1836.] FISH THAT EAT CORALS. 457 



coral branches : I opened the intestines of several, and 

 found them distended with yellowish calcareous sandy 

 mud. The slimy disgusting HoluthtiricB (allied to our star- 

 fish), which the Chinese gourmands are so 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 holuthuricB^ the fish, the 

 numerous burrowing 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, how- 

 ever, of this mud, which when wet strikingly resembled 

 pounded chalk, was found by Professor Ehrenberg to be 

 partly composed of siliceous-shielded infusoria. 



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

 on our passage to the Isle of France. 1 am glad we have 

 visited these islands : such formations surely rank high 

 amongst the wonderful objects of this world. Captain 

 Fitz Roy found no bottom with a line 7200 feet in length, 

 at the distance of only 2200 yards from the shore ; hence 

 this island forms a lofty submarine mountain, with sides 

 steeper even than those of the most abrupt volcanic cone. 

 The saucer-shaped summit is nearly ten miles across ; and 

 every single atom,* from the least particle to the largest 

 fragment of rock, in this great pile, which however is 

 small compared with very many other lagoon-islands, 

 bears the stamp of having been subjected to organic 

 arrangement. We feel surprise when travellers tell us of 

 the vast dimensions of the Pyramids and other great 

 ruins, but how utterly insignificant are the greatest of 

 these, when compared to these mountains of stone accumu- 

 lated by the agency of various minute and tender animals ! 

 This is a wonder which does not at first strike the eye of 

 tiie body, but, after reflection, the eye of reason. 



I will now give a very brief account of (he three great 

 classes of coral-reefs ; namely, Atolls, Barrier, and Fring- 

 ing-reefs, and will explain my views ton their formation. 



* I exclude, of coiirge, nome soil which has been imported here in vewels from 

 MaL-icca and Java, and lilcewige nome small frapmentii of pumice, drifted here 

 ' •• flie waves. The one block of green-stone, moreover, on the northern island 

 st be excepted. 



t These were first read before the Geological Society in May, 1837, and have 

 c been developed in a separate volume on the "Structure nnd Diatribution 

 Coral Kcefs." 



