114 GEOLOGl OF THE DEKTEB BASLN. 



elevation, now the mass of Coal Creek Peak, Around this early eminence 

 were laid down, in probably uninterrupted succession, sediments of the 

 Triassic, Jurassic, Dakota, and even younger formations, the later beds 

 overlapping the older on the slopes of the elevation. By the uplift of the 

 Colorado Range the beds wore brought approximately into their present 

 positions, and 1>\ erosion have Keen broughl into the surface relations they 

 dow hold. In short, there exists here another of the unconformities so 

 frequent along the Colorado Range in the Denver field, with the differ- 

 ence that in this ease the unconformity is probably confined to the line of 



the Arehean anil sedinieiitaries. 



In the uplift of the range, however, there appeared in the northern 



portion of this locality, close to the line of union between the sedimentary 



beds and the granite, a crumple similar in structure to a fold en echelon, 

 the remnants of which now exist only in the small anticline in the Triassic 

 rocks ami in the isolated outcrops of the Jura and Dakota on the moun- 

 tain side, erosion subsequent to the uplift of the range having destroyed 



all other trace-. 



rill, REGIOH FROM THE BOXTLDEE UNCONFORMITIES TO COAL CREEK PEAK. 



[•HE FAULT VI rHE SOOTHERS LIMIT OF THE REGION OF rHE BOULDER UNCONFORMITIES. 



This appears at a point about _.\ miles south of Boulder, as an 

 east-and-wesl lateral displacement of about 500 feet, in the Dakota and 

 adjoining measures, the line of the fracture being now occupied by a 

 mountain stream. Notwithstanding the very considerable displacement 

 in the Dakota, neither the Trias below nor the Pierre above seems to 

 have been involved in an important degree. The fracture is at right 



angles to the present strike of the beds, and the fault plane is apparently 

 vertical. The strata to the south of the break are thrown to the east, 

 the reverse of the throws in the similarly disposed faults in the southern 

 hall' of the Golden region. This fact, in connection with the location of 

 the fault — at the very limit of the affected area of unconformity, yet at an 

 early bend in the strata — while indicating indirect influence l»v attendant 

 structural conditions, points to a time of actual development subsequent 

 to the early folds and synchronous with the uplift oi' the range and the 

 assumption by the strata of their present position. 



