METAMORPHOSES OP CORAL. 535 



3000 feet ? Yet the Geologist of the present day has little hesi- 

 tation in regarding these formations, as having taken their origin 

 from the labours of these apparently-insignificant and simply- 

 organised beings. As at the present time, the greater proportion 

 of these structures appears composed of the Lamelliform corals 

 (g 1069) ; but the remains of Alcyonian polypes are by no 

 means unfrequent in the limestone rocks, and are especially abun- 

 dant in particular strata ; and some of the harder forms of the 

 CiliobracMate group are occasionally found. 



1108. There are many instances in which the Coral struc- 

 tures of comparatively recent origin have undergone a metamor- 

 phosis, which causes them to lose, in greater or less degree, their 

 original aspect. Large masses, when long exposed to the air, 

 become changed into a solid, often somewhat crystalline, rock ; 

 in which the traces of organic structure are very indistinct, and 

 with w r hich the Mountain or Secondary Limestone closely cor- 

 responds. This is observed in the Bermudas, a group of 

 islands, which seems to have been for the most part formed by 

 Coral Polypes of the same species with those now existing in the 

 seas around. Moreover, the Coral Sand, formed by the action 

 of the waves upon the living structure, often becomes consoli- 

 dated into a hard stone by the filtering of water through it ; 

 a small quantity of the carbonate of lime being probably dissolved 

 at the surface (where the carbonic acid of the air increases the 

 solvent power of the water), and set free again below, so as to 

 glue together the separate particles. It is in such a mass, that 

 the human skeleton ia imbedded, which was found on the shore 

 at Guadaloupe, and is now placed in the British Museum. 

 This stone, when minutely examined, is found to consist of a 

 number of rounded grains, cemented, as it were, together ; and 

 it closely resembles the rock known to the Geologist as Oolite. 

 Further, where shallow water exists around Coral islands, the 

 bottom is found to be covered with a layer of white mud, which 

 is formed by the decay of the animal matter that held together 

 the particles of carbonate of lime in the stony corals ; and these, 

 being thus set free in a finely-divided state, fall to the bottom in 

 a form which, if dry, would constitute Chalk. Thus we may 



