CORAL-REEFS. 2g 



Pontes 1 with cylindrical branches, one of which forms circular 

 clumps, with the exterior branches only alive; and lastly, 

 a coral something like an Explanaria, but with stars on 

 both surfaces, growing in thin, brittle, stony, foliaceous 

 expansions, especially in the deeper basins of the lagoon. 

 The reefs on which these corals grow are very irregular in 

 form, are full of cavities, and have not a solid flat surface 

 of dead rock, like that surrounding the lagoon; nor can 

 they be nearly so hard, for the inhabitants made with crow- 

 bars a channel of considerable length through these reefs, 

 in which a schooner, built on the S.E. islet, was floated out. 

 It is a very interesting circumstance, pointed out to us by 

 Mr. Liesk, that this channel, although made less than ten 

 years before our visit, was then, as we saw, almost choked 

 up with living coral, so that fresh excavations would 

 be absolutely necessary to allow another vessel to pass 

 through it. 



The sediment from the deepest parts in the lagoon, when 

 wet, appeared chalky, but, when dry, like very fine sand, 

 Large soft banks of similar, but even finer grained mud, 

 occur on the S.E. shore of the lagoon, affording a thick 

 growth of a Fucus, 2 on which turtle feed : this mud, 

 although discoloured by vegetable matter, appears from its 

 entire solution in acids to be purely calcareous. I have 

 seen in the Museum of the Geological Society, a similar 

 but more remarkable substance, brought by Lieut. Nelson 

 from the reefs of Bermuda, which, when shown to several 



1 This Porites has somewhat the habit of P. clavaria. but the 

 branches are not knobbed at their ends. When alive it is of a yellow 

 colour, but after having been washed in fresh water and placed to dry, 

 a jet-black slimy substance exuded from the entire surface, so that the 

 specimen now appears as if it had been dipped in ink. 



2 A genus of sea- weeds. — Ed. 



