PLANT LOCALITIES. 19 



made, it ])re.sent.s the features of a true jet. The fracture is couchoidal, 

 resiuous, and deep bhiok in color The only leaf-iuipression seen in the 

 clay containing- this hgnite was a well-marked imprint of Sclcrojitcris clliptira. 



The next locality yielding- plant-impressions found in going north is in 

 the vicinity of Brooke station. The localities on Potomac Run are near 

 the western edge of the Potomac area. Brooke station is on the eastern 

 edge. The area in this region is about four miles wide. Brooke station 

 is on the Atlantic Coast Line Railroad, nine miles north of Fredericks- 

 burg. In the vicinity of Brooke the contact of the Eocene with the Poto- 

 mac may be seen. The cuttings for the railroad give the exposures here of 

 the plant-bearing beds. Two localities in this vicinity, a short distance 

 apart, have been found to yield plant-impressions. One of these occurs in 

 a cut on the railroad at the 72d mile-post from Richmond, and the other 

 about one-fourth of a mile farther north and near the railroad crossing over 

 Ac(piia Creek. The Potomac formation exposed at these two places shows 

 marked lithologic ditferences, aiul a diversity in the plants is also found. 



The cut on the railroad which exposes the fossiliferous material begins 

 at the mile-post and extends for some distance down the railroad to the 

 north. The Potomac here has resting- upon it a thin layer of Eocene, which 

 in two places thickens up by di[)pi)ig and cutting out the Potomac below 

 the level of the track. This thickening- takes place in two narrow bands, 

 which represent two pre-Eocene ravines cut out of the Potomac. They 

 run in a northwest and southeast direction, very nearl}- in accordance with 

 the direction of the present minor streams of the region. The Potomac ma- 

 terial is very irregular in structure and compo.sition. It is composed in the 

 main of sand, with tlic usual \ai-ying character and current-bedded struct- 

 ure, in which is found clay irregidarly arranged. The clay that contains 

 plant-imiiressions is mostly disturbed and deposited in pockets and rude 

 layers which have no detinitu course, and in which the clay is much mixed 

 with sand, ali'ected with slickensides, and confusedly cemented together 

 by pressure. ]\Iost of the plants seem to have been caught between the 

 particles of cla}^ as they were pressed together, hence it is dilhcult to get 

 out good specimens; but in one portion of the side of the cut, on the left 

 facing north, a thin irregular stratum was formed by the deposition of fine 



