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from the facts that force may be propagated a considerable distance 

 through ice, not only in a horizontal direction, as it is in such a 

 case as that of the Mere de Glace, but also, though to a lesser 

 extent, in a downward direction as well. The results in this latter 

 case, as in the former, being affected by the initial direction and 

 force of the disturbing current as compared with those of the 

 current disturbed. In treating of glacial erosion this subject will 

 be adverted to again. 



Vertical Ctnuiation of the Ice. — It has long been known to 

 observers of glacial phenomena, that the lower parts of the ice 

 nearer the source of glacier tend to become its surface layers farther 

 down the stream. This phenomenon was discussed at some length 

 by J. D. Forbes ("Occasional Papers," p. 202, et seq.) and after- 

 wards more fully by Professor James Geikie, who had perceived 

 the bearing of the facts mentioned by Forbes and applied them to 

 the explanation of the upward transportal of boulders. (I may 

 add that I had myself independently arrived at nearly the same 

 conclusions from a study of the same facts, before I knew of 

 Professor Geikie's paper. The subject was "in the air" at the 

 time.) This tendency of the lower parts of the ice to work up to 

 the surface has been shewu to be partly due to the constant 

 tendency of flowing ice to move in the direction of least resistance; 

 so that where the ice encounters much frontal resistance, as it does 

 in pushing its way over an obstacle, its lower parts, while moving 

 forward, tend to flow also upward, relatively to the general level of 

 that part of the glacier. But the principal reason why the lower 

 strata of a flowing mass of ice tend to work up to the surface would 

 appear rather to be that, while the surface layers of ice are con- 

 stantly being removed through their melting by atmospheric causes, 

 the general level is maintained with equal constancy through the 

 upward swelling (or turgescence) of the ice consequent upon the 

 pressure exerted by the ice nearer the source of the glacier. As 

 the top ice is melted off successively lower strata swell up to the 

 surface, while the whole mass is slowly moving outward from its 

 source ; so that what was the bottom layer at one point becomes, 



