ADDENDA. TO VOL. I. 227 



Sphenopteris latilolat Font., I am disposed to regard as identical 

 with 8. Fittoni, Sew.: cf. Vol. I. p. Ill, Fig. 11, and PI. VI. 

 Fig. 2. The specimens figured by Duwson are for the most 

 part very small and imperfectly preserved, and the task of deter- 

 mination has necessarily been extremely difficult. 



AMERICA. 



Prof. Lester Ward writes to me as follows in reference to the 

 geological age of the Potomac formation ! : 



"As you may know, I have been engaged for several years 

 on our Potomac formation, and I have established the fact that 

 it is by no means so simple a group as might be supposed from 

 what has been thus far said about it. I have been able to 

 subdivide it into no less than six somewhat distinct horizons, 

 each of which is fairly well marked off stratigraphically, and 

 has its own peculiar flora. The uppermost of these subdivisions 

 embraces the well-known Amboy clays of New Jersey, which 

 have yielded a very rich flora, a monograph of which had been 

 nearly completed by Dr. Newberry at the time of his death, 

 and has been edited by Dr. Arthur Hollick, and has now gone 

 to press to be published by the U.S. Geological Survey. The 

 difference between the lowest and highest of these beds is very 

 great, and the flora is correspondingly different. I suppose that 

 the series as a whole includes nearly the entire Lower Cretaceous. 



"It is only with the older Potomac that your Wealden of 

 England can properly be compared. It is in that that we have 

 the remarkable cycad trunks, so much like those of the Isle 

 of Purbeck, which I suppose are really Jurassic ; although, as 

 you show, they are most intimately connected with the overlying 

 Wealden." 



PORTUGAL. 



Reference was made in Volume I. (p. xxiii.), to Saporta's 

 important work on the fossil flora of Portugal, and a few notes 

 were added with regard to some of the more interesting species. 



1 Letter, July 3, 1894. 



