10 VREDENBURG : RECENT ARTESIAN EXPERIMENTS IN INDIA. 



of concrete placed at some distance below the level of saturation 

 of the ground. 



It is certain that these "spring wells" hardly answer to the 

 popular idea of an artesian well, and naturally they would not be 

 regarded as belonging to that category by those authors who 

 restrict the use of the term to flowing wells. It may be suggested, 

 that if the fact that a well is a flowing one be taken as essential to 

 artesian conditions, a further restriction must be made so as to 

 apply the name only to such flowing wells as are fed by a deep 

 reservoir of water under considerable pressure. This restriction is 

 necessary so as to exclude a certain class of wells which yield a 

 copious flow, although not possessing any of the characters of an 

 artesian well. Such are certain percolation wells so situated with 

 respect to the topography of their neighbourhood, that, by means 

 of a shallow artificial channel, the water which they collect can be 

 discharged by gravitation alone. As an instance may be quoted 

 the wells which supply water to the town of Rawalpindi. They 



Water-supply, of derive their supply by percolation from some 



Rawalpindi. coarse alluvial gravels which occupy a longi- 



tudinal valley bordered by rocky ridges. This valley is situated at 

 the foot of the hills, but at a greater altitude than the town, to which 

 the supply of the wells is carried by gravitation alone. The wells 

 which supply the city of Karachi, sunk in the gravels of a broad 

 river-bed that never contains any water flowing at the surface, 

 except in times of exceptional flood, are essentially of the same 

 nature. 



Here, then, we have percolation with an abundant flow, while 

 the "spring-wells" of the Gangetic alluvium might be taken as 

 examples of artesian action without overflow. In fact, the difficulty 

 which is often experienced as to whether a certain well should be 

 classed as artesian or not, has led certain writers to discard the 

 term entirely. This is perhaps a somewhat extreme view, for 

 although the category cannot be defined within absolutely strict 

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