FLORA OF OLDER POTOMAr FOR^L\TTO\. :]97 



ownei' of the land coiitcinplattMl woi-kin^ the swamp for luig^ots of ofo. 

 If the Potomac Rivrr liad not cut awa>' th(> deposits foi' the s{iace of 10 or 

 15 miles it would pi-ol)al)ly have been possible to follow ihe transition fioiu 

 the light-colored indurated sands to the fen-usjinous sands of the same ajje 

 and type without any al)rupt change from the one to the other. And now 

 that the Ai'undel has yielded a considerable flora consisting almost whollv 

 of Rappahannock species, there is no longer any (|uestion of the pi-actical 

 identity in age of the \'ii'ginia and Maryland beds. The Patuxent repr(>- 

 sents the regularly stratified sands and clays of the Older Potomac, and the 

 Arundel consists of the lignite beds that are included in the latt(M-. 

 The Patapsco formation is thus defined: 



The deposits of the Patai).sci) formation con.sist cliielly of iiiirhly colored and 

 variegated clays which grade over into lighten- colored .sands and clays, while sandy 

 Ien.ses of coarser materials are sometimes interstratified, which are occasionally 

 indurated and at. times form " pii)e ore." The clays are in places dark colored, 

 massive, and more or less lignitic. At times they are laminated ("slaty") and 

 bear large nunihers of leaf impressions. Fossiliferous flakes and nodules of " white" 

 and "red ore" alst) occasionally occur. The sands sometimes contam much decom- 

 I)osed feldspar, and rounded lumps of clay are also found. The sands are frequentiv 

 cross-bedded and give evidence of rapid deposition. Workable beds of " paint rock," 

 as the highly ferruginous clays are termeil, are found at many jjoints, usually near 

 the base of the formation. 



It is more difficult to correlate tliis with Virginia beds than it is to'cor- 

 relate the two formations already considered. 1 was of course wrong in 

 supposing that the iron-ore clays extended to the top of these beds, but I 

 was influenced by the view so long held by nearly everybody that the 

 Maryland beds in general constituted an "upper clay member" higher 

 than the "lower sandstone memlier" of Virginia. I had, however, dis- 

 covered that the Older Potomac "flanks it for its whole length" through 

 the State of Maryland. I stated positively that the white ore, or steel ore, 

 was found in the Rappahannock series, but I supposed that the brown ore 

 was higher. As no plants except cycads had been found in either at that 

 time, the age could not be determined by paleontological evidence. 



It now appears from Professor Fontaine's report on the fossil 

 plants, many of which were found in beds referi'ed to the Patap.sco, 

 that there is scarcely any tlitference l)et\veen the flora of the Patapsco 

 and that of the Arundel, and that both belong to the Rappahaimock 



