THE BOULDER VALLEY EEGIOX. 135 



existence of the lower Laramie sandstones and coal measures in the block 

 on the west, opposed to the Fox Hills and to the basal sandstones A of 

 the Laramie in the block on the east. The recognition of the Laramie 

 is from an occasional characteristic outcrop, together with a sandy soil 

 peculiar to areas immediately underlain by its lower members; the Fox 

 Hills is recognized by its concretionary limestones and its fossils, the 

 outcrop forming- a narrow strip of land along the eastern side of the fault. 

 The terminal points of the fault are invisible on account of the Hat and 

 covered condition of the region in which they lie, but observations were 

 obtained within a short distance of either end, as given on the map, which 

 prove an extent of at least the distance platted. Whether the fault is <>\' 

 the reverse type or not is undetermined. Its downthrow is on the west, 

 the stratigraphic displacement being about 200 feet near its southern end. 

 in the vicinity of the railroad, hut probably decreasing somewhat to the 

 northeast. 



The Harper fault was discovered through boring for coal and water, 

 no trace of it whatever being found at the surface. It has considerable 

 economic importance, involving as it does the presence or absence of coal 

 and the depth at which it may he found in the affected region. From the 

 data furnished by the Messrs. Harper, the bore holes north of the fault 

 afford satisfactory evidence of the presence of coal measures, while the hole 

 to the south, put down hut a. short distance from the productive drillings 

 across the line, is stated hv them as showing no coal whatever at over 

 double the depth. From the outcrops of the Fox Hills near the southern 

 end of the Sand Gulch fault, it is probable that the surface immediately 

 south of the Harper break is underlain hv strata at least lower than the 

 coal series. Farther out in the valley of Coal ('reek, by reason of a 

 southeasterly dip, higher measures succeed, until just north of the creek the 

 coal itself is found in an old shaft, at a depth of 160 feet below the surface. 

 North of the fault the strata are apparently crumpled, first dipping from the 

 break, then turning up to the northwest, forming a shallow local syncline. 

 The extent of the fault to the southwest is unknown. In its relation to 

 the other faults of the Boulder Valley system, it belongs to the series of 

 fractures having 1 the trend of N. 50° to GO E. 



