AGRICULTURAL GEOLOGY 
JOHN E. SMITH 
During reconstruction, as the present period is frequently 
termed, many new applications of the principles of pure science 
to special fields of endeavor are being made. The principles of 
geology thus applied during recent years have given rise to eco- 
nomic geology, mining geology, engineering geology, oil geology 
and perhaps to that branch of the subject indicated by the above 
title, for it is not entirely new. The application of the principles 
of the science to the solution of the geological problems that are 
met in agricultural enterprises and. pursuits, in brief, the relation 
of geology to rural welfare may appropriately be considered as 
agricultural geology. 
Such a problem 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 absolutely 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 require- 
ment of this necessity, the United States Geological Survey main- 
tains a branch of service whose work is concerned with the water 
resources of the entire country. The purity of subsurface 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 ai^e 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 contamina- 
tion 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 Pied- 
mont belt, an artesian well may yield a few hundred gallons daily ; 
under another, that of a pervious sedimentary rock overlaid by 
impervious ones which outcrop in a moist region of higher eleva- 
