22 CORAL-REEFS. 



and thinly branched; but a Pontes, apparently of the 

 same species with that on the outside, is found there, 

 although it does not seem to thrive, and certainly does 

 not attain the thousandth part in bulk of the masses 

 opposed to the breakers. 



The woodcut shows the form of the bottom off the 

 reef: the water deepens for a space between one and two 

 hundred yards wide, very gradually to 25 fathoms (A in 

 section), beyond which the sides plunge into the unfathom- 

 able ocean at an angle of 45 . * To the depth of ten or 

 twelve fathoms the bottom is exceedingly rugged, and seems 

 formed of great masses of living coral, similar to those 

 on the margin. The arming of the lead here invariably 

 came up quite clean, but deeply indented, and chains 

 and anchors which were lowered, in the hopes of tearing 

 up the coral, were broken. Many small fragments, how- 

 ever, of Millepora alcicornis were brought up; and on 

 the arming from an eight-fathom cast, there was a perfect 

 impression of an Astraga, apparently alive. I examined 

 the rolled fragments cast on the beach during gales, in 

 order further to ascertain what corals grew outside the 

 reef. The fragments consisted of many kinds, of which 

 the Porites already mentioned and a Madrepora, apparently 

 the M. cory??ibosa, were the most abundant. As I searched 

 in vain in the hollows on the reef and in the lagoon, for 

 a living specimen of this Madrepore, I conclude that it 



1 The soundings from which this section is laid down were taken 

 with great care by Captain Fitzroy himself. He used a bell-shaped 

 lead, having a diameter of four inches, and the armings each time 

 were cut off and brought on board for me to examine. The arming 

 is a preparation of tallow, placed in the concavity at the bottom of 

 the lead. Sand, and even small fragments of rock, will adhere to 

 it ; and if the bottom be of rock it brings up an exact impression of 

 its surface. 



