POTOMAC FORMATION IN VIRGINIA AND MARYLAND. 593 



and there is nothing left but to examine the evidence of the fossil plants 

 which is marshaled in Professor Fontaine's report on the collections that 

 these authors have themselves chiefly made. It is scarcel)^ necessary to 

 say that the comparison can not be confined to the data of this table alone, 

 for the collections made from the Virginia beds since the appearance of 

 Monograph XV are too small. The comparisons must he made with the 

 entire Potomac flora of Virginia, published and unpublished. The collec- 

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

 tive. Those from Arhngton, Langdon, Vinegar Hill, Federal Hill, and 

 the new reservoir are quite as full as those from many of the original 

 Virginia localities. 



Of the 176 species of the table 100 occur in the beds of the District of 

 Columbia or of Maryland other than Rosiers Bluff, the other 76 being con- 

 fined to Virginia localities and to Rosiers Bluff. We have therefore at 

 present to do only with the 100 species. Of these, 76 are also found in the 

 Rappahannock beds of Virginia. To make up the other 24 we have 12 

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

 that were formerh^ confined to the Brooke horizon in Virginia. Of the 

 new species and those that have never been found in Virginia I shall 

 speak later on. Two species, Glyptostrobus {Taxodium) brookensis and 

 Sphenolepidiuvi virginicum, which were not known to occur in the Rappa- 

 hannock beds of Virginia 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. Glyptostrobiis brookensis is also abundant in the 

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

 fined to the Brooke beds of Virginia are (1) Glyptostrobus ramosus%, now 

 found in the dump of the mines at Hanover, (2) Menispermites virginiensis, 

 found at the Bewley estate and Federal Hill and also common in the Mount 

 Vernon beds, and (3) the ament 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 found 

 in the Rappahannock and Mount Vernon beds of Virginia. Their occur- 

 rence in the Brooke beds also only serves 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 Bibbins is therefore 

 practically identical with that of the James River and Rappahannock 



MON XLVIII — 05 38 



