Chalk and Flint of the South-east of England. 87 



But if I have hitherto been unsuccessful in the microscopical 

 exploration of our tertiary strata, an unexpected assemblage of the 

 American miocene forms has been found in the digestive organs of 

 certain living mollusca. Mr. Lee's discovery of recent Coscino- 

 disci in the barnacle (announced in the ' Medals of Creation ') has 

 been followed up by his detection of numerous species and genera 

 of infusoria in the stomach of the common scallop {Pecten maxi- 

 mus^) . These recent animalcules present almost all the genera and 

 some of the species that prevail in the tertiary marls of Virginia; 

 in particular two very striking and abundant fossils of the Rich- 

 mond earth, the elegant Coscinodiscus radiatus and the Dictyocha 

 fibula. So close is the analogy, not only of the individual shields, 

 but even of their collocation, that it w ould be difficult for an ex- 

 perienced observer to distinguish slides mounted with the re- 

 spective organisms, although the one group is from deposits of 

 unfathomable antiquity, and the other from the British seas. 



I have already stated that the modern calcareous deposits of 

 the Bermuda Islands contain layers of infusorial earth ; these are 

 made up of organisms resembling those of America and the recent 

 species found in the scallop. 



One more fact in connexion with this subject remains to be 

 mentioned. Along the shore of the Sussex coast to the east of 

 Brighton, a bed of sand and calcareous mud, the detritus of 

 the neighbouring cliffs, is in the progress of formation ; and in 

 this sedimentary deposit my son, Reginald Neville Mantell, has 

 discovered shells of recent Rotalia, Nodosaria, and other poly- 

 thalamia, associated with the siliceous shields of Coscinodisci, Dic- 

 tyochce, and other infusoria, and with fossil Rot alia and Texti- 

 laricefrom the chalk. Here then at the present moment a deposit 

 is in progress, whose organic contents consist of an assemblage 

 of the living species of the animalcules of the present sea with the 

 fossil forms of the ancient chalk ocean ; in like manner in the bed 

 of the Nile, the polythalamia of the Nummulite rock are being 

 imbedded with the existing mollusca of that river : collocations 

 of this nature may perhaps exercise the ingenuity of the geolo- 

 gists of future times, and give rise to speculations of as little 

 value as some of those with which I have ventured to trespass on 

 the indulgence of the Society. 



In conclusion I would remark, that the preceding observations 

 are the result of the examination of organisms within the reach 

 of the best microscopes which modern art has produced; yet 

 there can be no doubt, that if the powers of our instruments 

 could be increased, fossil structures yet more minute and far 



* See Annals of Nat. Hist. April 1845. 



