esides, during the rainy months, large supplies of pebbles,
sand, and mud, which numerous streams from the Grampians, Cheviots, and
other chains, send down to the sea. To what regions, then, is all this
matter consigned? It is not retained in mechanical suspension by the
waters of the ocean, nor does it mix with them in a state of chemical
solution--it is deposited _somewhere_, yet certainly not in the
immediate neighborhood of our shores; for, in that case, there would
soon be a cessation of the encroachment of the sea, and large tracts of
low land, like Romney Marsh, would almost everywhere encircle our
island.

As there is now a depth of water exceeding thirty feet, in some spots
where towns like Dunwich flourished but a few centuries ago, it is clear
that the current not only carries far away the materials of the wasted
cliffs, but is capable also of excavating the bed of the sea to a
certain moderate depth.

So great is the quantity of matter held in suspension by the tidal
current on our shores, that the waters are in some places artificially
introduced into certain lands below the level of the sea; and by
repeating this operation, which is called "warping," for two or three
years, considerable tracts have been raised, in the estuary of the
Humber, to the height of about six feet. If a current, charged with such
materials, meets with deep depressions in the bed of the ocean, it must
often fill them up; just as a river, when it meets with a lake in its
course, fills it gradually with sediment.

I have said (p. 337) that the action of the waves and currents on
sea-cliffs, or their power to remove matter from above to below the
sea-level, is insignificant in comparison with the power of rivers to
perform the same task. As an illustration we may take the coast of
Holderness described in the last chapter (p. 304). It is composed, as we
have seen, of very destructible materials, is thirty-six miles long, and
its average height may be taken at forty feet. As it has wasted away at
the rate of two and a quarter yards annually, for a long period, it will
be found on calculation that the quantity of matter thrown down into the
sea every year, and removed by the current, amounts to 51,321,600 cubic
feet. It has been shown that the united Ganges and Brahmapootra carry
down to the Bay of Bengal 40,000,000,000 of cubic feet of solid matter
every year, so that their transporting power is no less than 780 times
greater than tha