AND STRUCTURE OF THE BELEMNlTE. 401 



These veins may perhaps be considered as veins of secretion, 

 formed in the fissures which may have occurred in the strata, 

 during the dependence of the operations which produced the 

 tuberose arrangement of the flints. 



We are indebted to the ingenuity of Professor Buckland of 

 Oxford for another idea respecting flint. It was observed, 

 that a variety of the nodules which occurred in particular gra- 

 vel pits, presented something of an uniform shape, which, 

 when broken, were found to contain zoophytic remains, such 

 as alcyonia, corals, and sponges of different kinds, sometimes 

 so perfect, as to be extricable from the outer case, when for- 

 tunately and carefully broken ; at other times, when the exter- 

 nal contour of the nodule bespoke a similar internal appear- 

 ance, the mass would be found perfectly solid throughout, and 

 the shape only of the organic body traced on the internal frac- 

 ture, in colours of a shade differing from the general mass of 

 the flint, or slightly tinged of a delicate purple, when the tex- 

 ture passed into that of calcedony ; and so uniformly were 

 these appearances connected, that where the slightest symp- 

 tom of any of them occurred, it was held as indicative of one 

 and the same origin. The origin of flint itself was by this 

 analogy attributed to organization, though perhaps on grounds 

 not altogether thoroughly investigated. 



We find little in the French works tending to illustrate this 

 subject. Brochant, following Werner, considers flint to owe 

 its origin to infiltration. Brogniart states, that some have 

 supposed flint to be formed by infiltration, introduced into ca- 

 vities formerly occupied by mollusca and zoophytes, — an hypo- 

 thesis which, he says, though admitted by a number of geolo- 

 gists, is exposed to considerable difficulties ; and he adds, that 

 the observation of M. Gillet Laumont tends to support this 

 supposition ; he having remarked that a tail of silex often pro- 



3 e 2 ceeds 



