480 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



problems that would otherwise have been left in doubt. To them I desire 

 in this place to make ample acknowledgments, and especially do I wish to 

 express my obligation to Mr. Charles Schuchert, of the United States 

 National Museum. A preliminary study of this collection was made by 

 him before the work was assigned to me, and he also supplied me with facil- 

 ities in the National Museum, gave me free access to the Museum collec- 

 tions for comparison, permitted the use of his Bibliography of North Amer- 

 ican Brachiopoda, then unpublished, and placed at my disposal his fine col- 

 lection of brachiopods and his no less extensive knowledge of the same. It 

 gives me pleasure also to acknowledge my obligations to Mr. John L. 

 Ridgway, by whom the greater number of the drawings accompanying 

 this report were made. 



DEVONIAN. 



The material believed to be of Devonian age is unsatisfactory in that 

 it is scanty and often poorly preserved, while the species represented are 

 almost the worst that could have been selected for stratigraphic correla- 

 tion. Consisting mostly of corals, with a few gastropods and brachiopods, 

 it would be difficult, unassisted by the richer though related fauna of 

 Nevada, to affirm of some of the local representations anything more than 

 that they are older than the Carboniferous and younger than the Ordovician. 

 The strata represented fall into three groups, distinguished somewhat by 

 their lithologic character as well as by the fossils which they carry. More 

 extensive collections would probably show a closer connection than now 

 appears. 



The age of the exposure on the north side of Soda Butte Creek has 

 not been definitely ascertained. It is represented only by an undetermined 

 species of Favosites, in a fragmentary condition. The most likely reference 

 would be to the Silurian or Devonian, for if Carboniferous the coral belongs 

 to none of the few related species known in Carboniferous rocks. The 

 locality is therefore provisionally referred to the Devonian, since no fossils 

 of Silurian age have been recognized in the Yellowstone Park. 



The locality at Wall Canyon, Clark Fork Valley, stands by itself. 

 It is represented only by Pleurotomaria isaacsi (?) (a solitary specimen), both 

 fossil and matrix being highly siliceous. P. isaacsi was described from 

 Lower Devonian strata, probably of the age of the Schoharie grit, but its 

 range is not known, and my identification is questionable. 



