592 MESOZOIC FLORAS OF UNITED STATES. 



Colchester road, all but one of the Brooke localities in the White House 

 Bluff, Hell Hole, Mouth of Hell Hole, and Chinkapin Hollow. None of 

 the localities in the District of Columbia were known to Professor Fon- 

 taine at the date of the publication of his monograph, and of those in 

 Maryland he was acquainted only with that of Federal Hill — (this does not 

 include the cycads treated by him). 



As clearly shown in the treatment of these localities, the beds at 

 Alum Rock, Cockpit Point, Woodbridge, the Colchester road, and Chinka- 

 pin Hollow are on the horizon of the Rappahannock series, the two first 

 named being actually in the typical Rappahannock freestone. Those at 

 the 72d Milepost cut, at the White House Bluff, including the ones above 

 Doag Creek overlying the Mount Vernon clays, and those at Hell Hole and 

 the mouth of Hell Hole, are all on the horizon of the Brooke or Aquia 

 Creek beds. Professor Fontaine's doul^ts regarding the Hell Hole material 

 are quickly dispelled by a casual comparison of it with the chocolate clay 

 of the Mount Vernon beds, while, as the table shows, the species are 

 mostly those of the Brooke beds and not of the Mount Vernon beds. 

 The testimony of the species, however, must be admitted to l^e somewhat 

 conflicting or unsatisfactory, those best represented having a wide range. 

 The Rosiers Bluff locality also certainly represents the Brooke series, most 

 of the species being the same as those found in Virginia on that horizon. 

 This bluff seems to be a simple extension of the White House Bluff across 

 the Potomac, but lying, as it does, somewhat farther coastward in the 

 formation, the underlying Mount Vernon clays and Rappahannock free- 

 stone beds of the Virginia shore are here below the level of the river. 

 This, however, as Professor Fontaine now thinks, is the only plant-bearing 

 locality on this horizon known on the left bank of the Potomac. 



It remains to consider the other localities in Maryland, and for this 

 discussion I shall treat those of the District of Columbia as belonging to 

 the same general group as all the beds across the State of Maryland. 

 There is no essential difference. It is in the correlation of these Maryland 

 beds with those of Virginia that the chief interest of this paper centers. 

 As shown in the historical part. Professor Clark and Mr. Bibbins, influenced, 

 as they admit, by the views entertained by Professor Marsh, regard their 

 Patuxent and Arundel formations as lower than any in Virginia, and as 

 probably Jurassic. I have discussed this point as fully as is necessary, 



