tRanslatory momements 177 



'•'transverse thrusts." Jukes-Brown calls them "heaves." Scott calls 

 them "horizontal faults" or "heave faults," A vertical fault is one with 

 a dip of 90 degrees (see below) ; and, by analogy, a horizontal fault should 

 be one with a zero dip and should not refer to strike-slip faults. 

 Oblique-slip faults, where the net slip lies between these directions. 



CLASSES OF STRIKE FAULTS 



Most geological text-books and books on field methods have confined 

 themselves almost exclusively to the discussion of dip-slip faults, and 

 have given little attention to the other two classes. 



Strike faults have usually been treated as though they were also dip- 

 slip faults and classified into 



Normal faults, where the hanging wall has been depressed relatively to 

 the foot wall. 



Reverse faults, where the hanging wall has been raised relatively to the 

 foot wall. 



Vertical faults, where the dip is 90 degrees. 



The relative displacement has usually been determined by means of a 

 dislocated bed. Although exception may well be taken to these terms, 

 their retention is recommended, because they are in general use and are 

 well understood. The word "reverse" is preferable to "reversed" (which 

 has been almost universally used), as the latter implies the reversal of an 

 action. 



The horizontal distance between two points on opposite sides of a fault, 

 measured on a line at right angles to the fault strike, is always shortened 

 by a reverse strike fault, lengthened by a normal strike fault and un- 

 changed in length by a vertical fault. 



EXTENSION OF THE WORDS "NORMAL" AND "REVERSE" TO DIAGONAL AND 



DIP FAULTS 



The expressions "normal" and "reverse" may be used in connection 

 with oblique and dip faults, even when they are strike-slip or oblique-slip 

 faults, provided they are applied to designate the apparent relative dis- 

 placement of the two parts of a dislocated stratum, or other recognized 

 surface, in a vertical plane at right angles to the fault strike. It does 

 not follow, in the case of oblique-slip faults, that a horizontal line at 

 right angles to the fault strike would be lengthened by a normal or short- 

 ened by a reverse fault. This has been pointed out by Mr. Ransome" 

 and may be illustrated by figures 7 and 8. In figure 7 a reverse fault, aa 



21 Economic Geology, vol. i, pp. 783-787. 



