32 WALKS AND TALKS. 



strata, from which the water drains away, no supply will be 

 struck. As soon, however, as we reach one of the subtcr- 

 ram-an basins or cisterns, a supply is found. Should we dig 

 a hole through the bottom of the cistern, we would, of course, 

 lose much .if not all of the water. But we might continue 

 down to the next water-basin. 



Let us suppose another well is needed, a few rods away. 

 We must not be too sanguine in the expectation of getting 

 water at the same depth. Perhaps the new well is beyond 

 the limits of the higher water-basin; we must then dig to 

 some lower one. Perhaps the new well is on higher ground ; 

 it does not follow that we must dig to the level of the basin 

 in the first well. In the higher ground may be a higher 

 water-basin ; and so the second well, though several feet higher 

 than the first, may not require to be so deep. 



Do not suppose these water-beds are everywhere of such 

 limited extent. There are districts where the same bed may 

 be traced one or two miles. The bed, in such cases, is 

 nearly horizontal; and that condition of the underground 

 structure is indicated by a level condition of the surface. 



Now, how are springs produced ? Suppose a river valley 

 as cut through a deep mass of the Drift, must it not cut 

 the water-bearing sheets with the rest? And when that is 

 done, will not the water flow out? Certainly, just as when 

 we knock a hole in a cistern. So a hill-side spring is noth- 

 ing but a leak in one of nature's cisterns. The water in es- 

 caping from the cut edge of the sheet finds some spot where least 

 resistance is experienced, and there it escapes in largest quan- 

 tity. It forms a sort of stream, and by degrees wears a little 

 channel, which extends back into the bank, opening at its 

 mouth in a little arch under which the water finally escapes. 

 Of course, all the work was accomplished before we ever saw 

 the spring. A well is an artificial spring. 



Generally, the water of a hill-side spring is allowed to flow 

 off to a brook or rivulet. In the course of a number of miles, 

 scores or hundreds of springs may discharge their contributions 

 into the stream. In fact, the greater part of the water in the 



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41 



