FOSSIL ANIMALCULES. 183 



A sponge or other organic body often forms 

 the nucleus of the flint nodules, and the original 

 substance of the fossil is generally transformed 

 into silex, and yet the most delicate structure 

 preserved. In other examples the organisms en- 

 closed in the flint have undergone no change, but 

 appear as if immersed and preserved in a semi- 

 transparent medium. Such is the state in which 

 the foraminiferous shells (rotalice, textilarice, 

 " Medals of Creation," p. 232), and minute corals, 

 often occur.* 



Fossil animalcules. — For the most part the 

 microscopic shells in chalk and flint are filled with 

 amorphous mineral matter ; but recent observa- 

 tions have shown, that in numerous examples the 

 shell contains the body of the animal, in some 

 instances silicified, but in others in the state of a dried 

 animal substance, like the ink-bag of the cuttle- 

 fish in lias,j- the soft parts of cephalopoda in 

 clay,;}; and the capsule of the eye and the mem- 

 branes of the stomach of certain fishes, in chalk. § 



* An exquisite example of this kind was discovered liy the Marquess of 

 Northampton in a chalk flint from Brighton In a polished slice of this 

 specimen, presented to me by his Lordship, there are branches of several deli- 

 cate corals (pustulopora, relepora, idmonea, "Medals," p. 284,) and forami- 

 nifera, as perfect, and unaltered in appearance, as if immersed in glass. 



t Dr. Buckland, " Bridgwater Treatise." 



% Professor Owen on the Belemnite. 



§ " Wonders of Geology." 



