ation of these
deep-sea strata come from organic remains, which are continually
falling upon the sea floor. In part, this waste is derived from
creatures which dwell upon the bottom; in considerable measure,
however, it is from the dead bodies of those forms which live near the
surface of the sea, and which when dying sink slowly through the
intermediate realm to the bottom.

Owing to the absence of sunlight, the prevailingly cold water of the
deeper seas, and the lack of vegetation in those realms, the growth of
organic forms on the deep-sea floor is relatively slow. Thus it
happens that each shell or other contribution to the sediment lies for
some time on the bottom before it is buried. While in this condition
it is apt to be devoured by some of the many species which dwell on
the bottom and subsist from the remains of animals and plants which
they find there. In all cases the fossilization of any form depends
upon the accumulation of sediment before the processes of destruction
have overtaken them, and among these processes we must give the first
place to the creatures which subsist on shells, bones, or other
substances of like nature which find their way to the ocean floor. In
the absolute darkness, the still water, and the exceeding cold of the
deeper seas, animals find difficult conditions for development.
Moreover, in this deep realm there is no native vegetation, and, in
general, but little material of this nature descends to the bottom
from the surface of the sea. The result is, the animals have to
subsist on the remains of other animals which at some step in the
succession have obtained their provender from the plants which belong
on the surface or in the shallow waters of the sea. This limitation
of the food supply causes the depths of the sea to be a realm of
continual hunger, a region where every particle of organic matter is
apt to be seized upon by some needy creature.

In consequence of the fact that little organic matter on the deeper
sea floors escapes being devoured, the most of the material of this
nature which goes into strata enters that state in a finely divided
condition. In the group of worms alone--forms which in a great
diversity of species inhabit the sea floor--we find creatures which
are specially adapted to digesting the _debris_ which gathers on the
sea bottom. Wandering over this surface, much in the manner of our
ordinary earthworms, these creatures devour the mud, voiding the
matte