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THE SEAS
‘
ericlosed seas, separated from the oceans by islands or
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peninsulas, such as the Behring Sea and the English
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Channel; gulfs and bays, such as the
Gulf of Aden, Gulf
Of Maine and Bay of Bengal; and straits such as the
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Straits of Gibraltar and of Dover.
.
Over two-thirds of the earth’s surface is covered thus
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by the oceans and their adjacent waters, the actual proportion of the water to the land masses being according
to latest computations about 2.4 to I.
These water masses
are not distributed evenly over the surface of the
only 43 per cent. lying in the northern hemisphere as
opposed to 57 per cent. in the southern.
The ratio of
water to land also varies in the different hemispheres and
,
it is possible to divide the earth into a water hemisphere
whose centre lies a’little south—east of New Zealand and a
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land hemisphere with a centre near the mouth of the Loire
Even in the land hemisphere the water area
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exceeds that of the land by a small amount, while in the
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'
water herisphere only oué—tenth is dry land.
Along the coasts of the great continents the water is
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shallow and a shelf is formed, either by
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Ï
erosion_ of the land through the ceaseless battering of the
;
ï
'
waves against its shores, Or by the seaward extension' of
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deposits of mud and silt brought down from the interior
:
of the continents by great rivers, or by the gradual sub- "
'
mergence of the land itself.
Thus there is a plateau, the
-
::
'
Continental Shelf (Eig. I), from_which the,dry land emerges
'
above the water level.
This area of shallow water, extend—
mg down to a’dePth of ‘about one hundred fathoms, varies
"
'
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considerably in width.
It is widest in those regions where
" '
there
been a gradual submergence of land, such as in
…
the North Seai'nto which also are carried mud and silt
from the many rivets on the surrounding land. It is
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narr0west where there. has probably been an upheaval of
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