RELATION OF LAKES TO CLIMATIC CONDITIONS. 77 



ill such instances seems to be secreted l)y tlie plants as a part of their 

 vital function, but the process is not well understood.^ 



The origin of oJilitic sand, consisting of little spheres formed of 

 concentric coats of calcium carbonate, along the shores of Great Salt lake, 

 has been referred to an analogous process.^ 



Coral-like growths of calcareous tufa in some of the strongly alkaline 

 lakes of the Great Basin are also thought to owe their origin to the 

 agency of low forms of plant life.^ 



An important feature in this function of sub-aqueous plants, is that 

 calcium carbonate may be precipitated from waters that are far below the 

 point of saturation. In some instances precipitation is known to occur in 

 this manner from water in which chemical tests fail to reveal more than a 

 trace of calcium. 



Ferric oxide is not known to be an important deposit in any of the 

 lakes of North America, although found in abundance in man}- swamps. 

 In Sweden, however, its precipitation from the water of fresh lakes is so 

 abundant that it is of commercial value. The iron is carried into the 

 lakes by streams, as a carbonate, and is precipitated on account of the loss 

 of carbon dioxide, in part at least, through the agency of low forms of 

 vegetative life. In some instances diatoms are thought to play an im- 

 portant part in secreting the iron. 



With this brief sketch of the manner in which precipitates ma}' be 

 formed in lakes, let us turn to actual cases where the process is in 

 o})eration. Of the considerable number of saline lakes of North America 

 that have been studied, two are here selected as types. These are Great 

 Salt lake, Utah, and Mono lake, California. 



Cii'oat Salt lake, Utah. — This celebrated sea is situated in the eastern 

 ])ortion of the Great Basin near the west base of the Wasatch mountains. 

 Its hydrographic basin has an area qf 54,000 square miles, and is divided 

 into two strongly contrasted portions. The eastern part is mountainous 

 and contains peaks 12,000 feet in height above the sea, or 8000 feet above 

 the lake. The western portion is composed of desert valleys but little 

 elevated above the lake surface, and separated l)y narro\\-, abrupt, desert 

 ranges rising from one to two thousand feet or more above adjacent valleys. 



1 W. U. Weed. "Tlie Formation of Travertine and Silicious Sinter by the Vegetation 

 of Hot Springs," 9tli Annual Heport, U. S. fieologica! Survey, 1HH7-S8, pp. G13-G7G. 



■- A. Uotlipiitz. "On tiie Formation of Oiijite," American (Jeologist, vol. 10, pp. 270-282. 



8 1. C. Husseli. "A Heconuoissance in Central Washington," liuUetin No. 108, U. S. 

 Geological Survey, i)p. 04-95. 



