GEOLOGICAL SURVEY OF THE TERRITORIES. 319 



the Kansas Pacific Railroad to Denver, of the Denver Pacific to Cheyenne, 

 and of the Colorado Central from Denver to Golden City, with the pros- 

 pect of its extension in another year to the mining towns in the mount- 

 ains, has greatly added to the importance of these mines, and led to 

 arrangements for working them upon a large scale. In September and 

 October last the writer again examined them, and also visited all the 

 coal-mines of importance in Wyoming and in Utah near the Union 

 Pacific road, and the following are some of the results of his investi- 

 gations and of the analyses he has made of the coals he has collected • 



All these coal-mines are found in a series of sandstones and fire-clay, 

 probably of lower tertiary age. No limestones occur with these strata, 

 and black slate is met with in small quantity only. The sandstones are 

 generally somewhat friable in texture, and are often exposed in bold 

 cliffs, the faces of which have weathered in very irregular shapes, and 

 frequently present deep holes and cavernous depressions. Its color is 

 from a light-yellowish to reddish brown, and sometimes gray. In places 

 it is sufficiently sound and firm to make a good building stone. The 

 fossils it contains are chiefly leaves of deciduous trees. No ferns and 

 other fossil plants are found in the formation like those common to the 

 true coal-measures. The black slates forming the roof of a coal-bed at 

 one locality in Wyoming Territory are found filled with fossil Unios, 

 which, as the writer is informed by Dr. J. S. Newberry, are probably an 

 nndescribed species. Fire-clay is perhaps the predominant material of 

 the formation. It occurs in beds of great thickness, especially in Col- 

 orado, and at Golden City it is manufactured into fire-bricks of excellent 

 quality. Clay iron-stone is occasionally interstratified with the clays 

 and black shales, and in Boulder County, Colorado, the summits and 

 sides of some of the hills near the coal-mines are partially covered with 

 masses of brown iron ore, that have the appearance of solid ledges, but 

 which were no doubt collections of clay iron-stone, left behind when the 

 lighter materials of the strata containing them were removed, and con- 

 verted subsequently by atmospheric agency into those brown hydrates. 



The coal-beds are often of great size, the largest now worked being 

 twenty-six or twenty-seven feet thick. This is on Bear River, on the 

 eastern border of Utah. For the most part they are remarkably free 

 from impurities, it being not rare to see a face of eight or even ten feet 

 of clean coal of brilliant luster, perfectly sound and solid in the mine, 

 without a particle of slate or any visible foreign matter that would injure 

 it. Iron pyrites, however, may generally be detected in small flakes and 

 thin disks, but very rarely in sufficient quantity to be injurious. Mineral 

 resin is a common ingredient of the Colorado coals, and was met with 

 at one of the mines only on the Union Pacific Railroad, that at Carbon. 

 The beds lie at an angle with the horizon ; some are vertical, none were 

 observed level. 



All the coals tend to crumble soon after being exposed to the weather; 

 but when protected they remain a long time unchanged, as is shown by 

 a large lump in the possession of the writer, which he obtained at a 

 mine in Boulder County, Colorado, in 1863, and which is still sound. 

 This tendency to crumble is the cause of great waste at the mines — all 

 the greater that these tertiary coals can scarcely ever be made to melt 

 and agglutinate into a firm coke. With rare exceptions, when submitted 

 to the coking process, they retain their form or crumble into a dry pow- 

 der. As seen by their analysis they all contain water in their composi- 

 tion, and this is very slowly given up even at the boiling temperature. 

 Its pressure necessarily detracts from the calorific power of the coals, 

 not merely by reason of the water taking the place of so much carbon, 



