s 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. So inclosed, the bubbles of air are subject to the
same compression as the ice itself, and become more flattened in
proportion as the snow has been more fully transformed into compact ice.
As long as the transformation of snow into ice is not complete, a rise
of its temperature to 32 deg. Fahrenheit, accompanied with thawing, reduces
it at once again to the condition of loose grains of _neve_; but when
more compact, it always presents the aspect of a mass composed of
angular fragments, wedged and dove-tailed together, and separated by
capillary fissures, the flattened air-bubbles trending in the same
direction in each fragment, but varying in their trend from one fragment
to another. There is, moreover, this important point to notice,--that,
the older the _neve_, the larger are its composing granules; and where
_neve_ passes into porous ice, small angular fragments are mixed with
rounded _neve_-granules, the angular fragments appearing larger and more
numerous, and the _neve_-granules fewer, in proportion as the _neve_-ice
has undergone most completely its transformation into compact
glacier-ice. These facts show conclusively that the dimensions and form
of the _neve_-granules, the size and shape of the angular fragments, the
porosity of the ice, the arrangement of its capillary fissures, and the
distribution and compression of the air-bubbles it contains, are all
connected features, mutually dependent. Whet