ARTESIAN WELL 



225 





which even exceeded the depth of 2,400 feet from the surface. M. Degoussdo 

 mentions in his ' Guide do Sondeur ' (1847), that he himself had executed no less than 

 sixteen deep borings in the De"partement do 1'Indre et Loire, of which ten are in the 

 town of Tours and six in its neighbourhood, presenting an average depth of about 

 500 feet. Two of these borings were, however, unsuccessful, and it appears that the 

 conditions under which they occurred with respect to the great watercourses of the 

 district, led to the supposition that the underground course of the waters was inter- 

 rupted by means of a fault or upheaval. 



At Calais the results obtained by the great artesian well there sunk were even more 

 striking than those obtained near Tours ; for after having in this place passed through 

 the drift above the chalk, the chalk itself and the whole of the sub-cretaceous strata, 

 the boring was continued in the transition rocks until it had attained a total depth 

 from the surface of about 1,150 feet. It will bo necessary hereafter to refer to this 

 well, and to the abnormal state of the geological formations under this district. 



An important Artesian well was also put down at Chichester, being carried through 

 the great Hampshire tertiary basin to the upper greensand, where it was stopped at 

 a depth of 1,054 feet from surface. Very little water was obtained. 



At Southampton the upper and lower chalk and chalk-marl were passed through, 

 but at a depth of 1,317 feet no valuable supply of water was obtained. A great 

 number of Artesian wells had in the meantime been sunk in the tertiary basins of 

 both London and Hampshire, and the drain thus established upon the subterranean 

 water-courses of those formations was so great that the waters which originally had 

 flowed over the surface of the ground, were no longer able to reach that height ; and 

 it became evident that the demand upon these water-bearing strata was rapidly 

 exceeding the supply. Under these circumstances the Hampstead and Highgate 

 Waterworks Company resolved to renew under London the attempt which had been 

 abandoned at Southampton ; and their advisers argued that, inasmuch as the outcrop 

 of the sub-cretaceous formations was continuous around the margin of the cretaceous 

 basin surrounding and underlying the London tertiaries, excepting on the eastern 

 border, those sub-cretaceous strata would be found under London just as they had 

 been actually found at Paris. 



This reasoning proved to be correct so far as the chalk-marl, the upper greensand, 

 and the gault were concerned ; but when those formations had been traversed (to a 

 depth of 1,11 3| feet), the boring tools, instead of entering upon the lower greensand, 

 which theoretically had been expected, entered upon and traversed, to a total depth of 

 1,302 feet, a series of marls, clays, and sandstones, which appear in all probability to 

 belong to the new red-sandstone series : all the intermediate strata being absent. 



A boring at Harwich also proved the existence of transition rocks of an early 

 period at a depth of 1,200 feet from the surface ; various rocks from the tertiaries to 

 the upper greensand and gault having been passed through. 



From the above data the interesting fact will be observed that no borehole in the 

 London basin has as yet succeeded in proving and obtaining water from the lower 

 greensand rocks ; the Southampton, Calais, Highgate, and Harwich wells having all 

 proved failures in this respect. It is a question to be proved by experiment whether 

 to the north-west of London the tertiary rocks would not be less likely to give place 

 to rocks of older formations, as they appear to do in the boreholes referred to. It 

 will be understood from the particulars given of the few boreholes, how much un- 

 certainty attends the art of boring, at least, as regards the obtaining of water by this 

 means. 



Some particulars may now be given of a number of the chief Artesian boreholes 

 put down in France and England. The following Table shows the depth and cost of 

 several of the French Artesian wells : 



14,500 

 3,560 

 3,045 

 1,216 

 320 

 190 

 200 

 64 

 78 

 15 



The deep wells of London are all in the chalk. The dbpths of some of the most 

 important are given in the following Table, which has been compiled from data given 

 by Mr. W. Whitaker, 'Memoirs of the Geological Survey,' vol. iv. (1872) : 



VOL. I. Q . 



