Washington and British Columbia. 639 



and a thin film of an efflorescence of these salts which 

 covers them produces this appearance. Beneath this 

 white film is mud, black, foul, and treacherous, which has 

 been the cause of the miring of cattle in the past. Dur- 

 ing the rainy season the whole lake is covered with water, 

 and then only a faint appearance of the circles is visible 

 beneath the surface of the fresh water. 



The smaller of these lakes, but the one more nearly 

 devoid of any other mineral matter except magnesium 



Fig. 2. 



Fig. 2. — Small spotted epsomite lake north of Oroville, Washington. 

 See explanatory cross-section, fig. 4. 



sulphate, is in the state of Washington. It has an area 

 of only four acres and a depth (determined by drilling) 

 of 30 feet. It has gone by the names of Salts Lake, 

 Poison Lake, Spotted Lake, and Bitter Lake. It is high 

 up in the hills (1000 feet above Oroville, or 2000 feet 

 above sea-level), in a little depression scooped out by 

 former glacial action. It has no outlet whatever, and 

 lies close to bed rock, which consists of metamorphic 

 rocks, dolomites, and shales. Near by, but at a slightly 

 higher elevation, are other smaller lakes or ponds of com- 

 paratively fresh water. In one of these is a deposit of 

 marl, which contains many little fresh water shells. 



