340 GEOLOGY OF THE DENVER BASIN. 



two points, the region of the Burnt Knoll and the southern rim of the 

 Marshall Lake basin; the axial extent of these rolls is between a half 

 mile and a mile, the transverse extent about a half mile. The axis of the 

 general syncline suiters the greatest depression between the Burnt Knoll 

 and the southern side of the Lake basin, a maximum depth of 500 to 

 700 feet being attained by the coal measures. 1 



The continuity of the strata involved in the syncline is frequently 

 interrupted by faulting. The outcrops of coal are broken and irregular, 

 and the region is cut into small areas of various opposing portions of the 

 Laramie and Fox Hills. Instead, therefore, of comparative geological sim- 

 plicity there is great complexity, beds terminating abruptly beneath the 

 surface or, bv reason of gentle dip, having been brought into such positions 

 that erosion has easily removed them in part or in whole. 



The western rim. — Beginning at the vertical beds at the northern end of 

 the foothill district, a little southwest of the town of Marshall, the exterior 



Fig. 13. — Section of coal benches, Davidson mesa and northward, east of Marshall. A r, 

 C, Sandstones. F, F, Faults. X, ritistuo-iH <;ip nf mesa. — coal. 



periphery of the coal passes directly down the steep slopes of South Boulder 

 Creek to the low line of bluffs immediately above the bottom lands. In 

 this distance the strata change from their highly inclined position to one of 

 gentle dip to the southeast. The outcrop of the coal beds follows the crest 

 of the lower bluffs to a short distance east of Marshall, after which, gradually 

 receding to a half mile from the valley bottom, it follows the low rise 

 constituting the second terrace, the lower ten-ace along here being formed 

 of the basal sandstone A of the Laramie, with occasionally a portion of 

 the I! stratum, the second terrace including the 1! sandstone and the 

 overlying coal measures. The trend of the coal outcrop in the second 



'In the tesl boring at the outlet of the Lake basin in the SW. I see. 14, T. 1 S., 1.'. 70 W., 

 Mr. R. C. Hills, of the ( iolorado Fuel Company, reports a depth reached of 645 feet , with the base of the 

 Laramie still below. In drilling, one 3-foot coal seam was passed, ami artesian water was obtained. 



