ending and dislocating any yielding strata of gravel, sand, or mud. The
banks on which icebergs occasionally run aground between Baffin's Bay
and Newfoundland, are many hundred feet under water, and the force with
which they are struck will depend not so much on the velocity as the
momentum of the floating ice-islands. The same berg is often carried
away by a change of wind, and then driven back again upon the same bank,
or it is made to rise and fall by the waves of the ocean, so that it may
alternately strike the bottom with its whole weight, and then be lifted
up again until it has deranged the superficial beds over a wide area. In
this manner the geologist may account, perhaps, for the circumstance
that in Scandinavia, Scotland, and other countries where erratics are
met with, the beds of sand, loam, and gravel are often vertical, bent,
and contorted into the most complicated folds, while the underlying
strata, although composed of equally pliant materials, are horizontal.
But some of these curvatures of loose strata may also have been due to
repeated alternations of layers of gravel and sand, ice and snow, the
melting of the latter having caused the intercalated beds of
indestructible matter to assume their present anomalous position.

There can be little doubt that icebergs must often break off the peaks
and projecting points of submarine mountains, and must grate upon and
polish their surface, furrowing or scratching them in precisely the same
way as we have seen that glaciers act on the solid rocks over which they
are propelled.[301]

To conclude: it appears that large stones, mud, and gravel are carried
down by the ice of rivers, estuaries, and glaciers, into the sea, where
the tides and currents of the ocean, aided by the wind, cause them to
drift for hundreds of miles from the place of their origin. Although it
will belong more properly to the seventh and eighth chapters to treat of
the transportation of solid matter by the movements of the ocean, I
shall add here what I have farther to say on this subject in connection
with ice.

The saline matter which sea-water holds in solution, prevents its
congelation, except where the most intense cold prevails. But the
drifting of the snow from the land often renders the surface-water
brackish near the coast, so that a sheet of ice is readily formed there,
and by this means a large quantity of gravel is frequently conveyed from
place to place, and heavy boulders als