of the Flints of the Upper Chalk. 303 



tion which caused it had ceased, the rapidly solidified flint com- 

 pressing it. 



5. Space will not allow me to add many of the additional 

 illustrations which crowd upon me. Several fresh facts have 

 been already named. I will therefore conclude with a brief 

 notice of two most important facts in the natural history of 

 flints and their inclosed bodies, which, by an extended series of 

 preparations, I have ascertained since my former paper was 

 written. Each of these points has furnished me with direct 

 evidence of that which I had before inferred, as most probable, 

 from collateral facts only. Each equally demonstrates the fal- 

 lacy of the sponge theory, and points to important truths in the 

 natural history of flints. As I propose to take an early oppor- 

 tunity of detailing the observations relative to the first point 

 alluded to, I will only call attention here to the general result. 



Flints are generally considered in the light of homogeneous 

 masses, mineralogically the same throughout each individual 

 mass, except in such cases as Mr. Bowerbank notices on p. 257, 

 and which notice by him shows that he is not aware of the facts 

 which I have now to state*. Indeed had he been so, the sponge 

 theory could never have been framed. Mr. Bowerbank speaks 

 (p. 257) of chalcedonic crystallization " wherever there has been 

 a small space originally not occupied by spongeous substance ;" 

 and at p. 250 he evidently implies that silicification took place 

 after all animal matter had drained out of the horny skeleton ; 

 and at p. 258 he cannot understand any reason for imagining 

 the Ventriculites to have been imbedded in flint while alive. 

 His remarks also, in this and other papers, upon agates, equally 

 show his opinion that the chalcedonic crystallization took place 

 only in spaces " originally not occupied by spongeous substance.'^ 

 Now I am prepared to show that, confining ourselves to the flints 

 of the upper chalk, our true point, the exact converse of this is 

 true, and that the places in which chalcedonic crystallization has 

 taken place are places which were originally occupied by the 

 spongeous or other animal substance f. I will not at present ab- 

 solutely affirm that in no other cases is chalcedonic crystallization 

 found, though I believe such to be the case. It is enough for 

 my present purpose if I can clearly show that this chalcedonic 

 crystallization is present in numberless instances in perfectly 



* Nor are these }ili£enomena noticed in Brongniart's ' Essai sur les orbi- 

 cules siliceux ;' — their possibility being indeed expressly put out of the ca- 

 tegory. See pp. 21 and 23 of that * Essai.' 



t It will be understood that I mean to express this as the ordinary cause 

 of hollows in chalk flints, which Mr. Bowerbank nowhere explains. Else- 

 where (in volcanic rocks, &c.), hollows existing from other known causes, 

 siliceous infiltration and crystallization would obey the ordinary laws. 



Ann, &^ Mag, K Hist, Volxix, 22 



