EVIDENCE OF HISTORY 219 



of a soil is not a constant quantity at all, 

 but, on the other hand, is changing continually 

 even during infinite sections of a single second. 



This is one method by which the movement 

 of ground water changes our soils so that "we 

 are not farming the same soils as our fathers." 

 A simple experiment demonstrates the truth 

 of this statement. A column of soil contained 

 in a bottomless tube several feet high is made 

 to rest in a basin containing common salt in 

 solution. Then the air is agitated gently at 

 the surface of the column, so as to induce 

 evaporation simulating the winds that blow, 

 in fact. In only a short time an analysis of 

 the top layer of soil reveals the fact that mole- 

 cules of salt common table salt have been 

 transported through several feet of soil and 

 abandoned at the surface by the elusive, 

 vaporizing molecule of capillary moisture. 



The movement of soil waters is profound. 

 No one has ever "fetched bottom" in gravita- 

 tional water in the soil. Whether the re- 

 sources of the upper soil are being fed by water 

 columns measured in feet or in miles no one 

 can say. It is probable, however, that the 

 movement is continuous from a great depth. 



These facts emphasize the necessity of keep- 



