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." 



V/ells. — The application of geological knowledge 

 to obtaining water by the sinking of wells, is too 

 obvious to need remark. The depth and abundance 

 of springs, the quality of the w^ater, 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 good 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 

 sjTiot by competent persons previous to their com- 

 mencement. 



In excavating or boring for wells, we should bear 

 in mind that common springs are product'd by the 

 percolation of rain water through porous to imper- 

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

 When the rock beneath is porous, care should be 

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



