THRUST FAULTS 



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monoclinal folds, which often pass into faults, the beds yielding 

 to flexure along part of their course, fracturing and dislocating in 

 other parts. 



II. Reversed or Thrust Faults (also called overthrust faults or 

 simply thrusts). — These are the opposite of the so-called normal 

 faults, the hade being toward the upthrow side, which thus forms 

 the hanging wall, while the downthrow side is the foot wall. 

 Faults of this class are due to compression, the strata breaking 

 and slipping past and over one another, instead of folding, and 

 they are characteristic of highly folded regions, sharp plications 

 often passing into thrust faults. Thrust faults are produced in 

 somewhat different ways, and have, accordingly, been divided by 

 Mr. Willis into four categories. 



(1) The shear thrust, when the strata are dislocated by com- 

 pression and carried along a fault plane over other beds ; the 

 strata shearing more easily than bending. Thrusts of this charac- 

 ter are independent of flexures. 



(2) The break thrust occurs when the strata are first folded 

 into an anticline and then fractured, the upper limb of the broken 

 fold being pushed forward over the lower. 



— B 



FlG. 109. — Erosion and break thrust, Holly Creek, Georgia. (Hayes.) 



(3) The stretch thrust is caused by plication and inversion, 

 by means of which the overturned limb is stretched, broken, and 

 dislocated. 



(4) The erosion thrust. When the outcrop of a rigid stratum 

 on the flank of an anticline is caused by erosion, it will meet with 



