404 R. M. Brydone^The Origin of Flint. 



between the chalk-filled Echinocorys and the flint-filled Echinocorys 

 might be due to the former having at the death of the animal come 

 to rest with the apex downwards and the mouth and vent exposed, 

 so that the dead body was cleared out by animalculse and not left 

 to decay, while the latter came to rest with the apex upwards 

 and the mouth and vent pressed into the ooze, so that the dead body 

 was left to decay and provoke the deposition of silica. 



Again, the possibility that the flints were formed at the surface 

 of the ooze can be written off altogether on fossil evidence. 

 The Chalk sea was full of encrusting animals, such as Spondylus 

 latus, OstrecB, Serpulce, and Porosphcerce. I have never seen a 

 case, and I do not know of one having been recorded of any 

 organism being found encrusting a flint, though that must have 

 happened freely if they had existed at the surface of the ooze. 

 It is rather surprising that the suggestion should ever have been 

 made, for it must be plain that as soon as a particle of flint 

 had formed at the surface it would, owing to its specific gravity, 

 sink out of sight at once in the practically liquid ooze. It would 

 presumably sink to such a depth as the consolidation of the ooze, 

 naturally increasing with depth, would admit, and might there form 

 a nucleus for concretionary growth of a flint. All particles of flint 

 arising at the surface of the ooze about the same time would 

 presumably sink to about the same depth, which might quite well 

 be below the range of a dredge, and would give rise to a row of 

 flints roughly parallel with the surface of the ooze, i.e. pseudo- 

 stratified. A question here suggests itself which I am unable to 

 answer, i.e. whether the specific gravity of a solution of silica might 

 be sufficient to produce the same result by a concentration of the 

 silica in solution at some depth below the surface of the ooze where 

 precipitation would occur, and the newly j^recipitated flints would 

 then sink to their natural static level. 



Again, it is a well-known thing that fossils of all descriptions are 

 frequently embedded in flints. I have not made any express test, 

 but it is my strong impression that fossils are much more abundant 

 at the periphery of flints than at any other internal contour-line, 

 or, indeed, in the whole of the interior. It is possible to regard these 

 external fossils as having contributed to determining the outline 

 of the flints by some power of attraction of the growing amorphous 

 mass of colloid silica, and the most likely cause of such an attraction 

 would be the presence on them of decaying animal matter, which 

 would involve penecontemporaneous formation of the flint. 



Again, as I have indicated above, the contents of hollow flints 

 afford a strong argument for the contemporaneous or penecon- 

 temporaneous origin of these flints, at any rate. 



On the whole a penecontemporaneous origin for row and tabular 

 flints seems to present the minimum of conflict with facts, while the 

 vein flint is obviously of some subsequent date at or after the 

 formation of the uplift cracks which it occupies. 



