126 MK. A. E. FINCKH. 



by ueiglibouriug species and by the all-invading lichenous Lithothamniou from 

 assuming anything like large dimensions. A great struggle for supremacy seems to be 

 going on, the Lithothamnion, however, eventually gaining an easy victory over the 

 corals and hydrocorallines. This vigorous growth extends for only 2 or 3 feet doAvu- 

 wards at the edge of the reef below the level of low- water spring tide ; below this 

 level the reef becomes comparatively destitute of organisms. 



Proceeding towards the lagoon the organisms gradually become more scarce, until at 

 a point where the waves no longer reach at low- water spring-tides, the reef is a 

 barren, comparatively smooth platform with but a few detached rock masses which in 

 most cases are not cemented down. 



On the lagoon side of the reef all the forms found on the ocean side are I'epresented, 

 but in addition, we get small pieces of the HcUopora cceruica, and here and there 

 fungoid corals. This edge slopes down into the shallow Avater of the lagoon. 



The reef platform on which the islet of Fualopa has been formed by the accumula- 

 tion of sand, coral, and Lithotliamnion fragments, is of great width, over 1300 yards, 

 jutting out as a long point into the lagoon. The edge of this lagoon platform consists 

 mainly of living, thinly branching Lithothamniou. Its almost perpendicular walls 

 show very little life below 2 feet from the surface of the platform. The platform 

 itself consists of dead cemented fragmental material with, here and there, pancake- 

 shaped ForitdK.. both the yellow {Pontes hmosa) and the purple variety, lying, for the 

 most part, loosely on it. The walls sink doA\n into 2 to 3 fathoms of water on to 

 the sandy lagoon bottom, which is made up of detached joints of Haliraeda and the 

 remains of branching Lithothamnion. 



In close proximity to the platform there are numerous shoals, mostly on the same 

 level as the platform and therefore awash at low-water spring tide. These shoals 

 show at the rim a vigorous growth ot every kind of coral found in the locality, 

 including HcUopora cctraleo. and Porites : but, as in the case of the reef, there is the 

 same struggle for existence going tm between themselves and the predominating 

 Lithothamnion. The central 2)arts of these shoals are dead, formed into the solid rock 

 by the binding effect of the Lithothamnion, and are studded here and there with small 

 corals, sponges, seaweeds, &c. 



Those shoals which are 2 or 3 fathoms below the surface of the water at low- water 

 spring tide, consist purely of coral or hydrocorallines, either Heliopora cai7-ulca or the 

 branching MUlepora, and mostly of one species onl}^ These so-called shoals are 

 merely clusters of growing c6ral, which having once attained a certain height become 

 overgrown at their roots by the lichenous Lithotliamnion. The interstices between 

 the branches of the coral are gradually filled in, partly with foraminiferal and other 

 sands, and the foundation is thus laid for the solid reef rock, which consists of 

 the stems of the coral with which the shoal began its existence, foraminiferal sand, 

 and the remains of the branching Litltothamnion and Ilalimeda, all being bound 

 together by the lichenous Lithothamnion. Even better examples ol' this process of 



