152 C. W. HAYES OVERTHRUST FAULTS OP THE APPALACHIANS. 



through the upper rigid bed D. Erosion of the latter might determine the 

 point at which the line would emerge at the surface. 



If the Coosa shales, represented in the diagram (figure 3, plate 3) by the 

 basal member A, were not of sufficiently low rigidity to take up the com- 

 pression by close folding, faults of steep hade and consequent great depth 

 would be formed. Again, if the Knox dolomite, B in the diagram, were not 

 sufficiently rigid to transmit the compressing force from ^to -ff under the 

 superincumbent load, it would be thrown into a series of normal Appalachian 

 folds ; and finally, if the difference in rigidity between the Floyd shales G 

 aud the Coal Measure sandstone D were not sufficient to determine the line of 

 least resistance in the former, the fracture would emerge at the surface with 

 a steep hade and form a normal east Tennessee fault. 



Washington, D. C, December, 1890. 



