Appalachian Faulting. 265 



from S that the moment of x into S A! is greater than the 

 resistance which the competent stratum opposes to bending. 



Now the force of compression, P, is resolved at A' into two 

 sets of components, those tangential and those radial to the 

 curve. As the curvature increases through the effect of the 

 moment a*xS A', the radial components increase in proportion 

 to the tangential and when their upward directed force ex- 

 ceeds the weight on the competent stratum at A 7 , a competent 

 anticline will develop there. 



The anticline A' is subsequent in time and causally related 

 to the anticline A. A' is therefore a consequent to A and 

 may be called a consequent fold in distinction from A, the 

 original fold. The distance of A! from A is determined by 

 the length of the limb SA', which is itself determined by con- 

 ditions in the strata; therefore so long as the stratigraphic 

 series remains invariable the distance A' A will be constant 

 and the two folds will be parallel. This is the condition which 

 any explanation of Appalachian folding must satisfy. 



The form of the anticline A' will probably vary in different 

 cases: it may be symmetrical or unsymmetrical, and if the 

 latter, it may be overthrown to one side or the other. With a 

 steep initial dip from A' toward S, there might be developed 

 an overturned limb facing the original fold (tig. 7) and then, 

 if both the original and the consequent folds were faulted the 

 thrust-faults would present opposite fault-dips. This however 



Fig. 7.— Development of opposed Fig. 8.— Development of parallel 



overturns. overturns. 



is the rare exception and the reason for the overturn of the 

 consequent in the same direction as the original fold appears 

 from a further analysis of the process. The form of the 

 gently sloping arm of the syncline S A 7 is determined largely 

 by the depression of S and is slightly convex upward from A 7 to 

 a point of inflexion, i, near S, (tig. 6). JSow the force P is con- 

 tinuously resolved upon the curve A' i into components acting 

 tangentially along the stratification and radially at right angles 

 to the same. The tangential components are opposed by the 

 resistance at S while the radial components tend to lift the 

 curved limb A' i against the weight of the overlying strata 

 and the resistance to bending. In the flat lying strata on the 

 other side of A' the force P is not resolved into components 

 so that the only force tending to elevate this part of the com- 

 petent stratum is the radial component at A'. This elevation 

 is opposed by the weight of the superincumbent load and the 



