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 
of 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 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 
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 stopped, as by clay. 
When the rock beneath is porous, care should be 
taken not to penetrate through the clay ; for, by m 
