THE NITRATE DEPOSITS OF CHILE 9 



leached appearance, due to the action of the rains and floods which 

 at rare periods visit the pampa (see Fig. 3). Sink holes, due to the 

 same cause, are not infrequent. Most of the deposits consist of 

 common salt (sodium chloride) or of nitrate (sodium nitrate), or of 

 both mixed together; while other saline materials occur more spar- 

 ingly. The salt beds are called by the Chilean salares and the nitrate 

 beds, salitreras. The material composing the nitrate beds is known 

 as caliche. 



Though both common salt and nitrate occur in very large quanti- 

 ties, the former is by far the more abundant, and covers immense 

 flats for many square miles in area along the western edge of the 

 pampa. Sometimes it is in comparatively pure beds, sometimes it is 

 mixed with clay, sand, and gravel, and sometimes it only impregnates 

 the surface of the pampa. These salt beds have not yet been exten- 

 sively explored, but they probably vary from a mere crust to several 

 or even many feet in thickness. The salt is not much used, though 

 a little is obtained for local consumption and is refined by dissolving 

 and evaporating the solution. 



The nitrate deposits, though less extensive than the common salt 

 deposits, are far more important commercially. Like them, they occur 

 in the low zone along the western edge of the pampa, but while the 

 salt flats are usually in the very bottoms of the basins, the nitrate 

 deposits are usually on a little higher ground. Sometimes the nitrate 

 deposits also occupy the bottoms of the basins, but their typical position 

 is on the lower slopes of the hills and ridges, forming terraces or benches 

 around the salt flats, and from a few feet to perhaps one hundred feet 

 or more above them. Sometimes there may be nitrate upon the 

 slopes and no salt in the flats, and sometimes there may be salt in 

 the flats and no nitrate on the slopes, whfle sometimes the deposits 

 of the two materials are more or less indiscriminately mixed or may 

 underlie or overlie each other; but in many cases we find them both 

 occupying the respective typical positions just mentioned. The 

 slopes on which the nitrate often occurs rise at low angles and are 

 sometimes scarcely distinguishable from the surrounding flat country. 



The nitrate deposits are of very variable thickness even over small 

 areas, and in one spot there may be several feet of the material, while 

 within a few yards there may be only a few inches, or none at all. 



