434 Mr Gardiner, The Coral Reefs of [Mar. 7, 



the "pocket." The greatest depth of the lagoon is 30 fathoms. 

 The bottom of the lagoon, if the shoals were removed, and the 

 whole elevated, would be a great plain surrounded by a ridge 

 sloping steeply up to a line of perpendicular cliffs broken only at 

 the few deep ship's channels ; on this plain the greatest heights 

 would be from 20 — 30 feet. The shoals in the lagoon do not vary 

 greatly in depth ; indeed most can be easily discerned by the 

 break of the sea on them at low tide, if the wind is at all fresh. 

 In dredging I searched especially for deep shoals, to find out if 

 they had any growth of organisms which might be expected, in 

 course of time, to bring them up to the surface ; I passed over 

 several, both with the dredge and tangles, but I obtained nothing 

 from them, nor were my dredges ever caught up, as they always 

 were every few yards on the shallow shoals. This shows that 

 their surface is smooth and regular. They seemed rather to be 

 gently sloping eminences on the bottom of the lagoon than shoals 

 growing up to the surface. One near the large ship's channel 

 to the south was perhaps an exception, as the dredge had to 

 be tripped several times, when I went over it, and subsequently I 

 lost a large tangle on it in 11 — 12 fathoms of water. Most of the 

 shoals have, however, only a few inches of water and are fairly flat 

 topped, without any central depression ; they extend less to 

 leeward than to windward, or in other words such summits, as 

 they have, are to leeward. They slope gently at the sides to 

 3 — 4 fathoms, succeeded by a cliff to a depth of 10 — 12 fathoms, 

 the normal depth of the lagoon being reached within 100 yards of 

 their edges, close up to which I have often obtained soundings of 

 14 and 16 fathoms. In the shallower water to windward, these 

 shoals can often be seen to overhang their bases, and to be mere 

 mushroom heads. Corals grow most luxuriantly at the sides 

 where they slope down before the cliff is reached, but many also 

 flourish on their summits. Pocillopora is very rare, but two 

 varieties of Millepora flourish, one near the openings in the reef, 

 and the other, a massive brown lamellar variety, on nearly all 

 the shoals of the lagoon. There is never on any shoal a great 

 variety in species, though on some the total quantity of coral is 

 very considerable, and often exceeds in amount the nullipores 

 growing on the same shoal. A considerable part of the surface is 

 to be found on all the shoals covered by species of Sarcophytum 

 and Halimeda. Of corals, the genera Favia and Madrepora are 

 the most abundant in species, while Porites arenosa (Esper) with 

 several varieties is the most common coral, and in many places 

 forms large masses several feet in diameter and of great thickness. 

 The genera Montipora, Goeloria, and Astraeopora are very local in 

 distribution, often assisting very materially. 



Between the patches and knolls of rock outside the lagoon 



