588 Mr. Mallet on the Brittleness and 



which are so imperfectly crystallized, a load which produces 

 a " permanent set as it is called by mechanics," produces in- 

 cipient rupture, for flexure continues to increase until at last 

 the bar breaks; and in general, the more perfect the crystal- 

 lization of any body is, whether metallic, saline or simple, the 

 more brittle it is, however great its modulus of cohesion, and 

 irrespective thereof. 



I affirm, therefore, that if glacier ice possess a crystalline 

 structure it is impossible for it to possess any plasticity what- 

 ever; and that it does possess a crystalline structure optical 

 phaenomena prove, as well as those presented by the disinte- 

 gration of glacier and iceberg ice. Indeed, it scarcely ad- 

 mits of a doubt, that ice is not capable of existing in any other 

 than a crystallized form. I am not aware of any instance that 

 can be given of any solid body composed of two elements, 

 one or both of which are non-metallic, where the atomic con- 

 stitution is in the same ratio as that of water, having any other 

 structure. 



But with respect to ice. Dr. Brewster has proved it to 

 have a crystallized structure in plates as removed from the 

 surface of frozen water; we see it shoot into crystals upon a 

 freezing pool; it forms in crystals as hoar frost, and we see it 

 fall in crystals as snow, and the mass of the glacier is made up 

 of snow crystals cemented into a mass by freezing together ; 

 and are we to suppose that in this act of consolidation these 

 minute snow crystals do not continue and impart their own 

 crystalline forms to the water frozen between them, but con- 

 trary to all analogy assume them to lose their own crystalline 

 structure without being liquefied, and not aggregate to them- 

 selves fresh matter of their own kind, to fill with crystals simi- 

 lar to themselves the interspaces amongst them ? 



I conceive, then, that what I have thus briefly and impar- 

 tially stated destroys the possibility of assuming glacier ice to 

 possess plasticity of any kind, without violation of all sound 

 reasoning upon the known molecular properties of ice and all 

 other crystallized bodies. 



Nor is it necessary to call in the aid of such a baseless hy- 

 pothesis to account for the most extreme and distorted cases 

 of glacier motion. Sufficient subdivision of the whole mass to 

 give enough of intermobility to its integrant masses is all that 

 is requisite to enable the enormous procession of colossal frag- 

 ments to be pushed, or slide and stagger, or be lifted through 

 the narrowest gorge of the glacier valley. 



Enormous as is the magnitude of eacli block of ice between 

 the crevasses at any given locality, it is a small piece com- 

 oared with the whole moving mass, with the forces engaged. 



