RUSSELL FORK FAULT. OF SOUTHWEST VIRGINIA = 355 
Gap southwestward. The southwest end is terminated by the 
Jacksboro cross fault and the northeast end by the Russell Fork 
cross fault to be described below in more detail. The general 
relations of these boundary faults may be more clearly seen by 
reference to the map and diagram, Figures 1 and 2, and to the 
structure sections, Figures 3 and 4. 
From Norton, Virginia, northeastward, coal-measure rocks are 
exposed at the surface throughout the entire width of the block; 
but from Norton southwestward the block may be divided into 
two parts, that part lying northwest of Stone and Cumberland 
mountains being synclinal in structure and composed of coal- 
measure rocks, whereas that part lying southeast of these moun- 
tains is anticlinal in structure and composed of rocks of very much 
greater age. ‘The syncline, which is now generally known as the 
Fic. 2.—Outline diagram of Cumberland block showing the bounding faults 
Middlesboro syncline, is a broad, flat-bottomed trough at the 
northeast end of the block, but farther west in the vicinity of Dante 
an arch appears which develops rapidly westward into the Powell 
Valley anticline that constitutes the southern part of the block. 
Both the Middlesboro syncline and the Powell Valley anticline are 
characterized by steep dips on the northwest limbs and gentle 
dips on the southeast limbs, as shown in the sections. The erosion 
by Powell River and its tributaries of the rising crown of the Powell 
Valley anticline accounts for the exposures of pre-Carboniferous 
rocks in the southern portion of the block and the narrowing of 
the coal-measure portion on the north. The general relation of 
these different structural units and their expression in the areal 
relationships of the Pennsylvanian and pre-Pennsylvanian rocks 
may be seen by reference to Figure 1. 
The topography of the block is intimately related to the struc- 
ture. Pine Mountain throughout its entire length is a conspicuous 
