ARTESIAN WELLS IN DORSET AND ELSEWHERE. 187 



may be enumerated springs, which let out the underground 

 waters in a variety of ways.* The artificial causes arise mainly 

 from too many boreholes and also from excessive pumping, so 

 that districts naturally artesian in their water supply are 

 becoming gradually sub -artesian a condition of things more 

 obvious after a prolonged deficiency of rainfall. 



In the case of b, relating to the disposition of the beds which 

 are supposed to yield water, there are three conditions (and 

 there may be more) where the artesian principle might be 

 expected to apply. The first and most obvious is the simple 

 syncline, where a variety of beds, or one thick water-bearing 

 formation like the Chalk, are evenly folded into a curve some- 

 what after the fashion of the U-tube, though, of course, with 

 a much flatter angle. The more gentle the incline the more 

 extensive will be the outcrop of the bed or series of beds on 

 which the rain will fall, and thus yield the supply of under- 

 ground water, having a tendency to gravitate towards the centre 

 of the syncline. A second condition, as previously intimated, 

 is that of a basin where the strata are for the most part 

 monoclinal, i.e., all dip in the same direction, but where one or 

 more strike faults arrest the flow of water towards the centre 

 and hold it back like a ligature across an artery. There is also 

 a third condition, where the strata are monoclinal, so far as is 

 known to the prospector, but whose termination at the unknown 

 end of the basin can only be a matter of inference. In some 

 cases which come under this definition the mere friction which 

 the water undergoes in its passage through the rocks may tend 

 to produce artesian action. This third condition seems to apply 

 to some of the artesian wells in Australia, and, as there is no 

 country where deep boring has been carried to such an extent, a 

 short notice of this subject will be found in the latter part of 

 this paper. 



* The source of the New River, for instance, which has supplied North 

 London with water for more than two centuries, is to be found in a, spring rising 

 out of the Hertfordshire Chalk, which yields 4| million gallons per day. 



