134 GEOLOGICAL SURVEY OF THE TERRITOEIES. 



Sontli Park also, are numerous examples of the outpouring of igneous 

 material. That internal heat connected with these igneous outbursts 

 may have affected the sedimentary rocks in the Boulder district, and 

 rendered the coal more compact and anthracitic, under pressure, seems 

 to me possible, at least. The rocks which appear to have been affected 

 by heat are seen only for a few miles south of the Boulder — from five 

 to ten miles. South of that no effects whatever have been observed. 



The neit finest exhibition of coal in Colorado to Marshall's mine is 

 that of the Murphy mine, on Ealston Creek, five miles north of Golden 

 City. The coal bed is nearly vertical in position, and varies in thick- 

 ness from fourteen to eighteen feet, averaging sixteen feet from side to 

 side. There are nine feet of remarkably good fire-clay on each side of 

 the coal, and above and below, or on the west and east sides, are the 

 usual beds of sandstone. This mine is very near the foot of the moun- 

 tains, and the belt of sedimentary rocks, which are all nearly vertical, 

 is very narrow here — not more than half a mile in width — and are 

 mostly concealed by debris. 



Mr. Muri^hy thinks that there are eleven beds of coal within the dis- 

 tance of one-fourth of a mile, all nearly or quite vertical in positiou, of 

 which the one opened is probably the oldest. The mine is opened on 

 the north side of the creek, and may doubtless be followed above water 

 line several miles to the northward, toward Coal Creek. 



On the south side of Ealston Creek the same bed has been opened, 

 and the indications are that it may be followed the same way south- 

 ward toward Golden City. The entire surface is so covered with super- 

 ficial deposits, and grassed over, that it is impossible to work out these 

 beds in detail, and the artificial excavations afford us the most reliable 

 knowledge. A hundred yards or more west of the coal bed there is a 

 high ridge running i)arallel with the mountain range, capped with lower 

 cretaceous sandstones No. 1. 



This ridge extends southward, with some interruptions, beyond 

 Golden City. 



At Golden City the upheaved sedimentary rocks are so swept away 

 that the metamorphic foot-hills are plainly visible. No rocks older than 

 the red beds or trias are exposed, and these somewhat obscurely. The 

 red and gray sandstones lie close on the sides of the metamorphic rocks, 

 inclining 30° and 54°. In the trias there is a bed of silica or an aggre- 

 gation of very fine grains of quartz which has attracted some attention, 

 and close to it a layer of bastard limestone or calcareous sandstone. All 

 the beds dip at a high angle and lie side by side, so that one can walk 

 across the ui)turned edges of them all, from the metamorphic to the 

 summit of the tertiary. Outside of the cretaceous beds there is a small 

 valley of erosion, and then come the tertiary beds. The strike of the coal 

 strata is very nearly north and south, and, so lar as I could ascertain, the 

 sequence of the beds from within, outward, is as follows : 



1st. Eusty, yellow, soft sandstone. 2d. A bed of fire-clay. 3d. Coal 

 about eight feet thick. 4th. Fire-clay. 5th. Eusty, yellow sandstone. 



The clay underneath the coal appears to be ten or fifteen feet thick, 

 with one or two unimportant seams of coal. These beds have been so 

 elevated that the upper edges have passed verticality 5° to 10°. The Clar- 

 is much used for fire-brick and potter's ware. In the bed of sandstone, 

 above the coal, we found several impressions of leaves of deciduous 

 trees, among them a Platanus, probably P. haycleni. From these we 

 pass across the edges of a series of beds of sandstone, with intervening 

 strata of iron ore. The thickness of all the tertiary beds here must be 

 1,200 to 1,500 feet. Near the outside is a bed of pudding-stone, and 



