206 REPORT OF NATIONAL MUSEUM, 1899. 



The predominating mineral in this region is Carnallite [Specimen No. 40225, 

 U.S.N.M.], a double chloride of potassium and magnesium, containing 26. 76 percent 

 chloride of 'potassium, 34.50 percent chloride of magnesium, and 38.74 per cent water, 

 corresponding to the formula KC1, MgCl 2 , 6H 2 O. In the pure state it is colorless and 

 transparent, and possesses a specific gravity of 1.618. It is very hygroscopic, and is 

 easily soluble in water, 100 parts of which dissolve 64.5 parts of the mineral. It may 

 be artificially formed from a solution of chloride of potassium, containing not less 

 than 26 per cent of chloride of magnesium. The deposit which figures to the right 

 of the Carnallite region is, as before mentioned, a secondary formation, and consists 

 principally of the mineral Kainite [Specimen No. 64735, U.S.N.M.]. This deposit, 

 though limited as compared to the other salt deposits, is yet of vast extent. The 

 average composition of this deposit is: 



Sulphate of potash 23.0 



Sulphate of magnesia 15. 6 



Chloride of magnesium 13. 



Chloride of sodium 34. 8 



Water 13.6 



100.0 



In the pure state it is colorless and almost transparent, and possesses a specific 

 gravity of 2.13; 100 parts of water dissolve 79.5 parts of it. Cold water does not 

 decompose it, but from its saturated hot solution the double sulphate of potash and 

 magnesia separates, and chloride of magnesium remains in solution. 



Methods of mining and manufacture. In the manufacture of salt 

 three principal methods are employed. The first, if, indeed, it can be 

 called manufacture, consists in mining the dry salt from an open 

 quarry, as in the Rio Virgen and Barcelona deposits, or by means of 

 subterranean galleries, the methods employed at Petite Anse and in 

 Galicia. 



At Petite Anse the method of mining and preparation, as given by 

 Mr. R. A. Pomeroy, 1 is as follows: 



Mining is done by means of galleries on two levels. There are 16 

 to 25 feet of earth above the salt deposit. The contour of the latter 

 conforms nearly with that of the surface. The working shaft is 168 

 feet deep. The depth to the first level or floor is 90 feet; to the sec- 

 ^ond, 70 feet farther. The remaining 8 feet are used for a dump. 

 The galleries of the first level were run, on an average, 40 feet in 

 width and 25 feet and upwards in height, leaving supporting pillars 40 

 feet in diameter. 



The galleries of the second level are run 80 feet in width and 45 feet 

 in height, leaving supporting pillars 60 feet in diameter. The lower 

 pillars are so left that the weight of the upper ones rests upon them 

 in part, if not wholly, with a thickness of at least 25 feet of salt rock 

 between. 



Galleries aggregating nearly 1 mile in length have been run on the 

 upper level and some 700 feet on the lower. 



In running a gallery the first work is the "undercutting" on the 

 level of the floor, of suflicient height to enable the miners to work 



transactions of the American Institute Mining Engineers, XVII, 1888-89, pp. 111. 



