WELLS. BORING. 



367 



quarter to one ; but in most cases limestone is found 

 mixed with clay beds, and in such cases the slopes 

 should be one and a half or two to one. In the 

 primitive strata, such as granite, slate, or gneiss, 

 slopes will stand at a quarter to one. In every in- 

 stance of deep cutting, the greatest pains should be 

 bestowed in examining the character of the mate- 

 rial to be removed, as much difficulty will be avoid- 

 ed by proceeding this way." 



Wells. — The application of geological knowledge 

 to obtaining water by the sinking of wells, is too 

 obvious to need remark. The depth and abundance 

 pf springs, the quality of the water, and its ascend- 

 ing power, depend entirely on geological causes, and 

 can only be estimated with correctness by the prac- 

 tical geologist. Since the construction of Artesian 

 wells, by boring the earth with an iron or steel rod, 

 it has been found that very go d water may be pro- 

 cured in situations, which, for the want of it, were 

 formerly considered uninhabitable, such as the des- 

 erts of Africa, Arabia, and Mesopotamia. Some 

 local situations are highly favourable to the forma- 

 tion of Artesian wells ; in others, on the contrary, 

 there is scarcely a probability of success ; in some 

 places a small depth will be sufficient to obtain wa- 

 ter, in others the depth must be very considerable ; 

 and these are questions which can be decided by 

 geology alone. It would be very easy to enumer- 

 ate many cases of failure and great pecuniary loss 

 in works of this kind, merely from neglecting these 

 obvious precautions, and a due examination of the 

 spot by competent persons previous to their com- 

 mencement. 



In excavating or boring for wells, we should bear 

 in mind that common springs are produced by the 

 percolation of rain water through porous to imper- 

 vious beds, where they are stopjfed, as by clay. 

 When the rock beneath is porous, care should be 

 taken not to penetrate through the clay ; for, by so 



