TRANSLATOR Y MOVEMENTS 173 



fe in figures 3 and 4. (The triangle def is parallel with the fault surface 

 in figure 4.) 16 



The bending of the strata near the fault may be so great that the direc- 

 tion of the shift is no longer even nearly parallel with the fault surface ; 

 it is better, then, to use the three following components of the shift : 



The strike-shift denotes the horizontal component of the shift parallel 

 with the fault strike, as already defined. 



The normal shift denotes the horizontal component of the shift at right 

 angles to the fault strike. It equals the horizontal shortening or length- 

 ening of the earth's surface at right angles to the fault strike, due to the 

 fault. 



The vertical shift denotes the vertical component of the shift. These 

 components of the shift may evidently be used when the shift is parallel 

 with the general trend of the fault surface. 



SEPARATION 



The separation of a bed, vein, or of any recognizable surface, is the 

 distance between the corresponding surface of the two parts of the dis- 

 rupted bed, etcetera, measured in any indicated direction. 17 The distance 

 must be measured between the corresponding surfaces on the two sides 

 of the faults — for instance, between the upper surfaces of the two parts 

 of the disrupted bed or between their lower surfaces — but not between the 

 upper surface of one part and the lower surface of the other. Moreover, 

 the surfaces considered must be parallel with the general extension of 

 the bed, vein, etcetera, such as the upper or lower surface of a bed or the 

 walls of a dike. 



The vertical separation is the separation measured along a vertical 

 line. 



The horizontal separation is the separation measured in any indicated 

 horizontal direction. 



The normal horizontal separation of a bed or other surface is its hori- 

 zontal separation measured at right angles to the strike of the bed, 

 etcetera. It is frequently determined from the outcrops of the bed at 

 the surface of the ground; it is then usually called the offset of the bod. 

 If figures 5 and 6 represent the ground plan of oblique faults on a level 

 surface, db, and not ac, would be the offset of the bed. ac would be the 

 horizontal separation along the fault strike, cb, in the same figures, 



"The dip-shift and strike-shirt are not accurately shown in figure 3, because the net 

 shift, <le, is not parallel with the fault piano, and the lines <Jc, df, and fr would not He 

 in one plane. But the definitions are clear and the figure Illustrates them fairly well, 



"The word "separation" is adopted from Bpurr, and is somewhat generalised. 



