FOSSIL DIATOMACEE OF VIRGINIA. 99 
pellicle left by the evaporation of a drop of water in which 
some of the marl has been mixed, teeming with the most 
beautiful structures. 
At Petersburg, in Virginia, a sandy marl occurs, inter- 
stratified with deposits which, from their shells, are referred 
to the older tertiary formations. Probably this marl is a 
continuation of that of Richmond, but it is full of many new 
forms, associated with those common in the earth of the 
latter locality.* 
It is an interesting fact, (first observed by Mr. Hamlin 
Lee,) that the common Scallop (Pecten maximus), as well as 
the Barnacle (Balanus), feed on diatomaceze, and their 
stomachs generally contain numerous cases of Coscinodisci, 
Dichtyochi, Actinocycli, &c. : a slide prepared and mounted 
with the contents of the stomachs of these mollusks, presents 
an assemblage of forms identical with those found in the 
tertiary earths of Virginia.t 
In the mud of the quicksands on the shore at Brighton, 
Mr. Reginald Mantell found recent Coscinodisci, &c. asso- 
ciated with fossil polythalamia that had been washed out of 
the chalk, and precipitated with the frustules of the recent 
diatomaceze, into the sediments now in progress. 
The prevalence of marine and fresh-water forms in the 
same deposit is not unusual ; and the remarks of Dr. Bailey 
on this fact are so pertinent, that I insert them, as a 
salutary caution against hasty generalizations on subjects 
connected with these investigations. After describing a 
species of Galionella (G. moniliformis), as an inhabitant only 
of salt and brackish water, and stating that he had also 
* Dr. Bailey, with great liberality, has so amply supplied myself 
and other observers with specimens of these deposits for examination, 
- that the fossils above described are familiar to all British microsco- 
pists. Figures of many of those organisms are given in the American 
Journal of Science. 
+ See my “Thoughts on Animalcules,” p. 103. 
