Mr. CoNYBEARE OH the origin of Organic Impressions, tsfc. 329 



differed essentially from every zoophyte, recent or fossil, with which 

 he was acquainted. 



The impressions In question are generally found in a state 

 of such indifferent preservation, and afford such insufficient data on 

 which any conjectures concerning their formation can be founded, 

 that we shall not be surprised to find the more perfect specimens now 

 submitted to the Society, decidedly militating against the hypothesis 

 proposed by the able fossilist above cited, and proving that the real 

 origin of these bodies Is widely different from that which he ha& 

 assigned, they being in fact siliceous casts moulded in little hollow 

 cells excavated In the substance of certain marine shells ; the work 

 perhaps of animalcules preying on those shells and on the vermes: 

 inhabiting them. It is almost unnecessary to add that these casts, 

 like the screw stones of Derbyshire, must have been formed by the 

 infiltration of the siliceous matter while yet in a fluid state into 

 the cavities of the shells which it enveloped, and that they have 

 been laid open and denuded in the specimens at present under con- 

 sideration, by subsequent exposure to some agent capable of dis-* 

 solving and removing the calcareous matter of the shell which 

 formed the matrix, while the siliceous impression resisted it and re- 

 mained unaltered. 



My first suspicion of these facts arose from a minute examina- 

 tion of the specimen represented in the drawings by fig. 1, PI. 14. 

 It presented several appearances which seemed to indicate the foil- 

 lowing conclusions. 



1. That the flat surface of flint over which the globules are In 

 that specimen distributed, had been originally occupied by a large 

 piece of the striated shell, the fragments of which occur so abund- 

 antly in the chalk-strata and accompanying flints, being very com- 

 monly considered as mutilated portions of a fossil pinna. 



Vol. II. 2 t 



