198 GEOGNOSY AND GEOLOGY. 
prevent a filling up by pieces of rocks, gravel, or other substance, which 
might slip in from the side. These tubes are adjusted in their place by 
means of the borer, 14. The instrument, 5, is employed to extract the 
tubes again, by screwing into them and thus elevating them from the cavity. 
It sometimes occurs, that the shafts to which the borers are attached, break 
off in the hole; in this case, the instrument, 9, is employed, which, being . 
screwed around the upper end of the broken shaft, takes firm hold of it. 
The other borers, 8, 10, 13, and 1-30 of the boring shed are used in 
particular cases. 
One of the most important and interesting Artesian wells ever constructed 
is that of Grenelle, near Paris, in which, for eight years, the operation was 
continued, and which was sunk to a depth of 1961 feet below the ground, 
or 1696 below the level of the sea, thus nearly four times as deep as the 
elevation of the cathedral-of Strasburg. (See fig. 3.) According to the 
report of the engineer, M. Mulot, who directed the boring, the geological 
peculiarities of the strata passed through, were as follows: 
1. Alluvial masses to the depth of twenty-seven feet. 
2. Argile plastique, with muschelkalk, quartzose and argillaceous sand, *: 
variegated clay, &c., to the depth of about 173 feet. 
3. White chalk, with beds of dolomite and silex, to the depth of 910 
feet. 
4. Compact grey chalk, with silex here and there in the upper portion, 
extending to a depth of 1480 feet. 
5. Chalky Glauconia strata to the depth of 1666 feet. 
6. The gault, with iron pyrites, phosphate of lime, and fossil remains in 
the upper portion ; green and white sand occurring in the lower and middle 
strata. 
Although some geologists have ascribed to subterranean lakes the origin 
of the water emerging from Artesian wells, there are many circumstances 
that conclusively prove that, in most cases at least, these waters are entirely 
of immediate atmospheric origin. An Artesian well at Tours, on the Loire, 
brought up remains of plants and shells from the calcaire grossier, the origin 
of which could be pronounced upon with all confidence. The plants were 
of such a character and appearance as that they could not have been in the 
water for more than three or four months. Other Artesian wells, as those 
at Elbeuf, Bochum, &c., have occasionally thrown up eels, groundlings, and 
~ other animals. 
Pi. 48, fig. 1 is intended to furnish a coup d’eil of the normal masses. 
The abnormal masses have been considered as the oldest, for the sake of 
separating them from the normal. 
A. 17. Abnormal masses, strata 1—4 
B. Normal masses, viz. : 
16-11. Primary or bottom series, ss 5-16 
10. Transition slate system, Kei AT 
9, 8. Carboniferous system, “« 19-22 
r-o. Kupferschiefer formation, “ — 23-26 
628 
