10 THE POTOMAC OR YOCTNGER MESOZOIC FLORA. 



been seen in it. The fossils found in tlie Petersburg area were all obtained 

 from the banks of the James River below Richmond. 



PLANT LOCALITIES. 



Deep Bottom is the locality farthest down the James River where 

 plant-impressions have been found, and here the Potomac disappears from 

 view. The spot is about four miles below the Dutch Grap Canal, being 

 located in a sharp bend of the river near a group of huts A small creek 

 enters here after having cut a deep ravine through all the formations down 

 to the top of the Potomac. At this spot the river bank is composed of Qua- 

 ternary, Eocene marl, and Potomac. In places the Quaternary rests on the 

 Potomac, but usually the Eocene bed intervenes. Just below the mouth 

 of the small stream above mentioned a thick mass of Quaternary is seen 

 resting on a confused mixture of materials that have the character of the 

 Potomac. 



The greater portion of the exposure of this latter is of a rather argilla- 

 ceous gray sand, that shows all the features so common in the disturbed clay 

 commonly found in the upper part of the Potomac. This material barely 

 rises above high-tide level. The argillaceous sand seems to be derived from 

 the erosion of some stratum which has been torn up and had its fragments 

 confusedl)^ redeposited. It is a structureless mass, made up of particles 

 of various sizes cemented together by pressure. Embedded in this sandy 

 matter We may tind some particles more argillaceous than the main mass, 

 which retain to some extent the structure and cleavage of the original 

 stratum. These furnish occasionally fragments of dicotyledons and other 

 plants of the same sort as those foitnd elsewhere in the Potomac. The gray 

 masses in which the plants are found are of the same general character as 

 the debris in which they are embedded, being simph^ more argillaceous. 

 Associated with these, and inclosed in the confused iTiatrix, we find large 

 rounded masses three or four feet in diameter, of a dark chocolate tenacious 

 clay, which is entirely different from the surrounding sandy matter. This 

 clay has the character of the chocolate clay so common elsewhere in the 

 Potomac formation. Its masses contain plant-impressions similar to those 

 of the gray argillaceous sand, but they are more perfectly preserved. 



