J. S. Newberry — Flora of the Great Falls Coal Field. 193 



logical importance, I forwarded specimens of each species to 

 Professor Fontaine asking that he would compare them with his 

 Potomac fossils and decide upon their identity or difference. 

 His letter in reply is so interesting that I herewith append a 

 copy of it. 



University of Virginia, Oct. 15, 1890. 



Dr. J. S. Newberry— 



Dear Sir : — I have examined the plant fossils that you ob- 

 tained from Great Falls, Montana, and sent to me for comparison 

 with the fossils of the Potomac formation. 



I find them to be as follows : 



1. Thyrsopteris rarinervis F. 



2. A plant near to Podozamites distantinerms F. 



3. Cladophlebis parva F. 



4. Sequoia JReichenbachi II. 



5. Pecopteris Browniana F. 



6. Aspidium Fredericksburg en se F. 



7. Sphenolepidium Virginieum F. 



8. A plant allied to Thyrsopteris brevifolia F. 



9. A plant near to Cladophlebis distans F. 



10. Thyrsopteris insignis F. 



11. Carpolithus Virginiensis F. 



12. A plant near to Cycadiospermum rotundatum F. 



13. Pecopteris microdonta F. 



14. Thyrsopteris brevipennis F. 



15. A plant near Cladophlebis constricta F. 



The above named identities and resemblances are found on 

 comparing the plants sent, with fossils of the Potomac formation 

 described in Monograph XV of the publications of the U. S. Ge- 

 ological Survey. 



The forms that I enumerate as "near" to named Potomac fos- 

 sils, 1 hesitate to identify with them on account of the small 

 amount or poor preservation of the material in hand available for 

 comparison. 



It should be stated that No. 9, which in foliage shows a facies 

 like Cladophlebis distorts has a fructification like that of some 

 Aspiclia and if identical with the Potomac plant this fact would 

 remove it from the genus Cladophlebis. 



Yours truly, W. M. Fontaine. 



The above identifications prove conclusively the general 

 identity of the geological horizons of the Potomac group, the 

 Great Falls group, the Kootanie group of Canada and the 

 Kome group of Greenland, and confirm the view advocated by 

 Professor Fontaine and myself that the Potomac group is 

 Lower Cretaceous and not Jurassic. 



Professor L. F. Ward in his review of the Potomac flora, 

 (this Journal,) leaves the question of the age of the Potomac 



