Lafayette Formation.—Darton. 181 
What, then, are the ages of the formations? Are we justified 
in assigning the lower buttes to the Miocene? It seems so. The 
indications point to this conclusion. If we adopt this determina- 
tion then we may with propriety assign the formation of the bluffs 
to the Pliocene. The question then arises, is the variation be- 
tween this upper Pliocene and the beds immediately under 
ereater than might be found in one formation? Considering the 
variableness of the Tertiary, so great dissimilarity might be 
found within the one division. In this case the upper bluffs 
would be the superior member, and the gravels, etc., the inferior 
member of the Pliocene. 
ON FOSSILS IN THE LAFAYETTE FORMATION IN 
Pee ee 
By N. H. Darron, U.S. Geological Survey, Washington, D. C. 
In a paper entitled omen and Cenozoic Formations of 
Eastern Virginia and Maryland,’’t+ I described the relations and 
distribution of this formation in the western portion of the coastal 
plain region, and announced its extension northward through 
northeastern Virginia and Maryland. 
During the past season I have found that the formation extends 
eastward down the coastal plain peninsulas nearly to Chesapeake 
bay. These peninsulas consist of remnants of an elevated plain, 
occupied by a sheet of Lafayette formation, and originally con- 
tinuous over the entire coastal plain. This plane is inclined 
gently eastward, its altitude decreasing from 500 feet in the Pied- 
mont region, to from 60 to 80 feet in the vicinity of Chesapeake 
bay, where it is terminated by an abrupt descent to the low Pleis- 
tocene terrace bordering the bay to a width of several miles. The 
great drainage depressions are excavated in this plain and the re- 
sulting peninsulas are more or less wiglely: fringed by the low, 
*This formation on the Atlantic coastal plain was first described under 
the name Appomattox, by McGee, in 1889, ina paper entitled “ Three 
mations of the Middle Atlantic Slope,” Am. Jour. Scz., 3d series, vol. 
35, Pp. 328-330. In the AMERICAN GEOLOGIST, vol. 8, pp. 129- 131, Hilgard 
proposed to revive the term “ Lafayette,” which was applied in the Mis- 
sissippi region in 1855-56, and the term was adopted by McGee and Dar- 
ton ina chapter on the Geology of Washington in the guide to Washing- 
ton, prepared for the ineeting of the International Congress of Geolo- 
gists, in August, 1891. 
+Geol. Soc. Am. Bul., vol. 1, pp. 481-450, map. 
