RESURRECTION OF THE CONTINENT. 



233 



tent, is a natural cistern, where Providence saves the rains 

 within reach of the surface — a cistern of filtered water, pre- 

 served m a cool and protected situation. Man penetrates 

 the drift a few feet at any place, and opens one of these 

 natural cisterns and supplies his wants (Fig. 83). 



But the dumb beasts have never learned to dig wells. 

 Observe that Providence has not neglected them. The 

 geological forces that have dug river gorges, and scooped 

 out valleys large a«d small, have cut across these beds of 

 clay, And tapped a myriad cisterns where their contents 



b o 



Fig. 83. Phenomena of Wells and Springs in Drift Materials, 

 a, a, a, etc. Beds of clay variously disposed in a mass of sandy materials, b, b, b. 

 Wells sunk in different situations, and finding a supply of water only when a 

 bed of clay is reached. A well on the top of a hill may be shallower than one 

 at the foot, c, c. The surface of the earth, d. Outcrop of bed of clay, causing a 

 spring. If the porous materials contain fragments of limestones, these spring 

 waters are hard, and deposit travertine from d toward b. A well carried below 

 its supplying-bed may lose its water again. 



escape upon a hill-side (Fig. 83), and form a spring at 

 which the untutored brute may slake his thirst without 

 the benefits of shovel and pick. But as all animals could 

 not conveniently resort to springs, and as there are certain 

 regions that have not been scored by denuding forces, we 

 find the hill-side spring wandering off in a modest rill. At 

 length it joins hands with a neighboring rill, and, with aug- 



