400 PROCEEDINGS OP SECTION C. 



sancl are the characteristic flat rocks, about 2ft. across and Sin. deep, 

 which are indurated corals, derived, possibly, from Avorn-down " negro- 

 heads," and under which a rich harvest of molluscs and ophiuroidea 

 can be found. 



The pseudo-lagoon gradually increases to a depth of several feet. 

 Six hundred yards from the shore, and an equal distance from the surf, 

 the first specimens of the blue coral (Heliopora) are met with. It reigns 

 supreme in this area in the form of bushy radiating colonies, with flat, 

 truncated upper surfaces never rising above the lowest tide mark. 



The penultimate zone consists of the " clinker embankment," 

 one of the most characteristic features of the reef. 



Imagine a railway embankment parallel to the surf line 2ft. or 

 3ft. high and about 20ft. across. It is composed of the confusedly 

 intermingled remains of madrepores and other corals of a similar habit, 

 the most delicate and most massive not being represented in any great 

 degree. In many places the long axes of the coral stems lie across the 

 bank, indicating a sort of "flow structure." Long tongues of coral 

 " clinker " radiate from this bank, projecting 40ft. or more toAvards 

 the islet. One can see the half-buried corals dying along the edge of 

 the advance wave of debris. The dip angle of the latter, due to the 

 combined action of the wind and tide, is about 6°, as in the case AA'ith 

 the coral sand-rock in the island beach. The structure indicates a 

 prime factor in the building of a coral islet such as that under discus- 

 sion. The " bank " has a front of 50yds. in this instance, and consists 

 wholly of fragments of corals broken off by the surf and swept to lee- 

 ward. No cementing action has yet taken place. 



Outside the clinker zone appear the rough craggy pools which 

 invariably lie just within the living coral. They extend over an area 

 about 30yds. Avide. Lastly, the visible living coral zone is reached, 

 which is much less extensive — as noted by Kent and denied by Agassiz 

 — than that on the northern shore. 



Owing to the strong surf driA^en up by the constant south-easter 

 it is dangerous to examine the Avindward edge closely. Alcyonaria 

 (soft corals) are comparatively rare, while the main types visible are 

 the strong spherical or pedestal-shaped masses of Goniastrea and Pontes. 



RESUME OF ZONES (E. HOPE ISLE) 

 Commencing at north end of traverse. 



1. Living coral rampart 10ft. 



" (inner zone) 30ft. 



2. Alcyonaria, &c 100yds. 



3. Algae {Halimeda, &c.) 200yds. 



Islet — Coral sand beach 20yds. 



Tree-clad Island 200yds. 



Beach and coral rock 20yds. 



1 . Charna beds lOOA'ds. 



