Prof. Huxley on the Structure of Glacier Ice. 247 
it looks. But these are questions for you to solve; and I will 
only venture on one other supposition, viz. that the water-cham- 
bers have the value of a register thermometer, indicating that 
the minimum temperature to which the mass of a glacier de- 
scends is never for long less than 32°; otherwise I cannot con- 
ceive 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 parallel 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. Further- 
more, as Prof. Agassiz points out, the water-chambers are ar- 
ranged 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 
of 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” glacier 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 difference 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 direc- 
tions; 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 composed of 
larger or smaller granules of exceedingly irregular form *, sepa- 
rated by very obvious fissures, but nevertheless so fitted into 
one another as to cohere with some firmness. The distance to 
which the fissures extend into the interior of the glacier (and 
* The superficial layer is particularly well described by the Messrs. 
Schlagintweit in their Untersuchungen iiber die physikalische Geographie 
der Alpen, 1850, 
