196 WELLS. 



From the A'aried character of the strata which compose the crust of 

 the globe it would follow, that subterranean streams must be formed un- 

 der a great variety of circumstances. The innumerable cracks and fis- 

 sures which some formations pi'esent, may give rise to a corresponding 

 number of streamlets communicating with each other in every direction, 

 or a bed of loose materials may receive the contributions of thousands 

 of such streams and form a reservoir of greater or less extent. 



It may often happen that a subterranean film or reservoir of water 

 is connected with another portion at a higher level in which case a hy- 

 drostatic pressure upon the superincumbent strata will be produced, pro- 

 portioned to the height of the source. When a perforation is made 

 through such strata the phenomenon of artesian or overflowing wells is 

 exhibited. 



Wells are constructed for the purpose of forming reservoirs of water 

 in situations where it would otherwise be diflicult or impossible to pro- 

 cure a supply. They are usually made of a cylindrical form from 6 to 

 7 feet in diameter and extended to such a depth as will insure the re- 

 quisite amount, which is determined by observing the quantity which 

 enters in a given time. 



Artesian wells difier both in principle and action from those of the 

 common kind, they are not more than from 2 to 4 inches in diameter, 

 and are often carried to a depth of many hundred feet. When they 

 happen to penetrate a subterranean reservoir connected with a source 

 more elevated than the surface at which the perforation is made, the wa- 

 ter rushes up with violence, and forms a perpetual fountain. 



The opeiation of boring, although more expeditious than the com- 

 mon mode of excavation, is attended with much labor and expense. 



The tools required in the work are of various kinds. Some are de- 

 signed for piercing through clay or sand, others for penetrating rocks, 

 and others for removing water and rubbish. These tools are attached 

 to the ends of iron rods fixed in a suitable handle and worked by two 

 or more men. The labor is greatly diminished by connecting the rods 

 with a spring-pole placed horizontally over the well. 



The principal inconvenience and expense arise from the necessity of 

 frequently raising and changing the rods, they are screwed together in 

 convenient lengths, and vv'hen several joints have been attached become 

 too heavy to be removed by hand. To facilitate the operation, a tripe- 

 dal standard is erected over the well and furnished with a pulley, as 

 each joint successively appears above the surface it is unscrewed ; the 

 rods are returned in the same manner, one joint being added at a time 

 until a sufficient length is obtained. As the operation must be repeated 



