Washington and British Columbia. 641 



other holes and pumped out again, until finally, when 

 saturated it was piped to the salts plant on the railroad, 

 over two miles away. 



It was discovered, however, that the spots represented 

 the base of inverted cone-shaped or cylindrical masses 

 of salts, the tip of the cone being attached to a lower 

 horizontal bed of solid ep somite beneath, in places as 

 much as fifteen feet in thickness. This fact was import- 

 ant to those working the deposit, for it was found that 



Fig. 4. 



White 

 Surface Pool or spot efflorescenc e 



■ ,M »etarnorphi c VT^^r^M^OvV' N/l/p-V C, X < -' Seek 



Fig. 4. — Hypothetical vertical cross-section to show structure of small 

 epsomite lake north of Oroville, Washington. 



this bed could be tunneled into and timbered, for the over- 

 lying black mud was quite impervious to water. The 

 epsomite in this lower bed is in the form of large clear 

 colorless crystals, some of which might be measured in 

 feet. Upon exposure of this material to the air, a white 

 frosted surface coating is formed, and it loses part of the 

 water of crystallization, probably becoming the mineral 

 Meserite, MgS0 4 .H 2 0. In time the whole mineral 

 changes into this new substance. Sodium sulphate and 

 other allied salts are practically absent. 



In drilling to the bottom of the lake, when first pros- 

 pecting, it was found that beneath the epsomite was a 

 thin layer of gypsum, and between the gypsum and the bed 

 rock was a thin layer of clayey material. The drilling 

 was done because it was erroneously thought that the 

 lake was in the crater of a volcano, and that it would have 

 great -depth. 



In handling the salts at the plant, the operating com- 

 pany had to separate, when necessary, the included mud 

 particles from the epsomite. This was done by dissolv- 

 ing, settling, and reprecipitation from a supersaturated 

 solution caused by heating, evaporating, and then cool- 

 ing the clear solution. Much of the material, however, 



