tructed, and the superincumbent water forced to a
higher level. But as the above-mentioned causes continue to act,
the ice is also elevated by a perpetual aggregation of particles,
till by a series of similar operations an icy mound or barrier is
formed, so high as to force the water over the opposite bank, and
thus produce an apparent inundation. But in a short time the
accumulated weight of a great many thousand cubic feet of water
presses so strongly against the barrier as to burst a passage
through some weak part, through which the water escapes and
subsides to its former level, leaving the singular appearance of a
wall or rampart of ice three or four feet high, and about two feet
in thickness, along the greatest part of the upper edge of the
weir. The ice composing this barrier where it adheres to the
stone, is of solid consistency, but the upper part consists of a
multitude of thin laminae or layers resting upon each other in a
confused manner, and at different degrees of inclination, their
interstices being occupied by innumerable icy spiculae, diverging
and crossing each other in all directions. The whole mass much
resembles the white and porous ice which may be seen at the edge
of a pond or small rill where the water has subsided during a
frost.

It may be further observed that a frost of this kind is very
limited in its duration, seldom lasting more than thirty-six or
forty hours. On the morning of the second day after its
commencement, a visible relaxation takes place in the temperature
of the atmosphere. Usually before noon, the wind on a sudden
shifts to the south-west, and a rapid thaw comes on, frequently
attended with rain. What appears somewhat remarkable is, that
during several hours after the commencement of the thaw, the
production of ice at the bottom of rivers seems to go on without
abatement, and upon examining a rapid stream, the stones over
which it flows will be found at this period completely incrusted
with the above description of icy plates. It seems evident from
this that the bed of the river, which has been reduced below the
freezing temperature, is not for some time affected by the change
of the atmosphere. This may be in some measure illustrated by the
well-known fact, that rain which falls upon a rock or stone wall,
is frequently converted into ice, though the air and the ground
are evidently in a state of thaw. Before the following morning,
the ice of which we have been speaking gen