FLORA OF OLDER POTOMAC FORMATION. 375 



at Fayetteville and for some distance above and below belong to the 

 lower division (see p. 390). 



In Professor Uhler's Albirupean Studies," 1892, he makes the clear- 

 est distinction thus far drawn between the upper and lower beds of what 

 is now included in the Potomac formation, and he insists upon their 

 stratigraphical unconformity. His description of the beds in Maryland 

 and New Jersey is clear and not open to serious criticism, but his dis- 

 cussion of the Virginia deposits is somewhat ambiguous and led some 

 to think that he intended to include the freestone in his All^irupean. 

 To enable anyone to judge for himself his own^words should be quoted. 

 They are as follows: 



My own studies of the deposits at Fredericksburg, Va., and other places between 

 that city and Mount Vernon, induce me to take a very different view from Professor 

 Fontaine of the structure of the region, and of the position held by the fossil plants 

 in the order of their succession in time. 



The following facts have influenced my belief in the theory of succession of the 

 strata or beds and their contents. The lowest iron-ore clays, at the base of which 

 the most archaic types of Angiosperms occur, are those beneath Federal Hill and 

 its connections in Baltimore. The same series of clays is identifiable in many places 

 all the way from near the North East River, at the head of Chesapeake Bay, to the 

 District of Columbia. Local.areas of similar clays which have not yet yielded their 

 characteristic plant fossils occur in Virginia, west of the Potomac River. Near 

 Falmouth and at at a few points between that place and Fredericksburg, Va., are 

 clays of the same plastic type and structure as those in Federal Hill. 



They do not agree in composition and structure with the hollow or lens in the 

 streets of Fredericksburg, from which Professor Fontaine and myself excavated 

 so many fossil leaves, twigs, etc. 



The Fredericksburg deposit is, to my view, a structure built at a much later 

 date than the Falmouth clays, and the series of strata to which it belongs has been 

 built within an eroded area. The sandstone member of the Aquia Creek region, as 

 seen below Fredericksburg and everywhere else in Maryland and Virginia, is a whole 

 formation higher than the aforesaid claj's. * * * 



The Albirupean appears, and extends at least from the border of the Triassic 

 region, north of Raritan Bay, across New Jersey, Delaware, and Maryland to below 

 Fredericksburg, Va. (see pp. 193-194, 199). 



It is true, as already shown, that the Aquia Creek or Brooke plant- 

 bearing beds are above the Fredericksburg beds, and the freestone, 

 which occurs at the railroad bridge across Aquia Creek, may be seen 



" Albirupean studies, by P. R. Uhler: Trans. Maryland Acad. Sci., Vol. I, June S, 1892, pp. 185-201. 



