174
THE SEAS
'
Again there Would have _to have been great numbers of
islands dotted about in the rst place to provide the neces_
sary basis for the countless atolls. .
*
,
,
Sir John Murray, of whom we have already heard in
connection with the investigation of the bottom deposits
of
ocean, was the rst to bring forward an alternative
theory of any general application.
The real crux of the
problem is how to account for the presence of these plat_
forms of land covered with not more than about thirty
fathoms of water, from which alone, barring the subsidence
of pre—existing land, corals could grow to the surface.
Murray thought these were produced by a raising of the
sea bottom.
This might take place as a result of a sub—
marine volcanic eruption throwing up a great mound of
debris (these things do frequently happen, islands being
occasionally thrown up above the surface of the sea in this
-
way, the light material of Which they are composed being
usually washed away very quickly afterwards).
It might
also be brought about by the accumulation of great banks
formed from the skeletons of the animals and plants of the
oating lifein the surface waters which are responsible for
the greater part of the deposits on the bottom of the
sea.
.
—
.
Now as soon as a platform is formed in this manner, reef
building corals would be able to establish themselves and to
._
begin growing upwards until they reached the surface,
as shown-in Figure 37.
Clearly thoseiri the centre, at the
,
highest point, wo_‘uld reach the surfaCe rst and ”the pre-.
'»
liminary indication of the beginning of an atoll, according
“to this theory, would be the appearance of a small circular
_
reef at.. But the corals in the centre, being unable to "
grow
further would die, while, those on the
_fringes would grow outwards, extending the at in all
directions.
Now, as in the case of the fringing reef—s
THE SEAS
'
Again there Would have _to have been great numbers of
islands dotted about in the rst place to provide the neces_
sary basis for the countless atolls. .
*
,
,
Sir John Murray, of whom we have already heard in
connection with the investigation of the bottom deposits
of
ocean, was the rst to bring forward an alternative
theory of any general application.
The real crux of the
problem is how to account for the presence of these plat_
forms of land covered with not more than about thirty
fathoms of water, from which alone, barring the subsidence
of pre—existing land, corals could grow to the surface.
Murray thought these were produced by a raising of the
sea bottom.
This might take place as a result of a sub—
marine volcanic eruption throwing up a great mound of
debris (these things do frequently happen, islands being
occasionally thrown up above the surface of the sea in this
-
way, the light material of Which they are composed being
usually washed away very quickly afterwards).
It might
also be brought about by the accumulation of great banks
formed from the skeletons of the animals and plants of the
oating lifein the surface waters which are responsible for
the greater part of the deposits on the bottom of the
sea.
.
—
.
Now as soon as a platform is formed in this manner, reef
building corals would be able to establish themselves and to
._
begin growing upwards until they reached the surface,
as shown-in Figure 37.
Clearly thoseiri the centre, at the
,
highest point, wo_‘uld reach the surfaCe rst and ”the pre-.
'»
liminary indication of the beginning of an atoll, according
“to this theory, would be the appearance of a small circular
_
reef at.. But the corals in the centre, being unable to "
grow
further would die, while, those on the
_fringes would grow outwards, extending the at in all
directions.
Now, as in the case of the fringing reef—s