Loss of Lime and Magnesia 277 



underground rivers are formed, and enormous amounts 

 of lime are carried to the sea to serve there as building 

 material for coral reefs, for the outer skeletons of shell- 

 fish, and other almost innumerable forms of marine life. 



With the passing ages this lime may be given back 

 to the land. Its life in the form of chalk cliffs, of crinoidal 

 limestone beds, and of shell marls, may perhaps again 

 go through the process of erosion and solution, and 

 travel to the ocean once more. Thus the lime and mag- 

 nesia of the rocks and soils migrate from land to sea and 

 from sea to land, just as the nitrogen and carbon of 

 the soils migrate from the land to the atmosphere, and 

 from the atmosphere to the land. 



The causes of the migration of lime and magnesia. 

 The migrations of lime and magnesia will be understood 

 more readily if we remember that lime carbonate by 

 itself is very slightly soluble in water. For all practical 

 purposes it is insoluble. When, however, the water 

 carries in solution carbon dioxid, the lime carbonate 

 is changed to a bicarbonate which is soluble. It follows, 

 therefore, that, the greater the intensity of decay in the 

 soil, the greater the amount of carbon dioxid formed and 

 of the lime carbonate rendered soluble and removed. 

 Every progressive farmer knows that in order to main- 

 tain his soil productive he must lime it from time to 

 time. It is only in the case of limestone soils that liming 

 seems usually, though not always, unnecessary. There 

 are records of chalk soils underlaid by chalk to which 

 the application of lime has been found profitable, so 

 completely had the lime carbonate been dissolved and 

 carried away. 



