382 THE BOTTOM OF THE SEA. 



branous tissue which penetrates the whole mass, and 

 which is then separated from the calcareous matter 

 contained in its meshes. The former, by its precipi- 

 -tatiou, forms that soft whitish substance, analogous to 

 chalk, which is found in the bottoms of creeks and 

 gulfs mixed with shelly sands, the debris of polypiers, 

 well-preserved shells, and consi'lerable masses of 

 meandrinae and astrese." 



The coral insects love warm water and constant 

 agitation. This last circumstance gives a very cha- 

 racteristic appearance to the calcareous deposits which 

 accompany them. Crystals of carbonate of lime are 

 deposited in the liquid mass, and become centres 

 around which new molecules of the same matter group 

 themselves. The constant agitation of the water gives 

 a rotatory motion to the little solid nuclei already 

 formed, whilst continued deposition goes on in such 

 a manner as to give them a spherical form. The 

 rock thus acquires a peculiar texture, called oolitic. 



Lastly, we may observe that coral does not flourisli 

 except in limpid water and on a rocky bottom. 



