f ice will be found adhering to the rock, stone,
or gravel at the bottom. If they are watched with attention, they
will be observed to rapidly increase in bulk, till at last, on
account of their inferior specific gravity, aided, perhaps, by the
action of the current, they detach themselves from the substances
to which they first adhered, and rise to the surface of the water.
The form of these pieces of ice is very irregular, depending in a
great measure on the size and shape of the stones or other
substances to which they were originally attached. Most of them
seem to be of an oblong or circular figure; they are generally
convex on the upper surface, and have a number of laminae and
spiculae shooting from them in various directions, especially from
their circumference. Sometimes when those floating pieces or
plates meet with any obstruction in the channel of the river, they
accumulate in such quantities as to cover the surface of the
water, and become frozen together in one large sheet, but this
kind of ice may be always readily distinguished from that produced
in the usual way by the action of the cold air on the surface,
which is smooth, transparent, and of an uniform texture; on the
contrary, one of these conglomerated fields or sheets is opaque,
uneven, full of asperities, and the form of each separate plate
composing it may be distinctly traced. In this situation, they
generally assume the shape of irregular polygons, with angles
somewhat rounded; a form apparently caused by the lateral pressure
of the contiguous pieces.

On the river Wharfe, near Otley, in the West Riding of Yorkshire,
is a weir or milldam where this phenomenon is sometimes manifested
in a striking manner. This structure is of hewn stone, forming a
plane inclined at an angle of from 35 degrees to 50 degrees,
fronting the north and extending from west to east, to the length
of 250 or 300 yards. When one of the above-mentioned frosts
occurs, the stone which composes the weir soon becomes incrusted
with ice, which increases so rapidly in thickness as in a short
time to impede the course of the stream, which falls over it in a
tolerably uniform sheet, and with considerable velocity; at the
same time, the wind blowing strongly from the north-west,
contributes to repel the water and freeze such as adheres to the
crest of the weir when its surface comes nearly in contact with
the air. The consequence is that in a short time the current is
entirely obs