400 ON THE FOBMATION OF THE CHALK STRATA, 



collected into separate masses, without any trace of its exist- 

 ence in the intermediate parts ; on the other hand, if we con- 

 ceive the melted flint to have been forcibly injected among the 

 chalk, and to have penetrated it, somewhat as mercury may by 

 pressure be made to penetrate through the pores of wood, it 

 might, on cooling, exhibit the same appearances that the chalk 

 beds of England do actually present us with." 



In the splendid work of Sir H. Englefield, On the Isle of 

 Wight, we find the following observations : " With respect to 

 the formation of flint itself, it cannot be doubted that this se- 

 paration of the siliceous matter from the calcareous took place 

 after the formation of the strata, and that the flints were not, 

 as it would appear at a first glance, deposited in alternate 

 strata with the chalk. The extraneous fossils found in the 

 chalk often afford singular proofs of this. Many echini are 

 seen filled with flint, which has, after completely filling up the 

 cavity of the shell, formed a large bulb at the orifice of it, as a 

 viscid fluid would do ;" and after some farther remarks, he 

 proceeds to ask, " What agent has in this manner, at two dif- 

 ferent times, separated the siliceous from the calcareous mat- 

 ter ? and. How could the flint, when separated, form itself into 

 masses in the solid chalk ? — for it cannot be supposed that the 

 flint only ran into cavities before empty, as in that case some 

 of these cavities ought to be found either totally or partially 

 void ; but no such have ever been discovered in chalk," p. 20. 



The two different periods of separation of which Sir Henuy 

 talks, allude to the supposed subsequent filling of certain fis- 

 sures, which traverse the chalk in a contrary direction to the 

 lines of the strata, which he describes as being " seldom above 

 two inches wide, and seem to have been formed from each side 

 towards the centre, which often contains some loose calca- 

 reous powder, inclosed between the two siliceous plates," p. 20. 



These 



