THE FIRESTONE. 185 



and immersing the residue in a transparent medium 

 (Canada balsam), the soft parts are as distinctly 

 seen, as in a recent dead specimen.* 



So little attention has been paid to the white 

 chalk fossils of the Island, that a few of the 

 common species of terebratula, spondylus, and 

 echini ; teeth of sharks; ventriculites, choanites, and 

 other zoophytes, comprise almost all the specimens 

 I have observed in private collections ; but there 

 can be no doubt that were the quarries and 

 natural sections diligently examined, an interest- 

 ing series might be obtained.-j- 



The Firestone. £ — The lower white chalk, in 

 some places, as at Dover, gradually passes down 

 into a bluish-grey chalk, and the latter into an 

 argillaceous limestone, well known by the name 

 of chalk-marl. In other localities the chalk 

 maintains its purity to its junction with the 

 marl. An intermixture of green sand charac- 

 terises the latter in many districts, and this 



* A Memoir on this subject, by the author, will appear in the third Part 

 of the Philosophical Transactions for 1846. 



t Figures and descriptions of British chalk fossils are given in my "Fossils 

 of the South Downs," "Wonders of Geology," and "Medals of Creation," 

 and "Geology of the South-Eastof England;" in Sowerby's "Mineral Con- 

 chology," Mr. Lyell's " Elements of Geology," and in Parkinson's " Organic 

 Remains of a Former World." 



t The name Upper-green-sand, generally given to these arenaceous marl 

 beds of the chalk formation, has been productive of so much confusion, that 

 the provincial term, Firestone, however inapplicable as a descriptive term, 

 seems preferable. 



