RUSSELL FORK FAULT OF SOUTHWEST VIRGINIA 367 
Schematic structure lines of sections. 
Present fault lines placed with reference to the block. 
— — — — — Reference line of block. 
Displacement lines of the sections. 
Sea-level lines of the sections. 
SRE SC ae Lines showing present position of fault boundaries and reference line of block. 
Fic. 8.—Serial diagram showing history of the deformation and displacement 
of the Cumberland block as interpreted by the writer. In sketch No. 7 of the series 
is shown the present condition in outline. The heaviest lines show the structure 
in the sections schematically. The lightest lines are the “‘sea-level” lines of the 
sections and the fault lines of the sections stil! referring to sketch 7 of the series 
above. The solid lines of medium weight are the present traces of the various faults. 
The medium-weight dotted line is an arbitrary axis line the positicn of which is the 
same with reference to the block in each sketch of the series. 
In sketch 1 of the foregoing series the present fault traces are shown by the light 
dotted lines of the background and the present position of the axis line by the light and 
straight dotted line. The then position of the fault traces and of the axis line of the 
block is shown in sketch 1 by the medium-weight solid and dotted lines respectively. 
The light ‘‘sea-level”’ lines and fault lines of the sections and the very heavy lines of 
the schematic sections are the same as in sketch 7. The arrows which point upward 
in the sketches indicate the direction of the main thrust; the arrows pointing down 
and to the right at the left-hand end of each sketch indicate the resisting stress of 
the buttress southwest of Jacksboro as described in the text. 
The first sketch assumes the prior formation of the Hunter Valley. The second 
shows some slight buckling of the southwest end of the block. The third shows more 
intense buckling here. The fourth shows more intense buckling and extension of 
the folding eastward along the line of the Pine Mountain fault. In No. 4 also is 
shown the beginning of the Jacksboro overthrust fault. In No. 5 this fault has 
extended far around the north side of the block and the Russell Fork fault has been 
initiated as a normal fault. Sketch 6 shows further extension of the faulting and 
only a small corner of the block near the northeast corner remains attached. In 
sketch 7 this small attachment is broken and the block has been thrust into its present 
position. The relative movement of the block at different stages has been shown by 
the gradual migration of the heavy dashed axial line toward its final position as shown 
by the light dotted axial line of each sketch. 
