326 B. WILLIS — LEWIS AND LIVINGSTON RANGES, MONTANA 



assic. The validity of the correlation has been discussed. The evidence 

 indicates that the strata are probably Algonkian. 



CRETACEOUS 



General note. — Cretaceous strata are but poorly exposed along the east- 

 ern base of Lewis range, although they form the subterrane beneath 

 hundreds of square miles of the plains. The mantle of drift is wide- 

 spread and often thick, and outcrops of rock in place are limited to occa- 

 sional freshly scoured gullies or ledges of sandstone along hilltops. Such 

 outcrops were noted, however, in traversing the plains from Cutbank 

 river to Saint Mary lake, and others were found about the mountain 

 slopes west of Saint Mary lakes, up Swift Current valley, on Kennedy 

 creek, about Chief mountain, and on Belly river. Weller collected 

 fossils sufficient to determine three horizons, namely, Dakota, Benton, 

 and Laramie, and through the light thrown by fossils on their relations 

 these occasional Cretaceous outcrops become interesting as elements of 

 a structure which they do not suffice to make clear. Their distribution 

 is such that the Dakota and Benton, while occupying normal relations 

 one to another, are apparently above the Laramie. The significance of 

 this from the point of view of structure is discussed under that head. 



No occurrences of rocks of Cretaceous age were observed w r est of the 

 Front range of the Rockies, and it is probable that there are none south 

 of the Crow Nest coalfields. 



Dakota. — Arenaceous and argillaceous shales and sandstones of Da- 

 kota age occur on North fork of Kennedy creek near its junction with 

 South fork, 5 I miles east by south from Chief mountain, at an elevation 

 of 4,800 feet. The exposures constitute a bluff 30 feet high, near the top 

 of which are layers bearing fossil plants and freshwater shells. A col- 

 lection of leaves, though badly broken up in transit, was examined by 

 Mr Knowlton, who reports Ficus proteoides ? Lesq., Magnolia boulayana 

 Lesq., Liquidambcif integrifolius Lesq., Liquidamba*obtusilobatiim Lesq. 

 A / Diospyro rotandifolia Lesq., Phyllites rhomboideus Lesq. " The above spe- 

 cies, says Knowlton, " are all characteristic Dakota Group forms, and 

 the beefs at this locality are referred without hesitation to this age." 

 The strike of these Dakota strata is nearly north and south and they dip 

 at a low angle, 0-10 degrees, westward. 



Benton. — Dark bluish black to leaden gray shales constitute the mass 

 of Cretaceous rocks west of Saint Mary lakes. With them are associated 

 thin beds of limestone and ferruginous sandstone. Weller's collections 

 from outcrops north of lower Sherburne lake in Swift Current valley, and 

 from southern slopes of Chief mountain, were submitted to Mr Stanton, 

 who identifies Inoceramus labiatus Schlotheim, Prionotropis sp., Ostrea con- 



