THE GREAT SALT LAKE. 161 



Evaporated water, as has been said, is almost pure ; 

 chlorides and other * salts and minerals are left behind and 

 accumulate, so that the smaller the body of water became 

 the salter it would be. This is what has taken place in the 

 Great Salt Lake of Utah, which was formerly much larger 

 and filled with fresh water, as is evident from the remains of 

 fresh-water shells on its ancient beach. At that time it had 

 an outlet into the Snake River and so to the Pacific, and its 

 waters were kept in a constant state of circulation ; whereas, 

 now that it has shrunk and has no outlet, all that is brought 

 into it must needs remain, with the exception of the water, 

 which is constantly evaporating, and that, too, a little faster 

 than it is poured in by the feeding streams. Consequently, 

 the lake must still be growing smaller and salter. 



The water is in fact far salter than that of the sea, being 

 saturated, i.e., it contains as much as it can hold, and de- 

 posits of salt are formed on the cliffs and rocks. If ever 

 the whole body of water should be evaporated, beds of pure 

 rock-salt would remain behind. 



Salt beds are forming at the present day on the borders 

 of the Black Sea, where all the rivers between the Danube 

 and Dnieper widen out into shallow lakes, which are sepa- 

 rated from the sea by narrow dams. Some of these lakes 

 become partially dry every summer, and salt is then depo- 

 sited in thin layers round the margin, but often as much as a 



* A salt is the substance formed when an acid combines with an alkali 

 and forms a body neither acid nor alkaline, but neutral. Thus : 

 Sodium and sulphuric acid make glauber salts. 

 Sodium and nitric acid ,, Chili saltpetre. 



Potassium and nitric acid , , nitre or saltpetre. 

 Calcium and sulphuric acid , . gypsum or calcium sulphate. 

 L 



