SOIL BUILDERS 5 



An interesting example of soil formation by 

 weathering is the heaving of stones to the surface, 

 especially in the clay soils of northern states. A 

 vivid recollection of my boyhood is the thankless 

 task of picking up stones from rocky New England 

 fields. This nad to be done every fall and every 

 spring. Though we might pick up and cart off 

 in the fall every stone to be seen, there would always 

 be many on top of the ground by the time 

 for spring plowing. 



These stones were heaved up. The clay soil 

 in which they were embedded became wet, froze 

 and expanded, throwing the stones upon the sur- 

 face, there being the least resistance in that di- 

 rection. So many of our small fields of a few acres 

 had immense piles of stones in each of the four 

 corners, the accumulation of many years. When 

 these stones are not picked up they lie upon the 

 surface and are slowly reduced to soil. 



Soil Becoming Rock. The reverse process, of 

 changing soil into rocks, is also taking place. 

 Many of the common rocks and stones that we 

 may pick up in our fields were once soil. Sand- 

 stone, which is now sought for trimming buildings, 

 is sand that has been hardened into stone. "Pud- 

 ding" stones, or conglomerates, are made of 

 travel. Sometimes these rocks may be broken up, 

 y weathering or erosion, and the soil in them 

 again become available for plant growth. Thus 

 the materials of the earth's surface may be worked 

 over and jjgcer during countless cycles of time. The 

 soil that nol$rjshes plants to-day may be the build- 

 ing stones of a future generation. The soil of every 

 farm has an antiquity of no ordinary character. 



Extreme Changes in Temperature Crack Rocks. 

 Weathering from changes in temperature is as 



