1 86 ARTESIAN WELLS IN DORSET AND ELSEWHERE. 



In the majority of these cases of deep boring, the operators 

 rely upon the "artesian" principle for raising the water to the 

 required height. This name has been applied to water-springs 

 rising above the surface of the ground by natural hydrostatic 

 pressure, the general principle being that there should exist a 

 more or less porous water-bearing stratum sandwiched between 

 two impervious layers such as clays. In the more normal 

 instances the water-bearing stratum with its impervious cap and 

 base should be disposed in the form of a syncline, and, where 

 this syncline is perfect, as in the case of the Paris basin, the most 

 wonderful results ensue.* There are, however, many exceptions 

 to this rule, so that (a) the water does not always rise to the 

 surface ; and (3) the perfect synclinal is replaced by other 

 conditions, such as a basin where the strata, though mainly 

 inclined in one direction, are dislocated by a longitudinal fault 

 parallel to the strike, which tends to throw up the water very 

 effectually. In the case of a, where the water does not always 

 rise to the surface, but requires to be pumped, this failure to 

 fulfil the perfect artesian conditions is perhaps the rule rather 

 than the exception in this country. Such wells have been called 

 " sub -artesian," and the principle is just the same, for the water 

 rises in the borehole through the influence of the hydrostatic 

 pressure, and in this respect differs from the ordinary shallow 

 well, where the local water level is maintained. That it does 

 not rise high enough is due to two sets of causes, the one 

 natural and the other artificial. Amongst the natural causes 



* We certainly owe to our neighbours across the Channel the successful 

 development of this principle. In February, 1841, the famous well of Greiielle 

 (a suburb of Paris) was completed to a depth of l,79Sft., passing through a 

 series of formations where almost every condition of success, both as regards the 

 nature of the beds and their sjmclinal arrangement, may be said to exist. When 

 the water-bearing stratum was pricked, the water spouted out at the rate of 

 864,000 gallons per day at a temperature of 82 Fah. The well at Passy, also 

 near Paris, is still more remarkable. The depth of this well is 1,923ft., and the 

 diameter of the tube at the base 2ft. 4in. ; it is said to throw up a continuous 

 stream of water at a rate of 5\ million gallons per day to a height of 54ft. above 

 ground. 



