Review of the Codroversy Regarding the 3Iotion of Glaciers. 147 



adherents of Moseley, De Charpentier, and De Saussure. But, like 

 the hist, this claim can not be allowed. No difficulty lies in the way 

 of admitting the crevasse as a necessary result of any theory that sup- 

 poses the glacier to move as ice, but the moment this ground is 

 abandoned, and the rigidity of the material in any way removed, the 

 crevasse becomes a standing obstacle, that has thus far defied removal. 

 Readers of Forbes' writings upon the subject know well with how- 

 much ingenuity and labor he has striven to clear it away, as though 

 fully aware of its fatal character, and they must also have felt how 

 little success he attained in the effort. The two seem irreconcilable 

 —viscosity and brittleuess. If the ice is plastic enough to flow, how 

 can it be brittle enough to allow yawning crevasses, hundreds of feet 

 deep, to form and grow within it ? And if this phenomenon applied 

 with such force against the viscous theory, with how much greater 

 force must it assail the liquid theory of Mr. Croll? According to his 

 own explanation of it, no sooner is a crack formed than the heat gams 

 access to the new surface, and passing into the ice, must produce the 

 same effect as at any other surface, and cause a downward motion of 

 the momentarily liquified particles, which must again close the opening 

 and stifle the crevasse at its very birth. A glacier, moving as Mr. 

 Croll supposes, can neither produce grooves on its channel, nor allow 

 crevasses on its bosom, but must fioiu onward, without more friction at 

 its base and with less unevenness on its surfiice than a river of water. 

 It is evidently impossible to admit a successive molecular liquidation, 

 which can produce a flow of 36 inches per day down a slope of 8°, 

 and at the same time a hardness capable of mamtaining vertical walls 

 of ice hundreds of feet in height, 



Mr. Croll has, it may be noticed, only quoted an example of a 

 crevasse formed by a change of interlineation in the bed of a glacier, 

 which is a comparatively easy problem. He has made no attempt to 

 claim, in support of his theory, the far more difficult case, where 

 crevasses develop themselves along and across the mass while moving 

 over an unchanging slope, such as margined ■crevasses. On his 

 theory, it Wi)uld be almost as reasonable to expose the formation of 

 such chasms in the surface of a river as on that of a glacier of con- 

 stantly melting ice. 



Is it possible, we may further ask, to account for the downward 

 movement of moraines and other foreign substances lying on the sur- 

 face of a glacier, or buried in its mass, on the theory of Mr. Croll ? 

 This is a necessary result of assuming its movement as ice, but it seems 

 quite incompatible with the admission that it must become liquid as 

 the condition of motion. In the case of an erratic block lying upon 



