THE NATIONAL INSTITUTION. 173 



and tertiary formations of the United States. Tlie 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 has completely replaced the cal- 

 careous matter, whilst others, as Panopea elongata, Cucullaa gigantea, ^c, fre- 

 quently consist of casts, with only a thin coating of the chalky calcareous matter 

 of the original shells. Pectunculas pulcinatus, 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 Cucull<Ba gi- 

 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 tertiarios. 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 Turritelli Mortoni, of Maryland, is gigantic in comparison with tho 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. selleeformi/i, 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 1332, 1 found abundance of Oitrea tellwfarmit at Nchon'i ferry, on the Sanlee rirer, but aaioci- 



