CHAPTER YII. 



THE GREEN RIVER COAL BASIN. 



The Great Basin is bounded upon the east by the Wahsatch Mountains, a 

 definite, single range vieing in altitude with the Sierra Nevada. Along its 

 western base lie the deepest plains of Utah, sinking to the level of 4,000 feet, 

 and occupied by low desert ranges, wide expanses of alkaline desert, and saline 

 lakes, of which Great Salt Lake is the largest and best known. Those low 

 mountain chains which lie traced across the desert with a north and south 

 trend, are ordinarily the tops of folds whose deep synclinal valleys are filled 

 with Tertiary and Quaternary detritus. They are composed of sedimentary 

 beds, dating from the Azoic up to the late Jurassic. It is common, however, to 

 find no rocks higher than the Carboniferous, for immense erosive action has grad- 

 ually removed the uppermost members of the series of tables, the Carboniferous 

 limestone offering sufficient resistance to the weathering forces to protect the 

 lower members of the group. The Wahsatch itself is one of the most impor- 

 tant mountain ranges of America. Its summits tower to the region of per- 

 petual snow and its bases are cleft down sometimes to the level of the Utah 

 plain. Canons of extraordinary abruptness are water-carved transversely through 

 its rock material, opening with bold, picturesque gateways upon the level of the 

 Mormon lowlands. The materials of this range are in general identical with 

 those of the other great Cordillera chains, but they are here developed and. 

 exposed on a scale of grandeur and clearness of relation which is nowhere 

 else apparent. Fifty-six thousand feet of conformable stratified rock make 

 up its bulk. A lower group is composed of about 25,000 feet of intercalated 

 quartzose, mica, and hornblendic schists The quartzites at the uppermost 

 limits of the group arrange themselves in finely stratified layers or soUd beds 

 of extreme thinness. Overlying these is a series from 3,000 to 4,000 feet in 

 thickness, embracing representatives of Silurian, Devonian, and Carboniferous 

 periods, eight-tenths of this Paleozoic group being composed of calcareous and 

 dolomitic materials, but interrupted during their lower half by intercalated 



