14 ON A PIECE OF CHALK i 



we call organs, is capable of feeding, growing, and 

 multiplying ; of separating from the ocean the 

 small proportion of carbonate of lime which is 

 dissolved in sea-water ; and of building up that 

 substance into a skeleton for itself, according to a 

 pattern which can be imitated by no other known 

 agency. 



The notion that animals can live and flourish in 

 the sea, at the vast depths from which apparently 

 living Gldbigcmncc have been brought up, does 

 not agree very well with our usual conceptions re- 

 specting the conditions of animal life ; and it is not 

 so absolutely impossible as it might at first sight 

 appear to be, that the Globigerince of the Atlantic 

 sea-bottom do not live and die where they are 

 found. 



As I have mentioned, the soundings from the 

 great Atlantic plain are almost entirely made up 

 of Globigerince, with the granules which have been 

 mentioned, and some few other calcareous shells ; 

 but a small percentage of the chalky mud per- 

 haps at most some five per cent, of it is of a 

 different nature, and consists of shells and skele- 

 tons composed of silex, or pure flint. These 

 silicious bodies belong partly to the lowly vege- 

 table organisms which are called Diatomacece, and 

 partly to the minute, and extremely simple, 

 animals, termed Radiolaria. It is quite certain 

 that these creatures do not live at the bottom of 

 the ocean, but at its surface where they may be 



