76 Dr. G. A. Mantell on the Animalculites of the 



ing descriptions of the Prussian philosopher. A short time since, 

 however, I discovered some layers of chalk vrhich are wholly com- 

 posed of polythalamia, principally of the genera Rotalia and Tex- 

 tilaria ; and it may perhaps be interesting to other observers if I 

 mention the circumstances which led me to institute a microsco- 

 pical examination of these deposits. 



Every one knows that in our white chalk corals are but spa- 

 ringly distributed, and that the species hitherto determined are 

 comparatively few. Those enumerated in Mr. Morrises 'Catalogue 

 of British Fossils^ amount to between twenty and thirty spe- 

 cies, and belong to sixteen or seventeen genera. The cretaceous 

 deposits of Maestricht and Faxoe present in this respect a striking 

 contrast with those of England. There are however a few loca- 

 lities in which certain layers of the chalk abound in small, deli- 

 cate, calcareous polypidoms; and of late years many beautiful 

 specimens of the genera Idmonea, Ceriopora, Pustulopora, Rete- 

 pora, &c. have been obtained from the neighbourhood of Dover. 

 For the most part the specimens are small, but occasionally 

 some occur of considerable size, as in the fine example on the 

 table (presented to me by Mrs. Smith of Tunbridge Wells), which 

 consists of hundreds of branches of Pustulopora and Idmonea, 

 intertwined into a mass more than two inches in thickness. 

 When clearing this beautiful fossil, the extremely friable nature 

 of the chalk, and the sensation of a peculiar asperity to the touch, 

 which experience had taught me was commonly characteristic of 

 the presence of minute fossil bodies, induced me to submit a few 

 grains to a microscopical survey ; and the entire block of chalk 

 in which the coral is imbedded, proved to be almost wholly con- 

 stituted of Rotalia and Tecctilarice, associated with spines of 

 sponges and of other Amorphozoa, and a few discs apparently of 

 Pyxidicula : the residue consists of the detritus of similar orga- 

 nisms and of polyparia. I have distributed samples of this coral- 

 line chalk among my friends, and the result of their exploration 

 is in accordance with my own. 



The incoherent character of the Dover coralline chalk, results 

 therefore from its organic composition, and the absence of any 

 cementing material. For in other cretaceous strata where an 

 infiltration of calc-spar has consolidated the rock, the chalk pos- 

 sesses great compactness and durability, and the organisms may 

 be seen in polished slices, and sometimes in relief on the surface. 

 That the white chalk was originally everywhere of the same or- 

 ganic constitution there can be no reasonable doubt ; and it is 

 remarkable how universal was the distribution of certain species 

 throughout the cretaceous ocean. The Rotalia globulosay Rot. 

 perforata^ and Textilaria glohulosa, have been found in every chalk 

 district in Europe; and I have the same species, through the 



