Association of American Geologists and Naturalists. 313 
lated equal in value to that derived from similar means on the 
coast of Sweden, as bearing on the great dynamics of our earth. 
Prof. Bailey read a paper referring to the observations he had made 
upon the microscopic fossils in specimens from the infusorial stratum 
and adjacent miocene deposits at Petersburg, Va., which had been sent 
to him for examination by M. Tuomey, Esq. of that place, the discov- 
erer of the locality. 
He stated that the infusorial earth, and the included casts of Crassa- 
tella, Pecten, &c. contained all the species of Coscinodiscus, Actinocy- 
clus, Dictyoca, &c. which he had previously described as characteristic 
of the deposits at Richmond and Rappahannock cliffs; and that in ad- 
dition he had detected many novel and interesting forms, figures of 
some of which were exhibited—among them a Triceratium, a large 
species of Zygoceros, analogous to forms found living at Boston, and a 
curious unknown fossil which he suspected might be a portion of a 
Zygoceros. 
In the infusorial specimens he detected no traces of Polythalmia, but 
found them abundant among the contents of the shells sent by M. Tuo- 
mey from the miocene beds of Petersburg—figures of some of these 
were shown, among which were species of Textularia, Rotalia, Trilo- 
culina, and also of a minute crustacean, resembling a Cypris in form, 
but which Mr. Dana had informed him might be analogous to the ma- 
rine genus Cytherina. 
Prof. B. then stated that he had detected Polythalmia, in a specimen 
of shelly limestone in the collection of Dr. Chilton in New York, which 
was used in the construction of the Alamo, and which was probably 
quarried in the neighborhood of the fortress. The species appeared 
similar to those of the cretaceous group. He also stated that he had 
examined a specimen of lignite from Cape Sable, Md., sent by M. Tu- 
omey, and found it decidedly coniferous. As amber occurs at the same 
locality, he suggested that these coniferous trees might have produced 
the fossil resin which it accompanies. 
Prof. H. D. Rogers then read the following letter from his 
brother, Prof. Wiliam B. Rogers of Virginia, on the limits of 
the infusorial stratum in Virginia. 
University of Virginia, April 23, 1843. 
Since my first discovery of the infusorial stratum on the Rappahan- 
nock and at Richmond, as referred to in my Report for the year 1840, 
I have succeeded in finding a similar deposit at numerous other locali- 
ties, extending from the Potomac River to near the southern boundary 
of the state. Among these points may be enumerated the Stratford 
cliffs on the Potomac, the vicinity of Westmoreland Court House, and 
Vol. xty, No. 2.—July-Sept. 1843. 40 
