328 PHYSIOGRAPHY 



From the foregoing it will be seen that great irregularities are 

 found on the sea bottom as on the land, but that the many small 

 unevennesses of the land, especially those made by running water, 

 wind, glaciers, etc., do not appear on the ocean's 15ed, except in 

 very shallow water. 



COMPOSITION OF SEA-WATER 



One hundred pounds of sea-water contains nearly three and 

 one-half (3.44) pounds of dissolved mineral matter. Of this, salt 

 makes up more than three-fourths (nearly 78%), but many other 

 substances occur in very small quantities. These mineral matters 

 in the sea-water make it a little heavier than fresh water. If all 

 the salts of the sea were taken out of solution and laid down as a 

 layer of solid matter on the ocean bottom, they would make a layer 

 about 175 feet thick. 



Sources of mineral matter. Mineral matter dissolved in water 

 is being carried to the sea by rivers all the time. Rivers have 

 brought the sea most of its mineral matter, though some of it may 

 have been dissolved from the rocks beneath the sea, or about its 

 shores. The mineral matter carried in solution to the sea by rivers 

 in a year would make nearly half a cubic mile. 



The minerals which are most plentiful in the sea are not those 

 which are most common in the rocks of the land. Those minerals 

 of the land which are most easily dissolved get into rivers, and 

 thence to the sea, in greater quantity than those which are less 

 soluble. But some of the minerals in the sea-water, such as salt, 

 do not exist in the common rocks of the land. They are made by 

 the union of a substance in the rocks, with a gas in the air or water. 

 Granite, for example, has no salt, but it contains sodium, which is 

 one of the elements of salt. When the sodium unites with chlorine 

 (a gas), the result is salt. It takes much granite to yield a little salt. 



Withdrawal of mineral matter from the sea. Of the mineral 

 matters carried to the sea by rivers, calcium carbonate, the sub- 

 stance of which most shells are made, is most important. The 

 amount of this substance in river water is nearly as great as that 

 of all others. Common salt is present in river water, but its amount 



