PO'I'OMAC FORMATION IN \Ii;(.INiA AND MARYLAND. 593 



and there is iiothinji; left l)ut to examine the evidence of the fossil plants 

 whicli is marshaled in Professor P'ontaine's report on the collections that 

 these authors have themselves chiefly made. It is scai-cely necessary to 

 say thai l he (■omj)ai'ison can not he confined to the data of this tahle alone, 

 for the collections made from the Virginia beds since lh<' appearance of 

 Monoo;raph X\' are too small. The comparisons must he made with the 

 entire Potomac flora of \'ir<;inia, pul)lished and unpublished. The collec- 

 tions ftom the Maryland localities may be regarded as fairly representa- 

 tive. Thos(> from .\rlington, Langdoii. \incgai' Hill, Federal Hill, and 

 the new reservoir ai'e ([uite as full as those from many of the original 

 \'irginia localiti(>s. 



Of the ]7() .sj)ecies of the table 100 occur in the beds of the District of 

 Cohimbia or of ]\hiryland other than Hosiers IMuff, the other 70 being con- 

 fined to \'irginia localities and to Hosiers Bluff. Wo have therefore at 

 present to do only with the 100 species. Of these, 7(5 are also found in the 

 Rappahannock beds of Virginia. To make u]) the other 24 w(> ha\-e 12 

 new species. 9 that were previously known only from Federal Hill and 3 

 that were formerly confined to the Brooke horizon in \'ii-ginia. Of the 

 new species and those that have never l)een found in \'ii-ginia 1 shall 

 speak later on. Two species, Ghjptostrohus {Taxodium) hrookensis and 

 Sphenoh /n'diioti n'rginicimi, which were not known to occur in the Rappa- 

 hannock beds of Mrginia at the date of the appearance of Monograph XV, 

 have now been found there, the first at Cockpit Point and Lorton and the 

 second at Cockpit Point. Ghjptostrnhu!^ hwokcnsis is also abundant in the 

 Mount Vernon beds. The three species oi- forms that were formerly con- 

 fined to the Brooke beds of \'irginia are (1) Glypfostrobus ramosusl, now 

 found in the dump of the mines at Hanover, (2) Men is/wriH ites virginiensis, 

 fountl at the Bewley estate and Federal Hill and also common in t he Mount 

 \'ei'non beds, and (.3) the anient of a conifer (b), rediscovered at Federal 

 Hill. Their diagnostic value can not be said to be great. 



It thus appears that practically all except the new species are foimd 

 in the Rappahannock and Mount \'ernon beds of Virginia. Their occur- 

 rence in th(> Brooke beds also only s(>rves to give them a somewhat more 

 modern aspect. The flora of the Maryland beds referred to the Patuxent, 

 Arundel, and Patapsco formations of Clark and Bibl)ins is therefore 

 practically itlentical with that of the James River and Rappahannock 



MON XLVIII — 05— — 38 



