354 GEOLOGY OF THE DENVER BASIN. 



wagon road crossing to its northern side and 2i miles west of Louisville, 

 the position of the rim is again clearly distinguishable in an outcrop of 

 basal sandstones which dip 15° SE. and strike N. 52° 30' E. The coal 

 horizon enters the mesa a little east of this, though no outcrop of coal is 

 visible: its presence in the vicinity is established by numerous drill holes 

 put down for prospecting purposes. In crossing the Davidson mesa the rim 

 of the syncline is concealed beneath the Quaternary cap, and it can only 

 lie conjectured that the coal measures gradually sink along the southern 

 arm of the Davidson fault, to finally attain the position in which they are 

 found north of the mesa at the abrupt turn in the Davidson ditch. In a 

 cut at this point, 20 to 25 feet below the surface of the ground, are two or 

 three narrow seams of coal, the thickest about 3 feet. These strike N. 30° 

 E. and dip 5° to 10° to the southeast. At the Superior mine, a half mile 

 east, the coal occurs at a depth of 90 feet, the collar of the shaft being 

 between 5 and 1<> feet higher than the coal at the head of the ditch. The 

 southeasterly dip seems, therefore, to be general for this portion of the 

 Held. Along the periphery of the measures no outcrop of coal shows, its 

 delineation being based on the general relations between topography and 

 strata, and on the fact that in a drill hole near the railroad sectiondiouse 

 2 miles north of Louisville the basal sandstones of the Laramie were alone 

 encountered, thus limiting the lower line of the coal series proper somewhere 

 to the southwest of the boring. The coal horizon, where present, finally 

 passes into the Sand Gulch fault, due strata along the southeastern edge 

 of this severed area, in the immediate vicinity of Sand Gulch fault, have a 

 decided dip to the northwest. This has been observed in drill holes and 

 shallow prospects on the southeastern slopes of the mesa, a half mile 

 northwest of Louisville. 



This small coal area between the Davidson and Sand Gulch faults, 

 which, from its chief opening, may be designated the Superior Area, has, 

 therefore, a synclinal structure, the axis lying somewhat to the southeast of 

 a median line and parallel to that of the main Coal Creek trough. The 

 depression is slight, the highest beds in the mesa being the coal measures; 

 in the bordering terraces, the basal sandstones only. 



The southwestern end of the Sand Gulch fault is not clearly defined. 



