The daily morning journal and courier., 1901-12-19

l WHICH are I1llleS Qeep, the Hlhllel pl
 depth would not appear at first sight tc
 be one of importance. We might con-
 clude, but enormously, that corals could
 exist in any depth of sea, and natural
 supposition might be that corals be-
 ginning to build in the bed of the ocean
 would in time make their appearance at
 the surface.
 The problems of Deep Sea Reefs.
 So far from this being the case, it
 may probably startle ones readers to
 learn that cOrals can only live in linn ited depth of water. In other words,
 they require to live near the surface
 and would perish in the depths of the
 sea. About 15O feet may be taken as
 the limit of coral life as regards depth,
 and if we consider this latter fact we
 readily perceive how we appear to have landed ourselves on the horns of di-
 lemma For if it be certain, as it is,
 that corals cannot live below 150 feet
 or thereby in the sea, the question nat
 urally follows, how comes it 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 i submarine mountains or elevations.
 These coming to within 150 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 l 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 foundations for coral reefs. All our knowledge of the ocean beds negatives any such idea. There are undulations and elevations no doubt in ocean beds, but there are no such submarine mountains as are pos tulated on this first theory of coral reefs The world had to wait a consid- erable period before better eXplana- ton of the difficulty was afforded.
 Darwins Solution of the Difficulty.
 Charles Darwin, in 1S43. as the result of his study of coral reefs in their na- tive regions, advanced the idea that the true explanation of coral formation was to be found in a geological fact, name ly, the sinking of land. We know as geologists that large tracts of land have subsided as other large tracts have been raised from the oceans depths. There is, therefore, no preliminary diff ficulty regarding the sinking of land. Darwin tells us in his story of coral reefs, that the commencement of the ic in what is oe1I1ad Tho "fringing reef" The island of Mauritius offers a good example for our eyes of such reef. Here the coral animals settle down on the sides of existing land and build reef running round the land at their own depth The coral reef here, therefore, is fringe or belt of coral, bordering the land. If the land remains stationary, no great changes can happen in the reef. The coral an- | mals cannot build further down, and as they cannot 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 read iy see that while the lower corals car ried out of their depths die the upper cOrals, taking advantage of the fresh space afforded them, will increase and grow. Thus, as the ringing reef disap pears the upward increase 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 increases more on the sea face than on the side next to the land, and as a consequence channel of shallow I~x. I i, described. If now we suppose the bar rier reef to sink in it's turn, and if, further, we presume that in the case of an island the original land completely disappears in the sea, we are again face to face with the same upward growth If the corals.
 Growth of the Great Coral Cup.
 The end of the story must therefore )e that, as the land has disappeared a great cup of coral has grown round 1t, md the edge or rim of this coral cup appearing at the surface of the ocean constitutes the kind of reef we find in lature. This third and last variety, which we may call the complete coral sland, is circular in shape. It has fol- ] owed the outline of the old forgotten
 
 if this reef, or atoil, as it is called will depend on the size of the for | -otten land which forms its foundation. l 'uch is Darwin's theory of the erection f coral reefs from the subsistence of and Another theory has of late years been f dvanced, the essence of which Is found ! n the idea that certain of these crcu- IF reefs or atois may have been form d upon some foundation or other aris- lg from the bed of the ocean Such a would require to be brought 3 within the limit in depth at which = he corals can live, and the round form |, f the atoil, enclosing a central lake or ', lgoon, is explained by this theory on U ne suppostion that wasting of corals 'ould take place in the interior as the o oral reef grew outwards or on it's sea Il ice. A serious difficulty in accepting 1is latter theory naturally arises when II e question the source of the founda- e' on which has been thus supposed to W se from the ocean bed. If we could It nd reason to suppose that the debris . ? the ocean, bed could accumulate. or r' lat chalk deposits could be raised in O lis way, the theory might find more u in the eyes of scientific men, tt it one calculation alone will show the n