t of the sea on the coast above-mentioned; and in order
to produce a result equal to that of the two Indian rivers, we must have
a line of wasting coast, like that of Holderness, nearly 28,000 miles in
length, or longer than the entire circumference of the globe by above
3000 miles. The reason of so great a difference in the results may be
understood when we reflect that the operations of the ocean are limited
to a single line of cliff surrounding a large area, whereas great rivers
with their tributaries, and the mountain torrents which flow into them,
act simultaneously on a length of bank almost indefinite.

Nevertheless we are by no means entitled to infer, that the denuding
force of the great ocean is a geological cause of small efficacy, or
inferior to that of rivers. Its chief influence is exerted at moderate
depths below the surface, on all those areas which are slowly rising, or
are attempting, as it were, to rise above the sea. From data hitherto
obtained respecting subterranean movements, we can scarcely speculate on
an average rate of upheaval of more than two or three feet in a century.
An elevation to this amount is taking place in Scandinavia, and probably
in many submarine areas as vast as those which we know to be sinking
from the proofs derived from circular lagoon islands or coral atolls.
(See chap. 50.) Suppose strata as destructible as those of the Wealden,
or the lower and upper cretaceous formation, or the tertiary deposits of
the British Isles to be thus slowly upheaved, how readily might they all
be swept away by waves and currents in an open sea! How entirely might
each stratum disappear as it was brought up successively and exposed to
the breakers! Shoals of wide extent might be produced, but it is
difficult to conceive how any continent could ever be formed under such
circumstances. Were it not indeed for the hardness and toughness of the
crystalline and volcanic rocks, which are often capable of resisting the
action of the waves, few lands might ever emerge from the midst of an
open sea.

_Supposed filling up of the German Ocean._--The German Ocean is deepest
on the Norwegian side, where the soundings give 190 fathoms; but the
mean depth of the whole basin may be stated at no more than thirty-one
fathoms.[462] The bed of this sea is traversed by several enormous
banks, the greatest of which is the Dogger Bank, extending for upwards
of 354 miles from north to south. The whole superficies of th