OCCASIONALLY the oceans make themselves felt in a dramatic and
often disastrous way; great waves resulting from a submarine earth-
quake may sweep across a low coastal area, laying it waste, or storm
waves may break down sea defences and flood low-lying land, or a ship
may be lost at sea. At other times the great ocean streams pass almost
unnoticed on their way, the tide ebbs and flows unobserved, and little
thought is given to the vital part the ocean plays in life on earth. It is
not only because the oceans are vast in area, covering over 70 per cent of
all the earth's surface, but because of their own intrinsic interest that
they are worthy of closer study.

Enormous quantities of water are moved by some ocean currents;
the Gulf Stream, for example, transports more than one thousand times
the greatest Mississippi flood from southern latitudes northwards.
Modern oceanographical work suggests that its influence on the climate
of north-west Europe is very complex; it has been suggested by Iselin
that the warming of the climate of this part of Europe may be greater
during periods of smaller transport by the Gulf Stream. There are some
facts which support this view, although it is no more than an interesting
suggestion at the moment.

The oceans pose many fascinating problems. The origin of the
ocean basins and the water which fills them is of fundamental im-
portance to an understanding of the global pattern of land and sea. The
fluctuations of the level of the oceans has far-reaching effects on land
and is at present closely linked to glacier fluctuations and through this
to climatic change. Sea-level is also the base level to which subaerial
erosion is working, in areas drained by rivers which reach the sea. It
is one of the tasks of modern geomorphology to establish the denuda-
tion chronology of areas in terms of changes in base level. The response
of the rivers to negative changes in base level is clearly dependent on the
gradient of the sea floor exposed by the fall in sea-level. Thus the nature
of the sea floor close to the land and the oscillations of sea-level are
important to geomorphological analysis.

The connexion between the oceans and the climate is an intimate one,
the two interacting in many different ways to influence each other.
Through the climate, the general character of the land areas is related
to the nature of the ocean water and its circulation. Recently new
techniques have been devised for the study of the oceans; one of the
very interesting and useful ones is a new method of measuring directly

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