COMPOSITION^ OF SEA-WATER. 



43 



The fact is, however, that countless myriads of ani- 

 mals extract fromthe waters of the ocean enough solid 

 matter to build continents of. The foraminifera), the 

 polypi, and the molluscs hence derive the calcareous 

 coverings which form their shells or skins. An esti- 

 mate may be formed of the stupendous nature of the 

 agency of these little creatures, by considering the 

 vast extent of the beds of calcareous rock which form 

 part of the earth's crust, and which are composed of 

 the debris of creatures so small that upwards of fifty- 

 eight thousand of them have been counted in a cubic 

 inch of chalk. No doubt other marine animals ex- 

 tract other salts from the ocean, and we must add to 

 their action that of the marine vegetation. Setting 

 these considerations aside for the present, the actual 

 composition of sea-water is found to be as follows : — 



Water .... 



Sea-salt, or chloride of sodium 



Chloride of magnosiura . 



Chloride of potassium 



Bromide of magnesia 



Sulphate of magnesia 



Sidphate of lime 



Carbonate of lime . 



Kesidnum, not determined, but consisting of 



guli)hurettcd hydrogen gas, hydrochlo- 



rete of ammonia, &c. &c. 



2-9 



1000-0 



Sea-water, being thus composed, is considerably 



