THE NONMETALLIC MINEKALS. 



393 



It is olsowhorc^ stated that the point on the slope of the mountains 

 wh(n'(^ the d(^posits of caliche are found is some 500 or (JOO feet hio-hcr 

 than the valley, but that the material diminishes in quantity and rich- 

 ness as the valley is approached and disappears entirely at the bottom. 



An examination of the workings of these beds discloses the follow- 

 ing conditions: 



(1) That the surface to the depth of 8 or 10 inches is covered with 

 a layer of fine, loose sand. 



Nctlite und Glau-berlie 



NUraie of Sodium 



Fig. 12. 



MAP OF NITRATE REGION, CHILE. 



After Fuchs and De Launav. 



(2) That underneath the sand is a cong-lomerate of amorphous por- 

 phyry, feldspar, chloride of sodium, magnesia, gypsum, etc. , cemented 

 by the sulphate of lime into a hard, compact mass to a depth of 6 to 

 10 feet, called the "costra" or crust. 



(3) That below this crust the caliche, or impure nitrate, is found, 

 presenting to the view a variety of colors — yellowish-white, orange, 

 bluish-grav, etc. 



