12 



Year-booh of the Deiyartment of Agriculture^ 1921. 



Fig 4. — Precipitation includes rain, moltod snow, sleet, and hail. The map is much 

 reduced and generalized from a map prepared b.v the Weather Bureau and published in 

 the 1 reeipitation and Humidity section of the Atlas of American Agriculture. The map 

 suggests why the United States should be divided agriculturally into an eastern and a 

 western half. However, the division shown in Figure 2 does not follow a line of equal 

 precipitation, but advances diagonally across two of the precipitation zones from 15 

 inches in ihe northwestern corner of North Dalvota to 2.5 inches on the south Toxas 

 coast where the evaporation is much great(>r and the rainfall more torrential and, conse- 

 quently, more moisture is required for crop production. 



Il 



