The Savannah morning news. (Savannah, Ga.) 1900-current, 1902-03-01

to be one of Importance. We might con-
clude, but enormously, that corals
could exist in any depth of sea, and
natural superstition might be that
corals beginning to build in the bed
of the ocean would, in time, make
their appearance at the surface. So
far from this being the case, 1t may
probably startle ones readers to learn
that corals can only live in a limited
depth of water. In other words, they
require to live near the surface, and
would perish in the depths of the sea.
About $50 feet may be taken as the
limit of coral life as regards depth, and
if we consider this latter fact We read
lily perceive how we appear to have
landed ourselves on the horns of di-
lemma. For if 1t be certain, as it is,
that corals cannot live below $50 feet
or whereabouts in the sea, the question
naturally follows: How comes it that
we find coral reefs rising in places
where the ocean is miles in depth?"
The oldest naturalist 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 arise
submarine mountains or elevations.
These coming to within $50 feet of the
surface would constitute a foundation
urally build upward 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
necessary to prove that the bed of the
ocean was elevated into submarine
hills, which could thus form founda-
tions for coral reefs. All our knowl-
edge of the ocean beds negative any
1..a.. 49,
elevations, no doubt, in ocean beds,
but there are no such submarine noun
tains as are postulated on this first
theory of coral reefs. The world had
to wait a considerable period before
a better explanation of the difficulty
was afforded.
Charles Darwin, in 1S43, as the result
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 biologists, that large tracts of land
have subsidized as other large tracts
have been raised from the oceans
depths. There is, therefore, no pre-
liminary difficulty regarding the sink
ing OF land. Darwin tells us, in his
story of coral reefs, that the commence
ment of the work is found in the
is called the "fringing reef" The ISL
and of Mauritius offers a good exam
pie before 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. II the land remains station
airy no great changes can happen in
the reef. The coral animals cannot
build further down, and as they can
not live out of the water, the reef,
while growing and increasing 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, die.
the upper corals, taking advantage of
the fresh space afforded them, viii in
crease 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 a belt of water between
the reef and the land. The reef in
creases more on the sea face than on
the side next to the land and as a
consequence a channel of shallow
water comes to be inclosed, as l have
described. If now we suppose the bar
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. 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 ma
ture. This third and last variety,
which we may call the complete coral
island is circular in shape. 1t has fol-
lowed the outline of the old, forgotten
land around which is grew, and the
side of this reef, or atoll as it is called,
will naturally depend on the size of the
forgotten land which forms it's founda-
ton. Such is Darwin's theory of the
erection of coral reefs from the sub
sidence of land.
Another theory has of late years
been advanced, ahe essence of which
Is found in the idea tfYat certain OF
these circular reefs or atolls may have
been formed upon some foundation or
other arising from the bed of the
ocean. Such foundation would require
to be brought to within the limit in
depth at which the corals can live, and
the round form OF the atol inclosing a
central lake or lagoon is explained by
this theory on the supposition that
wasting OF coral would take place ip
the interior as the coral reef grew out
ward or on its sea face. serious
difhculty In accepting this latter the