688 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



The following notes give the substance of Stone and Calvert's remarks, though 

 not a literal quotation. 



In the upper valley of Musselshell River and north of the Crazy Mountains the 

 basal Cretaceous rocks belong to the Kootenai formation, which rests conformably 

 on the Morrison formation. The Kootenai is 235 feet thick, is composed of shale 

 and sandstone, and is not coal bearing. It is overlain conformably by Colorado 

 shale, about 1,300 feet thick, prevailingly dark colored and carrying marine inverte- 

 brates. 



The four formations of the Montana group, Eagle, Claggett, Judith River, and 

 Bearpaw, are found here. The Eagle is mainly massive sandstone, about 200 feet 

 thick, and in some places carries coal which usually is unworkable. The Eagle is a 

 conspicuous ledge or ridge maker. The Claggett is composed of dark shales and 

 white to Ught-brown sandstones of marine and brackish-water origin, from 400 to 

 800 feet thick," and is overlain by the Judith River formation, which has about the 

 same range in thickness. The Judith River is prevailingly of fresh-water origin, 

 carries thin beds of coal, and has fossil shells, bones, and wood. 



Above the fresh-water Judith River is the upper marine Cretaceous shale, 

 700 to 1,000 feet thick, known as the Bearpaw shale. This shale is commonly 

 dark-colored and has fossiliferous limy nodules. The Cretaceous section is normal 

 to the top of the Bearpaw. Resting on these marine shales and evidently of a 

 transitional nature is about 300 feet of dark-colored fresh and brackish water shale 

 and sandstone. The stratigraphic relation of these beds is like that of the Fox Hills 

 sandstone, but enough fossils have not yet been obtained to make the correlation 

 positive. These beds are more or less tuffaceous. 



There is some question as to the age of the overlying Lance formation, which 

 is 1,000 to 2,400 feet thick and composed of light-colored fresh- water sandstone and 

 shale. The paleobotanic collections are ascribed by Knowlton to the Fort Union, 

 but the vertebrate and invertebrate fossils point to Cretaceous age for the same 

 beds. There is no doubt that they should be in part correlated with the " Ceratops 

 beds," but whether the latter are Cretaceous or Tertiary is as yet unsettled. 



Resting conformably on the Lance formation is another series of tuffaceous 

 sandstones and shales. The beds are about 2,200 feet thick at the north end of 

 the Crazy Mountains and 460 feet on Fish Creek northeast of the mountains. They 

 are of Fort Union age and will be described in future papers as the Lebo andesitic 

 member of the Fort Union formation. 



The youngest consolidated strata in the Crazy Mountains are the massive sand- 

 stones and shales of the Fort Union formation. They are of fresh-water origin and 

 are shown to be Tertiary both by plant and by animal remains. The thickness 

 is' unknown but exceeds 4,000 feet. 



At the north end of the Crazy Mountains the Upper Cretaceous formations 

 gradually lose their distinctive lithologic characteristics, and all from the Eagle to 

 the massive sandstones of the Fort Union become merged into a single series of 

 tuffaceous beds several thousand feet thick and constituting a single lithologic unit. 

 On the west side of the Crazy Mountains, therefore, th6 Eagle sandstone is overlain 

 conformably by a great series of sediments more or less andesitic in composition 



