SPRATIGRAPAY OF THE. POTOMAC GROUP 501 
The Patapsco and Raritan formations have afforded no 
animal remains which are of determinative value; the fossil 
plants all point strongly to the lower Cretaceous age of the 
beds. So large an amount of evidence has been brought for- 
ward in support of this view by Professors Ward, Fontaine and 
Newberry, that the authors have no hesitancy in accepting their 
_conclusions, and these two formations are therefore placed in the 
Cretaceous. 
THE TAXONOMIC VIEWS OF OTHER WRITERS. 
The earlier writers did not differentiate the Mesozoic deposits 
of the middle Atlantic slope into independent formations. For 
many years the basal clays and sands, which border the crystal- 
line rocks of the Piedmont Plateau on the east, were considered 
the eastern equivalent of the red sandstones and shales with 
their enclosed coals farther west. 
Professor W. B. Rogers, state geologist of Virginia, first 
sharply differentiated the eastern deposits from the western, and 
described the former under the name of the ‘‘Upper Second- 
any. in his state report. In later articles Professor Rogers 
refers these deposits ‘‘at least in part to the horizon of the 
Upper Jurassic. Possibly we may find here a passage group 
analogous to the Wealden of British Geology.”* On his geo- 
logical map of the Virginias, and in his more recent publications, 
the deposits of the Potomac group are referred to as the 
‘‘Jurasso-Cretaceous.”’ 
In the reports of Professor J. T. Ducatel, who was state 
geologist of Maryland between the years 1834 and 1841, com- 
paratively little attention was given to the clays and sands at 
the base of the Coastal Plain series, and neither their strati- 
graphic nor taxonomic position was clearly defined. The 
reéstablishment of official geological work in Maryland by 
Philip T. Tyson,3 who, as state agricultural chemist, published 
*Geology of the Virginias. Report of 1840, p. 438. 
? Geology of the Virginias, p. 712. 
3First Rept. State. Agri. Chem., 1860, pp. 41-43. 
