coal. 339 



The two coal seams now showing are: The upper, 2^ feet thick; the 

 lower, ,'U feet. This statement differs from that of Marvine, in the Report 



on Colorado for 1873, page 124, in which six beds arc mentioned; the one 

 worked, of a thickness of 7 feet. The measures at the creek strike a little 

 west of north and dip cast about 50°, although north and south of this 

 they become vertical. 



It is probable that from Coal ('reck northward the strata bordering 

 the great fold on the cast were considerably elevated, producing a gradual 

 diminution in this direction in the depth at which the coal is to be found. 

 The coal measures outcrop along the southern bluffs of South Boulder 

 Creek, there being here only a slight southeasterly dip 



THE BOULDER COAL FIELD. 



The entire coal field in the northwestern part of the Denver Basin is 

 in -the main confined to tin- two great synclines of the region; the one 

 known as the Davidson lying diagonally across the Davidson and Lake 

 mesas, its axis about a mile east of the town of Marshall; the other lying 

 along the valley of Coal Creek, designated the Coal ('reck syncline, and 

 including the Louisville, Erie, and other subdivisions. 



THE DAVIDSON SSNGLINE. 



General features. — The Davidson svncliiic in its greatest extent embraces 

 the Davidson-Lake mesa and its slopes from South Boulder Creek on 

 the north to upper Coal Creek on the south. The areas mined at the 

 time of examination wen- two, the Marshall and Davidson, but there are 

 several long-abandoned openings and prospects scattered over other por- 

 tions of the region. The western rim of the syncline as it appears in 

 the Laramie formation coincides with the western line of outcrop of the 

 basal sandstones; the eastern rim crosses the Davidson-Lake mesa in a, 

 northeast-and-soutbwest direction, very near the summit of the divide 

 between Coal Creek and the drainage to the South Boulder through the 

 town of Marshall. The southern end of the syncline is in the ridge 

 separating Coal ('reek from the Marshall Lake basin: the northern end lies 

 midway between the fortieth parallel and Boulder Creek. The syncline 

 is longitudinally crumpled by gentle yet clearly defined anticlinal rolls at 



