THE NONMETALLIC MINEKALS. 



393 



It is elsewhere stated that the point on the slope of the mountains 

 where the deposits of caliche are found is some 500 or 600 feet higher 

 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 \ajer of fine, loose sand. 



Ifctlite and Glattberife 



Fig. 12. 



MAP OF KITRATE REGION, CHILE. 



After Fuchs and De Launay. 



Nitrate of Sodium 



(2) That underneath the sand is a conglomerate 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-gray, etc. 



