ARTESIAN WELLS. 4ll'.| 



be lower), there will be no leakage, not even if the strata be somewhat permeable, for 

 the water in the confining beds presses down as much as the fountain-head causes 

 that of the porous bed to press up, since both have the same height. Capillarity dues 

 not disturb the truth of this. Under these conditions a flow may sometimes be secured 

 when it would be impossible if the intervening water-surface were lower. 



If the water between the well and fountain head is actually higher than the 

 latter, it will tend to penetrate the water-beariug stratum, so far as the overlying 

 beds permit, and will, to that extent, increase the supply of water seeking passage 

 through the porous lied, and will, by reaction, tend to elevate the fountain-head, if the 

 situation permit. 



Fig. 20.— Section intended to illustrate the :ii.l afforded by a high water-surface between the fountain-head and 

 the well. A, a porous bed; B, a confining bed below andC, a confining bed above. Hie dart 



the surface represents the terground water-surface. Its pressure downward is represented by the arrow 1 



pressure upward, due U- the elevation of the fountain i 1 nted bj the arrow //. rhe line I represents the 



level of the fountain bead. There can be no leakage upward through tin- bed C except near the well D. There mat I" 

 some penetration from the bed C into A. which would aid the flow. 



I conceive that one of the most favorable conditions for securing a fouutaiu is 

 found when thick semiporous beds, (.instantly saturated with water to a greater 

 height than the fountain-head, lie upon the porous stratum, and occupy the whole 

 country between the well and its source, as illustrated by fig. 15 [fig. I'd. above]. This 

 is not only a good but an advantageous substitute for a strictly impervious confining 

 bed. Under these hydrostatic conditions, limestone strata reposing on sandstone 

 furnish an excellent combination. 



If. on the other hand, the underground water-surface between the proposed well 

 and the source of supply is much lower than the fountain head there will be con 



^^■K. 



tion. sec text ) 



siderable leakage, unless the confining beds are very close textured and free from 

 fissures, for example, if ii be 100 feet lower there will lie a theoretical pressure of 

 nearly three atmospheres, or about 45 pounds to the square inch, upward, greater 

 than that of the underground water downward, disregarding the influence of capil- 

 larity, and this will be competent to cause more or less penetration of the water 

 upward through the pores and crevices of the rocks, and consequent loss of head 

 and forcing power. 



Both of the above points may be illustrated by the accompanying double profile 

 [fig.21],in which A represents a porous stratum inclosed between the impervious 



