354 MESOZOIC FLORAS OF UNITED STATES. 



the formation just described, but in their absence, which is usual m the river valleys, 

 this deposit rests immediately on the broken and denuded surface of the Secondary, 

 and by the intermixture of materials makes it more difficult to discriminate between 

 them. 



Excellent opportunities for observing the contact of the superficial deposit with 

 the denuded and much older formation below are presented in the neighborhood 

 of Washington, among which may be specially mentioned the vertical cut at the 

 extremity of Sixteenth street, at the base of the hill occupied by Columbian College, 

 and also the continuation of Fourteenth street, ascending the same hill. At the 

 former locality the crumbling felspathic sandstone, or slightly adhering sand, is 

 exposed to a height of about 35 feet, with a very gentle eastern dip, and having 

 the color, composition, and diagonal bedding characteristic of the Fredericksburg 

 and Aquia Creek sandstone. The gravel and cobblestone deposit lying upon it 

 descends with the slope of the hill to the general plain below, resting at a somewhat 

 steep angle against the denuded edges of the underlying beds. From this and other 

 localities it becomes obvious that the latter formation has been deeply and exten- 

 sively denuded before and during the deposition of the surface strata, which form 

 the chief subject of this communication. (See pp. 104-105.) 



Professor Fontaine must have commenced his investigations in the 

 Mesozoic of Virginia at about this time, for in his first important series 

 of papers'" on the subject he says: 



In this paper I present a summary of the results attained b}^ a series of examina- 

 tions made in the Mesozoic strata of Virginia. These examinations have occupied 

 the larger portion of my summer vacations for several years. (See p. 25.) 



In this paper he deals with both the Older and the Younger Mesozoic. 

 In the first paper of this series'* brief mention is made of the discussion 

 of the former of these beds and its relation to the author's monograph 

 on the flora of that epoch, which appeared four years later. It bore a 

 similar relation to his Younger Mesozoic Flora, except that his materials 

 were not yet so fully in hand, and much was done by him before that 

 work was begun. But the general relations of these two epochs to each 

 other were set forth in this paper and the differences not only in their 

 geographical position but also in their lithological character were clearly 

 pointed out. Considerable was also said of the flora. He divided the 

 beds into two "b ts," the "Fredericksburg belt" and the "Petersburg 

 belt," the former corresponding stratigraphically as well as geographically 



« Notes on the Mesozoic of Virginia, by Wm. M. Fontai-ne: Am. .Journ. Sci., 3d ser., Vol. XVII, January, 

 1879, pp. 25-39; February, 1879, pp. 151-157; March, 1879, pp. 229-239. Reprint, pp. 25-55. 

 b Twentieth Ann. Rep. U. S. Geol. Surv., Pt. II, 1900, p. 260. 



