284 
GEOLOGY IN RURAL WELFARE 
bearings upon rural welfare; that is, to the geological problems 
that are met with in agricultural enterprises and pursuits. 
In this relation it deals chiefly with the following topics: Water 
supply for the farm and school; farm losses and gains due to 
geological processes; drainage and irrigation; road and building 
materials; minerals used on the farm and in the home; minerals 
of the soil; origin and distribution of soil materials; geological 
influences affecting the distributions of vegetation; geological 
history of domestic plants and animals; and some other topics, 
not the least of which is the great cultural value of a knowledge 
of geology to the people of rural districts. 
Such a problem as indicated above is that of securing an 
abundant supply of pure water. In regions of copious rainfall 
it is essential, in those of average to minimum rainfall it is abso¬ 
lutely necessary to consider the properties and the structure of the 
substrata in their relation to water in order to obtain such a supply. 
Pursuant to the requirements of this necessity, the Federal Govern¬ 
ment maintains a branch of service whose work is concerned with 
the water resources of the entire country. The purity of sub¬ 
surface water depends chiefly on the filtering power of the 
yielding rocks. One of the best natural filters consists of residual 
material of considerable depth. Some rocks below this mantle are 
sufficiently pervious to contain, transmit, filter and consequently to 
yield pure water. Certain others are impervious. Another condition 
is found where the rocks contain joints or cracks along which water 
moves freely without filtration, conveying to wells or springs 
contamination from distant sources. This condition is a strong 
possibility in limestone regions. Artesian water which, in some 
localities flows from wells, may be found where the properties 
and structure of the containing rock bear such a relation to a 
supply of water as will produce it. Under one combination of 
these conditions, as in areas of jointed igneous or metamorphic 
rocks in the Piedmont Belt, artesian wells may yield a few 
hundred gallons daily; under another, that of a pervious sedi¬ 
mentary rock overlaid by impervious ones which outcrop in a 
moist region of higher elavation, as in the Great Plains, the yield 
may be several hundreds gallons per minute. 
Among the minerals most useful in agricultural pursuits are 
