140 



SCIENCE 



[N. S. Vol. LII. No. 1337 



the containing rock bears such, a relation to 

 ■^ supply of water as will produce it. Under 

 one comhination of these conditions, as in 

 areas of jointed igneous or metamorphic rocks 

 in the Piedmont 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 elevation, as in the 

 Great Plains, the yield may be several hun- 

 dred gallons per minute. 



Among the minerals most useful in agricul- 

 tural 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 res- 

 pective geological occurrences. In order that 

 careful discriminations may be made in their 

 purchase and use, those who have need for 

 them should be familiar with their distinguish- 

 ing properties and with their relative values. 



In numerous localities natural gas is ob- 

 tained 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 the gas- 

 jproducing regions from Pennsylvania and 

 ,West Virginia via Illinois southwestward to 

 Texas and in other places, where many farm- 

 ers depend almost wholly on the gas wells for 

 these services. Gasoline for the auto and the 

 tractor is now being extensively made from nat- 

 ural gas. At Anaconda, Montana, the tallest 

 smokestack in the world, 585 feet, was erected 

 to protect vegetation from destruction by 

 ismelter gases and soil fro'm ruin by erosion 

 due to this loss of its vegetative cover. 

 Ducktown, Tennessee, and other mining dis- 

 tricts afford additional illustrations of these 

 iprinciples. The gases and dust from the 

 pmelters, 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 fer- 

 tilizer. 



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 of the base on which the 

 road is to be constructed. In locating a road 

 along or near a slope or in any topographic 

 position where strata outcrop, the drainage 

 and therefore the safety and .x>ermanence of 

 the road, or its failure, depend on the kinds 

 of rock involved and on their structural re- 

 lation. The rapidly growing use of motor ve- 

 hicles emphasizes the importance of details in 

 .regard 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 agricultural 

 enterprises. Such materials are used in ma- 

 king brick, cement and concrete, in building 

 roads, bridges, dams and retaining walls and 

 in tlie erection of dwellings and other build- 

 ings. A knowledge of the properties and 

 adaptations of structural materials is essential 

 to the intelligent selection of them and to 

 their efficient use. It is also necessary in 

 many localities to understand thoroughly the 

 relations of the substrata to the surface in 

 order to choose safe locations for permanent 

 structures. 



The way in which undrained areas were 

 formed has much to do with the solution of 

 the problems that arise when drainage is 

 undertaken and with the kinds of soil re- 

 claimed when the project is completed. 

 Whether an area must be drained by means 

 of surface ditches or whether an exit may be 

 found through a pervious layer of rock below 

 depends wholly on the elevation and on the 

 nature and structure of the substrata. In 

 arid and semi-arid regions the possibility of 

 irrigation as well as the permanence of the 

 aqueduct is dependent also on geologic and 

 topographic factors. Of the sewage disposal 

 plants which are needed on all farms most 

 types can be located with safety in regard to 

 water supply only by considering fully the 

 conditions of geologic structure and materials 

 in the vicinity. 



The losses of soil by erosion due to the 



