176 
IOWA ACADEMY OF SCIENCE Vor,. XXVII, 1920 
tion, as in the Great Plains, the yield may be several hundred 
gallons per minute. 
Among the minerals most useful in agricultural pursuits are coal 
and other mineral fuels, the mineral oils (kerosene and gasoline), 
iron, salt, gypsum, lime, the minerals of the soil, and the fertilizer 
minerals yielding potash, phosphates and nitrates. The nature, 
quality, distribution and availability of most of these substances 
bear direct relations to their respective geological occurrences. 
In order that careful discriminations may be made in their pur- 
chase and use, those who have need for them should be familiar 
with their distinguishing properties and with their relative values. 
In numerous localities natural gas is obtained from considerable 
depth. Gas provides fuel and light for use in buildings and power 
for machinery. Examples of such uses are common in agricultural 
districts in gas-producing regions from Pennsylvania and West 
Virginia via Illinois southwestward to Texas and in other places, 
where many farmers depend almost wholly on the gas wells for 
these services. Gasoline for the auto and the tractor is now being 
extensively made from natural gas. At Anaconda, Montana, 
the tallest smokestack in the world, 585 feet, was erected to 
protect vegetation from destruction by smelter gas and soil from 
ruin by erosion due to this loss of its vegetative cover. Ducktown, 
Tennessee, and other mining districts afford additional illustra- 
tions of these principles. The gases and dust from the smelters, 
from the blast furnaces of the steel industry and from the flues of 
the cement mills, through skillfully devised systems of careful 
collection and concentration, are soon to yield a large proportion 
of the potash used as fertilizer. 
In road building the adaptation of various materials even when 
only sand and clay are needed is determined by the properties of 
the minerals and rocks considered for this purpose and by the 
nature o.f the base on which the road is to be constructed. In lo- 
cating a road along or near a slope or in any topographic position 
where strata outcrop, the drainage and therefore the safety and 
permanence of the road, or its failure, depend on the kinds of rock 
involved and on their structural relation. The rapidly growing 
use of motor vehicles emphasizes the importance of details in re- 
gard to road materials and road locations. 
From the rocks at the surface or below it, suitable material is 
obtained for buildings and other structures necessary in agricul- 
tural enterprises. Such materials are used in making brick, 
cement and concrete, in building roads, bridges, dams and re- 
