24 



Economic Geology. 



the adoption of the Artesian system. The extensive develop- 

 ment of secondary and tertiary formations over the surface 

 of the earth affords a wide field for boring operations, and 

 already in England, France, Germany, Italy, America, and 

 it is said in China, they have been extensively and success- 

 fully employed. To illustrate the geological principles on 

 which the action of Artesian springs depends, let us suppose 

 that the upper part of a hill, A, consists of a soft porous 

 sandstone, and that by noting its dip, it is observed to pass 

 at a low angle, beneath the plain B ; continuing the exa- 



mination of the locality it is found that the sandstone is 

 completely covered by a bed of close adhesive clay, over 

 which again a certain depth of surface soil reposes. Now 

 with this arrangement, which is not an uncommon one, it will 

 readily be observed, that the water falling on the sand- 

 stone being easily absorbed by it will naturally seek the 

 lower level of the plain, passing underneath clay, and 

 as the process of absorption will have been in progress for 

 ages, it is probable that the water-bearing stratum will 

 be highly charged. Should it have become thoroughly 

 saturated, a series of natural Artesian springs will be 

 found along the line of junction of the impervious 

 clay with the sandstone, and should this line be but 

 little elevated above the level of the plain, it would be 

 unadvisable to attempt boring, since the water would be 

 carried off by these natural drains. But if no springs are 

 found, or if they are only found at a considerable height 



