120 GEOLOGICAL SUEVEY OF THE TERRITORIES!. 



spurs of the Arclisean rocks. Then comes the zone of outcropping edges 

 of the Triassic, Jurassic, and Cretaceous beds, approximately shown by 

 the lining; the first two by oblique lines downward to the right, the 

 last by horizontal lines. To the east, so far as I know, all is of the 

 Lignitic formation. 



Sections illustrating the relations between these beds at several points 

 (indicated by numbers on the map) are given on Plate II. The basis of 

 this tnap is compiled from the IJnited States land survey, the town- 

 ships and sections being therefore authoritative. The limits of the 

 counties are shown by the oblique lining downward to the left, while 

 all the railroads at present in operation are also given. It will be seen 

 that, as before stated, the main coal-measures, so far as known and 

 opened, lie chiefly near the mountain-base. From near Bowlder City 

 so^uthward through Golden City to where the South Platte debouches 

 from the mountains is almost a continuous line of openings, among 

 which are the Marshall and Murphy mines, probably as well known as 

 any coal-mines in Colorado. Though at the north the beds dip gently 

 to the east, throughout nearly all the remainder of this line they stand 

 nearly vertical, and in places are thrown over beyond the vertical. To 

 the north, along the zone of hog-backs, this horizon would probably be 

 found lying a little above the Cretaceous beds, and it has, I understand, 

 been opened near both of the Thompson Creeks, but so far the demand 

 in this northern region has not required an active search for coal. 

 Instead of to the north, the main openings have been developed to 

 the northeast of Bowlder City, reaching to Platteville near old Fort 

 Saint Yrain. Of these, the Erie and Baker mines are the most prom- 

 inent. Whether belonging to the same or to a higher horizon in the 

 lignitic group than the former coal-openings, is not yet ascertained with 

 certainty. 



The best known coal-openings, then, may be considered as arranging ( 

 themselves along a line running from Platteville soathwestward to near i 

 Bowlder City, and then turning southward along the base of the mount-/ 

 ains to the South Platte. It is near the middle of this zone that th^ 

 best and thickest development of the coal seems to occur. Beside^ 

 these openings, excepting a few poor indications of coal at scattered 

 places, the only others that I have heard of lie from fifteen to seventeen 

 miles east of Denver City, and near the Box Elder station on th 

 Kansas Pacific Eailroad. i 



In describing what is known of the occurrence of coal at the varioii 

 I)oints indicated, I will speak first of this-eastern group, and then, coii- 

 mencing at the north, follow southward along the line of openings befoB 

 spoken of to the South Platte. The information is gathered mostly frm 

 the reports of Hodge, Hayden, and Lesquereux, supplemented by mufi 

 material given me by Mr. Berthoud. It is to be understood that In 

 speaking of " mines," such extensive openings as characterize the eat- 

 ern coal regions are by no means intended. As yet the demand for cftl 

 has been but small, and in nearly aU cases the mining has been crudein 

 method and small in extent, though the time is at hand when both |ts 

 improvement and enlargement will be very great. 



THE VARIOUS OOAL-OPENINGS. 



East of Denver, in township 4 south, and probably between raiies 

 65 and 66 west, a shaft has been sunk for some depth in <n high bpk 

 on the south side of Sand Creek, but is now abandoned. The coal |so 



