THE NATIONAL INSTITUTION. 
173 
and tertiary formations of the United States. The species evidently existed in the 
newest of the cretaceous rocks, which contains two other tertiary fossils. 
If it can be proved that no species of the secondary period was drifted by cur¬ 
rents into the eocene ocean, it is not unlikely that the green grains of silicate of 
iron, which are probably of volcanic origin, were formed as well in the tertiary as 
the cretaceous epoch. Indeed, in many localities of the former period, in Mary¬ 
land and Virginia, the green-sand is quite as abundant as in the secondary fossil- 
liferous “marls” of New-Jersey. 
The only localities of the lower tertiary which I have visited in Maryland, are 
at Upper Marlborough, Piscataway, and Fort Washington. It sinks beneath the 
medial tertiary beds, shortly after passing a line from the fort to Annapolis. Dr. 
Ducatel has detected it on the Potomac, opposite Crane Island, in Charles county. 
We know not any other locality southeast of this. The inclination of the tertia- 
ries in Maryland is very slight, and towards the southeast; so that the Potomac, 
below Washington, presents sections of each of the three divisions. The same 
group of organic remains occurs throughout the lower tertiary, with little variation 
in species compared with the upper divisions. The lowest bed consists of green 
and siliceous sands, mixed with clay, in which the fossils are chalky, and fall to 
pieces with the slightest pressure. The upper stratum is of a coarse arenaceous 
texture, with green grains, and quite indurated in masses, which fall out as the 
other portions of the rock become disintegrated by frost. Here we observe many 
of the shells perfectly preserved in silex, which lias completely replaced the cal¬ 
careous matter, whilst others, as Panopea elongata, Cucullcea gigantea , fyc., fre¬ 
quently consist of casts, with only a thin coating of the chalky calcareous matter 
of the original shells. Pectunculus pulvinatus, the variety described and figured 
by Deshayes, a very characteristic shell of the Paris eocene, is the most common 
of the silicified bivalves, standing in bold relief on the surfaces of the indurated 
masses. Cardita Blandingi is rare, and much smaller than the same species which 
occurs so abundantly in the sand at Claiborne, Alabama. The large Cuculleza gu 
gantea abounds in the vicinity of Fort Washington ; but in the synchronous de¬ 
posits of Piscataway and Upper Marlborough, it does not occur. Of course some 
variation in the group of species will be observed in every different locality; but it 
is far less in amount in the lower than in the newer tertiaries. There is also great 
difference in size among some species, when compared from different localities. 
Cardita planicosta is much larger in Maryland than in the sand at Claiborne; 
and Turritclli Mortoni, of Maryland, is gigantic in comparison with the largest 
specimens at Claiborne. 
The lower tertiary occurs on James river, near City Point, Virginia; a most in¬ 
teresting locality, from the juxtaposition of this formation with the medial tertiary, 
in which the organic remains of both are brought almost into contact, and yet not 
one species of any class of fossils is common to both. Here the remarkable oyster, 
O. selleeformis, separates the group of oceanic lower tertiary shells from those of the 
medial tertiary. At Claiborne, this Ostrea divides the eocene oceanic beds by an 
interval of seventy feet. This shell connects the white limestone of Vance’s 
ferry, Nelson’s ferry, and the Eutaw springs, South-Carolina,* with the eocene of 
* In 1832, I found abundance of Ostrea seller for mis at Nelson’s ferry, on the Santee river, but associ- 
