156 UPPER, OR FLINTY CHALK. 



ORGANIC REMAINS OF THE UPPER, AND LOWER CHALK. 



The organic remains of the chalk are very numerous ; but notwith- 

 standing the important additions which modern discoveries have made, 

 the fossil productions of this important deposit are still but imperfectly 

 known. 



The fossils of the French chalk have been described by M. M. 

 Cuvier, and Brongniart *, and those of the Enghsh, by Mr. Parkinson f^ 

 W. Phillips, and others. 



The contents of the Sussex beds, will be found to differ in many re- 

 spects from those previously noticed, while many species of fossils, described 

 by the authors above-mentioned, are unknown in this district. In their 

 mode of preservation, however, a perfect correspondence exists in the pro- 

 ductions of different localities They are for the most part remarkably entire, 

 the delicate coverings of the Crustacea, the spines of the shells, &c. re- 

 maining unbroken ; in short, their appearance, as Mr. Parkinson justly re- 

 marks, " warrants the conclusion, that they have been enveloped and sur- 

 rounded by the chalk, while Uving in their native beds ; and that this de- 

 position was effected at the bottom of a tranquil sea." 



In every instance the shells, echinites, madreporites, and encrinites, 

 are converted into calcareous spar, their cavities being filled with chalk, 

 flint, or sulphuret of iron. 



The remains of the softer zoopyhtes occur in the form of chalky casts, 

 tinged with a yellowish or reddish oxide of iron ; this appearance, which 

 facilitates the separation of the fossils from the chalk, results from the de- 

 composition of pyrites. The vertebrae and bones are soft and friable ; but 

 the teeth and palates are finely preserved, and have the natural pohsh of 

 the enamel, heightened by an impregnation with iron. The scales and fins 

 of fishes, and the coverings of the Crustacea, are changed into a brown 

 substance, which is exceedingly brittle, and fades upon exposure to the air, 



* Essai sur la Geographie Mineralogique des Enviro7is de Paris. Par M, M. G. Cuvier, e.t 

 Alex. Brongniart, p. 11. 

 ■ 4[ Geological Transactions, Vol. i. p. 344!. 



