We conclude with the recent Artesian Well, on a large scale, in the plain of Grenelle, which is thus described :

PRELIMINARY ESSAY. 67

THE ARTESIAN WELL AT GRENELLE, PARIS. " Artesian wells are so called from the probability that they were first constructed in Artois, although from the authority of several ancient writers, they appear to have been in use in the earliest ages. The Artesian well at Grenelle, has lately been completed, after eight years of constant labor and repeated difficulties. The south-western portion of Paris was but very poorly supplied with water, and at Grenelle, a suburb immediately adjoining the city, this deficiency was so seriously felt, that it became an object of the greatest importance to find means of remedying the evil. M. Mulot, an experienced geologist, being consulted as to the practicability of constructing a well on the Artesian principle, stated that the perforation would necessarily be of extraordinary depth, owing to the nature of the district. We extract from the " Magasin Pittoresque" the following geological description of the basin of Paris " : Two conditions, as it is well known, are requisite for the formation of an Artesian well first, the existence of a pervious stratum, :

such as gravel, placed between two impervious strata, such as clay secondly, the perco- ;

lation of the water through the pervious stratum, from a point higher than that to which it is required to rise. The basin of Paris is in the form of a hollow plate, formed by a stratum of chalk. In this basin have been successively deposited the tertiary strata, in the centre of which Paris is situated. On a circular space bounded by the towns of Laon. Mantes, Blois, Sancerre, Nogent-sur-Seine, and Epernay, these strata appear at the surface, and conceal the chalk, but on the other side of the towns we have mentioned, the edge of the basin being passed, the chalk is found generally on the surface." If we look at the order in which the tertiary strata occur, we shall then comprehend the obstacles M.