How the Soil Is Made 



65 



t/, i'. Geological Survey 

 Soil brought by a glacier and deposited as the ice melted. 



with a sheet of ice. This ice crept slowly southward, and 

 as it moved along it tore off all the soil and loose rocks on 

 the surface of the earth over which it passed. When it 

 melted it left them spread roughly over the coimtry. Such 

 material forms glacial soil. It is often deep but not very 

 rich. 



There is another kind of soil, formed by the wind. If you 

 have ever been in a dust storm you have seen the fine, pow- 

 dery substance that settles over everything and creeps 

 into the smallest cracks. In some countries where there 

 are strong winds and not much rain there is little vegeta- 

 tion on the surface to hold the soil. Year after year the 

 winds pick up particles of the dusty soil, whirl them high 

 in the air, and do not let them down again until they have 

 been carried many miles. In some far-off land where the 

 winds go down the dust particles settle again to the earth. 

 After a long, long time, enough dust collects to form a thick 



