March 12, 1897.] 



SCIENCE. 



415 



very small ; generally only one or two. 

 Very few individuals of the species are met 

 with, and they are usually local in occur- 

 rence. The species are nearly or quite all 

 peculiar to the Potomac. 



" There is an important Wealden element in 

 the flora. Many species of Potomac plants 

 are identical loitli species found in the Wealden 

 of Europe, and this is the oldest hnoimi fossil 

 flora that gives any considerable number of plants 

 identical with the Potomac species. Some of 

 these species of the European Wealden are 

 abundant and widely diffused plants in the 

 Potomac. But while the species common 

 to the European Wealden and the Potomac 

 are noteworthy, there is a still larger num- 

 ber of important species found in the Poto- 

 mac which are so neai'ly allied to Wealden 

 species that they are with difi&culty distin- 

 guished from them. These, although re- 

 garded as new species peculiar to the Vo- 

 tomSiC, are probably forms representing Wealden 

 species, being modified by differences of en- 

 vironment. 



" The Jurassic and the Wealden elements 

 combine to give a Jurassic or Mesozoic 

 facies to the flora, and hence, so far as they 

 go, give it a comparatively ancient charac- 

 ter. The Jurassic or Mesozoic type of flora 

 is, as is known, characterized by the over- 

 whelming predominance of four elements, 

 viz: Equiseta, ferns, cycads, and conifers, 

 and by the absence of angiosperms.* 



" The formations which possess the largest num- 

 ber of species identical ivith those of the Potomac 

 are those of the Middle Neocomian or Urgonian. 

 The strata of this age which occur in 

 Greenland (in Kome and other localities) 

 and the Wernsdorf beds of the northern 

 Carpathians yield an Urgonian flora, which 



* Both Professor Fontaine and Dr. Newberry use 

 the old botanical classification which made the 

 'Angiosperms' synonymous with the Dicotyledons. 

 It amounts to about the same thing here, however, 

 on account of the almost complete absence of Mono- 

 cotyledons in these floras. 



Heer and Schenk have described. In the 

 plants coming from these regions we find the 

 largest number of forms identical with Potomac 

 species. The number of Potomac species 

 nearly allied to Urgonian forms is still 

 larger. These identical and nearly allied 

 species include many of the most charac- 

 teristic, abundant, and widely diffused spe- 

 cies of the Potomac. If we are to deter- 

 mine the age by the largest number of 

 important species identical with those of 

 known fossil floras, then we ivould xvithout 

 hesitation set it down as ranging from the Lower 

 through the Middle Neocomian. A very large 

 and important element of the Potomac 

 flora is peculiar to this series. In this we 

 find without doubt the most abundant, 

 characteristic, and widely diffused species. 

 As these are new, they can not give any 

 direct evidence concerning the age of the 

 formation, but indirectly the existence of 

 such a large proportion of peculiar forms 

 is favorable to the assumption that the age 

 is Neocomian. The flora of this formation 

 is one of the least known, and any large 

 collection of richly fossiliferous material 

 from beds of Neocomian age could not fail 

 to furnish a great number of new species. 

 " Then again, the relatively great develop- 

 ment of the conifers, along with the existence 

 of an impoi'tant cycadaceous element, points 

 strongly to the Neocomian as the era of the forma- 

 tion. The survival of a considerable Ju- 

 rassic element in the flora also indicates that 

 it can hardly be younger than Neocomian. 

 While much the most important elements 

 of the flora indicate an age not more recent 

 than the Urgonian or Middle Neocomian, 

 there are some species which point to a 

 more recent era of deposition for the forma- 

 tion. There are one or two species which 

 are probably identical with forms found by 

 Heer in the Cenomanian beds of Greenland. 

 These are local and are represented by very 

 few individuals. A few of the species also 

 may be considered as nearly allied to some 



