260 FRAGMENTS OF SCIENCE 



has also "been regarded as conclusive evidence against the 

 theory of erosion. "Why," it has been asked, "did not 

 the glacier of the Khone go straight forward instead of 

 making this awkward bend?" But if the valley be a 

 crack, why did the crack make this bend? The craclv, 

 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 at which it has just arrived, the divellent force 

 on the molecules there situated is counteracted only by 

 half of 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, then, 

 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 illustrated in glacier streams, which 

 are made to cut either straight or sinuous channels by 

 causes apparently of the most trivial character. In his in- 

 teresting paper ' ' On the Lakes of Switzerland, ' ' M. Studer 

 also 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 in 1864; and, though 

 it was plain that M. Studer had good grounds for the se- 

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

 as to the necessity of a fissure. 



Again, in the interesting volume recently published by 



