THE ATOLL OF MINIKOI. 



35 



represented, but Pocillopora, Euphyllia, Pavonia, Astraea, Galaxea and Montipora were also 

 found. The modern facies or species of Madrepora grow from a central mass with branches 

 radiating out over their upper surfaces. The central stems grow straight upright, vertically 

 indeed, and are packed all over with corallites, possessing more or less raised calicles, which 



Fio. 9. Conglomerate mass near Wiiingili at low tide, showing the rugged appearance and undermining by tidal 



action. (Frum n photograph.) 



give them a very rough appearance. The branches extend more and more horizontally from 

 the centre outwards, but none grow downwards. The upper surfaces of the horizontal 

 branches are similar to the central stems, but their lower are smooth, corallites distant 

 from one another, calicles with no raised rims. The basal mass, in which the branches 

 appear to be rooted, is formed by a filling up of the interspaces between the branches 

 by a lighter corallum of open texture, a kind of coenenchyma. Such being the mode of 

 growth of Madrepora it follows that this genus forms an excellent criterion by which to 

 judge whether the conglomerate masses originally grew as such, or were otherwise formed, 

 as by a beach cou.solidation (PI. II. fig. 2). 



On the pinnacles and masses the branches of the different facies of Madrepora are much 

 worn but generally still entire. Some of the colonies seem to be a little tilted, but most are 

 clearly in the absolute jjosition in which they originally greiv^. Other genei'a of corals 

 amply confirm the evidence of elevation, which this fact implies, and imbedded Tridacna shells 

 with their open mouths in a horizontal position lend their support. 



It remains to consider the position in which the conglomerate was originally formed. 

 The fine-grained structure of some parts shows the presence of nullipores, but the latter 

 are never in sufficient quantity, allowing amply for denudation, for the whole to have 

 formed part of the surface of a reef awash. At the same time spreading nullipores, of 

 which there are indubitable traces, show that the rock must have been formed in a reef, 

 freely exposed to the sea, and cannot have been built up in a lagoon. At Minikoi I was 



1 It occurred to me that the specific gravity of the basal 

 mass might be such that the Madrepora would naturally 

 tend to take up this position. I hence had a large number 

 of colonies (about 30) placed on the reef near Teveratu point. 



The branches were broken off, the basal masses alone were 

 left. They lay in every conceivable position, more indeed on 

 the upper surface, as without its branches it became almost 

 flat. 



5—2 



