21 
termed,) with which many of you are familiar. Its highest 
members are composed of tertiary strata of sand and calcareous 
sandstone, beneath which are beds of mottled clay. The chalk 
on which this lies is 1,477 feet thick, resting on 150 feet of green 
sand, which in its turn lies on the gault. This last is for the 
most part composed of clay, and nearly impermeable to water. 
The whole over a width of many miles is arranged in the form 
of what geologists term a basin, that is to say, the strata from 
their outcrops have a tendency to slope towards a general centre, 
where for a space they lie more or less horizontally. 
On the margin of the basin, strata of green sand and gault 
rise to the surface at heights in many places approaching to 
330 feet above the sea, Grenelle being only about 100 feet 
above that level. Geologists knew that the water which fell on 
these strata at their outcrop would of necessity percolate in the 
direction of the inclination of the beds, so that, at the lower 
points of the curvature, a great body of water must exist, con- 
fined as it were in a sponge, and unable to escape below, be- 
cause of the impermeable quality of the beds on which the 
porous strata rest. This deep-seated reservoir being tapped by 
boring, the water would rise to the surface in the manner I have 
explained. 
In 1832 the municipal corporation of Paris, impressed with 
the sanitary necessity of further supplies of water, voted 18,000 
fiancs for the construction of three artesian wells— a sum so 
ridiculously small that the project was immediately abandoned. 
M. Mulct, however, one of their engineers, having previously 
sunk in the chalk at Suresne, at Chartres, and at Laon, to the 
depth of 1,082 feet, proved that it would be necessary to bore 
completely through that formation to ensure a sufficient supply. 
This conclusion, based on strict geological reasoning, was con- 
firmed by M. M. Arago and Walferdin, and in November 1833 
the work was begun. With infinite energy, skill, and per- 
severance, M. Mulct carried it on, overcoming every opposition, 
physical and moral ; for he had not only to conquer those natural 
difficulties that beset so unexampled an undertaking, but he had 
also to contend with municipal parsimony, that shrank from the 
continuance of supplying funds for a project based on purely 
