HISTORY OF THE CRETACEOrS FLINTS. 91 



pro tanto, therefore, the calcareous mud may be, and in all proba- 

 bility is, "a continuation of the Chalk formation." 



Discussion. 



Tho President stated that he had formerly studied this subject, 

 and come to the conclusion that, though deep-sea mud differs from 

 Chalk in many important particulars, yet still it was sufficiently 

 related to warrant a comparison. Since the remains of siliceous 

 organisms are absent from the Chalk, but flints present, whilst in 

 the deep-sea mud siliceous organisms are abundant and flints 

 absent, probably the material of the flints had been to a greater or 

 less extent derived from these organisms. Much, however, re- 

 mains to be learned. 



Mr. Evans said that the author seemed to have given a vera causa 

 for the intermittent character of the Chalk flints. He doubted if 

 the protoplasm could be in any sense a producer of flint. There 

 was always a certain amount of silica in solution in sea-water ; 

 and there seemed evidence that, after the deposition of the beds, 

 a considerable quantity of silica was aggregated by a sort of 

 dialyzing process. This was shown by the deposition of flints in 

 walls in the Chalk &c., so that it was possible that the absence of 

 flint from intermediate layers might be partly accounted for in this 

 way. 



Mr. Charlesworth said the origin of flint was in great confusion. 

 He recapitulated some of the views which had been entertained on 

 the question. He said that the author was mistaken in supposing 

 that Dr. Bowerbank and Dr. Mantell agreed as to the origin of flint ; 

 for tho latter did not suppose every piece of flint to be a sponge. 



Prof. Seelet thought the author had neglected the geological 

 history of the occurrence of flint. He thought the fissures filled 

 with flint, and the tabular layers investing nodules, showed that 

 probably the flint had gradually come into existence in the Chalk. 

 The flint in the fissures must be, as it were, filtered from tho 

 Chalk. In deahng with the question we must remember how flint 

 occurred in other formations ; and the question which dealt with 

 the occurrence of flint in the Chalk must deal with it in other 

 formations, and as replacing shell and coral, as filling cavities with- 

 out replacing the sbell, and as external investing masses round frag- 

 ments of fossils. He thought that the flinty masses of the Chalk 

 were very analogous to the septarian masses of the clays, and that tho 

 flints had grown, and even now were growing. The researches of 

 Dr. Graham on dialysis had cleared up the way in which flint in 

 Chalk may become soluble. 



Mr. Whitaker remarked that previous speakers had said most 

 that he had to say. It must be remembered that flints occurred 

 not only in layers of nodules but in tabular layers, as in tho Isle of 

 Thanet; several of these at the present day were water-bearing, 

 which would be favourable to the theory of subsequent formation. 

 It was probable that flint had been deposited in more than one way. 



