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 

 different parts of the country made under the delu- 



