STANTON: UPPER CRETACEOUS STRATIGRAPHY 65 



of the Survey over large areas in Montana and the hniits of 

 their areal distribution are now fairly well known. The most 

 persistent is the Eagle sandstone which has been recognized as 

 far south as the Bighorn Basin and northwest to the western 

 limit of the Great Plains in northern Montana, The overlying 

 Claggett, Judith River and Bearpaw formations in many local- 

 ities lose their distinguishing features within shorter distances. 

 None of them has been recognized as such east of the typical 

 area. In that direction the fresh- and brackish-water beds of 

 the Judith River doubtless soon grade laterally into marine shale 

 so that there is no basis for distinguishing Claggett and Bearpaw 

 from Pierre. Toward the south and west, on the other hand, 

 the marine sediments of the Claggett and Bearpaw tend to be 

 replaced and represented by estuarine and continental deposits. 



A striking example of rapid variation of this kind has been 

 described by Stone and Calvert^ ^ in the area surrounding the 

 Crazy Mountains where within a short distance the Claggett, 

 Judith River and Bearpaw finger out, and at last completely 

 lose their identity in andesitic tuffaceous deposits which have 

 been included in the Livingston formation. 



Conditions somewhat similar, except for the absence of vol- 

 canic material, are found in the Bighorn Basin where the Eagle 

 sandstone is recognized but the attempts to apply Claggett, 

 Judith River and Bearpaw to the overlying formations have 

 not been much more successful than the earlier attempts to 

 apply the Meek and Hayden nomenclature in the same area. 

 The marine Bearpaw shale just enters the northern end of the 

 basin as a thin bed which soon wedges out completely. The 

 reports of Woodruffs ^ and Washburne'^^ and the unpublished, 

 more detailed work of Hewett show that over a large part of 

 the Bighorn Basin especially on the west side there are no marine 

 sediments above the Eagle sandstone, which is itself there only 

 in small part marine, and that the thick interval between the 

 Eagle and the well-identified Fort Union is occupied by fresh- 

 ly Economic Geology, 5: 551-557, 652-669, 741-764, 1910. ^r 

 18 U. S. Geol. Survey, Bull. 341, pp. 200-219. 

 " Ibid., Bull. 341, 165-199. 



