554 CORAL FORMATIONS. April, 1836. 



even from the smallest particle to large fragments of rock, 

 bears the stamp of having been subjected to the power of 

 organic arrangement. Captain FitzRoy, at the distance of 

 but little more than a mile from the shore, sounded with a 

 line, 7200 feet long, and found no bottom. This island is, 

 therefore, a lofty submarine mountain, which has a greater 

 inclination than even those of volcanic origin on the land. 

 I will now give a sketch* of the general results at which I 

 have arrived, respecting the origin of the various classes of 

 reefs, which occur scattered over such large spaces of the 

 intertropical seas. 



The first consideration to attend to, is, that every observa- 

 tion leads to the conclusion that those lameUiforra corals, 

 which are the efficient agents in forming a reef, cannot live at 

 any considerable depth. As far as I have personally seen, I 

 judge of this from carefully examining the impressions on 

 the soundings, which were taken by Captain FitzRoy at 

 Keehng Island, close outside the breakers, and from some 

 others which I obtained at the Mauritius. At a depth under 

 ten fathoms, the arming came up as clean as if it had been 

 dropped on a carpet of thick turf ; but as the depth increased, 

 the particles of sand brought up became more and more 

 numerous, until, at last, it was evident the bottom consisted 

 of a smooth layer of calcareous sand, interrupted only at 

 intervals by shelves, composed probably of dead coral rock. 

 To carry on the analogy, the blades of grass grew thinner and 

 thinner, till, at last, the soil was so sterile, that nothing sprung 

 from it. 



As long as no facts, beyond those relating to the struc- 

 ture of lagoon islands were known, so as to establish some 

 more comprehensive theory, the behef that corals con- 

 structed their habitations, or, speaking more correctly, their 

 skeletons, on the circular crests of submarine craters, was 



from Malacca and Java, and the small fragments of pumice, drifted here, 

 together with the seeds of East Indian plants. The one block of green- 

 stone, moreover, on the Northern Lagoon must be excepted. 



* Tills sketch was read before the Geological Society, May, 1837. 



