THE CRETACEOUS RIM OF THE BLACK HILLS. 263 



It thus appears that the flora of the beds above Evans Quarry 

 is distinctly that of the Dakota Group, while all the plants found 

 below that horizon as distinctly indicate a Lower Cretaceous age. 

 The force of this evidence is to my mind irresistible, and it is 

 safe to predict that if any other paleontological evidence is ever 

 found it will confirm this conclusion. The question still remains 

 as to where the dividing line is to be drawn. Between the cycad 

 and fossil wood horizon and that of the Dakota leaves there are 

 some hundred feet of sandstones and shales. Sixty to seventy- 

 five feet of this consists of the massive or heavy-bedded building 

 stone, which in places becomes flinty and very hard. As the 

 thin shaly layer which separates this from the leaf bed may be 

 safely put with the latter into the Dakota proper, and there seems 

 no reason for separating the similarly constituted layer that inter- 

 venes between the cycad horizon and the base of the sandstone 

 from the one upon which it rests, the question is narrowed down 

 to that of the position of the quarry sandstone. That question I 

 will leave to the stratigraphical geologists. 



As to where in the Lower Cretaceous series the basal portion 

 of the Cretaceous rim of the Black Hills should be located, it 

 can only be said that the cycadean trunks elsewhere found in 

 North America have all come from well down in that series or 

 else from the Upper Trias. Leaving the latter cases out of the 

 account we have the Maryland specimens and the one from 

 Kansas. It was long supposed that the Maryland specimens 

 were derived from the Iron Ore Clays, which were referred by 

 McGee and Fontaine to an " Upper Clay Member." This is now 

 known not to be the case, and it has been demonstrated that the 

 cycads occur in the basal sands at the same horizon as the 

 Sequoian trunks, and probably the same as the Rappahannock 

 freestone, which has yielded more fossil plants than any other 

 horizon. Whether this is the same horizon as that of the James 

 river, where cycads and conifers prevail and no dicotyledonous 

 leaves have been found, or a somewhat higher one, need not now 

 be discussed, as the whole subject will soon be thoroughly pre- 

 sented along with the evidence. Certain it is that the Potomac 



