occupy an area small when contrasted with the vast
stretches of the land. The area of deposition is much less than
that of denudation; probably hardly as much as one twentieth.
And, again, the conditions of aeration and circulation which
largely promote chemical and solvent denudation in the soils are
relatively limited and ineffective in the detrital oceanic
deposits.

The summation of the amounts of dissolved and detrital materials
which denudation has brought into the ocean during the long
denudative history of the Earth, as we might anticipate, reveals
quantities of almost unrealisable greatness. The facts are among
the most impressive which geological science has brought to
light. Elsewhere in this volume they have been mentioned when
discussing the age of the Earth. In the present connection,
however, they are deserving of separate consideration.

The basis of our reasoning is that the ocean owes its saltness
mainly if not entirely to the denudative activities we have been
considering. We must establish this.

We may, in the first place, say that any other view at once
raises the greatest difficulties. The chemical composition of the
detrital sediments which are spread over

41

the continents and which build up the mountains, differs on the
average very considerably from that of the igneous rocks. We know
the former have been derived from the latter, and we know that
the difference in the composition of the two classes of materials
is due to the removal in solution of certain of the constituents
of the igneous rocks. But the ocean alone can have received this
dissolved matter. We know of no other place in which to look for
it. It is true that some part of this dissolved matter has been
again rejected by the ocean; thus the formation of limestone is
largely due to the abstraction of lime from sea water by organic
and other agencies. This, however, in no way relieves us of the
necessity of tracing to the ocean the substances dissolved from
the igneous rocks. It follows that we have here a very causa for
the saltness of the ocean. The view that the ocean "was salt from
the first" is without one known fact to support it, and leaves us
with the burden of the entire dissolved salts of geological time
to dispose of--Where and how?

The argument we have outlined above becomes convincingly strong
when examined more closely. For this purpose we first compare the
average chemical composition of the sedimentary and