Page:Popular Science Monthly Volume 42.djvu/621

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ARTESIAN WATERS IN THE ARID REGION.

and availability of underground waters, for not only have large sums been wasted in boring in unfavorable localities, but impracticable notions have been obtained from scientific treatises on this subject.

The laws of the distribution and utilization of underground water are as simple as those controlling the surface supply, but the popular fallacies concerning them are appalling. The most prevalent of these is that the waters originate at some remote point from their outlet, and flow in subterranean streams like the "blood in the human body," as a farmer once said, and that these streams must be tapped by the well borer or digger before water can be obtained. In nearly every community is some person supposed to possess the art of locating the exact spot above these currents by means of a switch called the divining rod. It is also a current fallacious belief that all underground water is due to rain which falls on the more or less distant mountains, and especially is this true in the region between the Rocky Mountains and the Mississippi, where every spring and well, even on the Texas

 
PSM V42 D621 Favorable structure for artesian water.jpg
Fig. 2.—Favorable Structure for Artesian Water, in which the Receiving Area is a Valley.
 

coastal plain a thousand miles distant, is commonly explained upon the hypothesis that the water comes from this lofty range.

These prevalent impressions in the minds of those untrained in geology are more excusable than the widely prevalent idea conveyed by cuts in geological text-books that the usual and ordinary conditions for artesian wells are in great synclinal areas in which the strata can be seen markedly dipping from two including mountain borders against which their edges are upturned as shown in the following figure.

While there is no theoretical objection to this ideal conception, the conditions it represents seldom occur in Nature; on the contrary, as will be shown later, mountain rocks are not the source of great artesian wells; neither do they usually occur in synclinal valleys, but the most favorable conditions are gently sloping monoclinal plains in which the receiving areas, instead of being the upturned mountain rocks, are, in fact, the escarpment valleys of the plains. (See Fig. 2.)

To understand the distribution of earth water, it is necessary to be familiar with the true laws of its occurrence. The rainfall is the source of all underground water, and with the exception of