178 J. STANLEY GARDINER. 
the first place I am convinced that in such shallow depths in an open ocean the calcareous 
remains of pelagic or of any free form of life could not to any large degree rest, on 
account of the tidal and oceanic currents, and hence it is to sedentary forms that we must 
look for an explanation. The latter has been, I believe, afforded by the discovery of deep 
coral banks in the Atlantic, of some of which Mr J. Y. Buchanan has given an account}. 
In my paper on Funafuti, Rotuma and Fiji I gave a number of quotations to show the 
vigorous growth of corals at considerable depths, but I did not then appreciate fully the 
effects of tide, current and wave actions. The banks, described by Mr Buchanan, appear 
to have been absolutely formed by these corals and to have been built up by them to 
comparatively shallow depths. Of the three banks described, the “Coral Patch” was of great 
interest, having an almost flat summit—least depth 485 fathoms—covered with living 
Lophohelia prolifera and surrounded by precipices from 550 to 850 fathoms. The “Seine 
bank” had broken coral with apparently some chlorophyllous organism on its summit at 
86 fathoms, and the “Dacia bank,” 49 fathoms in the centre, was slightly domed in shape 
with cliffs from 100 to over 300 fathoms. The deduction that the precipitous portions of 
these banks are formed by the dead coralla, the living polyps building on the dead “bones” 
of their parents, appears to me a perfectly legitimate and indeed the only possible one. The 
largest bank, the Dacia, is small as compared with the Maldive banks, being only 84 miles 
in diameter. Yet in the same paper indications of similar larger banks in the Atlantic 
are given, and it appears to me quite reasonable to suppose that the separate Maldive banks 
were bwilt up somewhat in the same way. The Maldive plateau being of long, narrow shape, 
of considerable size, at no great distance from continental land, and in the track of oceanic 
currents, would be attected differently to smaller banks. On the latter the conditions of 
food over the whole surface would be nearly the same, the organisms raining down on them 
fairly evenly from the water above. Such banks hence would be covered all over with corals, 
causing them to grow up nearly flat or slightly domed. On account of the direction of the 
Maldive plateau the currents would necessarily set right across it, and its sides accordingly, 
being best provided with food, should naturally be expected to grow up the faster. As they 
got higher and presented more obstructions, channels might well be broken through and 
further cleared out, giving rise to those found at the present day between the different atolls” 
Nullipores, as the shoals approached the surface, would naturally become of increasing 
importance, but there is some evidence to show that the class of corals, that built up the 
banks, cannot live in shallow depths, though the precise cause of this is not clear. It may 
partially be temperature, though pressure is a probable contributory cause as well, since their 
distribution in depth is limited in temperate regions as well. The Seine bank was covered 
with broken and dead corals, and the Dacia was probably also, its surface evidently being 
very rough. Perhaps 50 fathoms or so is the limit of the upward growth of the deep corals. 
Possibly they build up until they are finally extinguished by the reef-corals. Whatever may 
be the case is immaterial, as there is a third class of corals that can live either on the 
reefs or near the surface, where there is little competition, but flourishes best at 30 to 
50 fathoms. This class, as are the deeper corals, is not dependent on its algae for nutriment, 
1 “On Oceanic Shoals discovered in s.s. Dacia in October sedentary organisms. On account of the current being 
1883.” Proc. R. S. Edin., vol. x11. p. 428, 1885. accentuated by the upgrowth of the sides, the channels 
° As soon as the sides of the plateau commenced to grow _ would probably form at an early stage. The eddies, formed 
up, mud would necessarily be swept over the central part of _ by the currents through the channels meeting in the centre 
the plateau and would effectually kill any corals or other of the plateau, might account for the shape of the banks. 
