606 THE POPULAR SCIENCE MONTHLY. 



cline in a direction opposite to the general slope of the country, 

 no matter how favorable the conditions, they will furnish no 

 flowing artesian supply, for water can not rise above the height 

 of the receiving area. (Fig. 5.) 



If strata are excessively inclined, as in most mountain regions, 

 artesian wells are improbable if not impossible over any wide 

 area, for the strata soon dip below all available borings ; hence 

 the generally accepted idea that artesian wells are peculiar to 

 regions of great stratigraphic dip is fallacious. A dip of one 

 per cent is scarcely visible to the eye, but it will carry a stratum 

 downward 52'8 feet per mile; a dip of ten per cent is hardly 

 noticeable, but will carry a stratum 528 feet in a mile ; a dip of 

 forty-five degrees will carry a stratum deeper in a mile than any 

 drill has yet penetrated. 



If the earth's surface were level, and a homogeneous mass, 

 earth water would be at a uniform depth throughout, as in an 

 undrained field. But the surface is broken into mountains and 

 plains, and scored by valleys, and the line of saturation sinks 

 toward the level of these, where springs are often found escaping 

 at the level of the streams. There are in Nature two kinds of 

 valleys : (1) Unfinished, or active valleys, which are in the process 

 of being cut out at the present time by the streams seeking base 

 level ; and (2) finished, or ancient valleys, which originated in past 

 geologic time, and have been partially refilled with the debris of 

 the adjacent region. All the valleys in the mountains proper, and 

 of the eastern United States, belong to the first class, which may 

 be called stream valleys, and their function is to furnish a channel 

 for the passage of the surface waters to the sea. The valleys of 

 the second class, or basin valleys are characteristic of the great 

 arid region, and, with one or two exceptions, they are void of 

 running surface water. 



In mountains the surface and underground water is constantly 

 seeking the level of the surrounding valleys, owing to the action 

 of gravity. In general, mountains owe their existence to the 

 superior hardness and imperviousness of their strata, and are of 

 little importance to the problems of underground water. 



Basin plains surrounded by the great areas of mountain sur- 

 face are more favorably situated for the occurrence of under- 

 ground water in quantity than those with a smaller surrounding 

 area of mountain slopes, for impervious mountains serve to con- 

 centrate the rain-water which runs down their slopes upon the 

 pervious valleys, thereby increasing the available water supply 

 beneath the latter. (Fig. 6.) 



The water of saturation in buttes and mesas, which usually 

 consist of horizontal strata, is reduced by gravity toward the level 

 of the surrounding plain, or, when alternations of pervious and 



