766 DESCRIPTIVE GEOLOGY. 



Mountains. On the other hand, they are rich in forms showing the pecu- 

 liar phenomena of rhyohtic groundmasses. 



Kawsoh Mountains. — The depressed region between the Montezuma 

 Eange and the outlying hills of the Kawsoh Mountains is occupied by an 

 important development of disturbed Miocene rocks, which form a low but 

 scarcely perceptible divide between the Humboldt Valley and the Hot 

 Spring Valley to the w^estward. In the region of Hot Spring Station, 

 although they are somewhat obscurely exposed, they appear to lie nearly 

 horizontal, but, in passing northward toward Mirage Station, they become 

 more and more inclined to the northwest, reaching a maximum dip of 25°. 

 After a considerable erosion, which is subsequent to their upheaval, they 

 -have been overflowed by massive sheets of black basalt, which here, between 

 the two ranges, occurs as isolated hills capping the sedimentary strata. 

 In the hills about two miles north of the diorite outcrop, shown on the geo- 

 logical map at the northern end of the Kawsoh Mountains, there is a sec- 

 tion of these Miocene rocks exposed to the thickness of about 700 feet. 

 Beginning at the top and following the series downward, we have: 



1. Basalt 



2. Coarse, sandy grit 30-40 feet. 



3. Saccharoidal cream-colored limestone, carrying fresh- water fossils > ro f «- 



A. ]\Iarly grits - , ) 



r>. Fine grained friable sandstone 70 feet. 



6. Formation concealed by Quaternary accumulations 100 leet. 



7. Marly grit. 50-CO feet. 



8. Infusorial silica 200 leet. 



9. Palagonite tufa, base not exposed , . 250 feet. 



At other localities skirting the northern edge of the Kawsoh Mount- 

 ains very similar exposures are offered, in places the upper members being 

 covered by basaltic masses, and in most of them the palagonite tufas by 

 drifting desert sands. 



At Fossil Hill, the cr^am-colored friable limestones abound in organic 

 remains, of which the following speciei have been identified b}^ Prof. F. B. 

 Meek : 



Carinifex (tortifex) Binneyi. 



Carinifex (vortifex) Troyoni. 



