Observations on Glaciers, 



347 



You are already aware that this structure consists in the 

 alternation of more or less perfectly crystallized ice in paral- 

 lel layers, often thinning out altogether like veins in marble, 

 not unfrequently parallel and uniform like a ribboned calce- 

 dony or jasper. 



I will, for brevity, merely state the modifications which this 

 fundamental type undergoes, bringing together glaciers of all 

 classes, but reserving the detail of examples and proofs, of which 

 my experience has already furnished me with a great number, 

 to another occasion. If a glacier lies long and narrow, as the 

 Lower Aar, or the Mer de Glace of Chamouni, the frontal dip 

 is the least conspicuous part of the phenomenon ; and if it 

 terminate in an icy cascade, as in the second case, it might 

 escape observation altogether. The vertical planes parallel 

 to the length, or nearly so, usurp nearly all the breadth of the 

 glacier, and only in the centre is a narrow space, where no| 

 unfrequently the structure appears quite undefined. I have 

 satisfactorily made out, however, in every glacier which I 

 have had the means of examining with that view, that the 

 conoidal structure, however obscured, exists in all parts of the 

 true glacier, modified, according to its length and breadth, in 

 the manner which figs. 3 and 4 indicate. I need not add, that 



Fig. 3. 



Fig. 4. 



these rude sketches are not intended to be considered as rigor- 

 ously exact, but only to explain generally my meaning. 



There is yet another modification, but only a modification, 

 of the above, namely, in the case of extremely steep glaciers, 

 but which are coherent, and not crevassed into pyramids. 

 There are numberless examples of these in all the higher val- 



