ICE AND GLACIERS. 127 



the ice which, as I before mentioned, is below zero immediately 

 after pressure has been applied is again raised to this tempera- 

 ture and begins to melt. The crevices then fill with water, 

 and such ice then consists of a quantity of minute granules 

 from the size of a pin's head to that of a pea, which are closely 

 pushed into one another at the edges and projections, and in 

 part have coalesced, while the narrow fissures between them 

 are full of water. A block of ice thus formed of ice-granules 

 adheres firmly together ; but if particles be detached from its 

 corners they are seen to consist of these angular granules. Gla- 

 cier ice, when it begins to melt, is seen to possess the same 

 structure, except that the pieces of which it consists are mostly 

 larger than in artificial ice, attaining the size of a pigeon's egg. 



Glacier ice and compressed ice are thus seen to be substances 

 of a granular structure, in opposition to regularly crystallised 

 ice, such as is formed on the surface of still water. We here 

 meet with the same differences as between calcareous spar and 

 marble, both of which consist of carbonate of lime ; but while 

 the former is in large, regular crystals, the latter is made up of 

 irregularly agglomerated crystalline grains. In calcareous spar, 

 as well as in crystallised ice, the cracks produced by inserting the 

 point of a knife extend through the mass, while in granular ice a 

 crack which arises in one of the bodies where it must yield does 

 not necessarily spread beyond the limits of the granule. 



Ice which has been compressed from snow, and has thus from 

 the outset consisted of innumerable very fine crystalline needles, 

 is seen to be particularly plastic. Yet in appearance it materially 

 differs from glacier ice, for it is very opaque, owing to the great 

 quantity of air which was originally inclosed in the flaky mass 

 of snow, and which remains there as extremely minute bubbles. 

 It can be made clearer by pressing a cylinder of such ice between 

 wooden boards ; the air-bubbles appear then on the top of the 

 cylinder as a light foam. If the discs are again broken, placed 

 in the mould, and pressed into a cylinder, the air may gradually 

 be more and more eliminated, and the ice be made clearer. No 

 doubt in glaciers the originally whitish -mass of ne>e is thus 

 gradually transformed into the clear, transparent ice of the glacier 



