250 YAOI eG SAU ES LSA CIRS 
formation, about 200 feet of sandstone and conglomerates; and the 
Ruby formation, with a maximum thickness of 2500 feet of sandstones, 
shales, and conglomerates made up to a large extent of eruptive débris. 
These formations are separated by an unconformity from the underly- 
ing Laramie, and to the west of this area pass beneath the beds of the 
Wasatch Eocene; in the absence of fossil evidence they have been 
classed as Cretaceous. 
The geological structure of this region affordsgevidence of no less 
than four important orographic movements, involving the making of 
new land, the erosion and planing down of the same, and the inaugura- 
tion of a new cycle of sedimentation, which account for the great varia- 
tion in thickness of certain formations. First, during post-Archean 
time, the first deposits, after which were Upper Cambrian (Sawatch 
quartzite); second, during Carboniferous time, followed by deposition 
of Weber shales and Maroon conglomerates; third, during Mesozoic 
time, followed by deposition of the Gunnison sandstone; and fourth, 
after Laramie time, followed by the Ohio, Ruby, and Eocene forma- 
tions. 
Mineral resources.—The most important economic product of the 
region is its coal, which is found in the lower part of the Laramie 
Cretaceous formation, between beds of sandstone. ‘The quality of the 
coal varies, according to local conditions more or less favorable to 
metamorphism, from dry bituminous, through coking coal, to semi- 
anthracite and anthracite. Next in importance are its silver ores, 
which occur for the most part in true veins or fault fissures in all 
varieties of rock, but mainly in the sedimentary beds of upper horizons 
near eruptive rocks. ‘The ores are generally rich, but in small bodies, 
and, in consequence of natural obstacles to cheap mining, have not 
been extensively worked. Gold has been found in paying quantities 
in the alluvium of a single gulch; lead and copper are accessory pro- 
ducts in limited amounts. 
