RELATIONS OF DIP, STRIKE AND OUTCROP 8oi 



outcrop and strike (Fig. i86b), no matter what the surface slope. 

 In all other cases, however, the outcrop on a sloping surface will 

 differ in direction from the true strike of the strata, and is apt to 

 mislead unless this fact is borne in mind. In general, it may be 

 said that the lines made by the intersection of inclined strata with 

 a sloping surface have their dozvn-slope end deflected in the direc- 

 tion of the dip of the strata. (Fig. i86c.) If the dip is vertical, 

 this deflection will not alter the direction. If the lines of inter- 



Synclinorium. 



Greylock, Mass. (After Dale.) 



section run at right angles to the slope of the surface, there is no 

 down-slope end, and hence no deflection. (Fig. i86a.) Again, it 

 should be stated that the true strike and the true dip are always at 

 right angles to each other, and any slope whose intersection with the 

 inclined stratum makes a line at right angles to the line of dip must 

 show the true strike in the outcrops in its surface. (Fig. i86a.) 



In the diagram, Fig. i86c, the inclined plane, A B C C A' has its 

 outcrop and strike coinciding where cut by the horizontal surface 



Fig. i86a. 



R c' w 



Fig. 1 86b. 



E F G H, but where cut by the inclined surface D E H I the out- 

 crop is deflected toward the down-dip side. It is evident from com- 

 parison with Fig. 1 86b that any vertical plane, as A B X Y Z, whose 

 intersection with the horizontal surface coincides with that of the in- 

 clined plane A B C C A', will intersect the inclined surface along a 

 line B X continuous with the line A B and having the same com- 

 pass direction. This is evidently the true strike, and the angle 

 X B C marks the angle of deflection from this direction of the in- 

 tersection of the inclined plane on the sloping surface, /. c, the 



