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 which 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 m our white chalk corals are but spa- 
ringly distributed, and that the species hitherto determimed are 
comparatively few. Those enumerated in Mr. Morris’s ‘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 Jdmonea, 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 Rotalie and Textilarie, associated with spines of 
sponges and of other Amorphozoa, and a few discs apparently of 
Pyzidicula: 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 cale-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 origmally 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 globulosa, Rot. 
perforata, and Teatilaria globulosa, have been found in every chalk 
district in Europe; and I have the same species, through the 
