108 GEOLOGY OF THE DKNVKi; BASIN. 



strike of the Trias is the same throughout its upper and lower mem- 

 bers — in general about N. 10° W., with occasional local variations due to 



local or accidental causes. The strike of the dura is difficult of obser- 

 vation, bu1 from the few exposures existing it is probably in general 

 accord with the Dakota. The latter formation varies in strike from the 

 normal, X. In \V., beyond the area of unconformities, to N. 25 W. in 



die southern third of the affected area, X. 10 W. in the middle third, and 

 north to X. ."> I''., in the northern third. At a number of points within the 

 region there is also local divergence from the strike given, due to crushing, 

 crumpling, and minor faulting of the beds. 



Of the strike relations of the Dakota to overlying and underlying 

 formations, two particular instances require notice, din- first is with 

 reference to the dura, in the gulch between Gregory and Polecat canyons 

 in the southern portion of the field; there is here an apparent discrepancy 

 in strike between the two formations of 25°, the Jura conforming to the 

 older beds, the Dakota and beds above striking obliquely to this in a 

 direction X. .'i W. This discrepancy is probably the result of local dis- 

 placement, perhaps occurring during the erosion of the gulch. The second 

 instance, involving the strike Delations of the Dakota and Niobrara, occurs 



immediately south of the Sunshine road, where the absence of the Benton 



has brought the two formations in direct contact at an angle of 27°, the 



Niobrara crossing the edges of the Dakota beds. This is probably due to 

 a displacement of the Dakota prior to deposition of the Niobrara. The 

 general angle of divergence is plainly visible in the trend of the two 

 formations northward from this point. 



The Benton presents bu1 lew opportunities for the determination of 

 its strike, and it is chiefly on broad stratigraphical observations already 

 mentioned that it has been drawn coincident with that of the Niobrara. 



The Niobrara displays the same great bend to the westward that has 

 been noted for the Dakota, with the additional degree of curvature resulting 

 from the absence of the Benton over its central portion. With the Pierre 

 it is conformable. 



General geological deductions. Fl'tllll tllC foregoing facts tilt' CXisteHCC of tWO 



well-defined unconformities within the series of formations in the vicinity 



