Geological Society. 73 



of firestone which form the line of junction with the gault, and are 

 not uncommon in the gault itself in several localities in Surrey and 

 Kent. 



Dr. Fitton, in his memoir ' On the Strata below the Chalk ' 

 (Geol. Trans, vol. iv. part 2. p. 11), has given an account of similar 

 concretions from Folkstone, where he observed them in some cases 

 surrounding or incorporated with fossil remains, and filling the in- 

 terior of Ammonites. Dr. Alantell has observed them also in the 

 Shanklin sand in Western Susse.x, in Surrey, near Ventnor in the 

 Isle of Wight, and in Kent, and they especially abound in the Igua- 

 nodon quarry of Kentish rag near Maidstone, belonging to Mr. W. 

 H. Bensted. 



Mr. Bensted having long paid attention to this subject, more 

 than two years ago submitted to Dr. Mantell specimens of fossil 

 shells, the cavities of which were filled with a dark brown sul)stance 

 in ever}' respect identical with the nodular and irregular concretions 

 of coprolitic matter whicli abound in the surrounding sandstone. 

 Mr. Bensted expressed his belief that the carbonaceous substance 

 was derived from the soft bodies of the MoUusca, and that the con- 

 cretionary and amorphous portions of the same matter dispersed 

 throughout the sandstone of this bed, were masses of the fossilized 

 bodies of the animals which had become disengaged from their shells, 

 and had floated in the sea till enveloped in the sand and mud, which 

 is now concreted to the coarse sandstone called Kentish Rag. In 

 proof of this opinion reference is made to an account published in 

 the ' American Journal of Science' for 18-37, of the effects of an epi- 

 demic among the shell-fish of the Ohio, which, killing the animals, 

 their decomposed bodies rose to the surface of the water, leaving the 

 shells in the bed of the stream, and floating away covered the banks 

 of the river. Mr. Bensted points out that nearly the whole of the 

 shells in the Kentish rag of his quarry appear to have been dead 

 shells, and infers that their death might have been owing to a similar 

 cause Avith that which destroyed the Uniones in America ; while their 

 bodies intermingling with the drift wood on a sand-bank furnished 

 the concretions described in this communication. 



The Rev. J. B. Reade submitted some of the substance of these 

 bodies to an analysis by Mr. Rigg, who confirmed Dr. Mantell's 

 suspicion of the presence of animal carbon in it, and states that the 

 darker portion of the substance contains about .35 per cent, of its 

 weight of carbon in an organized state. 



Dr. Mantell adds, that a microscopical examination with a low 

 power detects innumerable portions of the periosteum and nacreous 

 laminae of the shells of extreme thinness intermingled with the car- 

 bonaceous matter, together with numerous siliceous spiculse of 

 sponges, very minute spines of Echinodermuta, and fragments of 

 Polyparia, and remarks that these extraneous bodies probably became 

 intermingled among the soft animal mass before the latter had un- 

 dergone decomposition. He proposes to term the substance Mol- 

 luskite, and states that it constitutes the dark spots and markings in 

 the Sussex and Purbeck marbles. 



