6 Geological and Miscellaneous Notice of Tarapaca. 



marl impregnated with saline matter and mixed with fragments of 

 shells. 



This salt, technically termed caliche, varies in the quantity of 

 nitrate of soda which it affords, from twenty to seventy five per 

 cent. With it there is generally more or less insoluble matter, 

 consisting of red marl and fragments of shells, in some beds 

 amounting to nine per cent., but averaging not more than three 

 per cent. It possesses a granular structure, arising from irregu- 

 lar rhombic crystals, which vary considerably in size in differ- 

 ent localities. Some of the beds are exceedingly compact, and 

 when wrought, require to be blasted with gunpowder; while 

 others are easily broken with the aid of a pick and shovel. 

 Cavities are occasionally found partly filled with crystals, reg- 

 ular in form and nearly pure. The color varies in different 

 beds, and in different parts of the same bed. Some specimens 

 possess the whiteness of refined loaf sugar ; others are reddish 

 brown, lemon yellow, and gray. Every variety is found in the 

 same bed, but the compact white and yellow is most abundant 

 between the quebrada of Tiliviche and the point called Molina. 

 The composition of average specimens from the beds which are 

 worked, as determined by Mr. A. A. Hayes, is as follows : 

 Nitrate of soda, ...... 64.98 



Sulphate of soda, . . . . . . 3.00 



Chloride of sodium, 28.69 



Iodic salts, ....... 0.63 



Shells and marl, 2.60 



99.90 

 We are indebted to the same gentleman for our knowledge of 

 the presence of iodate of soda and chloro-iodate of magnesia in 

 combination with this salt.* 



In various parts of the western coast of South America, be- 

 tween 18° and 23° of south latitude, nitrate of soda is found 

 impregnating the soil in connection with other saline matter, and 

 in some instances forming a thin crust on the surface ; but no 

 where in extensive beds as in the province of Tarapaca, between 

 19° 30' and 20° 45' south latitude, and 69° 50' and 70° 5' west 



* The ' mother' water, at some of the refineries on the pampa, are very rich in 

 iodic salts; their presence was first observed by noticing the deep blue color pro- 

 duced by some crumbs of bread which had accidentally fallen into the vats. 



