356 MESOZOIC FLORAS OF UNITED STATES. 



beautiful ferns of Wealden type. All the attainable evidence points stronglj^ to 

 the conclusion that the age of these upper beds is Wealden. Professor Rogers 

 mentions that they yield at Fredericksburg two or three species of ferns and stumps 

 of Cycads of the genus Cycadeoidea. None of these have been seen b}^ me (see . 

 p. 157; Reprint, pp. 44-45)." 



This is, SO far as I am aware, the first time that the Maryland cycads 

 were referred to the genus Cycadeoidea. 



Why the Older Potomac beds are not to be found in. New Jersey 

 underlying the Amboy clays or Raritan formation has been a difficult 

 question. This latter formation rests unconformably upon the Triassic 

 sandstones in most parts of that State with no indication of the Older 

 Cretaceous beds at their base. The prevailing theory is that the later 

 beds transgressed far to the landward beyond the margin of the older 

 ones. This could be demonstrated only by borings far enough to the 

 eastward to strike the older beds. The only such boring that has been 

 made in which this theory received partial confirmation is that of the 

 Jamesburg well. Jamesburg is about 9 miles from the Triassic border, 

 in the direction of the dip. The well was bored by Mr. H. F. Walling 

 in 1880 to a depth of 481 feet. The lower 26 feet were through coarse 

 sand, white clay, and gravel, but it is not stated whether the clay was 

 feldspathic. These materials may or may not belong to the Older 

 Potomac.'' This case can not therefore be said to solve the problem. 



Another problem is to account for the absence of the Newer Poto- 

 mac in Virginia, where in many places the Eocene (Pamunkey) and 

 other later beds rest imconformably upon the Older Potomac. It has 

 been supposed that they may have been eroded away before the date 

 of the deposit of these last-mentioned beds. The artesian well bored 

 by Gen. A. A. Humphreys, at Fort Monroe, from 1864 to 1869, to a depth 

 of 907 feet," lends some support to this view, as the lower 7 feet went 

 through "reddish mottled clays," which are wanting in the Older 

 Potomac and are characteristic of the Newer Potomac. 



« Relative to this last statement I wrote to Professor Fontaine to inquire when and where Professor Rogers 

 published it. He investigated the matter and replied that he must have been mistaken in attributing it to 

 him, as he now knows of no evidence of cycads having been seen in Virginia. He doubtless naturally drew 

 this inference from Professor Rogers's statement quoted above (see p. 347). 



6 See Ann. Rep. State Geologist of New Jersey for 1880, Ti-enton, 1880, pp. 166-167. 



c The Virginias, Vol. Ill, October, 1SS2, pp. 151-152; Geology of the Virginias, pp. 733-735. 



