as to the Age of the Potomac Formation. 125 



plants that have near relatives in that deposit. The Urgonian 

 therefore furnishes six identical and sixteen allied species. 



Gault. — The Cretaceous deposit at Cape Staratschin, in 

 Spitzbergen, which has been referred to the Gault, contains 

 two of the species that have been enumerated as occurring in 

 the Kome beds and also in the Potomac formation, and also 

 two other species which resemble Potomac plants. 



Cenomanian. — The rich Cretaceous flora of Atane, Green- 

 land, so carefully worked up by Heer and correlated with the 

 Cenomanian of Europe, furnishes six species which have been 

 detected in Potomac strata, but all but three of these, Pecop- 

 teris socialis Heer, Aspidium Oerstedi Heer, and Sequoia 

 ambigua Heer, have already been enumerated from the Kome 

 beds through which they extend up into those of Atane. The 

 number of additional species with which there are related 

 Potomac forms amounts to nine, but the relationships are in 

 some cases quite distant. 



The Cenomanian of Bohemia and Moravia has 1 identical 

 and 6 allied species, and that of Saxony (Niederschona) 2 

 identical and 3 allied, but one of the identical species is the 

 same in both and has a wide range, while the other also occurs 

 in the Wernsdorf beds. 



We thus have for the Cenomanian 7 identical and 23 allied 

 species. 



Dakota Group. — In the Dakota Group, which should prob- 

 ably also have been classed as Cenomanian, only two plants 

 occur which are also found in the Potomac formation, and 

 both of these are found in other localities, one of them having 

 a very wide range and distribution. The Potomac Dicotyle- 

 dons are all specifically, and nearly all generically, distinct 

 from those of the Dakota Group, but ten species are compared 

 and may be related to Dakota forms. 



Senonian. — Under this designation I have grouped the 

 upper Cretaceous beds of Patoot, Greenland, of the Peace and 

 Pine River district of the British Northwest Territory, of 

 Quedlinburg in the Harz, the Gosau beds of Tyrol, the West- 

 phalian beds, so well worked by Hosius and Yon der Marck, 

 and the sands of Aix-la-Chapelle. The same species recur 

 largely in these beds, Sequoia Peichenbachi being found in 

 them all. Five species are common to the Potomac formation 

 and one or more to these localities, but all of these are found 

 in older strata. Nine Potomac plants are also compared and 

 perhaps related to Senonian species. 



Laramie Group. — Only one species, the widespread Sequoia 

 Peichenbachi, is common to the Potomac formation and Lar- 

 amie group, and no further comparisons are made. 



Eocene. — The two comparisons made with Eocene plants, 

 viz : Araucaria podocarpoides with Podocarpus incerta Ett. 



