THE SOIL 27 



sand miles wide, extended from the Arctic region southward over a 

 large part of the northern portion of the United States, grinding 

 rocks, tearing down hills, and filling up valleys. Many of these 

 rocks worked their way through the ice, and, moving with the 

 ice, scoured the solid rock underneath until ground into powder. 

 Finally, when the glacier melted, the fine powdered rock was de- 

 posited and formed a pro- 

 ductive soil made so by 

 the assembling of a variety 

 of mineral elements. It is 

 thought that this great 

 mantle of ice at one time 

 reached to the fortieth par- 

 allel of latitude in North 

 America. 



Wind-blown Soils. In 

 some countries we find that 

 heavy winds stir up the 

 soil and move it from one 

 place to another. This is 

 especially likely to happen 

 in sandy regions. Fre- 

 quently these small par- 

 ticles of sand and dust will 

 be blown with such violence 

 that they will scour off and 



dislodge other particles of soil on high ridges and ledges in ex- 

 posed places. The cutting and scouring force of sand when 

 driven by high winds is much greater than one would ordinarily 

 expect. On the Great Plains in the West telegraph poles are 

 frequently worn away and cut almost through at the base where 

 these drifting sands come in contact with them. Along the 

 Coast Route of the Santa Fe Pacific in California the sand in 

 some places drifts so upon the railroad tracks that high board 

 fences have to be built to keep the tracks from being covered 

 by the drifting sand. Similar conditions exist in various places 

 along the Gulf coast, the Atlantic seaboard, and the shores of 

 the Great Lakes in the northern and northeastern part of the 



