Proceedings of the British Association, 137 



oysters discovers to us their infusorial food ; and, after undergoing 

 the process of digestion in the stomach, the siliceous shields of these 

 Infusoria, deprived of their organic and carbonaceous integuments, 

 are ejected as effete matter. In a paper communicated last year to 

 the Microscopical Society of London, on animals of the chalk still 

 found in a living state in the stomachs of oysters, these Infusoria 

 were described and enumerated. The apparent identity existing 

 between these recent living Infusoria and the fossil, makes the 

 inquiry of considerable interest to the geologist ; for the addition of 

 this connecting link to the chain of organized beings extends a continu- 

 ous line of the same organic structure from the secondary formation 

 to the tertiary, and seems to preclude the supposition of Prof. 

 Phillips, that below the tertiary formation are no recent species. 

 Whether or not this conclusion be admitted, it is a fact, ascertained 

 by pursuing this inquiry, that the oysters and other bivalves, which 

 are innumerable in the Kimmeridge clay, lived, like recent oysters, 

 upon Infusoria ; and, consequently the conclusion is unavoidable, 

 that the Kimmeridge clay, like the chalk, contains a considerable 

 per-centage of these minute and indestructible bodies which the 

 microscope discovers in it, and is not the mere comminuted detritus 

 of more ancient and unorganized materials. With these facts 

 established, we may still further conclude, from analogy, that a 

 similar ciliary apparatus, and similar infusorial food were common to 

 the still earlier bivalves in the seas of the transition formation ; and 

 we may then ask — What right have we, in the absence of a careful 

 microscopic examination of still earlier rocks, to deny the possibility 

 of any portion of their mass being due to the agency of siliceous 

 Infusoria ? 



