8i8 



PRINCIPLES OF STRATIGRAPHY 



the strata. When the fault plane cuts the obtuse angle between the 

 strata and the surface, i. e., when its dip is greater than that of the 

 strata, the "up-dip" end lies on that side (to the right of the plane 

 in the figures). When it cuts the acute angle, i. e., dips at a less 

 angle than the strata, the up-dip end lies on the acute side (left side 

 of the fault plane in the figures). With the part thus oriented, the 



Fig. 199. Sections showing the effects of strike faults in ehminating beds 

 (A, F, I and J) and in repeating beds (B, C, E, G, and H). 



general law may be stated that, if the "up-dip"' end moves down, we 

 have repetition of strata, while, if the up-dip end moves up, elimi- 

 nation of strata results. Conversely, when strata are repeated or 

 eliminated, the up-dip end must be assumed as having moved either 

 down or up. If the angle of the fault plane is ascertained, the fault 

 will appear to be either thrust or gravity, according to the greater 

 or less angle of inclination of the fault plane, as compared with the 



