of the Flints of the Upper Chalk. 7 



fitions to which it is impossible that, on the sponge theory, it 

 could have gained access. 



The specimen of Mososaurus [Leiodon of Owen *), discovered 

 by Mr. Charlesworth, exhibits the pulp cavities of the teeth par- 

 tially filled with flint. This is sufficiently remarkable ; but those 

 teeth being large, and the cavities not being wholly filled with 

 the flint, it may not perhaps, alone, be considered as absolutely 

 conclusive. What is wanting in this case is however fully sup- 

 plied by the following : — 



I have a flint, in the centre of which is found, by a happy frac- 

 ture, a jaw on which are made visible, by the fracture, at least 

 sixteen teeth (see figure). They are very minute; the largest 



Jaw of Enchodus (?) in flint. 



not exceeding in size the point of a pin the eighth of an inch in 

 length. On examining this very interesting specimen under the 

 microscope, it is found that, though the jaw itself is perfect and 

 not silicifiedt, the pulp cavity of each tooth in which the fracture 

 has exposed it is entirely filled with solid flint. How did that 

 flint get there ? Geological phsenomena will indeed be easily ex- 

 plainable if we are to believe that any sponge gemmule ever found 

 its way into these minute and perfectly inaccessible spaces, and 

 still more that, having found its way there, it was able to exist and 

 grow there without any possible access to the very essential means 

 of its existence, the sea- water. That the silex when in solution 

 possessed however the power, and that it was one of its qualities, 

 to penetrate some of the most intimate tissues of organic bodies 

 within its range, will appear from the next class of facts cited ; 

 in reference to which, as well as to the last-named facts, it may 

 be stated that soft animal matter appears to have had a greater 



• Odontography, p. 261. and pi. 72 ; and a section is figured in the Lon- 

 don Geological Journal for Sept. 1846. 



t See this phaenomenon alluded to in a very interesting paper by Dr. Man- 

 tell in the * Annals and Magazine of Natural History,' vol. xvi. p. 80. The 

 whole article is well-worthy of attentive perusal. The same principle will 

 consistently explain why, as often seen, though a Ventriculite was enveloped 

 in flint, the shells on it were left bare, not having so much affinity for the 

 siliceous fluid as the soft animal substance of the Ventriculite. On the sponge 

 theory this frequent fact would be utterly inexplicable. 



