20 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



them by a separate name, and I have here called them "Bear",^ from 

 Bear Butte around which they are typically developed. They may 

 perhaps be equivalent, approximately, to the Tullock, but this would 

 be an assumption that might result in serious misapprehension. They 

 are far removed from and discontinuous with the type Tullock, into 

 which it will never be possible to trace them, and their lithologic 

 character is not the same. It is improbable that they are exactly 

 equivalent to the Tullock, and even if this should prove to be the 

 case it would seem warranted and necessary to retain for them a 

 local name. At present correlation with the Tullock would be only 

 a guess, which might well prove to be incorrect. 

 Typical exposures of the Bear are shown in plate 2. 



Fort Uoton 



The use of the name "Fort Union" has been so loose and ill-defined 

 that it has become necessary for every writer who uses it to propose 

 his own individual definition or to run the risk of being completely 

 misunderstood. In general it has been applied to beds in the Dakotas, 

 Montana, and Wyoming, in the northwestern high-plains region (and 

 in part intermontane areas) that are, or are supposed to be, later than 

 the Lance and earlier than the Wasatch, This apparently satisfac- 

 tory definition is in fact most indefinite. In the first place, there 

 has not always been general agreement even to this extent, Knowlton, 

 for instance, placing beds generally referred to or correlated with the 

 Lance in the "Lower Fort Union." In the second place, the definition 

 is dependent on that of Lance and of Wasatch, which are themselves 

 very ill-defined. It is certain in some areas (notably Polecat Bench 

 in northern Wyoming, as shown by Jepsen) and probable in most or 

 all that strata generally referred to the Lance, often under the name 

 of Tullock but not necessarily equivalent to the type Tullock, are in 

 reality distinctly later than the typical Lance or the equivalent Hell 

 Creek and both faunally and stratigraphically are more nearly 

 related to the overlying beds, that is, to the Fort Union. Thus even 

 aside from the question of accurate recognition of the boundaries and 

 correlation of members of these formations and groups, there is often 

 doubt as to which group should include a given member. The time- 

 honored name "Wasatch" is still more ambiguous, to the point that 

 very few of the beds called "Wasatch" are really equivalent to any 

 part of the type Wasatch. Granted that the use of the name is usually 

 intended to imply approximate correlation with the Gray Bull, there 

 still remain many doubts as to its proper contents, for there is generally 

 a thick series of beds, Tiffany, Clark Fork, and so on, that are some- 



» I am indebted to Miss M. Grace Wilmarth, of the U. S. GeologiealSurvey, for informing me that "Bear" 

 and also "Melville" (defined on a later page) are not included in her records as ever having been used 

 previously as the names of stratigraphic units. 



