438 ' TERENCE T. QUIRKE 



of this low-angle zone of parting to the surface at an increasing 

 degree of steepness;^ in other cases rupture occurs within the 

 bending part of the crust near the plane of maximum shear with a 

 break low-angled at depth and increasing in steepness near the 

 surface. In either case displacement of less than one mile results 

 in a steep-angle fault, an ordinary reverse fault, but displacement 

 of several miles results in reduction of steepness of the fault plane 

 by the abrasion of the footwall and by advancement of the low- 

 angle part of the hanging wall to the surface. Thus some 

 low-angle overthrust faults and high-angle reverse faults may 

 represent different stages of a single process. 



' T. C. Chamberlin, Econ. Geol., II (1907), 597-99. 



