68O OYSTERS, AND ALL ABOUT THEM. 



Sea-water contains in solution the gaseous, mineral, 

 vegetable, and animal substances present in the waters of 

 the rivers which flow into the sea. These remain behind 

 when the surface water of the sea is evaporated, as it is 

 continuously, by the heat of the sun, hence perhaps one of 

 the causes of the present highly saline condition of the sea. 

 On the other hand, sea-plants and fishes are always 

 abstracting solid matter from the sea, and adding to 

 submarine deposits. Probably the sea gains access or has 

 gained to soluble saline deposits such as those now oocur- 

 ing in the beds or mines of salt of our own country, and in 

 the beds or mines containing many saline chemical sub- 

 stances now worked in Prussia. The suspended matters in 

 the affluent rivers slowly settle in the sea, and, with the 

 shells and skeletons of animals, &c., no doubt slowly raise 

 its floor. 



The dissolved solids in sea-water with their names and 

 proportions are shown in the following Table. The 

 different rates of evaporation from the surface of the sea in 

 tropical as compared with polar regions, and in compara- 

 tively quiet as compared with boisterous seas, and the 

 influence of dilution by the fresh water of contiguous 

 rivers, causes some variation in the composition of the 

 water of different seas and of different portions of the same 

 sea. The saline taste of sea-water is due chiefly to the 

 large proportion of common salt present, four and a half 

 ounces per gallon, its bitterish character to the magnesium 

 salts. Its greater buoyancy than fresh water is due to its 

 greater density, one gallon weighing rather more than ten 

 pounds and a quarter as againt ten pounds in the case of 

 pure water; in other words, in comparison with 1000 parts 

 of pure water, the specific gravity is 1027^-. 



