CLASSIFICATION OF SOILS 5 1 



tant in the formation of soils remote from streams or 

 lakes, as in the ease of soils deposited by glaciers. 



51. Glacial Action. — At one time in the earth's 

 history, the ice-fields of polar regions covered much 

 larger areas than at present. 19 Changes of climate 

 caused a recession of the ice-fields, and resulted in the 

 movement of large bodies of ice, carrying along rocks 

 and frozen soil. The movement and pressure of the 

 ice pulverized the rock and produced soil. This 

 action is well illustrated at the present time where 

 mountains rise above the snow line, and the ice and 

 snow melting at the base are replaced by ice and 

 snow from above moving down the side of the moun- 

 tain. When the glacier receded, stranded ice masses 

 were distributed over the land. These melted slowly 

 and by their grinding action hollowed out places 

 which finally became lakes. The numerous lakes at 

 the source of the Mississippi River and in central Min- 

 nesota are supposed to have been formed by glacial 

 action. The terminal of a glacier is called a moraine 

 and is covered with large boulders which have not 

 been disintegrated. The course of a glacier is fre- 

 quently traced by the markings or scratches of the 

 mass on rock ledges. In glacial soils, the rocks are 

 never angular, but are smooth because of the grinding 

 action during transportation. The area of glacial soils 

 in the northern portion of the United States is quite 

 large. These soils are, as a rule, fertile because of 



