PLANT LOCALITIES. 11 



A little farther down the river the top of the Potomac formation shows 

 itself undisturbed, rising' two or ttn-ee feet above low tide. It is a dark tena- 

 cious clay, full of small fragments of plants. The Eocene greensand marl 

 rests upon it. About two hundred yards distant, in the bottom of the ravine 

 cut by tlie creek, the Potomac shows itself again undisturbed, but here oidy 

 sand ajjpears The spot affording the plant-impressions seems to be one of 

 the erosion horizons so common in the top of the Potomac, This locality 

 will be referred to as " Deep Bottom." 



The next plant-bearing locality met with in ascending the river is at 

 the lower entrance of Trent's Reach. Trent's Reach is the great bend in the 

 James River to avoid which the Dutch Gap Canal was cut. The exposures 

 of the Potomac strata in this reach are extensive, but none of them are note- 

 worthy as yielding plants, except a bluff in the river bank diagonally op- 

 posite the lower end of the canal, and on the south side of the river. The 

 spot may be located by its showing the first high bank seen on entering 

 Trent's Reach. At this place a spring branch enters the river near the 

 ruins of a small wharf The bank immediately at and below the wharf 

 contains ten to fifteen feet of the chocolate Potomac clay, but this material, 

 though highly favorable for the preservation of plant-impressions, revealed 

 none. 



The high baidc extends thirty or forty yards above the mouth of the 

 branch, l)ut the material composing it changes considerably, becoming an 

 irregular mixture of sand and clay. This portion of the bank has such 

 sudden and irregular changes of structure and material as to defy descrip- 

 tion. Most of the impressions were found aliout fifteen yards above the 

 mouth of the branch. They occur at different horizons in the bluff and so 

 irregularly that no description can serve as a guide for finding them. 'I'hey 

 may be looked for in the highest part of the Potomac, which shows about 

 fifteen feet of material, and is capped by Quaternary. 



The upper portion for the thickness of three or four feet shows occa- 

 sionally good impressions. The uppermost portion is quite argillaceous," in 

 a layer four to six inches thick. This has a brownish color and contains au 

 immense number of fragments of plants, with now and then good impres- 

 sions. The fragments seem originally to have made up a large part of the 



