FLORA OF LAKOTA OF BLACK HILLS. 315 



another Lower Potomac element. The other form, Nageiopsis longifolia," 

 from the small amount of material that it shows, does not possess much 

 value, but so far as its evidence goes it adds to the Lower Potomac a 

 affinities. 



We may conclude then fairly, I think, that these Geyser strata Ijelong 

 to the same formation with the Great Falls group of beds, and that the 

 evidence of the Geyser fossils confirms the conclusion previously made by 

 Doctor Newberry and myself, that the age of this group is Wealden, 

 being essentially of the same age as the Lower Potomac of Virginia. 



FLORA OF THK LAKOTA FORMATIOX OF THE BLACK HILLS. 



Passing eastward, the next series of plant-bearing beds of the Lower 

 Cretaceous that we encounter whose flora has been made known is that of 

 the Black Hills in Wyoming and South Dakota. Before I began my 

 investigations in 1893 these beds were regarded by all geologists as belong- 

 ing to the Dakota formation, and it is therefore doubly unfortunate that 

 Mr. Darton should have applied to them the name Lakota,'' a name so 

 closely resembling Dakota that typographical errors are unavoidable. 



As I have already published ' an exhaustive report on the Cretaceous 

 flora of the Black Hills, chiefly on the flora of the Lakota formation, and 

 as this report is as accessible to all persons interested as are the present 

 papers, it is hot considered necessary again to go over any of the ground 

 covered by it. The bibliographical references are very full in that report, 

 so that even these need not be repeated, and the record may be regarded 

 as complete down to the end of October, 1898. 



I was even able to embody in that paper ( pp. 548-551) an account of 

 my expedition to the Black Hills in October, 1898, in company with Mr. 

 H. F. Wells, who had collected so many cycadean trunks for Professor 

 Marsh, in the course of which we visited all the localities known to him. 

 In both the Minnekahta and Blackhawk regions there were large numbers 

 of specimens still lying on the ground, some of them as flne as any sent in, 



n This Potomac plant has since been found to occur in the Jurasso-Cretaceous beds of Alaska. — L. F. W 

 6 Bull. Geol. Soc. Am., Vol. X, December, 1S89, p. 387: Twenty-first Ann. Rep. U. S. Geol. Surv., Pt. IV, 



1901, pp. 526-529. On p. 527 of the last-named paper he states that " the name Lakota is derived from one of 



the tribal divisions of the Sioux Indians." 



c The Cretaceous formation of the Black Hills as indicated by the fossil plants ; Nineteenth Ann. Rep. U. S. 



Geol. Surv., Pt. II, 1899, pp. 521-946, pi. liii-clxxii. 



