enth of one per cent, or less. In the deeper seas, it
is doubtful whether the rate of animal growth is such as to permit the
formation of any beds which have less than one half of their mass made
up of materials which fell through the water.

In certain areas of the open seas the upper part of the water is dwelt
in by a host of creatures, mostly foraminifera, which extract
limestone from the water, and, on dying, send their shells to the
bottom. Thus in the North Atlantic, even where the sea floor is of
great depth beneath the surface, there is constantly accumulating a
mass of limy matter, which is forming very massive limestone strata,
somewhat resembling chalk deposits, such as abundantly occur in Great
Britain, in the neighbouring parts of Europe, in Texas, and elsewhere.
Accumulations such as this, where the supply is derived from the
surface of the water, are not affected by the accidents which divide
beds made on the bottom in the manner before described. They may,
therefore, have the singularly continuous character which we note in
the English chalk, where, for the thickness of hundreds of feet, we
may have no evident partitions, except certain divisions, which have
evidently originated long after the beds were formed.

We have already noted the fact that, while the floors of the deeper
seas appear to lack mountainous elevations, those arising from the
folding of strata, they are plentifully scattered over with volcanic
cones. We may therefore suppose that, in general, the deposits formed
on the sea floor are to a great extent affected by the materials which
these vents cast forth. Lava streams and showers represent only a
part of the contributions from volcanoes, which finally find their way
to the bottom. In larger part, the materials thrown forth are probably
first dissolved in the water and then taken up by the organic species;
only after the death of these creatures does the waste go to the
bottom. As hosts of these creatures have no solid skeleton to
contribute to the sea floor, such mineral matter as they may obtain is
after their death at once restored to the sea.

Not only does the contribution of organic sediment diminish in
quantity with the depth which is attained, but the deeper parts of the
ocean bed appear to be in a condition where no accumulations of this
nature are made, and this for the reason that the water dissolves the
organic matter more rapidly than it is laid down. Thus in place of
li