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NEW YORK STATE MUSEUM 



I'ig. 4 



Figure 3 illustrating a strike, and figui-e 4 a dip fault. FF is the fault plane, AA, 

 BB, and EE Indicate the dipping rock layers. In the former figure the fault plane 

 cuts the surface parallel to the strike, causing a strike fault, in the latter the 

 strike is cut at right angles, producing a dip fault. On the left the unfaulted 

 hlock is shown, with the position of the fault dotted. In the center the conditions 

 preyailing shortly after completion of the faulting are shown, the downthrow block 

 on the right, and with the prominent fault scarp. On the right the conditions pre- 

 vailing after sufficient time has elapsed for wearing away the upthrow block down 

 to thp level of the other side, or rather for wearing the two sides down to a uni- 

 form level, are indicated, this being approximately tbe condition of most of the faults 

 of the region at the present time. In the strike fault this results in the entire^ dis- 

 appearance from the surface of the stratum BB, in the vicinity of the fault, the 

 actual thickness of rock so disappearing being comprised in the space between the 

 dotted lines on either side of BB. By varying the amounts of hade and dip, or 

 their directions, repetition of strata at the surface, instead of disappearance, may 

 result. In the dip fault the effect is to shift the outcrop of a given stratum, so 

 that in an old fault, the surface having been worn down, the ends are shifted for- 

 ward or back, as the case may be, on opposite sides of the fault, as BB is shifted 

 in the diagram. The amount of this shifting increases with increased throw of the 

 fault, and diminishes with increased dip of the rocks. 1^'ew faults meet these condi- 

 tions of correspondence with dip or strike direction exactly, but many make such 

 slight angles with these directions that they, are practically fulfilled. 



