378 MESOZOIC FLORAS OF UNITED STATES. 



State of Maryland and was found at hundreds of exposures from Wash- 

 ington, 'D. C, to Wilmington, Del. Farther north. the basal clays often 

 assume a lilac hue, but do not otherwise differ from the purer (non- 

 lignitic) basal clays of Virginia. 



On the opposite or coastward side of the Potomac belt the con- 

 ditions in Maryland are very different from those of Virginia. Here, 

 ever^'where northeast of the Potomac River, there are heavy beds more 

 recent than Siuy of the Potomac beds of Virginia holding the higher 

 t3'pes of dicotjdedonous plants similar to those of the Amboj^ clays. 

 These beds alwaj'-s underlie the marine Cretaceous deposits (Severn^ 

 Matawan), or Tertiary (Pamunkey, Chesapeake), and usually rest on 

 variegated clays. As the consideration of these upper beds, which I 

 Call the Newer Potomac, and which are probably to be correlated with 

 the plastic clays or Raritan formation of New Jersey, as well as with 

 the Tuscaloosa formation of the South, is deferred for the present, I 

 will confine myself here to the beds that underlie them and certainly 

 belong to the Older Potomac. 



Between the coarse lithified sands alcove described as the probal^le 

 homologue of the Rappahannock freestone and the higher beds last 

 mentioned there occur in Marjdand a series of beds which can not be 

 compared lithologicall}^ with anything found in Virginia, and as at that 

 time (1892) no fossil plants except silicified wood, lignite, and cycacl 

 trunks had been found in them it was difficult to correlate them. Thev 

 contain below iron-stained clays and sands, iron ore, both white and 

 red, pockets of lignite, and some sand and gravel, and above variegated 

 clays of all shades and descriptions, interstratified with fine sand, and 

 have a thickness of some 300 feet. At Federal Hill in Baltimore a more 

 complete exposure of most of the Potomac beds of Maryland could be 

 worked out from the various clay pits there than is to be found at any 

 other point, and the section here was carefully made and has been pub- 

 lished. Most of the plants taken from this locality were regarded b}' 

 Professor Fontaine as representing his Brooke flora and coming from 

 the upper part of the Older Potomac, but after examining the later 

 collections made there in the light of other collections from Maryland 

 he has now changed his mind and refers all the Federal Hill l^eds to the 

 Rappahannock series. 



