488 



E. BLACKWELDEIi THE GROS VENTRE SLIDE 



Eiver has excavated its valle}^ rouglily parallel to the strike of a thick 

 series of rocks which dip gently northward. Along the south side of the 

 valley, therefore, the strata dip at angles of about 10 to 20 degrees away 



Figure 1. — A diacjiammatic Sketch of the Valley of Lake Creek as it is supposed to have 



teen lief ore landslide Action hegan 



from the Gros Ventre Mountains and toward the river. Locally this 

 monocline is gently fluted with small cross-folds, and one of these forms 

 the east side of the slide. In this locality the prevailing rocks are soft 



Figure 2. — A diagrammatic Sketch of Lake Creek Valley in 1911 



These diagrams should not be regarded as faithful pictures ; they merely serve to illus- 

 trate the general conditions 



Upper Mesozoic shales with some beds of sandstone and a little lime- 

 stone. They range in age from the Morrison and even Sundance (Juras- 

 sic) formations up to horizons equivalent to the Benton. Soft shale and 

 clay predominate. 



