774 DESCRIPTIVE GEOLOGY. 



Miocene beds, broken through and for the most part capped by basalt, which 

 forms the higher peaks and ridges. Characteristic Miocene strata, including 

 the cream-colored limestone, infusorial silica, and palagonitic tufas, are 

 exposed along the base of hills, concealed in a great measure by horizontal 

 Pliocene beds and drifting desert sands. The palagonitic tufa is well shown 

 southeast from Hawes Station, near the Carson River, where it appears 

 somewhat finer and purer than at Fossil Hill. • The best exposures of the 

 sedimentary series are found south of the line of the map, in low hills below 

 the ancient lake-terraces. 



An analysis of the cream- colored limestone from the hills near Valley 

 Wells yielded Mr, B. E. Brewster the following : 



Silica- 31.119 



Alumina, ) 

 Ferric oxide, ) 



Lime - 35.817 



Magnesia 0.864 



Carbonic acid 29.165 



Water 2.101 



99.498 

 The basalts requii'e but little special mention ; in petrographical habit, 

 they are allied to those of the Kawsoh Mountains and Truckee Valley. 

 They are fine-grained anamesites, black and grayish-black in color, and 

 rich in globulitic glass-base. In a deep ravine, opening out toward the 

 Carson River, they are well shown in precipitous walls, 80 feet in height, of 

 vesicular rock, in which the vesicles are lenticular in shape, and lined with 

 a pale lilac siliceous secretion, many of them more or less filled with chalce- 

 donic matter. These lenticular cavities, usually arranged horizontally, often 

 reach an inch or more in length. 



It may be well to note here a thermal spring which rises out of the 

 sedimentary beds, in the region of eruptive rocks, just south of the map, 

 and near the road going from Wadsworth directly southward, by Valley 

 Wells. It is a stagnant pool, 3 feet wide, having a temperature of 73°. It 

 is said that the water for the past few years has been growing gradually 

 cooler. 



