i 4 o OUTLINES OF I liOLOGY 



shows that some strata are cut out as they approach the 

 junction-line ; this plainly indicates the line to be one of 

 dislocation. 



A great many faults run with the dip, and are called 

 dip-faults ($<f> in Fig. 28) ; another series runs with the 

 strike, forming strike-faults $$ in Fig. 28). But as dis- 

 locations may occur in any direction, and cross dip and 

 strike at any angle, these two series are not very sharply 

 marked off from, but may pass into each other, or the 

 same dislocation may be a dip- fault when looked at 

 from one side and a strike -fault when viewed from 

 the other (as at <f>"<f>" and z z in Fig. 28). Owing to the 

 way in which denudation has smoothed down the surface 

 of the ground, a dip-fault has the effect of shifting the 

 outcrop of an inclined stratum so as to make it appear 

 as if horizontally displaced. In the map (Fig. 28), 

 for example, the beds D and E, dipping south, are tra- 

 versed by a dip-fault with a down-throw to the east. 

 The line of outcrop is consequently shifted northwards on 

 the side of down-throw. If the beds had dipped north- 

 wards, then a down-throw to the east would have moved 

 the outcrop southwards. A strike-fault, when it exactly 

 coincides with the line of strike on both sides, makes no 

 change in the line of outcrop, except in bringing two 

 parallel bands closer together. It may, however, carry 

 some important strata out of sight, or prevent them from 

 ever being seen at the surface at all. Thus in the map 

 (Fig. 28), the bed C is completely cut out against the 

 strike-fault <'</>'. If it were not seen at the surface else- 

 where, its existence could not be known unless from 

 some underground boring. 



