THE BOULDER VALLEY REGION. 



1 25 



structure with the general country beyond. The southeastern rim, also, 

 is broken in continuity by faulting of the beds, a sharp displacement 

 being observable in the railroad cut, in the bluffs of Coal ('reck, south of 

 Louisville. The greatest depth beneath the valley of Coal Creek attained 

 by the base of the Laramie is between 300 and 350 feet, in the region of 

 the Lafayette trough. 



The subordinate troughs of the Coal < 'reek syncline are five, the 

 Superior, Louisville, Lafayette, Mitchell, and Canfield-Erie. 



The Superior trough is a shallow depression of somewhat irregular 

 configuration near the northwestern edge of the general syncline. It 

 occupies the eastern end of the Davidson mesa and a portion of the valley 

 and bench lands on the north and south. It is severed from the Louisville 

 trough, which lies just southeast, by the Sand Gulch and Harper faults, 

 against which its beds are slightly upturned. At the southwest end, how- 

 ever, beneath the bottoms of Coal ('reek, ir is probably continuous with 



S.E. 



the Louisville depression, the dividing fold or fracture having disappeared. 

 The northern end of the Superior trough is a little north of the fortieth 

 parallel. The amount of depression that the strata have undergone is 

 comparatively slight, but is somewhat greater in the southern half than 

 in the northern. The highest beds present along the center of the trough 

 are the lower strata of the upper Laramie. 



The Louisville trough extends from a point a little southwest of the 

 Denver, Marshall and Boulder Railroad, about ."> miles above Louisville, 

 down the valley of Coal ('reek a distance of 1 or 2 miles below the 

 town, where it passes diagonally into the ridge to the north and probably 

 merges with the western portion of the Lafayette and Erie synclines. A 

 generalized transverse section of the fold is shown in fig. 9. 



The axis of the Louisville syncline lies considerably southeast of the 

 town. The northwestern rim of the trough passes along the western and 



