78 DRY-FARMING 
of aridity increase. They are less marked as we go 
eastward or westward toward the regions of more 
abundant rainfall; that is to say, the most highly 
developed arid soils are found in the Great Basin 
and Colorado River districts. The least developed 
‘are on the eastern edge of the Great Plains. 
The judging of soils 
A chemical analysis of a soil, unless accompanied 
by a large amount of other information, is of little 
value to the farmer. The main points in judging a 
prospective dry-farm are: the depth of the soil, the 
uniformity of the soil to a depth of at least 10 feet, 
the native vegetation, the climatic conditions as 
relating to early and late frosts, the total annual rain- 
fall and its distribution, and the kinds and yields of 
crops that have been grown in the neighborhood. 
The depth of the soil is best determined by the use 
of an auger (Fig. 21). A simple soil auger is made 
from the ordinary carpenter’s auger, 14 to 2 inches 
in diameter, by lengthening its shaft to 3 feet or 
more. Where it is not desirable to carry sectional 
augers, it is often advisable to have three augers 
made: one 3 feet, the other 6, and the third 9 or 10 
feet in length. The short auger is used first and the 
others afterwards as the depth of the boring in- 
creases. The boring should be made in a large 
number of average places — preferably one boring or 
