Mechanics of Low-Angle Overthrust Faulting as Illustrated by Cumberland Thrust Block, Virginia, Kentucky, and Tennessee

The structural relations of the Cumberland overthrust block are such as would occur if gliding on the thrust plane took place parallel with the bedding along certain shale beds in such a way that the thrust plane followed a lower shale bed for some distance, then sheared diagonally up across the intervening beds to a higher shale, followed that for several miles, and again sheared across the bedding to the surface. Reasons are given for the belief that subsidiary faults and folds within the block are superficial and do not extend below the thrust plane. This possibility should be borne in mind when exploration of such structures for oil or gas is contemplated. Study of the Cumberland block throws new light on the broader problems of the nature of folding and faulting in the sedimentary rocks bordering great mountain ranges and on the function of friction in setting limits to the distance through which overthrust blocks can be moved.