4 SOILS 



heat and ice. Ever since the surface of the earth 

 cooled, making a crust of rock, these agencies have 

 been constantly at work, breaking up this crust, 

 wearing away fragments of rock and carrying 

 them to lower levels. They are Nature's plows. 

 All mountains and hills are slowly wearing away. 

 We can no longer regard them as "firm and ever- 

 lasting." " Whole mountain chains of geologic 

 yesterday have disappeared from view," says 

 Merrill, "and we read their history only in their 

 ruins." The Appalachian Mountains have al- 

 ready lost by weathering and erosion as much 

 material as now remains. Even within the mem- 

 ory of one man, a hill may become noticeably 

 lower. 



The whole earth is being levelled very slowly, 

 yet quite perceptibly. The face of every rock is 

 roughened and chipped by the elements. Drops 

 of rain wear away particles of it; water freezes in 

 the crevices, expands, and chips off fragments. 

 The air searches these crevices and corrodes them, 

 as it does iron. Everywhere cliffs are lower, rocks 

 are smaller and soils are finer than they used to be. 

 The big rock that the farmer has plowed around 

 for thirty years is smaller now than it was when he 

 first "rode horse" for his father. The stones on 

 the gravelly knoll pass between the cultivator teeth 

 easier than they used to. All about us, in the wild 

 and on the farm, are indisputable evidences that 

 soil is being made by the weathering of rocks. 

 Most farm soils are still incomplete tney contain 

 rocks and stones that are slowly being made into 

 soil. A few, as the clays and alluvial soils, are 

 changing less; but even the finest clay soil is af- 

 fected by weathering to some extent. The reducing 

 and fining process is universal and ceaseless. 



