88 GEOLOGY OF THE DENVEE BASIN. 



increases from the base toward the summit. Over the middle of the 

 anomalous tract, however, a vertical dip prevails, as in the case of nearly 

 all the formations in this portion of the area. 



The fact of chief interest regarding the Montana group is its remark- 

 able and rapid disappearance between Bear and Coal creeks as distance is 

 gained from either of these streams toward the center of the region at 

 Golden. Immediately north of Bear ('reek its strike relations with the 

 underlying formations are rather more exaggerated than at mosl other 

 points, and consequently more clearly brought out in the surface exposures 

 there occurring. In this vicinity successive beds of the Pierre may be 

 traced over their general line of strike by means of their lithological 

 characteristics and the general prevalence of certain fossils at particular 

 horizons, from points L,000 feet or mure to the east of the Niobrara at the 

 bluffs of Bear Creek to others within only 200 or 300 feet of the older 

 formation, 1 or "_' miles to the north. The angle thus made by the differ- 

 ence in strike between the Niobrara and 1'ierre is on an average about 15°, 

 but decreases to the north, opposite the middle of the Dakota hogback, 

 beyond which the strikes are, for a considerable distance, more nearly 

 parallel. 



In the northern part of the region, opposite the first hogback north of 

 Golden, the exposures of the Montana -roup are rare, lint a halt' mile north 

 of Van Bibber ('reek, and from this point to Ralston, the discrepancy in 

 strike observable to the smith has for a time almost wholly disappeared; 

 beyond Ralston Creek, however, a divergence of 20° is still noticed in the 

 genera] trend of the Laramie and Dakota sandstones, which extends to a 

 line due east from the entrance- to the canyon of Coal Creek. This area is 

 regarded as corresponding to that in the vicinity of Hear Creek in the 

 south, over which a thickness of Montana beds equivalent to that on the 

 southern border of the field is regained, by which the geological symmetry 

 of the region is rendered complete. 



( >ver the middle portion of the region the Montana beds follow closely 

 the behavior of the Laramie, hut show frequent variations in thickness 

 and corresponding changes in their strike relations with the beds below. 

 Regarding the individual members of the Montana group, if the general 



