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INTERNAL STRUCTURE AND 
probable, that, while pressure has the larger 
share in producing the onward movement of the 
glacier, as well as in the transformation of the 
snow into ice, a careful analysis of all the facts 
will show that this pressure is owing partly to 
the weight of the mass itself, partly to the push- 
ing on of the accumulated snow from behind, 
partly to its sliding along the surface upon which 
it rests, partly to the weight of water pervading 
the whole, partly to the softening of the rigid 
ice by the infiltration of water, and partly, also, 
to the dilatation of the mass, resulting from the 
freezing of this water. These causes, of course, 
modify the ice itself, while they contribute to 
the motion. Further investigations are required 
to ascertain in what proportion these different 
influences contribute to the general result, and 
at what time and under what circumstances they 
modify most directly the motion of the glacier. 
That a glacier cannot be altogether compared 
to a river, although there is an unmistakable 
analogy between the flow of the one and the 
onward movement of the other, seems to me 
plain, — since the river, by the combination of 
its tributaries, goes on increasing in bulk in con- 
sequence of the incompressibility of water, while 
a glacier gradually thins out in consequence of 
the packing of its mass, however large and nu- 
merous may be its accessions. The analogy fails 
