the current ceases the mud sinks to the bottom, the earthy particles
composing it, being heavier than water, would sink in still water in
times inversely proportional to their size and specific gravity. This,
I think, is a satisfactory explanation of the manner in which the ice
formed at the surface finds its way to the bottom; its adherence to the
bottom, I think, is explained by the phenomenon of _regelation_, first
observed by Faraday; he found that when the wetted surfaces of two
pieces of ice were pressed together they froze together, and that this
took place under water even when above the freezing point. Professor
James D. Forbes found that the same thing occurred by mere contact
without pressure, and that ice would become attached to other substances
in a similar manner. Regelation was observed by these philosophers in
carefully arranged experiments with prepared surfaces fitting together
accurately, and kept in contact sufficiently long to allow the freezing
together to take place. In nature these favorable conditions would
seldom occur in the masses of ice commonly observed, but we must admit,
on the evidence of the recorded experiments, that, under particular
circumstances, pieces of ice will freeze together or adhere to other
substances in situations where there can be no abstraction of heat.

[Footnote 1: Paper clx., in the Transactions of the Society, 1878, vol.
vii., pages 109-168.]

When a piece of ice of considerable size comes in contact under water
with ice or other substance, it would usually touch in an area very
small in proportion to its mass, and other forces acting upon it,
and tending to move it, would usually exceed the freezing force, and
regelation would not take place. In the minute needles formed at the
surface of the water the tendency to adhere would be much the same as in
larger masses touching at points only, while the external forces acting