NITRATE PROSPECTS IN THE AMARGOSA VALLEY. 3 



long period of continued movement and great erosion, the debris 

 being removed from the area. This condition was modified some time 

 in the Tertiary by the origin of a chain of lakes, probably corre- 

 sponding roughly to the present valley of the Amargosa, in and 

 around which the Tertiary series was laid down. These lakes were 

 similar in general character to the other Tertiary lakes which have 

 been recognized in various parts of Nevada and California. 



The succeeding history of the region has been one of the effects 

 of continued crustal movement and of fluctuating climate upon these 

 lakes and their successors. Now drained by overflow or outlet cut- 

 ting, now inclosed by desiccation or differential uplift, this series 



FIG. 2. Valley of the Amargosa River near Sperry, showing erosion of the Tertiary ( ?) 



series. 



of lakes and desert valleys has left a record of considerable com- 

 plexity, which is yet almost entirely unread. 



THE NITRATE HILLS. 



The indications of nitrate have been found in low, rounded hills 

 formed of the clay strata of the Tertiary (?) series above men- 

 tioned. (Figs. 3 and 4.) Always these hills have been greatly 

 eroded, and their surface is composed of a loose, structureless clay 

 formed by the weathering of the original stratified clays. This coat- 

 ing of loose material is from 10 to 30 inches deep and below it lie the 

 tilted stratified clays, these being occasionally exposed by recent 

 erosion. The loose surface clay is seldom noticeably saline, but occa- 

 sional salt efflorescences are visible where shallow holes and the like 

 have caused a local concentration of rain water. The underlying 



