J20 STHATA IN THE NEIGHBOURHOOD OF LONDON. 



blended with its substance, to being merely united with its 

 surface, and fonning the white coat of the flint. It 

 hat been, witliout doubt, from certain appearences result- 

 ing from this union, that Mr. Carrosi and others have been 

 led to believe in the change of lime to flint. 

 Tbtory of the There can be hardly any hesitation in agreeing with Mr. 



formaion of j g^^^j, that the most probable explanation of the forma- 

 imoeaded Hint. ' ' 



tion 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 irre- 

 " gular cavities, that were afterward filled up, by infiltra- 

 *• tion, with flint"*. The decomposition of the softer parts 

 of the animals, which were thus entombed, may be con- 

 sidered as a very probable source of a part of those gaseous 

 matters, which formed these cavities : and the conneetior^ 

 of the animal remains with these nodules of flint is easily ex- 

 plained, by supposing the shells, crusts of the^cAmi, &c., 

 to have projected into these cavities, or to have been ad» 

 herent to their sides, at the period at which this infiltration 

 took place. 

 The flint That the separation and deposition of the matter forming 



formed by crys- these siliceous nodules I'.avebeen the vt^ork of crystallization, is 

 rendered evident by the cavities left either in these nodules, 

 or in the fossils, being generally lined with quartz crystals, 

 A difficulty While endeavouring thus to explain the formation of these 



answered. flinty nodules, and the filling up of the cavities of the fossils 

 with flint, a difficulty arises from observing these bodies insUf 

 lated as it were in their bed of chalk : it not being easy to 

 conceive, how so copious an infiltration should have taken 

 place into these cavities, while^the surrounding chalk should 

 only have received a slight intermixture of siliceous grains. 

 Formation of Something analogous is however observable in the forma- 

 •rl*T*f"* tiou of the calcareous stalactite ; since in those cayerns, in 

 which these concretions have been forming for a very long 

 period, the infiltration, by which they are formed, is found 

 to continue to the present d-4y ; proving, that the interstices 

 of the superincumbent stone have not yet been filled by the 

 concreting of theparthy particles held in solution in the per- 



f Systepi of Mineralogy by Prof. Jameson, toI. I, p. 172. 



eclating 



