METAMORPHOSES OF CORAL. 515 



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

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

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

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

 with which 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 is 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 

 trace very distinctly the mode in which three principal kinds of 

 limestone rocks may have taken their origin from Coral 

 formations. 



1163. Now, the Mountain or Carboniferous Limestone, a 

 rock very abundant in Britain, extending over large areas 

 beneath the coal-fields, and sometimes exhibiting a thikness of 

 nearly 3000 feet, though in some parts evidently composed of 

 accumulations of Shells, Encrinite stems, &c., exhibits the Coral 

 structure very distinctly in many situations ; and these parts are 

 so blended with the neighbouring rock, as to make it appear 

 probable that the latter also was once in the state of coral, but 



