EASTERN AND SOUTHERN UNITED STATES. 
125 
the State. The best known fossil-bearing localities are Fort Washington, situated a 
few miles below the city of Washington, Piscataway, on Piscataway Creek, and Upper 
Marlborough, in Prince George’s County, which have been made known principally 
through the labors of Mr. Conrad. 
The positive determination of the relation which these older Tertiary deposits hold 
to the typical American Eocene series as exhibited in Alabama, can only be arrived 
at when a direct stratigraphical continuity can be traced between the deposits of the 
two States, or between their previously recognized representatives in the intervening 
States. This is due to the fact that several members of the Eocene serie.s appear to be 
absent from this portion of the Atlantic border, but exactly which it has as yet 
been impossible to determine. The presence of strata of Jacksonian age has never 
been detected, nor have we any positive knowledge concerning the existence in the 
State of any beds which may be looked upon as the equivalents of the Orbitoide lime- 
stone, although Oligocene (Vicksburgian) strata may exist along the Chesapeake. 
But whether the deposits in question — Fort Washington, Piscataway, and Upper Marl- 
borough — represent the Claibornian, Buhrstone or Eo-Lignitic is a matter of consider- 
able uncertainty, perhaps largely due to their comparatively feeble development. 
Almost the only evidence we have bearing upon this point is derived from the character 
of the contained fossils, but even here the results obtained are far from satisfactory, and 
for two reasons : in the first place, the character of the Eocene fossils is largely uniform 
throughout the greater portion of the entire series, as is shown by nearly the lowest 
and highest exposures in the State of Alabama ; and in the second place, the great 
distance interv^ening between the two localities — Alabama and Maryland may readily 
account for certain differences in the general aspect of the two fossil faunas, which 
otherwise would probably be attributable to a non-contemporaneity in the periods of 
their introduction. The evidence afforded by lithological characters is almost equally 
iinsatisfiictory, since there is a frequent repetition of the general rock aspect— green- 
sands, clays, and siliceous marls— observable at different stages of the series. Conrad, 
the only investigator whose observations on this subject are of scientific value, affirms 
that the majority of the fossil mollusca are of the Claiborne type, and he consequently 
..K- i-'j. t, o-pnoral wav with those exposed on the Ala- 
17 JOUR. A. N. S. PHILA., VOL. IX. 
