g 



tion of minerals whenever tin- conditions become most favorable. 



(7) Cavities arc formed in rock masses by the principles of 

 isostacy and di:istnphi>m in the maintenance of equal stress as 

 evidenced in mountain making. Through diastrophism the 

 strata become converted into a series of anticlines and synclines. 

 Each type of folds often gives rise to fissures and a general 

 shattering of the rock mass. While these two types of folds 

 occasion the greatest disturbance, a pronounced effect is pro- 

 duced by the monocline in which there are two lines of yielding, 

 one at the crest and the other at the base. These conditions 

 produce a favorable environment for ore bodies. 



Faults. A fault is a fracture or disturbance of the strata 



.\VN v /x:.; . ; ; :.- '. 



FIG. 5. Ideal section showing a fracture filled along a fault plane. 



breaking the continuity of the formations. (See Fig. 5.) As 

 faults are usually inclined somewhat to the horizon there is 

 both a vertical and a horizontal displacement of the strata, 

 as shown in Fig. 6. The throw is the amount of the upward 

 or the downward displacement of the strata. The dip is the 

 inclination of the fault plane to the horizon. The hade is the 

 inclination of the fault plane to the vertical. The strike is the 

 direction of the outcrop of the fault plane at a horizontal 

 surface. A fault produced by gravity is called a normal fault, 

 and one produced by compression a thrust fault, yet it is possible 

 in a few instances that normal faults have been produced by 

 compression. It is of the utmost importance in mining to know 



