20 THE rOTOMAC OR YOUNGER MESOZOIC FLORA. 



clay. Tliis possessed some regiilarit}^ of structure and was cleavable. It 

 afforded a number of interesting- plants beautifully preserved. Unfortu- 

 nately the amount was very limited and th(5 stratum was worked out. 

 As most of the clay here is lumpy and confusedly thrown togetlier in 

 particles of some size, the plants, although quite numerous in species, are 

 generally very fragmentary. The S2)ecimens occur mostly a few yards 

 north of the mile-post, the best being obtained on the left hand looking 

 north. 



This locality is remarkable for the large number of species of dicoty- 

 ledons and conifers found, and also for the number of plants occurring 

 nowhere else. Most of the conifers and dicotyledons have apparently a 

 more recent character than the predominant plants found at the more south- 

 ern localities ; but the identity in mode of occurrence, and the number of 

 connecting links seen in the plants here, indicate that the flora of this locality 

 is not essentially different in age from that of the rest of the Potomac. This 

 spot will be designated as " 72d mile-post," near Brooke. The fossils at 

 this place give us another illustration of the localization of many of the 

 Potomac plants. 



As stated, the number of species occurring here is large, and several 

 of these are very abundant. Nearly all are wanting at the locality })res- 

 ently to be described, while some of the most common of the species at the 

 latter are wanting near the mile-post. 



Going down the railroad about one-fourth of a mile in a northerly 

 direction, on the right hand side where a creek crosses the road, we find a 

 considerable area from which the earth has been removed to make a " fill." 

 This has caused an abrupt bank to be left about fifty yards from the rail- 

 road. Most of this bank is composed of the current-bedded Potomac sand, 

 but in the top of the bank is a stratum of gray shale about eight feet thick. 

 This is undisturbed material, .and shows distinct stratification. Portions of 

 it are sandy and coarse, but a number of thin layers are composed of fine 

 clay, and abound in plant-impressions ; which, however, all belong to a very 

 few species. Most of the impressions occur near the top. By far tlie most 

 abundant of the impressions ai-e tliose of Sapindopsis, which also abound at 

 the 72d mile-post The locality has been very thoroughly explored, and 



