64 STANTON: UPPER CRETACEOUS STRATIGRAPHY 



develop a similar great coal-bearing formation in the upper or 

 Montana portion. These widely different neighboring sections 

 seem to me to represent the varied and shifting sediments laid 

 down in and on the borders of a single body of water. Slight 

 warping of the surface, or local changes in the rate of sedimenta- 

 tion from whatever cause, would serve to shift the area of sea 

 and coastal swamp from time to time. 



One more standard section, with the changes and variations 

 in its formations as they are followed away from their typical 

 area, remains to be examined. In connection with their strat- 

 igraphic study of the Judith River formation Stanton and 

 Hatcher'*' established the following succession in northern central 

 Montana: 



Bear-paw shale. Dark clay shale with marine fauna, 750 feet? 



Judith River Jormation. Variable shales and soft sandstones with 

 dinosaurs and other reptiles and fresh- and brackish-water invertebrates, 

 500 feet. 



Claggett formation. Dark clay shale with several beds of sandstone 

 especially in the upper portion. Marine fossils throughout — those of 

 the sandstones containing many Fox Hills species, =^ 400 feet. 



Eagle sandstone. White, gray and yellowish sandstone with shale 

 and coal in upper part. Marine shells, land plants and dinosaurs. 

 200 to 300 feet. 



Colorado shale. Dark marine shale, 800 feet or more. 



(See Section No. 5, p. 59.) 



Compared with the southwestern Colorado section the top of 

 the Colorado shale in this section is believed to be somewhat 

 lower in the general column than the top of the Mancos but with 

 this exception the Eagle, Claggett, and Judith River, taken to- 

 gether, are comparable in a general way with the Mesaverde, 

 and the Bearpaw is approximately in the position of the Lewis. 



The formations above the Colorado shale described in the 

 neighborhood of Judith, Montana, were found to be easily rec- 

 ognizable along the Missouri River in the type area above and 

 below the mouth of Judith River ; on Milk River from the neigh- 

 borhood of Havre to the Canadian boundary and beyond; and 

 southward in the valley of the Musselshell. These formations 

 have since been mapped by the geologists of the Fuel Section 



16 U. S. Geol. Survey, Bull. 257, pp. 11-14. 



