On the Artesian Well of Grenelle, 141 



We all know that it was owing to the influence of M. Arago 

 that the vote .of the Municipal Council of Paris was obtained 

 for the continuation of the boring operations from the depth 

 of 50O rtietveg to that of 600. It was doubted at that time if 

 the water would rise to the surface ; and one of the reasons 

 which decided the vote was, the ascent of water in tJie wells 

 boi^^ed at Elbeuf, by which water was obtained from the sub- 

 terranean sheet of water which was sought for at Paris. M. 

 Arago was sure that the water at Elbeuf could rise to a height 

 of from 27 to 30 metres above the surface^ which itself is 8 

 metres above the level of the sea. Now, the surface at Gre- 

 nelle being 31 metres above the level of the sea, the compa- 

 rison between these two points gave him reason to hope that 

 ^he column of water "would rise to the surface at Paris. • 



It may be remembered, on the other hand, that in 1839 I was 

 enabled to confirm this result by means of other considerations. 

 I searched for the limit of the chalk in a south-easterly direc- 

 tion from Paris, by ascending the natural inclination of the 

 waters at the surface of the ground, and which is indicated 

 by the course of the Seine and by that of the Marne. The chalk 

 ceases in the environs of Troyes ; the marls and the clays of 

 the Gault, which the borer then traversed at Grenelle, suc- 

 ceed the chalk, and the green sands make their appearance 

 near Lusigny, where they form the orifices through which the 

 waters begin to infiltrate. Thus, the height to which the 

 water penetrates near Lusigny, of 130 metres above the level 

 of the sea, and the other levels of the green sands to the SE. 

 and NE., presenting themselves sometimes at still higher ele- 

 vations, I was able, by comparing them wdth the surface of 

 Grenelle, which is 31 metres above the level of the sea, to 

 come likewise to the conclusion that, when the borer should 

 reach the water sought for at Paris, the water ought to rise 

 sensibly above the sm*face of the ground.* 

 II. Section of the Bore of the Artesian Well of Grenelle^ with ex- 



plantory notes. Communicated by Sir John Robison, K.H. 



F.R.S.E., &c. 



The bore passes through strata of various kinds, such as, 

 * Bulletin de la Soci^to Geologiqae de France* 



