_Paris_.--The wells sunk in the Paris basin, of which Fig. 254 is a section, are very numerous, and many of them of great depth. Fig. 255 is a plan indicating the position of the principal wells, and Figs. 256 to 258 sections giving each a summary of the nature and thickness of the formations passed through. For boring these wells special tools had to be used, which have already been described at length in Chap. VI. A large Artesian well was, in 1867, being constructed by Dru at Butte-aux-Cailles, Fig. 255, for the supply of the city of Paris, which is intended to be carried down through the greensand to a depth of 2600 or 2900 feet to reach the Portland limestone. The boring in 1867 was 490 feet deep, and its diameter 47 inches. During the previous 2-1/2 years, M. Dru was engaged in sinking a similar well of 19 inches diameter for supplying the Sugar Refinery of M. Say, in Paris, Fig. 255; 1570 feet deep of this well had been bored in 1867, see Fig. 258. The well at Grenelle was sunk by Mulot in 1832, and after more than eight years' incessant labour, water rose on the 26th of February, 1842, from the total depth of 1806 feet 9 inches. The diameter of the bore-hole is 8 inches, ending, as is seen in the detail sections, Figs. 259 to 262, in the lower greensand. The well of Passy was intended to be executed in the Paris basin which it was to traverse with a diameter, hitherto unattempted, of 1 mètre (3·2809 feet); that of the Grenelle well being only 20 centimètres (8 inches). It was calculated that it would reach the water-bearing stratum at nearly the same depth as the latter, and would yield 8000 mètres or 10,000 cubic mètres in twenty-four hours, or about 1,786,240 gallons to 2,232,800 gallons a day. Figs. 263 to 266 show a detail section of the strata passed. [Illustration: Fig. 255. Reference.--P. Passy. G. Grenelle. B. Butte-aux-Cailles. R. Sugar Refinery.] [Illustration: PASSY. Fig. 256.] [Illustration: GRENELLE. Fig. 257.] [Illustration: SUGAR REFINERY. Fig. 258.]