264 THE JOURNAL OF GEOLOGY. 



cycads belong to the lower part of that formation. The Kansas 

 specimen is confidently referred by Professor Cragin to the 

 Trinity Group of the Comanche series of Hill, which forms the 

 lowest division of that series. Professor Hill is disposed to 

 accept this conclusion, and Professor Prosser of Washburn Col- 

 lege, Topeka, sees no reason to doubt its accuracy. 



The other plants, as has been seen, occur about one hundred 

 feet below the cycad bed. Professor Fontaine's report above 

 quoted places their significance in its true light and leaves little 

 to add. The occurrence of Asplenium Dickso?iianu)n shows simply 

 that this common form persisted in the same area through a long 

 period. But this it was already known to do. Should it, how- 

 ever, prove to be the TJiyrsopteris rari?iervis Font., it would be a 

 characteristic lower Potomac species. 



The forms that Professor Fontaine refers to Glossozamites 

 argue entirely for a Lower Cretaceous or even earlier age. Eight 

 species of that genus are known, ranging from the Upper Trias 

 to the Urgonian. Some are from the Lias, but most of them are 

 found in the Wealden and Neocomian. They had a wide geo- 

 graphical range, occurring in Greenland (Kome beds), India 

 (Damxuda series), and in various parts of Europe. One species, 

 G. dista?is, is from the lower Potomac of Fredericksburg, Virginia. 



Gleichenia Zippei (Corda) Heer was first described by Corda, 

 who referred it to Pecopteris, from the Gosau formation of 

 Bohemia, supposed to be above the Cenomanian. It has since 

 been found in the true Cenomanian of Bohemia and in the 

 Quadersandstein of Germany. Heer found it in all the Cre- 

 taceous beds of Greenland (Kome, Atane, Patoot), also in the 

 Cretaceous of Spitzbergen. Newberry detected it in the Amboy 

 Clays. It varies considerably, and the name may include more 

 than one species. Fontaine compares the Black Hills specimens 

 only with Heer's Kome forms, and is not certain that they may 

 not rather represent his own Aspidmm heterophyllwn from the 

 Lower Potomac of Fredericksburg. The evidence afforded by 

 this species, therefore, is not strong, but it certainly does not 

 occur in the Dakota Group elsewhere so far as known. 



