12 THE POTOMAC OE YOUNGER MESOZOIC FLORA. 



material of the layer, but now many of them have weathered out, so that 

 the clay is very porous and is full of the cavities left by them. Most 

 of these fragments are coniferous, and many belong to the species of 

 Frcndopsis which is found only here. This stratum has yielded a number 

 of interesting plants. We find in it the following, among other less note- 

 worthy forms: Baieropsis {B. lyluripartita minor), WiUiamsonia, Diodnitcs, 

 Pachi/phjjUum, and Frendopsis parccramosa. 



Some portions of the material under this layer show a tendency to 

 lamination ; and here occurs a different group of plants, but the}' are scat- 

 tered so irregularly that one can never tell where they may be found. Here 

 is the largest form of Baieropsis seen at Dutch Gap, viz., B.pihiripartita, and 

 various coniferous twigs and cones, as well as several ferns. In one part 

 of the bluff a log was seen silicified in one portion and changed to lignite 

 in another. The locality will be referred to in the description of species as 

 "Entrance of Trent's Reach." 



Plant-impressions occur in both banks of Dutch Gap Canal. This 

 canal is only about one hundred yards long. The banks are layers of sand 

 and clay irregularly intermixed, and varying much in thickness. The clay 

 is in both forms, the disturbed and the undisturbed; the latter containing 

 most of the impressions. It has both of the characteristic colors, the gray 

 and the reddish. In most of the bank the clay occurs in masses and pockets 

 of variable thickness, apparently replacing portions of the sand. In one_ 

 portion of the right bank thin layers of dark gray clay and sand are inter- 

 stratified. These clay layers sometimes contain very large impressions of 

 Diodnitcs Buchianus, which are over a foot in length, indicating that the leaf 

 must have been in some cases a yard long. This material is so fragile that 

 it was impossible to get out specimens nearly as large as they showed them- 

 selves to be as they lay in the clay. When Diodnitcs Buchianus is abundant, 

 as it is here in places, very few other plants are found. The plants occur 

 irregularly in the sides of the canal and apparently in small pockets in the 

 clay. The greater portion of the material is entirely free from them. 

 Diodnitcs Buchianus and a few ferns, with some conifers, especially of the 

 Sphcnolepidium and Sequoia types, are the most common forms in the general 

 mass of the clay. 



