When examining beds of clay and marl, or even of compact
limestone, especially in large mountain-masses, I have frequently
observed that the rock presents a net-work of minute fissures pervading
the whole, without producing a distinct solution of continuity, though
generally determining the lines according to which it breaks under
sudden shocks. The net-work of capillary fissures pervading the glacier
may fairly be compared to these rents in hard rocks,--with this
difference, however, that in ice they are more permeable to water than
in stone.
How this net-work of capillary fissures is formed has not been
ascertained by direct observation. Following, however, the
transformation of the snow and _neve_ into compact ice, it is easily
conceived that the porous mass of snow, as it falls in the upper regions
of the Alps, and in the broad caldrons in which the glaciers properly
originate, cannot pass into solid ice, by the process described in a
former article, without retaining within itself larger or smaller
quantities of air. This air is finally surrounded from all sides by the
cementation of the granules of _neve_, through the freezing of the water
that penetrates it.
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