254 



DISLOCATIONS OF STRATA 



no resistance when the compressing force is again applied, but 

 will ride forward over the underlying bed. 



Thrust (or reversed) faults hade at greater angles (or, in other 

 words, dip at smaller angles) than do the normal ones, and in some 

 of the great thrusts the fault planes are almost horizontal : thrusts 

 are always along the strike, never parallel with the dip. If not of 

 too great throw and heave, thrust faults repeat the outcrop of 

 strata, as do the normal strike faults, but in those of very large 

 displacement, the beds which are brought into close juxtaposition 



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FIG. iio. — Great thrust fault, near Highgate Springs, Vt. The upthrow side 

 has been denuded away and the hammer spans the fault, connecting beds which 

 are stratigraphically many thousands of feet apart. (U. S. G. S.) 



are so widely separated stratigraphically, that no repetition occurs. 

 Faults of this class occur on a grand scale in the Appalachian 

 Mountains, especially in the southern part of that system, and even 

 more notable examples are to be found in the northwestern part of 

 Scotland. 



The Causes of Folding and Faulting 



The first step in this inquiry must be to determine the direction 

 in which the folding force acted. It might seem natural, at first 



