FAULTS. 33 



greater discordance than those which at present 

 subsist." 



In rocks belonging to the Kainozoic and Mesozoic 

 epochs, the contraction in general has been less than 

 in the rocks belonging to the Palaeozoic epoch, while 

 the latter rocks present a marked contrast to the 

 metamorphic rocks. Consequently in the Kainozoic 

 and Mesozoic rocks, faults and fissures may be few 

 and small ; in the Palaeozoic rocks, they may be 

 numerous and large ; while in highly metamorphosed 

 rocks, they are often nearly innumerable. 



Faults may be simple or compound. A simple 

 fault is that in which the movement has taken place 

 along a single line, and the motion has been so 

 regular that little or none of the adjoining rocks 

 were worn or torn away. In a compound fault, there 

 are two or more lines connected with the movement, 

 and a greater or less thickness of " fault-rock " has 

 in most cases been formed. If a movement takes 

 place along a straight or nearly straight master joint 

 (fig. 7, PI. I), little or no abrasion can take place; 

 but if a similar movement were to happen in an un- 

 even joint (b, c, fig. 8, PI. L), the pressure and 

 motion would break off the jutting-out portions of 

 the beds, as represented by the parts included be- 

 tween the dotted lines #, c, and , d (fig. 8, PI. I.) 

 This figure represents a regular joint of this class, 



1 Henwood, ibid., p. 370. 



C 



