THE oceans form a vast receptacle into which much of the waste pro-
ducts of subaerial erosion eventually find their way, via the rivers,
glaciers and wind. A great number of the remains of oceanic organisms
also accumulate in them, as well as material brought into the water more
directly from the interior of the Earth via the volcanoes which stud much
of the ocean floor, particularly in the Pacific Ocean. The sediments also
include a minute amount of extra-terrestrial material in the form of
meteoric dust.

The classification and character of these materials can give much
valuable information concerning the nature of the ocean and the pro-
cesses at work within it, as well as having at times a more direct bearing
on such important topics as the modification of the world climate and
all that depends on it. In fact, in the depths of the oceans have been
found some of the most valuable data concerning climatic changes
during the glacial period.

The deposits in the oceans can be subdivided broadly into two main
categories, the shallow-water sediments and the deep-water ones,
although recent work on the character of the deeper sediments suggests
that terrigenous sediments may find their way into the deep oceans at
positions very far from land. The classification is not so much based on
the position in which the sediments are found as on their origin and
character.

Thus the major divisions are made between terrigenous material
derived from the land, organic material, which may have been brought
to the seas in solution from the land, part of it being converted into the
skeletons of minute oceanic organisms, which accumulate when they
die as sediment on the ocean floor, and the volcanic ash deposits. By far
the greater area is covered by deep-sea, pelagic sediments, which are
easier to classify than the much more variable sediments of the coastal
zones. They may be broadly subdivided into inorganic and organic
deposits as follows:

-233-