STANTON: UPPER CRETACEOUS STRATIGRAPHY 69 



the Blackfeet country was slightly elevated so that it was occupied 

 by coastal swamps and lagoons only a few feet above tide into 

 which slight depressive movements occasionally brought local 

 and temporary brackish waters and still more rarely a brief incur- 

 sion of the sea, as is proved in one case by the fossils found at 

 Cutbank. The Bearpaw shale marks a more important marine 

 incursion which probably covered the whole area and continued 

 for some time though it is questionable whether it lasted as long 

 here as it did in central Montana. At the close of Bearpaw sed- 

 imentation there was clearly another considerable period of trans- 

 ition when the area wavered near tide level and received first 

 marine and then brackish-water sediments before land conditions 

 were at last permanently established. 



We are now in position to understand the difficulties which 

 Dawson^i encountered in describing and interpreting his section 

 of the ''Belly River series" along Milk River north of the inter- 

 national boundary. It was another case of applying the ter- 

 minology of a single section thru a long stretch of country in which 

 the stratigraphic development varied. In the eastern portion 

 where Dawson got the best evidence that the ''Belly River" is 

 intercalated between two marine formations the section is like 

 that at the mouth of Judith River while in the western portion 

 it is the same as in the Blackfeet Indian reservation. In 1903 

 Hatcher and Stanton visited the localities near Pakowki Lake 

 and correctly identified as Claggett the ''lower dark shale" there 

 exposed beneath the "Belly River," thus estabhshing the iden- 

 tity of the "Belly River" of that section with the Judith River 

 formation. The mapping of Stebinger has now shown that the 

 "lower dark shale" on the escarpment of Rocky Spring Plateau 

 about 40 miles west of Pakowki Lake is Colorado shale and Daw- 

 son's "Belly River" from that point west includes the Eagle 

 sandstone and all the overlying rocks to the base of the Bearpaw. 

 Between these two localities the marine Claggett shale has merged 

 into non-marine sandstones and shales. 



In conclusion the general statement is justified that the Upper 

 Cretaceous sediments of the Rocky Mountain region show as 



21 Geol. Survey of Canada, Kept, for 1882-83-84, pp. Ill C-126 C. 



