STRATIGRAPHY OF THE POTOMAC GROUP 503 
Potomac deposits until almost within the last decade. In 1885 
Professor R. P. Whitfield, as the result of several years’ study, 
published an important monograph upon ‘‘The Brachiopoda and 
Lamellibranchiata of the Raritan Clays and Greensand Marls of 
’ 
New Jersey,” in which several Lamellibranchs from the ‘Plastic 
Clays” of Professor Cook are described. While the investiga- 
tions leading up to Professor Whitfield’s report were in progress 
Professor William M. Fontaine, of the University of Virginia, 
began his elaborate study of the Mesozoic flora of Virginia. 
The published account of this work, however, did not appear 
until after the important stratigraphic study of Professor W J 
McGee, of the United States Geological Survey, which began a 
few years subsequently. 
The investigations of Professor McGee upon the Potomac 
deposits were seriously commenced in the summer of 1885, and 
were participated in by Professor L. F. Ward, of the United 
States Geological Survey, and these gentlemen also codperated 
soon after with Professor Fontaine. Some preliminary work 
had already been done by Professor McGee’ in the previous 
year and the name ‘“‘Potomac formation”’ proposed. Professor 
McGee continued his investigations of the Potomac formation 
during several years, and published a number of important 
papers regarding its stratigraphic features, the most compre- 
hensive of these being entitled ‘‘Three Formations of the Middle 
Atlantic Slope.”’? 
During this same period Professor P. R. Uhler,3 of Baltimore, 
investigated the relations of the Potomac deposits in the 
Patapsco basin of central Maryland and proposed the division of 
these basal deposits into a lower member which he called the 
”) 
‘‘Baltimorean,” and an upper member which was designated the 
“Albirupean.” In later publications+ the term Potomac was 
accepted as the equivalent of the Baltimorean, and the ‘“‘Alter- 
*Rept. Health Officer, Dist. Columbia 1884-5 (1886), p. 20. 
? Amer. Jour. Sci., 3d ser. Vol. XXXV, 1888, pp. 120-143. 
3Proc. Amer. Phil. Soc., Vol. XXV, 1888, pp. 42-53. 
4Md. Acad. Sci., Vol. I, 1892, pp. 185-202. 
