178
THE, SEAS
exceptional interest.
Known as the “
glacial—control ”
theory, this states that during the great ice ages so much
,
Water was locked away in the form of ice that the surface
'
of the sea was lowered by between twenty—ve and thirtyve fathoms in the tropics.
During this period the pre—
existig coral reefs (for coral reefs are known from the
earliest times of which we have any geologicalevidence)
were destroyed, but when the glacial period passed the water
which returned to the sea gradually raised it to its former
level and at the same time became Warmed up, and in this
warm water new coral colonies became established on the
at platforms- into which those regions of the sea bottom
_
exposed during the glacial period
been converted;
'
As--the water r03e the corals
these platforrhs
‘
grow upwards with it; in just the same manner as
'
Darwin sùpposed, only in the former case it was the sea;
-
which
changing its level and in the latter the earth.
There is support for this ingenious theory from
Mayor who calculated from-the growth of corals in'Samoa
that the reefs in that region at any Tate, could all have
been formed since the last glacial epoch.
On the. other
hand, we have no denite knowledge as to the amountof
,
,
water which was taken from the
during the ice age,
while there is abundant evidence that many reefs are not
_
founded onvP1atforms which could haVe been formed in
_
this way.
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.“
,'