368 
WELLS. — MINING. 
doing, the water will be let out. In this manner 
it is ascertained that many low grounds and wet, 
marshy soils may be drained, merely by boring the 
earth. Among highly inclined and even vertical 
strata, water may sometimes be obtained at differ- 
ent levels, from the saturation of slate, gneiss, or 
other beds, to a certain degree pervious to water 
at such levels, so that if a well be formed in such 
situations, the water will penetrate into the cavity, 
and fill it up to the height to which the line of sat- 
uration extends. Such is the case in the gneiss 
rock of the island of New- York, into which Arte- 
sian wells have been sunk in various places to the 
depth of from 100 to 600 feet. 
Mining. — Those who have read the preceding part 
of this treatise must have perceived that the geo- 
logical facts which have been stated have a direct 
bearing upon the art of mining. And certainly, 
judging from the immense amounts which have 
been expended in fruitless explorations in various 
parts of the country, for coal, lead, gold, silver, &c., 
we should say there is no country on the globe where 
geological knowledge is so much needed as in this. 
Such is the morbid thirst and eagerness for wealth, 
that the people are ready to commence their re- 
searches on the slightest indications. Companies 
have been formed and excavations made, in locali- 
ties where a practical geologist would have said at 
a glance there was no probability that the substance 
for which they were searching would be found. 
" Certain mineral substances occur, so constantly 
associated with other particular minerals, that, on 
finding one, the others may be expected to occur 
associated with it. Without a knowledge of these 
associations, and various other facts connected with 
geology, which require much practical knowledge, 
attempts at new discoveries, except by mere chance, 
must be fruitless. The hundreds of excavations in 
idiiTerent parts of the country* made under the delu- 
