"CERATOPS beds" OF WYOMING AND MONTANA 249 



of unfossiliferous sandstone and sandy shale probably representing 

 the Fox Hills. Resting unconformably on this member are about 

 500 to 600 feet of "somber beds" extending up to the "typical buff 

 and light-gray Fort Union shales and sandstones which are exposed 

 near Yule P. O." The unconformity is presumably expressed by 

 an uneven surface as at Hell Creek. About 200 feet above this 

 unconformity dinosaur bones were collected which have been identified 

 by C. W. Gilmore as Triceratops horridus Marsh, and several species 

 of plants referred by Doctor Knowlton to the Fort Union were obtained 

 rom the same and higher portions of the ''somber beds. " Among the 

 invertebrates submitted by Doctor Leonard for examination one lot 

 from near Yule consists entirely of Ostrea suhtrigonalis E. & S., which 

 I considered sufficient evidence of Cretaceous age and stated in my 

 manuscript report that if there is any Laramie in the region it probably 

 includes this oyster bed. In a recent letter Doctor Leonard makes 

 the following statements concerning the various collections from the 

 , somber beds:" 



The plants which I sent to Doctor Knowlton and the specimens of 

 Ostrea suhtrigonalis were not collected from the same stratum and 

 came from localities several miles apart. As near as I could deter- 

 mine the plants which came from near Yule are from a bed somewhat 

 lower than the layer containing the shells {Ostrea). A few of the 

 plants, those from near Marmarth and the mouth of Bacon Creek, are 

 from the same beds as those containing the dinosaurs. 



Before Doctor Knowlton identified the Fort Union leaves from 

 there I was inclined to regard as Cretaceous all the somber beds below 

 the typical light-colored Fort Union, particularly after your statement 

 regarding the probable age of Ostrea suhtrigonalis. 



I believe with you that we are here dealing with beds near the line 

 between Cretaceous and Tertiary and it is possible that the upper 

 200 feet or so of the "somber beds" containing thick coal beds, 

 may be Fort Union, and the lower portion which is barren of coal and 

 contains dinosaurs may be Cretaceous. But one difficulty with this 

 view is that Ostrea was found in the upper portion and several leaves 

 identified as Fort Union species were found in the lower portion carry- 

 ing the bones. The fossils do not seem to tell the same story as to the 

 age of the beds in question. 



The significance of these facts and especially the occurrence of 

 the oyster bed will be discussed later. 



