350 Mr. Parkinson on the Strata^ 



observable, nor is the least dulness of the delicate lines and emboss- 

 ments of the crusts, or of the spines of the echini, to be detected. 



That the deposition of chalk and of flint was sometimes alternate, 

 and even, as it is expressed by Messrs. Cuvier and Brongniart, perio- 

 dical, appears from the seams or strata of flinty nodules, and particu- 

 larly from the widely extended flat or tabular flinty depositions 

 interposed between the chalk. 



But that the chalk was permeated by the silex at some distance of 

 time after the deposition of the former, seems also to be proved by 

 the state of the fossils of this stratum. There does not appear to be 

 a single instance in which the animal remains are impregnated with 

 silex. On the contrary, the substance of all these fossils has become 

 calcareous spar, and their cavities have been filled with flint ; thus 

 plainly evincing that sufficient time must have elapsed for the crys- 

 tallization of the calcareous spar, previously to the infiltration of the 

 flint. 



It may not be improper to remark, that in no instance does the 

 flint, although in contact with the calcareous spar, appear to have 

 become mixed with it. The reverse of this is the case with the 

 chalk, since this latter may be seen in almost every degree of union 

 with the flint ; from being blended with its substance, to being merely 

 united with its surface, and forming the white coat of the flint. It 

 has been, without doubt, from certain appearances resulting from 

 this union, that M. Carrosi and others have been led to believe in 

 the change of lime to flint. 



There can be hardly any hesitation in agreeing with Mr. Jameson, 

 that the most probable explanation of the formation of imbedded 

 flint is that which was first proposed by Werner, " that during the 

 " deposition of chalk, air was evolved, which in endeavouring to 

 " escape, formed irregular cavities, that were afterwards filled up, by 



