DESCRIPTION OF THE SPECIES. 183 



plurijyartita, Brachijphijllum, Fremlopsis parccmmosa, etc. In the riglit bank 

 of Dutcli Gap Canal, in the tliin partings of dark gray clay, interstratified 

 with sandy layers, very large impressions occur and the fossils are very 

 numerous. They seem to occur irregularly distributed and in pockets. 

 Some of the imprints seen lying in the clay were 12 to 18 inches long and 

 as wide, but owing to the brittleness of the rock they were much broken 

 in taking them out. At a spot about 200 yards above tlie fishing-hut at 

 Dutch Gap, where hardly any other fossil occurs, the leaves of this plant 

 are so abundant as to till the clay for the thickness of a foot or more. It 

 is a curious fact that at this point, and at several localities north of Fred- 

 ericksburg, if the remains of this plant occur in great numbers in the 

 clay, they seem to exclude others. The distribution is apparently some- 

 what peculiar. On leaving James River not a trace of the plant is to be 

 seen until Kankey's place is reached. Here immense numbers of the 

 leaves occur in the dark clay with hardly any other plants. None were 

 found at Fredericksburg, and as the amount of material obtained there 

 was large, we may safely assume that it did not exist at that locality. It 

 occurs as the principal fossil in the cut where tlie railroad crosses the 

 Ocooquan. It is abundant near Telegraph Station, but only fragments 

 occur at White House and at Fort Washington. It has not been cer- 

 tainly identified north of Fort Washington. Some small bits of leaves 

 found at Baltimore, on Belt and Covington streets, seem to belong to this 

 species, but they can not be certainly identified. It was indicated by 

 fragments found in the excavation for the reservoir at Washington. 



Ettiiigshausen, in his Beitrag zur Flora der Wealden Periode, de- 

 scribed this plant under the name PtcrophiiJlum Duchkmum, as occurring 

 in the Wernsdorf strata of the northern Carpathians, considering these 

 as of Wealden age. He gives a figure of a fragment belonging, as he 

 thought, to a cycad leaf three or four feet long. Schenk (Die foss. Pflan- 

 zen der Wernsdorf-Schichten) shows that these strata, according to the 

 investigations of Hohenegger and Zittel, are not Wealden but Urgonian 

 in age, younger than the oldest Neocomian, and older than the Gault. It 

 is very fortunate that the Potomac formation has yielded so many fiiK^ 

 specimens of this plant, as they add a good deal to our knowledge of it. 



