12 STRUCTURE OF CORAL ROCK. 



but striking as near as possible north and south. 

 The surface of the reef was composed of soft, spongy, 

 fine-grained rock, many slabs of which were lying 

 about, under which we found a few shells and crabs 

 concealed, and in the holes of water were some living 

 corals and many beautifully coloured fish. The 

 spongy rock, when broken open, often exhibited a 

 cellular structure in some parts, while others were 

 entirely granular. There was not unfrequently an 

 insensible gradation from one part to the other, as 

 if fragments of coral had gradually wasted away ex- 

 ternally and coalesced, the internal parts of each 

 retaining more or less of their organic structure. 

 Many old fragments of coral, also lying loose about 

 the reef, although merely worn and weathered out- 

 side, were quite crystalline internally, the organic 

 cellular structure being sometimes greatly obscured 

 by a subsequent mineral structure, the formation 

 namely of crystals of carbonate of lime. 



On getting under weigh, we ran out to the 

 edge of the bank, which was about six miles to 

 the eastward, and within the space of a mile we 

 passed from 30 to 85 fathoms. Everything brought 

 up by the lead, from coarse fragments of coral 

 to the finest sand, was wholly calcareous, all dis- 

 solving in muriatic acid. In the afternoon the 

 wind freshened, with a heavy sea, and we ran back 

 and anchored under the lee of Wreck Island and its 

 reef. 



Jan. l!) r c 20. — Blowing a fresh gale of wind, with 



