S06 Mr. Toulmin Smith on the Formation 



solid flints, and that, in all such cases, I can demonstrate the 

 origin of the space it occupies. In my former paper several facts 

 were named (pp. 4, 7, 8, 9, 16, &c.) showing that the places of 

 the soft parts of animals had been penetrated by silex. I felt 

 however and admitted a difficulty in fully explaining this. That 

 felt difficulty led me to make a long series of preparations, which 

 seem to have at length cleared up the point and thrown much 

 light on the whole formation of flint. 



If a section of moderate thickness is properly, taken from a 

 flint in which experience teaches the observer that a Ventriculite 

 or true sponge has been inclosed, it will be found, in holding the 

 specimen up between the eye and the light, that a part of it, 

 having a very defined outline, is much more transparent than 

 the remainder. On examining that more transparent part under 

 an inch achromatic, traces, more or less distinct, of crystallization 

 will be obvious. Continued and extended observation — the means 

 of which I shall be most happy to supply to any who may feel 

 interested in the question — is necessary to realize the result, 

 which will however in the end inevitably be the conviction that 

 those lighter shades are the places formerly occupied by the soft 

 parts of animals or sponges once inclosed — in a living or unde- 

 composed state — in the flint which had suddenly and solidly en- 

 cased them in an amorphous condition ; that the soft parts first, 

 and afterwards the firmer parts, of those animals subsequently de- 

 composed, leaving, in the then solid flint which encased them, a hol- 

 low mould of the exact form of the living animal ', that subsequently 

 to this it was that silex, suspended in a gaseous or liquid form 

 (1 incline to think the former the more frequent*), found its way 

 into these then hollow spaces and there crystallized f ; that, where 

 any of the firmer fibrous parts happened to remain, they served as 

 nuclei round which crystallization formed ; that if the silex were 

 thus presented in sufficient abundance, it gradually filled up the 

 entire hollow space, leaving a perfectly solid flint ; if not so abun- 

 dant it crystallized round the remaining fibres only, presenting us 

 with those open reticulations of such exquisite beauty with which 

 carefully-made sections have most amply rewarded my labours in 

 the course of these preparations. 



* Mr. Bowerbank's objection (p. 258) to thermal heat is unfounded. Shells, 

 &c. may be subjected to a greater heat than that necessary to suspend the 

 silex in a gaseous state without danger. Dr. Mantell has reprinted some in- 

 teresting experiments on the suspension of silex in steam, and, though this 

 does not seem necessary, the permeation of rocks by heated gases is so well 

 known, that it presents perhaps a more obvious general (not universal) 

 explanation of the gradual accumulation of the matter than any other 

 hypothesis. 



t The note (p. 6) applies in all these cases. If there were no orifice, 

 neither could gases of decomposition escape nor the chalcedony enter. The 

 place of the original orifice may always be found, either marginal or radical. 



