nature of the soil which composes the Plain of Grenelle. On the surface it is formed of gravel, pebbles, and fragments of rock, which have been deposited by the waters at some period anterior to any historical record. Below this surface M. Mulot knew, by geological inductions and previous experience, that at Grenelle marl and clay would be found in the place of the limestone which in general forms the stratum immediately beneath. M. Mulot was aware that he must bore about four hundred and forty yards in depth, before he should meet with the sources which flow in the gravel below the limestone, and supply the wells of St. Ouen, St Denis, and Stains. Beneath the marl and clay, the boring-rods had to per- forate pure gravel, plastic clay, and finally chalk, which forms the bottom of the basin in which the tertiary strata have been deposited. No calculations or geological knowledge could determine the thickness of this stratum of chalk, which, from its powers of resist- ance might present a nearly insurmountable obstacle. The experience obtained in boring the wells of Elbeuf, Rouen, and Tours, was in this respect but a very imperfect guide. But supposing this obstacle to be overcome, was he sure of finding a supply of water below this mass of chalk ? In the first place, the strata below the chalk possessed, as we shall see, all the necessary conditions for producing Artesian springs, namely, suc- cessive layers of clay and gravel, or pervious and impervious beds. M. Mulot confidently relied upon his former experience of the borings of the wells at Rouen, Elbeuf and Tours, where abundant supplies of water had been found below the chalk, between similar strata of clay and gravel. " But one other condition is requisite to effect the rising of the water in an Artesian well, viz. that the point of infiltration should be higher than the orifice above which the water is to rise. This also was the case at Grenelle. In fact, M. Arago had shewn that 68 PRELIMINARY ESSAY. the water of the spring in question would necessarily rise to the surface, because, in the well at Elbeuf, which is nearly nine yards above the level of the sea, the water rises from twenty-seven to twenty-nine yards above the surface of the earth, and consequently from thirty-six to thirty-eight yards above the level of the ocean. Now, as the orifice at Gre- nelle is only thirty-four yards above this same level, it follows that if the same spring were met with, the water must rise above the surface of thev earth at Crenelle. " The necessary works were now commenced with boring-rods about nine yards long, attached to each other, and which could be raised or lowered by mechanical means ; and an ingenious method was adapted for giving them a circular motion. The diameter of the bore hole was about six inches. The instrument attached to the end of the lowest boring-rod, was changed according to the different strata which were successively reach- ed, the form adapted for passing through the softer materials of the surface, being unsuit- able to boring through the chalk and flint, a hollow tube being used for the former, while the latter was penetrated by a chisel-shaped instrument. The size of the rods diminished in proportion to the depth, and as the subterranean water was not reached so soon as was expected, it became requisite five several times to enlarge the diameter of the bore, to admit of the work being successfully continued. Accidents occurred also, which tried the utmost patience of the projectors. In May, 1837, when the boring had extended to a depth of four hundred and eighteen yards, the hollow tube, with nearly ninety yards of the boring-rods attached to it, broke, and fell to the bottom of the hole, and it was necessary to extract the broken parts before any further progress could be made. The difficulty of accom- plishing this may be conceived, when it is stated that the different fragments were not withdrawn until after the lapse of fifteen months. A description of the ingenious mode by which this was effected, would be too technical for our work. Again, in April, 1840, before it could be recovered, several months were spent in excavating round it. A similar occurrence created an obstacle which impeded the work for three months, but instead of being withdrawn, the detached part was driven literally into the stratum, which happened to be gravel. At length, in February, 1841, after eight years' labor, the rods suddenly descended several yards ; they had pierced the vault of the subterranean waters of which M. Mulct had been so long in search. In the course of a few hours the water rose to