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PROCEEDINGS 01' 
identical with those of the St. Lawrence river, Sweden and Norway, referred by 
Mr. Lyell, to the post-pliocene period. 
The upper tertiary is divided in the table into three sections, not that 1 would 
assert positively that there is much, if any difference in age, but because of the 
peculiar groups and distribution of species.. The lowest section is most unlike the 
two upper, in consequence of exhibiting a group of shells approximating that living 
in the Gulf of Mexico, but it must be remembered that some species ranging as far 
north as Massachusetts, also occur with the fossils, and that probably when these 
were living in the sea, the peninsula of Florida was yet submerged. This form of 
the coast would have given the Gulf stream more influence in distributing southern 
forms far northward along the coast. But some change of climate, at the close of 
this period, seems not improbable from the circumstance that the common estuary 
fossil of the Gulf of Mexico, Gnathodon cuneatus, of Gray, was banished from the 
brackish waters of Georgia, South and North-Carolina, Virginia and Maryland, at 
this geological epoch. This shell lives so far from the sea, in mud fiats, exposed at 
low tide, that it is not likely to have been destroyed by any change in the Gulf 
stream, or a receding of its imparted temperature from the coast. If this alteration 
of temperature can be established by new investigations, the deposits can hardly 
be of the same age as those of Raritan bay and the St. Lawrence river. In the 
former locality, there is no evidence of the slightest variation of temperature from 
the historical period, whilst, the latter is supposed to contain a group peculiar to 
higher latitudes. This, however, wants confirmation, since most of the .species are 
known to exist on the coasts of Maine and Massachusetts. 
Medial Tertiary Period. 
In a recent excursion with my friend Mr, Markoe, I made a hasty examination 
of some localities in Anne Arundel, Calvert, and St. Mary’s counties. Except the 
lower tertiary at Upper Marlborough, these were chiefly referable to the medial ter¬ 
tiary period. The first point of observation was near Fair Haven, Anne Arundel 
county, where Mr. Markoe had previously obtained some interesting relics. This is 
the northern extremity of the formation on the west shore of the Chesapeake ; a line 
run from Fair Haven to a point opposite Crane Island, in the Potomac, dividing 
the lower from the medial tertiary. At Fair Haven we observe a range of coast 
about fifty feet in elevation. Valleys of denudation sloping to the shore of the 
Chesapeake, interrupt the continuity of the bank, which presents a front of isolated 
perpendicular cliffs at irregular intervals. The lowest bed, which is on a level with 
the tide, is composed of clay, containing a stratum of Ostrea percrassa, a new Pec- 
ten, P. Humphreys!!,* and other undetermined shells. This stratum rises to the 
height of about five feet above the level of the bay. Above is a light-colored clay, 
containing great numbers of black water-worn siliceous casts of small shells, 
chiefly Turritella, the species not yet determined. To this succeeds a whitish clay 
without fossils. 
* .Named after Dr. Humphreys, of St. John’s College, at Annapolis. 
