168 
THE GEOLOGIST. 
concretions of coprolitic matter which abound in the surround- 
ing sandstone. Mr. Bensted expressed his behef that the car- 
bonaceous substance was derived from the soft bodies of the 
Mollusca_, and that the concretionary and amorphous portions of 
the same matter dispersed throughout the sandstone of this bed, 
were masses of the fossihzed 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 ^ Ame- 
rican Journal of Science^ for 1837, of the effects of an epidemic 
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 with 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. Beade submitted some of the substances of 
these bodies to an analysis by Mr. Bigg, who confirmed Dr. 
MantelFs 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 na- 
creous laminae of the shells of extreme thinness intermingled 
with the carbonaceous matter, together with numerous siliceous 
spiculse of sponges, very minute spines of Echinodermataj and 
fragments of Pohjparia, and remarks that these extraneous 
bodies probably became intermingled among the soft animal 
mass before the latter had undergone decomposition. lie pro- 
