FLORA OF OLDER POTOMAC FORMATION. 397 



owner of the land contemplated working the swamp for nuggets of ore. 

 If the Potomac River had not cut away the deposits for the space of 10 or 

 15 miles it would probably have been possible to follow the transition from 

 the light-colored indurated sands to the ferruginous sands of the same age 

 and type without any abrupt change from the one to the other. And now 

 that the Arundel has yielded a considerable flora consisting almost wholly 

 of Rappahannock species, there is no longer any question of the practical 

 identity in age of the Virginia and Maryland beds. The Patuxent repre- 

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

 Arundel consists of the lignite beds that are included in the latter. 

 The Patapsco formation is thus defined : 



The deposits of the Patapsco formation consist chiefly of highly colored and 

 variegated clays which grade over into lighter colored sands and clays, while sandy 

 lenses of coarser materials are sometimes interstratified, which are occasionally 

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

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

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

 and "red ore" also occasionally occur. The sands sometimes contain much decom- 

 posed feldspar, and rounded lumps of clay are also found. The sands are frequently 

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

 as the highly ferruginous clays are termed, are found at many points, usually near 

 the base of the formation. 



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

 relate the two formations already considered. I 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 member" 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 referred to the Patapsco, 

 that there is scarcely any difference between the flora of the Patapsco 

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



