POTASH SALTS AND OTHER SALINES IN THE GREAT BASIN REGION. 5 
Pre-Tertiary rocks embrace a comparatively large area of the basin region. The chief 
formations are: Cambrian, Silurian, Devonian, Carboniferous, Triassic, and Jurassic. 
Pre-Cambrian formations have been described by King, Spurr, and Ball, but are rela- 
tively unimportant. The eastern and southeastern part of Nevada is characterized 
by Cambrian, Silurian, Devonian, and Carboniferous rocks. These rocks are quartz- 
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Fig. 1.— Diagrams showing the proportion of mountain and intermountain area in the several districts. 
ites, slates, limestones, and sandstones. Triassic and Jurassic formations are rela- 
tively less abundant and occur in widely distributed patches in the west-central and 
southwest portions of the basin region. They consist of limestones, slates, shales, 
and thin beds of quartzite. In the Triassic are also found beds of gypsum. 
Post-Jurassic orogenic movement, accompanied by granitic intrusions, ushered in 
a period of land elevation and erosion, which continued throughout Cretaceous time. 
