412 



MESOZOIC FLORAS OF UNITED STATES. 



of Maryland, and nearly all from that section of the Potomac belt which 

 lies between the city of Baltimore and the District of Columbia. 



The width of that zone of the Potomac belt which includes the sup- 

 posed original sources is about 10 miles, the vertical range being from 

 tide level up to 300 feet. 



The following table shows the taxonomy of the Potomac group, as well 

 as the relations of its deposits to the subjacent and superjacent terranes, 

 according to the usage of the Maryland Geological Survey. The accom- 

 panying map and sections published by this Survey, PL LXXX, shows the 

 distribution of the formations of the Potomac group in Maryland and their 

 stratigraphic relations. The principal localities for fossils have been 

 added. For a full discussion of the taxonomy of the Potomac beds 

 employed in this paper, together with its correlation with other taxono- 

 mies, the reader is referred to the paper cited on p. 520 above. 



Table shovnng the relations of the formatioixs of the Potomac group to subjacent and superjacent terranes. 



Raritan Lower Cretaceous Estuarine. 



Patapsco Lower Cretaceous. Estuarine. 



Arundel.. Upper Jurassic Estuarine?. 



Patuxent ! Upper Jurassic. . . 



Newark" Triassic 



Algonkian . 



Estuarine? 



Estuarine and ig- 

 neous. 



Pre-Cambrian. 



Metamorphie, sedi- 

 mentary, and ig- 

 neous. 



Sands and clays. 



Clays and sands. 



Clays. 



Sands and clays. 



Red sandstone, lime- 

 stone, breccia, shale, 

 and trap. 



Crystalline rocks. 



a The Newark is usually wanting in tlie section, and the overlying formations frequently so. When the latter are 

 present only one or two commonly occur at the same time to the landward, while to the seaward there may be several. 



Only one of the Potomac cycad trunks (W. C, B., No. 1481) is posi- 

 tively claimed to have been seen in situ, its alleged bed being a compact 

 argillaceous sand near the sunamit of the Patuxent terrane. With a few 



