ARTESIAN WELLS. 97 



from (6) to (a) wet ; but as soon as it reaches the 

 sandy fault at (a), it is immediately absorbed, and 

 again reaches the porous strata, along which it had 

 travelled before being forced to the surface at (b). 

 It will be observed that the strata at the point of 

 dislocation are not represented as in a line with the 

 portions from which they have been dissevered. 

 This is termed the upthrow of the fault, as at (b) ; 

 and the dethrow, as at (a). For the sake of the 

 illustration, the displacement is here shown as very 

 slight ; but in some cases these elevations and de- 

 pressions of the strata extend to many hundreds of 

 feet, as for instance at the mines of the British Iron 

 Company at Cefu Mawre, in North Wales, where 

 the dethrow of the fault is three hundred and sixty 

 feet. 



" Sometimes the strata are disposed in the form 

 of a basin. In this case, the water percolating 

 through the more elevated ground, near what may 

 be termed the rim, collects in the lower parts of the 

 strata toward the centre, then forcing its way to the 

 surface, if the upper impervious beds be thin ; or, 

 if otherwise, remaining a concealed reservoir, ready 

 to yield its supplies to the shaft or boring-rod of 

 the well-sinker, and sometimes forming a living 

 fountain capable of rising many feet above the 

 surface. 



" It is in this way that what are called artesian 

 wells are formed. The following diagram repre- 

 9 



