DEVELOPMENT OF THE REEF 245 



the study of the problem, for it now becomes evident that 

 oceanic banks may rise to the Limiting Line of Sedimentation ; 

 and from that line the reef-building corals may start their 

 building operations. 



The Formation of Reefs. — Theoretically, where the one 

 process leaves off the other begins ; but, practically, it is most 

 probable that a host of other creatures help to bridge over the 

 gap between the cessation of the building by sedimentation and 

 the building of the corals of the reef. It is probable that 

 the Nulliporce, Litliotliamnionem, and other calcareous algse 

 outstrip the reef corals in their bathymetrical range, and they 

 probably begin to clothe the summit of the sedimentation 

 bank. As they grow, fragments of their growth die, or become 

 broken off and are added to the foundation of the reef. 

 Animals with hard tissues live on the reef, and their remains 

 become added to the debris ; the whole surface becomes 

 raised, and at the same time consolidated. Particles, which 

 could find no resting-place upon the bare exposed bank, 

 doubtless become held fast in the uneven surface of the growth 

 that has now clothed its summit ; and sedimentary action may 

 again add its increment, although the whole , structure is now 

 within the wave-stirred area. It is probably in this fashion 

 that the foundation of the reef is laid and the immediate 

 clothing of the sedimentation bank is brought about — the 

 lower forms making a platform upon which the corals them- 

 selves actually build. 



The pioneers of coral growth are probably not those species 

 which are represented at the wave-washed surface of the fully 

 developed reef. Many deep-sea corals have been found to 

 clothe submarine banks, and the work of Basset-Smith and 

 J. Y. Buchanan has established the ability of these corals to 

 raise banks by their own growth from very considerable depths. 

 It is these corals {Dendrophyllia, Heliopora, Lophohelia, &c.) 

 which first contribute, by their building, to make a coral reef 

 on a sedimentation bank. 



Sites of Reef Coeal Building other than Sedimen- 

 tation Banks. — Since the reef-building corals may start their 



