CORAL FORMATIONS. 



259 



fond of, also feed largely, as I am informed by Dr. 

 Allan, on corals ; and the bony apparatus within 

 their bodies seems well adapted for this end. 

 These holuthurise, the fish, the numerous burrow- 

 ing shells and nereidous worms which perforate 

 every block of dead coral, must be very efficient 

 agents in producing the fine white mud which lies 

 at the bottom and on the shores of the lagoon. A 

 portion, however, of this mud, which, when wet, 

 strikingly resembled pounded chalk, was found by 

 Professor Ehrenberg to be partly composed of si- 

 liceous-shielded infusoria. 



April 12th. — In the morning we stood out of the 

 lagoon on our passage to the Isle of France. I am 

 glad we have visited these islands : such fonna- 

 tions surely rank high amongst the wonderful ob- 

 jects of this world. Captain Fitz Roy found no 

 bottom with a line 7200 feet in length, at the dis- 

 tance of only 2200 yards from the shore ; hence 

 this island forms a lofty sub-marine mountain, with 

 sides steeper even than those of the most abrupt 

 volcanic cone. The saucer-shaped summit is near- 

 ly ten miles across ; and every single atom,* from 

 the least particle to the lai'gest fragment of rock, 

 in this great pile, which, however, is small com- 

 pared with very many other lagoon-islands, bears 

 the stamp of having been subjected to organic ai'- 

 rangement. "We feel surprise when travellers tell 

 us of the vast dimensions of the Pyramids and oth- 

 er great ruins, but how utterly insignificant are the 

 greatest of these when compared to these inount- 

 ains of stone, accumulated by the agency of various 

 minute and tender animals ! This is a wonder 



* I exclude, of course, some soil which has been imported 

 here in vessels from Malacca and Java, and likewise some small 

 fragments of pumice, drifted here by the waves. The one block 

 of greenstone, moreover, on the northern island, must be ex 

 cepted. 



