DEPRESSIONS IN THE EARTH'S SURFACE. 149 



so, and the residue would be brackish or salty. Con- 

 ditions of this kind exist in almost every country as 

 a, normal state of things. Where the rainfall is abun- 

 dant, as it is on most mountain chains, or the precipi- 

 tation is in snow, the rivers reach the ocean ; but in 

 arid districts the streams are small and the evapora- 

 tion correspondingly large, hench fresh water lakes 

 are few, and brackish pools prevail. 



The ocean is a boundless body of water with no 

 outlet, and the salts of the earth being washed into it, 

 and having no means of escape, must constantly ac- 

 cumulate. The inflowing rivers are innumerable, yet 

 the loss through evaporation equals the supply, and 

 maintains the recognized sea-level. 



Seas are defined as basins of salt water, and lakes 

 as bodies of water whose contents are 'fresh, though 

 the reverse exists in exceptional instances. The Sea 

 of Galilee is perfectly fresh, and the largest lake of 

 Utah is intensely saline. A body of water may be 

 fresh a part of the year, and brackish the rest of the 

 season. When the inflow is great enough to maintain 

 an outlet, the pool of water is strictly a lake ; and is 

 a sea when a reverse state exists. There are bodies 

 of water in California which are legitimately seas in 

 summer, yet lakes in winter. 



Fresh water lakes are mostly located far above 

 sea-level sometimes at vast heights. The most ele- 

 vated thus far known is Lake Sirikol, its surface be- 

 ing 15,000 feet above the Sea of Aral, into which its 

 waters flow through the river Oxus. Next to it in 

 height is Lake Titicaca, in Bolivia, at an elevation of 

 nearly 13,000 feet above the ocean. 



The Caspian Sea is the largest inland water on 

 the globe, covering 130,000 square miles. The Volga 



