8 STRUCTURE OBSERVED IN THE ICE OF GLACIERS. [1841. 



primary cause of these fissures is, that the pressure of the ice 

 at C forces the glacier to distend itself into continually widen- 

 ing rings, which its rigidity resists, and therefore it becomes 

 traversed by radial crevasses. 



The veined structure itself, I have already said, arises from 

 the alternation of more or less compact bands of ice. The 

 breadth of these varies from a small fraction of an inch to 

 several inches. The more porous of these bands are the likeliest 

 vehicles for the transmission of water from the higher to the 

 lower part of a glacier ; and that opinion receives some con- 

 firmation from the fact, that, at a certain depth, in crevasses, 

 we may see the veined structure marked out and exaggerated 

 "by the frozen stalagmite, which is protruded from the section of 

 jhe more porous layers. 



In conclusion (for the present), this structure deserves the 

 attention of geologists generally, as showing how the appearance 

 of the most delicate stratification, and of sedimentary deposition, 

 may be produced in homogeneous masses, where nothing of the 

 kind has occurred. For a short time, indeed, I was of opinion 

 that this structure resulted from true stratification ; but a 

 closer examination of the mass convinced me that, inexplicable 

 as the fact remains, it must be accounted for in some other 

 way. We have endeavoured to show an empirical connection 

 which appears to exist between the structural planes and the 

 sustaining walls of the glacier, and likewise that the recurrence 

 of congelation and thaw appears to strengthen the formation of 

 the bands. But this cannot be considered as in any degree 

 amounting to an explanation. The analogous difficulty of slaty 

 cleavage in rocks presents itself as not improbably connected 

 with a similar unknown cause, whose action pervaded the mass 

 of the crystallizing rock undergoing metamorphic change, as 

 this pervades the mass of the crystallizing glacier. In the 

 former case, we have cleavage planes perfectly parallel, almost 

 indefinitely extending with unaltered features over vast surfaces 

 of the most rugged country, changing neither direction, dip, nor 

 interval, with hill or valley, cliff or scar, and passing alike 



