94 
CHALK FOSSILS. 
the authors above named, are unknown in this 
district. In their mode of preservation, liowever, 
a perfect correspondence exists in the productions 
of ditferent localities. They are for the most part 
remarkably entire, the delicate coverings of the 
Crustacea, the spines of the shells, &c. remaining 
unbroken ; in short, their appearance, as Mr. Par- 
kinson justly remarks, “ warrants the conclusion, 
that they have been enveloped by the chalk, while 
living in their native habitats, and that this was ef- 
fected in the tranquil depths of a profound ocean.” 
In every instance the shells, echinites, madre- 
porites, and encrinites are converted into cal- 
careous spar, their cavities being filled with chalk, 
flint, or sulphiiret of iron. 
The remains of the softer zoopJiytes occur in the 
form of chalky casts, tinged with a yellowish or 
reddish oxide of iron : this appearance, which 
facilitates the separation of the fossils from tlie 
chalk, results from the decomposition of pyrites. 
The vertebrae and bones are soft and friable ; but 
the teeth and palates are finely preserved, and have 
the natural polish of the enamel, heightened by an 
impregnation with iron. The scales andfins of fishes, 
and the coverings of the Crustacea, are changed into 
a brown substance, which is exceedingly brittle, 
and fades upon exposure to the air. 
The zoological characters of the chalk prove 
unquestionably that almost tlie whole of the ani- 
mals and vegetables, whose remains it entombs, 
were inliabitants of the sea ; and the jirojiortion of 
those shells whicli arc ])elagian, or, in otlicr words, 
inhabited deej) waters, is so great as to show that 
