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1S2 On Coral Reefs and Islands. 



pearing beyond 20 fathoms ; and at the Maldives and Chagos. at 

 a less depth. Other facts brought forward by Mr. Darwin, relate' 

 to Caryophylhee and those species which have a wide range be- 

 yond reef-forming zoophytes. 



It thus appears that all recent investigators since Q,uoy and 

 Gaymard have agreed in assigning a comparatively small depth to 

 growing corals. The observations on this point, made during 

 the cruise of the Expedition, tend to confirm this opinion. The 

 conclusion is borne out by the fact that soundings in the course 

 of the various and extensive surveys afford no evidence of grow- 

 ing coral beyond twenty fathoms. Where the depth was fifteen 

 fathoms, coral sand and fragments were almost uniformly reported. 

 Among the Feejee Islands, the extent of coral reef-grounds sur- 

 veyed was many hundreds of square miles, besides the more care- 

 ful examination of harbors. The reefs of the Navigator Islands 

 were also sounded out, with others at the Society Group, besides 

 numerous coral islands; and through all these regions no evi- 

 dence was obtained of corals living at a greater depth than 15 or 

 20 fathoms. Within the reefs west of Viti Lebu and Vanua Lebu, 

 the anchor of the Peacock was dropped sixty times in water from 

 12 to 24 fathoms deep, and in no case struck among growing 

 corals ; it usually sunk into a muddy or sandy bottom. Patches 

 of reef were encountered at times, but they were at a less depth 

 than 12 fathoms. By means of a drag, occasionally dropped in 

 the same channels, some fleshy Alcyonia, and a few Hydroidea 

 were brought up, but no reef-forming species. 



Outside of the reef of Upolu, corals were seen by the writer 

 growing in twelve fathoms. Lieutenant Emmons brought up 

 with a boat-anchor a large Dendrophyllia from a depth of four- 

 teen and a half fathoms at the Feejees; and this species was 

 afterwards found near the surface. Dendrophyllia, it may be 

 remembered, is one of the deep water genera. 



These facts, it may be said, are only negative, as the sounding- 

 lead, especially in the manner it is thrown in surveys, would fail 

 of giving decisive results. The character of a growing coral bed 

 is so strongly marked in its uneven surface, its deep holes and 

 many entangling stems, to the vexation of the surveyor, that in 

 general the danger of mistake is small. But allowing uncertainty 

 as great as supposed, there can be little doubt after so numerous 

 observations over so extended regions of reefs. 



The depth of the water in harbors and about shores where i 



there is no coral, confirms the view here presented. At Upolu, 

 the depth of the harbors varies generally from twelve to twenty 

 fathoms. On the south side of this island, Lieutenant Perry, off 

 Falealili, one hundred yards from the rocky shores, found bare 

 rocks in eighteen and nineteen fathoms, with no evidence of 

 coraL There is no cause here which will explain the absence of 



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