FI.OKA OK ()LI>i:i; POTOMAC FORMATION. :> < O 



at I'ayfMlcvillc and for sonic distanco aliovo and Ik'Iow liolong to the 

 lower division (see p. oiK)). 



In Professor filler's All)irupean Studies." 1S«)2, he makes the clear- 

 est distinction thus far drawn l)etween the upper and lower beds of what 

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

 stratifiraphical unconformity. His description of the beds in Maryhind 

 and New .hn'sev is cleai- and not open to serious criticism, hut his dis- 

 cussion of the Virjiinia deposits is somewhat ambiguous and led some 

 to think that he intended to include the freestone in his Albirupean. 

 To enable anyone to judge for himself his own words should l)e (quoted. 

 They are as follows: 



My own sludics of tlic clcposits at Fmlcnckshiirii;, Va., and otlicr places Ix-twccii 

 dial <-it y and Mount Vernon, indu.-e ine to take a very dilVerent view from Professor 

 Foiiiiiine of tlie structure of the region, and of I lie posiiion held l.y the fossil plants 

 in ihe order of their succession in time. 



The followino; facts have iiilhieiieed my helief in the theory of succession of llie 

 strata or l.eds and their cont.-nts. Tlie lowest iron-ore clays, at the base of which 

 the must andiaic ty])es of Angiosperms occur, are tlio.se })eneath Feileral 1 1 ill and 

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

 all the way from near the Nortli East. Kiver, at the head of Chesapeake Bay, lot he 

 District of Columbia. Local ai-eas of similar clays which have not yet yielded their 

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

 Falmouth and at at a lew ])oints between that place and Fredericksl)urg, Va., are 

 clays of the same i)!astic type and structure as those in Federal Hill. 



'i'hey 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 thi' Atpiia Creek region, as 

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

 formation liigher than the aforesaid clays. * * * 



The Albirupean api)ears, and extends at least from the border of the Triassic 

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

 Fredeiicksbnrg, Va. (see pj). 19:5-194, 199). 



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

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

 which (X'ctu's at the railroad bridge across Aquia Creek, may be seen 



" .\ll>ini|)oan .<itii(li..s, by 1'. I!, flil.'r: Tnni^. Marvlancl .\nul. Sri., Vol. I, .Tane S. l.S()2. pp. rs.V2ni. 



