148 Review of the Controversy Begarding the 3fotion of Glaciers. 



its surface, the slight friction of the molecules, as they successively 

 thaw and glide downward by infinitesimally small steps, would be 

 quite incompetent to communicate their motion to the underlying mass 

 of stone. A stake set firmly in the ice must in the same way be left 

 behind, as the momentarily liquified particles steal past it with no 

 more friction than that of the water in a river against the trunk of a 

 tree upon its bank. Instead of recording, as in fact they do, the daily 

 and hourly flow of the glacier, they would remain permanently where 

 at first they had been set. And the bodies of victims who have the 

 misfortune to fall into the depths of some yawning crevasse, instead of 

 reappearing at the foot of the glacier after an interval of twenty, 

 forty, or eighty years,* would remain forever sealed up where they 

 fell, while the liquid molecules successively slide past them. In this 

 respect, also, it is impossible to reconcile the consequences which would 

 flow from Mr. Croll's theory Avith the well known facts of glacial 

 nature. In yet another point is this theory irreconcilable with fact. 

 The motion of a glacier, it is well known, is not uniform, but diflTer- 

 ential. The surface moves more rapidly than the parts below, and the 

 middle more rapidly than the sides. But if, as Mr. CroU maintains, 

 the entrance of heat and its conduction through the mass of the ice, as 

 a wave of liquidity, is the sole and suflficient cause of the movement, the 

 results produced would not accord with the observations. The upper 

 layer may be supposed to move faster than the lower without incon- 

 sistency, but theory would certainly require that the side should move 

 faster than the middle. There can be no reason for supposing that a 

 liquid molecule near the margin has any greater difficulty in moving 

 down the slope than a liquid molecule in the middle. Each is sur. 

 rounded by other molecules in the solid state, each has the same degree 

 of friction to overcome, and the same interval of time for accomplishing 

 its movement. But the ice at the margin of the stream being thinner 

 than that in the middle, is more thoroughly under the influence of the 

 lie^t, which would less slowly penetrate it, and would be then reflected 

 from the rocky bed, consequently, every particle must pass more often 

 into the liquid form^ and for this reason should travel faster than the 

 particles Ij'ing in mid-stream. f 



* The remains of the guides lost in 1820, in Dr. Hauiel's attempt to cross Mt. Blanc, were 

 found imbedded in the ice of the glacier des Bossons, in 1863. The men and their things were 

 torn to pieces and widely separated. All around them the ice was covered in every direction, 

 for twenty or thirty feet, with the hair of one knapsack, spread over an area three or four hund- 

 red times greater than that of the knapsack." This, says Mr. Crowell, is not an isolated ex- 

 ample of the seatterinu that takes place in or on a glacier. I myself saw, on the Theodule 

 glacier, the remains of the Syndic of Val Tournanche scattered over a space of several acres." 

 t The more rapid flow of a river in (he middle does not invalidate this argument. The 

 water in a river is all sulyect to the same moving force — gravitation — everywhere equal in 

 amount. But Mr. Croll's theory obliges us to admit that the ice along the margins of a glacier 

 is in much more complete subjection to the influence of heat than is that in the middle, and, 

 consequently, possesses what is equivalent to a greater motive force. 



