STRATIGRAPHIC POSITION OF LANCE FORMATION 373 



Stanton, who says, 1 "When studying the section it was believed 

 that the upper four members belong to the Lance formation, but 

 afterward when comparison was made with sections of the south 

 end of the field it seemed more possible that all the beds examined 

 here belong to the Fox Hills." If this portion of the section is 

 placed in the Lance formation, where it certainly appears to belong, 

 the thickness of the Fox Hills in the section is reduced to 285 feet, 

 or but little more than half of the maximum thickness assigned 

 to beds of this age in the Converse County region. While this 

 evidence may not be considered conclusive, it must at least be 

 admitted that it strongly suggests the possibility that even here, 

 as in the areas already discussed in the Dakotas and Montana, 

 the Fox Hills is of variable thickness, due to the erosion of the upper 

 portions before the deposition of the Lance formation. 



It is to be admitted, however, that all who have studied the 

 Converse County areas have had, and still have, difficulty in fixing 

 the upper line of the Fox Hills, but in this connection it is to be 

 pointed out that while many students have visited or collected 

 in the region, it still awaits the careful, painstaking study that has 

 been given other fields, such, for instance, as the areas in the 

 Dakotas and Eastern Montana, which have been described by 

 Mr. Calvert. And in this connection it may be mentioned that 

 although in Converse County the exact location and extent of the 

 unconformity between Fox Hills and Lance is not definitely known, 

 the time interval is undoubtedly indicated, since 150 miles to the 

 southeast (i.e., opposite the mouth of the Medicine Bow River) 

 the same dinosaur-bearing beds are above an unconformity which 

 separates them from 6,000 feet of unquestioned "Laramie," while 

 100 miles to the east in the Dakotas, the Lance formation rests 

 on an uneven surface which in some cases represents the removal 

 of practically the whole thickness of the Fox Hills of the region. 



As a possible explanation of the difficulty experienced in detect- 

 ing the presence of the unconformity between the Fox Hills and 

 overlying Lance formation in this area, the following facts may 

 be offered: the localities in Eastern Montana and Western South 

 Dakota where the examples of the distinct angular and erosional 



1 Am. Jour. Sci., XXX (1910), 185. 



