118 HATCHER — OLIGOCENE AND MIOCENE DEPOSITS, [Aprils, 



to their exact age and correlation. Considering the absence of 

 such direct paleontological evidence, it may be just as well to con- 

 tinue to refer this entire series to the Loup Fork; but I believe it 

 more probable that the Gering sandstones, and perhaps a portion at 

 least of the overlying Monroe Creek beds, will prove eventually to 

 belong to the John Day rather than the Loup Fork. The maximum 

 thickness of these two formations in Converse County, Wyoming, 

 can hardly be less than 1500 feet, and almost nothing is known of 

 the fauna of this entire series. Although for the most part quite 

 barren of fossils, it would seem that somewhere throughout its great 

 vertical and lateral extent there must be fossiliferous horizons, and 

 that within these representatives of the John Day fauna will yet be 

 found. The paucity of these beds as compared with the great 

 wealth of fossils in the underlying and overlying deposits, have 

 heretofore caused them to be almost totally neglected by collectors. 

 I believe a better classification of these beds would be obtained by 

 making Darton's Arikaree coordinate with the Loup Fork, includ- 

 ing within it the Gering sandstones and Monroe Creek beds, cor- 

 relating it provisionally with the John Day. 



The following table is submitted as expressing the present author's 

 views as to the proper classification of the Oligocene and Miocene 

 deposits of this region. It is based on our present knowledge of 

 the faunal and lithological characters of the various horizons as 

 they have been determined, chiefly in northwestern Nebraska and 

 southwestern South Dakota, where these deposits are best repre- 

 sented and have been most thoroughly studied. 



Table of Oligocene and Miocene Formations of Western 



Plains. 

 f Goodnight = Palo Duro = Ogalalla. 



(Nebraska = Upper Deep River, 

 Harrison z= Hiatus between Lower^and Upper Deep 

 River. 



{Monroe Creek = Upper John Day and Lower Deep 

 River. 

 ^ Gering Sandstones r= Lower John Day. 



p Leptauchenia Clays, including Protoceras Sand- 

 I stones. 



Oligocene = White River. I Oreodon Clays, including Metamynodon Sand- 

 I stones. 



[ Titanotherium Sandstones and Clays. 



