ually losing
temperature. In other words, the conditions which we assume bring
about volcanic action do not exist beneath the old land.

Beneath the seas, except in their very greatest depths, and perhaps
even there, the process of forming strata is continually going on.
Next the shores, sometimes for a hundred or two miles away to seaward,
the principal contribution may be the sediment worn from the lands by
the waves and the rivers. Farther away it is to a large extent made up
of the remains of animals and plants, which when dying give their
skeletons to form the strata. Much of the materials laid down--perhaps
in all more than half--consist of volcanic dust, ashes, and pumice,
which drifts very long times before it finds its way to the bottom. We
have as yet no data of a precise kind for determining the average rate
of accumulation of sediments upon the sea floor, but from what is
known of the wearing of the lands, and the amount of volcanic waste
which finds its way to the seas, it is probably not less than about a
foot in ten thousand years; it is most likely, indeed, much to exceed
this amount. From data afforded by the eruptions in Java and in other
fields where the quantity of volcanic dust contributed to the seas can
be estimated, the writer is disposed to believe that the average rate
of sedimentation on the sea floors is twice as great as the estimate
above given.

Accumulating at the average rate of one foot in ten thousand years, it
would require a million years to produce a hundred feet of sediments;
a hundred million to form ten thousand feet, and five hundred million
to create the thickness of about ten miles of bed. At the rate of two
feet in ten thousand years, the thickness accumulated would be about
twenty miles. When we come to consider the duration of the earth's
geologic history, we shall find reasons for believing that the
formation of sediment may have continued for as much as five hundred
million years.

The foregoing inquiries concerning the origin of volcanoes show that
at the present time they are clearly connected with some process which
goes on beneath the sea. An extension of the inquiry indicates that
this relation has existed in earlier geological times; for, although
the living volcanoes are limited to places within three hundred miles
of the sea, we find lava flows, ashes, and other volcanic
accumulations far in the interior of the continents, though the energy
which brought them