THE SOIL 15 



a mass of ice many hundreds of feet thick. It extended from the 

 Arctic regions southward to central Pennsylvania and from New 

 England to the Rocky Mountains, covering two thirds of North 

 America. The glacier moved far more slowly than does water, 

 but its grinding and transporting power was much greater. It 

 wore down hills and filled up valleys. Like a giant millstone, it 

 ground rocks to powder. At last it melted, depositing a layer of 

 soil. 



A GREENLAND GLACIER 



The ice-mass is darkened by soil and rock waste. The rounded pebbles and rocks have 

 been transported hundreds of miles and deposited by the melting glacier. 



Soils of the United States. The underlying surface rock of the 

 northern part of the United States is chiefly sandstone; had the 

 soil been formed from this, it would have been thin and poor. 

 The soil formed by the glacial deposit is usually deep and fertile, 

 being formed by the grinding and mixing of a variety of rocks. 



