214 
THE FORMATION OF GLACIERS. 
the edge of the larger mass, and float out upon 
the surface of the water. Icebergs were first 
traced back to their true origin by the nature of 
the land-ice of which they are always composed, 
and which is quite distinct in structure and con- 
sistency from the marine ice produced by frozen 
sea-water, and called “ ice-flow ” by the Arctic 
explorers, as well as from the pond or river ice, 
resulting from the simple congelation of fresh 
water, the laminated structure of which is in 
striking contrast to the granular structure of 
glacier ice. 
Water is changed to ice at a certain tempera- 
ture under the same law of crystallization by 
which any inorganic bodies in a fluid state may 
assume a solid condition, taking the shape of per- 
fectly regular crystals, which combine at certain 
angles with mathematical precision. The frost 
does not form a solid, continuous sheet of ice 
over an expanse of water, but produces crystals, 
little ice-blades, as it were, which shoot into each 
other at angles of thirty or sixty degrees, form- 
ing the closest net-work. Of course, under the 
process of alternate freezing and thawing, these 
crystals lose their regularity, and soon become 
merged in each other. But even then a mass of 
ice is not continuous or compact throughout, for 
it is rendered completely porous by air-bubbles, 
the presence of which is easily explained. Ice 
