10 ATOLLS. Ch. I. 



angles, and forms an exceedingly strong honey- combed 

 mass, which generally assumes a circular form, the 

 marginal plates alone being alive. Between these plates 

 and in the protected crevices on the reef, a multitude 

 of branching zoophytes and other productions flourish, 

 but the Porites and Millepora alone seem able to resist 

 the fury of the breakers on its upper and outer edge ; 

 at the depth of a few fathoms other kinds of stony 

 corals live. Mr. Liesk, who was intimately acquainted 

 with every part of this reef, and likewise with that of 

 North Keeling atoll, assured me that these corals in- 

 variably compose the outer margin. The lagoon is in- 

 habited by quite a distinct set of corals, generally brittle 

 and thinly branched ; but a Porites, 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 wood-cut (No. 3) shows the form of the bottom 

 outside the reef: the water deepens very gradually 

 for a space of between one and two hundred yards 

 wide, to a depth of 25 fathoms (A in section), beyond 

 which the sides plunge into the unfathomable ocean 

 at an angle of 45 . 1 To the depth of ten or twelve 



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

 with great care by Captain FitzKoy 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 

 preparaticn 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. 



