9G 



CLAY AND SAND FAULTS. 



necessary to drive their cattle many miles for water. 

 It sometimes happens that these fissures or cracks 

 penetrate to enormous depths, and are of great width, 

 and filled with sand or clay. These are termed 

 ' faults ' by miners ; and some which we lately ex- 

 amined, at distances of from three to four hundred 

 yards from the surface, were from five to fifteen 

 yards in width. These faults, when of clay, are 

 generally the cause of springs appearing at the 

 surface; they arrest the progress of the water in 

 some of the porous strata, and compel it to find an 

 exit by passing to the surface between the clay and 

 the face of the upturned strata. When the fault 

 is of sand or gravel, the opposite eff"ect takes place, 

 if it communicates with any porous stratum, and 

 water which may have been flowing over the surface 

 is at once absorbed. 



" In the following diagram, let us suppose that 

 (b) represents such a clay fault as has been de- 



scribed, and that (a) represents a sandy one, and 

 that (c) and (d) represent porous strata charged 

 with water. On the water reaching the fault at (&), 

 it will be compelled to find its way to the surface, 

 forming a spring, and rendering the retentive soil 



