THE GREEN EIYEE COAL BASIN. 453 



and calcareous grits. They are chiefly composed of fine, siliceous sand, con- 

 taining here and there finely comminuted micas, and interrupted at frequent 

 intervals by zones of conglomerates, whose well-rounded pebbles of metamor- 

 phic rocks point for their origin unquestionably to the strata of the Y/ahsatch. 

 Near the summit of the 9,000 feet, a looser texture begins, and this change 

 is rendered very noticeable by the introduction of beds of coal, which, for an 

 unknown distance upward, probably several thousand feet, reappear through 

 a zone of constantly changing sand and mud rocks. The fossil life, which 

 clearly indicates a Cretaceous age for the deepest members up to and includ- 

 ing the first two or three important coal beds, from that point gradually 

 changes with a corresponding alteration of the sediments, indicating a transi- 

 tion to a fresh-water period. The coal continued to be deposited sometime 

 after the marine fauna had been succeeded by fresh-water types. The 

 species of fossils are in no case identical with the California Cretaceous beds, 

 which occupy a similar geological position on the west of the Sierra Nevada. 

 Their affinities decidedly approach those of the Atlantic slopes, while the 

 fresh-water species, which are found in connection with the uppermost coal 

 beds, seem to belong to the early Tertiary period. We have then here the 

 uppermost members of the Cretaceous series, laid down in the period of the 

 oceanic sway, and quite freely charged with the fossil relics of marine life; 

 then an uninterrupted passage of conformable beds, through the brackish 

 period up, till the whole Green River Basin became a single sheet of fresh 

 water. The area and boundaries of this great Tertiary lake, which, by the 

 gradual depression of the Mississippi Valley, was drained of oceanic waters, 

 is fully discussed in the geological volumes of this Report. It is only the 

 purpose of the present chapter to indicate the general relations of the coal- 

 bearing series to the rocks which immediately preceded, and those which 

 have been laid down subsequently. 



The chain of Uintah Mountains which, in latitude 41°, starts from the 

 crest of the Wahsatch Mountains and projects eastward for certainly 150 miles, 

 making a right-angle with the Wahsatch system, belongs, like all the greater 

 ranges, to the Jurassic upheaval. Its great height lifted a broad, central 

 zone above the level of the Cretaceous ocean. Upon both of its flanks, up to 

 an altitude of 7,000 feet, repose unconformably the buff" sandstones and the 



