RIVER AND LAKE DEPOSITS 193 
Chemical Deposits. —In the Far West, and many 
other arid lands, lakes without outlets have become 
salt through-constant evaporation. In time this action 
may go so far that some of the salts are of necessity 
deposited (Fig. 102). By this means layers of com- 
mon salt, gypsum, etc., may accumulate; and in desert 
lands, these are frequently found marking the site of 
recently dried lakes. They may even now be seen 
forming in some salt lakes. 
By a climatic change to aridity, preventing overflow, 
even our Great Lakes would become salt, and in their 
beds, chemical precipitates might eventually be made. 
In the Great Basin of the West there were once great 
lakes which were fresh and had outlets, where now, 
by a change in climate, only salt beds, alkali flats, or 
salt lakes are left in the lowest parts of the old lake 
basins. The Great Salt Lake is the largest of these 
remnants. 
The water of this great inland lake is so salt that 
it furnishes a source of this substance. Led into shal- 
low pans, it is exposed to the dry air of the desert 
and evaporated so that a layer of salt is precipitated. 
Here man is doing artificially what nature has done 
elsewhere when entire lakes have been so evaporated, 
and beds of salt accumulated in the former lake 
bottom. We are at present drawing upon these stores _ 
in the earth for much of the salt which we use. 
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