DAKOTA, COLORADO, AND MONTANA FORMATIONS 301 



on the Athabaska river the Tar sands, representing a period contem- 

 poraneous with the Dakota of Manitoba, have a marine fauna.* 



On the Elk Elver escarpment shore conditions prevailed for a consider- 

 able time after the inauguration of the Dakota period, and the formation 

 is represented by a great thickness of conglomerates and sandstones. 



Colorado 



By eliminating the recognized formations above, there remain some 

 725 feet of a succession of sandy shales and shale bands grading down- 

 ward in the section to black shales which can be taken as representatives 

 of the Colorado formation. As it is partly littoral, its thickness does not 

 seem to represent the deposition of the entire period, and thus in the top 

 of the Dakota is probably included the marginal deposits of the advanc- 

 ing shoreline, concealing a probable time hiatus at the top of the Dakota. 



Montana Formation 



Following the succession as delineated by Messrs Stanton and Hatcher 

 in northern Montana, a conspicuous light colored sandstone, 50 feet in 

 thickness, may be called the Eagle formation. Above this 250 feet of 

 banded clays and sandstones would be the Claggett formation or "lower 

 dark shales" of Dawson's southern Alberta section. A sandstone forma- 

 tion above it, with a thickness of '750 feet, holding the only fresh-water 

 fossils found in the section, would be the Judith Eiver formation. This 

 latter does not contain in this locality an extensive land flora and there 

 are but slight indications of possible coal seams. The shales above the 

 sandstones are very much like those hitherto called Pierre, and the only 

 marine invertebrates, with the exception of those from the Fernie shales, 

 collected during the past season are from these upper shales and are typi- 

 cal Pierre. 



On the Bow river, east of Calgary, the Pierre described by Doctor 

 Dawson includes a sandstone series about 50 feet in thickness, which is 

 again found more largely developed on the Bed Deer river north. In the 

 foothills this sandstone is 200 feet in thickness along the Bow river 

 and is sometimes conglomeritic, but decreases in thickness toward the 

 south and is only about 50 feet on Sheep creek. It consists of three well 

 marked bands of sandstone, which maintain their character through this 

 range and occupy a position in the upper third of the formation. The 

 Pierre described by Mr J. B. Tyrell on the North Saskatchewan con- 

 tains intercalated sandstone beds at all horizons from the top to near the 

 base, and all bear marine fossils of Foxhill type; so that as a formation 



* Ottawa Naturalist, vol. xii, p. 37. 



