GEOLOGY OF THE MESOZOIC AEEAS. 3 



part, for the sake of distinction, may be called the Hanover Area. South of 

 the Chickahominy, and extending for some distance north and south of James 

 River, lies the main body of this Mesozoic area. As this contains all the 

 workable coal, this portion may be called the Richmond Coal Field. It 

 has afforded nearly all the plants described in this memoir. The following 

 localities, mentioned in the description of the plants, are the most important 

 sources of plant material, and are situated in this part of the area: 



On the west side, near the village of Manakin, situated on the north 

 bank of James River, occur the Dover Mines A deep shaft sunk here for 

 the purpose of exploration, called the Aspinwall Shaft, has in the material 

 taken out afforded some fine plants. Many more, no doubt, might have 

 been obtained if I could have visited this shaft while it was being dug. I 

 did not examine the material taken out until many years afterwards, and 

 most of the impressions had been destroyed. It may be proper to state in 

 this connection that the plants described in this memoir are by no means a 

 measure of the richness of the flora of the beds yielding them. The work 

 of collecting them has been attended with many difficulties. Since about 

 1840 almost no shafting has been done. The coal has been mainly followed 

 by "inclines" from the outcrop, or raised through the old shafts ; conse- 

 quently, now, one must depend for collections chiefly on the old "dumps," 

 and most of the material on these is thoroughly decomposed. In the early 

 working of the coal in this field, as I learn from persons engaged in it, many 

 fine specimens were obtained, most of which are now lost. Prof. William 

 B. Rogers collected some of them, and gave some descriptions, and a few 

 figures, that are referred to in my descriptions of the species. Sir Charles 

 Lyell also obtained some that were described by Bunbury in the Quarterly 

 Journal of the Geological Society. So far as I know, this is all that has 

 been done in the way of figuring and describing these plants. Many of 

 Professor Rogers's plants were not described, and I fear that the best por- 

 tion of his collections has been lost. 



Carbon Hill is another locality that has yielded me some good material. 

 This is situated about six miles north of James River, on the eastern edge 

 of the area. Here I was fortunate enough to find some material that had 

 been taken out of a gangway cut to tap the lower coal bed. The roof 



