34 PHYSIOGRAPHY. [chap. 



drop of water brought up by these fountains. It may have 

 fallen originally as rain upon the chalk hills around London, 

 perhaps twenty miles off, and after slowly trickling through a 

 long, dark underground course, where it was pent up under 

 pressure, ultimately found relief in the bore-hole of the 

 Artesian well 



London and Paris are situated under very similar 

 geological conditions, and what is said with respect to the 

 deep wells of one city applies with but little modification to 

 those of the other. In the Paris basin, the Artesian system 

 has been very largely carried out, and many of the borings 

 have reached extraordinary depths. Thus at Crenelle, a 

 suburb of the south-western part of Paris, there is a famous 

 Artesian well, 1,798 feet deep, fed by the rains which fall on 

 the permeable strata of Champagne at a distance of 100 

 miles from Paris. Several other borings have since been 

 carried to much greater depths than that reached by the 

 well at Crenelle. 



Having explained the origin of ordinary springs and the 

 nature of Artesian wells — which in truth are merely artificial 

 springs — ^it is now time to return to the study of the Thames 

 basin, the springs of which are the immediate source of all 

 the fresh water in the river, except the small portion derived 

 from the rain which falls directly into it. 



The alternations of pervious and impervious strata 

 which constitute that district, present all the necessary 

 conditions for an abundant supply of springs yielding 

 excellent water. " In the whole course of our experience," 

 said the Rivers' Pollution Commissioners, in their sixth 

 Report, " we have found no catchment-basin ' so rich in 



1 The catchment-basin is a term applied to all that part of a river- 

 basin from which rain is collecled, and from which therefore the river 

 is fed (p. 145). 



