FLORA OF OLDER POTOMAC FORMATION. 353 



the relations of these beds in the States of Virginia, Maryland, Delaware, 

 and New Jersey, and although it was not then known that the more 

 northeasterly outcrops represent a higher phase of the formation, with an 

 entirely different flora, the views here expressed represent the common 

 opinion prior to the investigations of Professor Fontaine, Doctor New- 

 berry, and myself of the floras yielded by these beds. He says: 



In the be]t partially occupied by the surface deposit here referred to there is 

 exposed another group of strata with which, at first view, the sandy and argillaceous 

 layers of this formation might readily be confounded. These are the silicious, 

 argillaceous, and pebbly beds, which, underlj^ing the Tertiary in Virginia, and the 

 well-marked Cretaceous formation farther north, have, in the latter region, been 

 regarded as belonging to the base of the Cretaceous series of the Altantic States. 

 In Virginia the formation consists typically of a rather coarse and sometimes pebbly 

 sandstone, in which the grains of quartz and feldspar are feebly cemented by kaolin, 

 derived from the decomposition of the latter, and of argillaceous and silicious clays 

 variousl}^ colored and more or less charged with vegetable remains, either silicified 

 or in the condition of lignite. These constitute the group of beds designated in 

 the Virginia geological reports as the LTpper Secondary Sandstone, and referred 

 by me long since (1842) to the upper part of the Jurassic series, correspondmg 

 probably to the Purbeck beds of British geologists. From the Potomac northward 

 this group of deposits, as exposed in the deep railroad cuts between Washington and 

 Baltimore and on to Wilmington, is made up of variegated, soft, argillaceous, and 

 silicious beds, which, from the preponderance of ferruginous coloring toward the 

 Delaware, has been called by Professor Booth the red clay formation. At a few points 

 only toward the bottom of the deposit it brings to view a bed of the felspathic sand, 

 or crumbling sandstone, above referred to. Traced transversely, it is seen to dip 

 beneath the Cretaceous greensand at various points in New Jersey, Delaware, and 

 Marjdand, but in Virginia disappears in its eastward dip beneath the Eocene 

 Tertiary. 



How far we may consider this group of sediments in Maryland, Delaware, and 

 New Jersey as merely a continuation of the Vu'ginia formation above described 

 can be determined only by further investigation. But the discovery in them at 

 Baltimore, by Professor Tyson, of stumps of cycads would seem to bring them 

 into near relation with the formation at Fredericksburg containing similar remains, 

 and to favor then* being referred, at least in part, to the horizon of the upper Jurassic 

 rocks. Possibly we may find here a passage group analo ;ou' to the Wealden oi 

 British geology. Whatever may be the result of further ( If Jvery, it would seem 

 to be premature at this time to assume the whole of these deposits from the Potomac 

 northward as belonging to the Cretaceous series. 



Where the Tertiary or Cretaceous rocks are present in this belt there is, of 

 course, no danger of confounding the superficial gravel and cobblestone deposit ^\^th 



MON XLVIII — 05 23 



