ON THE STRUCTURE OF GLACIER ICE 



that the water retains its fluidity, and how it is that the water- 

 chambers are compressed. It may seem a common-place comparison, 

 but the ice and its cavities containing water remind me of nothing so 

 much as a Gruyere cheese, in which one so often meets with closed 

 cavities containing fluid and air. Let the Neve represent moist curds 

 and the glacier valley the cheese-press, and the analogy is perhaps 

 closer than it looks. But these are questions for you to solve ; and I 

 will only venture on one other supposition, viz. that the water- 

 chambers have the value of a register thermometer, indicating that 

 the minimum temperature to which the mass of a glacier descends is 

 never for long less than 32° ; otherwise I cannot conceive how the 

 water should remain fluid ; and if it were once frozen, how could it 

 melt again ? 



M. Agassiz makes a very important observation in (4), and one 

 which I am glad to be able to confirm in the main. I took some 

 pains to ascertain the general direction of the planes of the water- 

 chambers, and I found that in the substance of the blue veins they 

 were sometimes paraHel to the plane of the latter, while in the white 

 ice their planes were always more or less inclined to the veins, usually 

 forming an acute angle, and never, so far as I have seen, a right angle 

 with them. Furthermore, as Prof Agassiz points out, the water- 

 chambers are arranged in groups, all the members of the same group 

 having parallel planes, while their direction is more or less inclined to 

 that of neighbouring groups. It seems to me very probable that, as 

 Prof Agassiz suggests, the different directions of the planes of the 

 cavities may indicate internal changes of place of segments af ice 

 corresponding with the groups ; but, as I have already said, no fissures 

 separating these segments are to be found in the deep ice of a glacier, 

 and hence we cannot with propriety speak of them as " fragments." 



Such is the structure which I have found to obtain in all " deep " 

 tdacier ice. by which I mean, all ice situated more than a few inches 

 below the surface. It is as solid as glass or marble, and as devoid of 

 any but accidental and gross fissures. The glacier, however, where 

 exposed to the atmosphere, presents what may be called a "superficial 

 layer " of very different character. Every one who has had occasion 

 to cut an escalier, must have been struck with the diff'erence between 

 the resistance to the ice-axe at the first blow and that at the fourth or 

 fifth. At the first, the jar to the hand is slight, and fragments of ice 

 fly in all directions ; but at the last, one might almost as well be 

 hewing some hard though splintery wood. The reason of this at 

 once becomes apparent on examining the superficial ice. It is com- 



