332 



J. STANLEY GARDINER. 



Summary of Table. 



imagined as solid rock, would be 807 cms. (4) Estimating from the height of the iixed corals 

 and assuming that the interspaces would be filled in by nullipores and material from other areas, 

 the rate of growth would be 2567 cms. or about 14^ fathoms. If the Fungia, which lie between 

 and under other corals, be added to the latter, the rate becomes nearly 16 fathoms in 1000 years. 



The first two methods are quite erroneous, for, whereas the whole area of a growing reef 

 would be covered with growing corals, only a small part in the area collected was so overgro^vn. 

 The third gives a possible rate for an extremely poor area, where the corals, before they attain 

 any size, are usually killed off by boring organisms or unfavourable conditions. The last is more 

 useful, but assumes that the rate of increase in height is the same year by year in and throughout 

 the life of any coral or reef Organisms do not generally obey fixed mathematical laws, but 

 the presumption is that, given the most perfect circumstances, a coral should increase both in 

 the number of its polyps and size according to a regular geometrical progression''. The increase 

 in height above is taken in arithmetical progression, which certainly must give too small results 

 when based on the first 3 years of the existence of the corals. The area to the west of Hulule 

 is not a particularly favourable one, but the conclusion that its reefs might grow at the rate 

 of a fathom in about 60 years is certainly not too high. 



The main interest of the problem lies in the rate of growth outwards of a reef, where 

 it is freely exposed to the ocean, and the rate of upward growth of a reef on any oceanic 

 bank, arising to within suitable depths from the surface. The inquiry is greatly complicated 

 in such positions by questions of temperature, currents, exposure, depths, etc. The difficulty 

 that the larvae have in affixing themselves could scarcely be much greater than in this canal 

 at Hulule, while the other conditions on an open bank or on the outer slope of a reef 

 would undoubtedly be more favourable. The vigour of the coral growth from 5 to 15 fathoms 



' Average of all the specimens of the several classes. but also Psammocora, Euphyllia and Pocillopora. 



^ Average of the whole forty-five specimens added up ■* Against this might be set the natural death of corals by 



separately. 



' Mostly broken fragments of fine branching Madrepora, 



senescence — of which there is some evidence — but any va- 

 cancies are at once filled in by fresh coral growth. 



