The Savannah morning news., 1901-12-29

Co., corner William and John streets.
New York.
that we find coral reefs rising in places
where the ocean is miles in depth?"
The older naturalists endeavored to
explain away this difficulty by assum-
| ing that the corals must find some
| foundation. They supposed that from
the bed of the ocean there must rise
1 submarine mountains or elevations.
These coming to within $50 feet of the
surface would constitute a foundation
for the corals, which then would nat
urally build upwards to the surface.
| This view of matters, however, was
soon exploded by the realization of an
awkward fact. On the principle of
first catching your hare, it was neces-
sary to prove that the bed of the ocean
was elevated into submarine hills,
which could thus form foundations for
coral reefs. All our knowledge of the
ocean beds negatives any such idea.
! There are fluctuations and elevations
no doubt in ocean beds, but there are
no such submarine mountains as are
| postulated on this first theory of coral
reefs The world had to wait consid-
cradle period before a better explana-
ton of the difficulty was afforded.
Darwin's Solution of the Difficulty.
Charles Dapwin, in 1S43, as the re-
suit of his study of coral reefs in their
native regions, advanced the idea that
the true explanation of coral formation
| was to be found in a geological fact,
namely, the sinking of land. We know
! as geogolists that large tracts of land
! have subsidized as other large tracts
! have been raised from the oceans
depths. There is, therefore, no prelimi-
nary difficulty regarding the sinking
! of land. Darwin tells us, in his story
| of coral reefs, that the commencement
| of the work is found in what is called
the bringing reef" The island of
Mauritious offers good example for
| our eyes of such a reef. Here the coral
animals settle down on the sides of
| existing land and build a reef running
round the land at their own depth. The
coral reef here, therefore, is a fringe
or belt of coral, bordering the land.
| If the land remains stationary, no
| great changes can happen in the reef.
The coral animals cannot build further
down, and as they cannot live out of
water, the reef, while growing and in
| creasing within it's own limits, will
practically remain without material
! change. But if we suppose the land
to sink, we readily see that while the
| lower corals carried out of their depths
| of the fresh space afforded them, will
increase and grow. Thus, as the firing
! ing reef disappears the upward in
| crease of the coral gives us a second
| kind of reef. This is the barrier reef.
Here we find belt of water between
the reef and the land. The reef in
| creases more on tn sea surface than
on the side next to the land, and as
a consequence a channel of shallow
water comes to be enclosed as l have
described. If now we suppose the bar
| rier reef to sink in its turn, and IT,
| further, we presume that in the case
of an island the original land COM
pletely disappears in the sea, we are
again face to face with the same up
ward growth of the corals.
Growth of the Great Coral Cup.
The end of the story must therefore
| be that as the land has disappeared,
a great cup of coral has grown round
! it, and the edge or rim of this coral
cup appearing at the surface of the
ocean constitutes the third kind of reef
we find in nature This third and last
variety, which we may call the com
! plete coral island is circular in shape
| 1t has followed the outline OF the old
! forgotten land around which it grew
and the size of this reef, or atoll, as
it is called, will naturally depend on
the size of the forgotten land which
| forms its foundation. Such is Darwin's
| theory of the erection of coral reefs
from the subsistence of land.
Another theory has of late years been
| advanced, the essence of which is found
in the idea that certain of these circu-
| lar reefs or atolls may have been
formed upon some foundation or other
arising from the bed of the ocean.
| Such a foundation would require to be
To "a Of
which the corals can live, and the round
form of the atoll enclosing a central
| lake or lagoon, is explained by this
theory on the supposition that vast
ing of coral would take place in the
interior as the coral reef grew out
wards or on its sea face. serious
difficulty in accepting this latter theory
naturally arise when we question the
| cource of the foundation which has
been thus supposed to rise from the
| ocean bed. If we could find reason to
| suppose that the debris of the ocean
bed could accumulate, or that chalk
deposits could be raised in this way.
the theory might find more acceptance
in the eyes of scientific men, but one
calculation alone will show the disad-
vantage of this theory as compared
with the simpler view of Darwin. It
is said that every layer of ea-water
| 100 fathoms deep and a mile square in
extent, will afford more than sixteen
| tons of carbonte of lime If this mater
| ial be used by the chalk animalcules,
| IL might be supposed fouidation could
| in this way be formed; but If these six
teen tons of chalk could be spread over
a mile square. It would only form a
layer not more than .O001 of an inch
in thickness, or at most the tenth of
an ich.
ImprobabiIity of the Later Theory.
The time occupied in building up a
foundation from miles of sea-depth on
| this estimate would be simply incon-
| ceivable; or, as another authority es-
| times, the annual accumulation of
chalk could not exceed the 1-9000th
part of an ich, and therefore 1t would
require 100000 years TO form a layer
one foot thick. On this basis, If, from
the ocean bed. 100 fathoms of water,
say are to be built through to the low
| est limit OF the coral life, we should re-
! quire a layer seventy-hve fathoms
| thick. To effect this forty-five millions
of years would be required at the
ordinary rate of deposition. On grounds
! like these we may well rest content 10
hold that Darwin's theory explains the
erection of coral reefs consistently with
| the facts OF nature, and not the least
wonderful part of the story OF the
corals consists In the construction OF
an adequate explanation of a difficulty
| which prior 10 Darwn's time seemed
insuperable 10 scientific men.
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