 who met last year at Samaden visited the end of the Morte- 

 ratsch glacier, and there convinced themselves that a glacier had 

 no tendency whatever to imbed itself in the soil. I scarcely 

 think that the question of glacier erosion, as applied either to 

 lakes or valleys, is to be disposed of so easily. My experience 

 regarding the Morteratsch glacier shall now be recounted. I 

 this year took with me a theodolite to Pontresina, and while 

 there had to congratulate myself on the invaluable aid of my 

 friend Mr. Hirst, who in 1857 did such good service upon the 

 Mer de Glace and its tributaries. We set out three lines across 

 the Morteratsch glacier, one of which crossed the ice-stream 

 near the well-known hut of the painter Georgei, while the two 

 others were staked out, the one above the hut and the other 

 below it. Calling the highest line A, the line which crossed 

 the glacier at the hut B, and the lowest line C, the following are 

 the mean hourly motions of the three lines, deduced from obser- 

 vations which extended over several days. On each line eleven 

 stakes were fixed, which are designated by the figures 1, 2, 3, 

 &c. in the Tables. 



T2 



