SPECIAL TERMS 



181 



A horst is a mass elevated relatively to the surrounding masses and 

 separated from them by faults. 



A grab en is a mass depressed relatively to the surrounding masses and 

 separated from them by faults. 



A fault block is a mass bounded on its sides, completely or in part, by 

 faults. It may be elevated or depressed relatively to the adjoining mass, 

 or it may be elevated relatively to the mass on one side and depressed 

 relatively to that on the other. A mass that is not entirely inclosed by 

 faults may properly be termed a fault block only when it can be regarded 

 as a structural unit whose relations to the adjacent masses has been 

 dominantly determined by faulting. 



Figure 10. — Section of a normal dip-slip Fault 

 (See figure 9 for legend) 



The pitch of a line lying in the fault-plane, such as the trace of a dis- 

 located bed or vein, is the angle between the line and the horizontal 

 measured in the fault-plane. The angle between the same line and the 

 horizontal measured in a vertical plane through the line is the dip of the 

 line. 



Suggestions fob Teaching 22 



The extent of the instruction on the subject of faults and their nomen- 

 clature must be determined by the character of the class and by the judg- 



— This section has open added at the request of several Fellows of the Society, it 



must necessarily he concise. 



