368 CHESTER K. WENTWORTH 
the trace of the Pine Mountain fault and of only slight overthrust 
and more restricted compression in the Russell Fork fault with 
its trace at a much greater angle with the main overthrust. 
The stronger development of the Powell Valley anticline and 
the presence of the Wallen Valley fault only at the southwest are 
also strongly in accord with this suggested interpretation. 
The greater intensity of stress implied by the compound char- 
acter of the Pine Mountain overthrust at C (Fig. 2) and the prob- 
able development of the Powell Valley anticline before the rocks 
of the block were competent to transmit the stresses to the Pine 
Mountain fold which later broke in a fault, point strongly to 
the initiation of the faulting at the south end of the Jacksboro 
cross fault to allow the necessary shortening of the strata on the 
northeast side of that fault. The four faults as interpreted by 
Keith, and corroborated by the displacement of the north limb 
of Powell Valley anticline in the Briceville quadrangle, give clear 
evidence of a movement of at least ten miles to the northwest. At 
Skegg Gap the evidence does not indicate over two miles of over- 
thrust at the most. 
In the course of his meditation on this study the writer has 
made very briefly a few computations, based on extremely general 
and only very approximate assumptions, which are given below. 
Their value is solely to indicate orders of magnitude, and it is 
hoped that they may serve, as they did in the case of the writer, 
to visualize the immensity of forces involved. 
FORCE TO SHEAR AND FORCE TO THRUST 
ASSUMPTIONS 
Block 125 milesX 25 miles} mile 
Density 170 lbs. per cubic foot 
Coefficient of friction, mean between rough and smooth granite, o. 60 
Shearing strength 200 pounds per square inch 
Average extent of overthrust, 6 miles 
RESULTS 
Force to shear block loose over entire area= 25X10" pounds 
Force to move block against friction on horizontal plane= 23 X 105 pounds 
Work done in moving block 6 miles at angle of 5 degrees=85 X 10” foot pounds 
Equivalent to 420,000 horse-power working for 100,000 years 
Estimated coal in block = 50X 10? tons 
