CHEMISTRY OF NATURAL WATERS. 181 



takes place in the ocean. As shown in the table, the carbonates mostly 

 disappear, the sulphates increase slightly in percentage, while chlorides 

 (mostly common salt) become the characteristic ingredient. 



WATERS OF INLAND SEAS. 



When rivers empt)' into a basin that has no outlet, their waters are 

 evaporated in the same manner as in the ocean, and both their mechanical 

 and chemical impurities are left as additions to the filling of the depression. 

 Examples of such areas of interior drainage are well known in various 

 parts of the woi'ld. In southern Asia, the Caspian, Aral, Dead Sea, and 

 many other saline lakes, are the evaporating basins for independent hydro- 

 graphic areas. The region of the Sahara in northern Africa is also shut off 

 fruni the general oceanic circulation, but, owing to the high mean tempera- 

 ture there prevalent, the surface waters are mostly dissipated before lakes 

 are formed. In South America another basin situated in the elevated table- 

 lands of Peru and Bolivia Is without drainage to tlie ocean. In North 

 America there are small ai'eas of a similar nature in Mexico; but the typ- 

 ical example on this continent is furnished by the Great Basin. Man}- of 

 the lakes and seas situated in these various interior basins are without out- 

 let, and are highly charged with saline matter. In some instances the per- 

 centages of the most abundant salts have I'eached their points of saturation 

 and precipitation is taking place. The greater density of many inclosed 

 lakes as compared with the ocean is due to the fact that concentration has 

 been greatest in the restricted basins The paucity of animal aaid plant life 

 in most inclosed lakes has also some slight bearing on the problem. 



To facilitate the comparison of the inclosed lakes of this country with 

 similar waters elsewhere, we introduce a somewhat extended table of 

 analyses of this class of lakes, embracing all within the United States the 

 composition of which is known. This table includes the densest of natural 

 waters and exhibits the extreme of a series that commenced with the nearly 

 pui'e water formed by the condensation of atmospheric vapor. 



When inclosed lakes were first studied it was quite naturally supposed 

 that their usual saline condition could only be accounted for by assuming 

 that they were isolated bodies of sea-water which had been shut ofi" from 



