IO SOILS 



The carbonic acid of the air serves its part, also, but in 

 another way. It works with water and in this manner: 

 the two substances carbonic acid and water readily 

 commingle and produce a liquid that is strong as a sol- 

 vent, effective as a dissolving agent, so as to weaken the 

 rocks, and active as a selective power which seeks the 

 soft minerals of earthy formations and quarries them 

 for plant builders to use. 



Oxygen and carbonic acid work whether man would 

 have them or not ; they ask not his permit when they 

 shall work nor where ; and neither do they ask on what 

 materials they shall satisfy their desires. They work for 

 Nature and to her they belong, and in this case they re- 

 fuse to bow or to conform to man's wishes. 



But air and water are usually most effective as soil 

 makers when they are working together, for they accom- 

 plish more and do it more quickly. You have seen per- 

 haps some iron tool that for years has remained in the 

 bottom of a well, the water having made no perceptible 

 headway against it. Because no air was there, rust did 

 not result. And again, you have seen another iron tool 

 kept in an atmosphere that was dry. You note no per- 

 ceptible disintegration because moisture is highly essen- 

 tial for iron to change into its own powdery dust. 



In dry climates rocks last longer than in moist climates 

 for the reasons explained in reference to the dissolving 

 action of air, carbonic acid, and moisture. 



Changes in temperature play a part. In the early 

 days the earth had a larger garment to clothe it than it 

 now possesses. It was very hot a boiling mass, at first. 

 As time went on, the outer crust became cool, and at the 

 same time this crust hardened and became fixed in char- 

 acter, but only temporarily ; only long enough for the 

 cooled crust to deepen its thickness, when the entire body 



