KELATION OF LAKES TO CLLMATIC CONDITIONS. 69 



greiiter host of iulaiul wiitur bodies of almost every variety imaginable, 

 attract the attention and cause our pen to linger ; but here again we can 

 only say that the}' belong to a great class of which types have been briefly 

 described. 



Saline Lakes. 



Saline lakes are formed principally in two wa3^s. First, by the isola- 

 tion of bodies of sea water, as Avhere a rise of the land cuts off an arm 

 of the ocean, or sand bars or coral reefs enclose lagoons. Second, ]>y 

 the concentration by evaporation of ordinary river waters in enclosed 

 basins. The first are of oceanic and the second of terrestrial origin. 



Saline lakes of oeeaiiic origin. — There are no conspicuous exam- 

 ples of this class of lakes in' North America, although lagoons cut off 

 from the ocean by sand bars do occur, especially along the southern 

 Atlantic coast. 



A large lake of salt Avater that was isolated fiom the ocean by a rise 

 of the intervening land formerly occupied the valley of Lake Champlain, 

 but has been freshened and its surface lowered by overflow. 



The type of saline lakes which were formerly arms of the ocean is 

 furnished by the Casj)ian sea, the largest body of inland water known. 

 The observations of many travelers have shoAvn that this sea has l)een 

 divided from the ocean by the elevation of the intervening land. The 

 climate of southwestern Asia is arid, and over large areas eva[)oration is 

 in excess of precipitation. For this reason the Caspian has contracted its 

 borders, in spite of the large contribution of water delivered to it by the 

 Volga and other streams. 



There is evidence in the chemical composition of the waters of the 

 Caspian, and in the tojwgraphy of land separating it from the Black sea, 

 to indicate that at fii'st it was freshened by overflow, as in the case of 

 the ancient lake of Champlain valley, and that its present salinity has 

 resnltcd })rincipally from the concentration of river waters. It may l)e 

 considered, tlierefore, of oceanic or of terrestrial origin as one chocxst's. 



The Caspian is 180,000 square miles in area, or iicailv six times the 

 size of Lake Superior. Its niaxiiiimii dcptli is in the iieighl)orliood of 

 8,000 feet, and exceeds tlie dei)lh of any otlier lake known. It is with- 

 out ontlet. Its Avaters contain 0.204 i)arts in a thonsand of mineral 

 matter in solution, consisting |>iinciii;illv of sodium (•liloii(K' and niag- 

 Ut'siuni sul|ih;iti'. The waters of the oce;in. it will be leuieuO lered. eon- 



