OF THE APPALACHIAN CHAIN. 511 



prolonged upivard tension, or pressure exerted along a single line, 

 might gradually create a broad and lofty anticlinal flexure, and 

 might, by a mere siiifting of the line, into positions always paral- 

 lel to its first one, accomplish in time the elevation of all the axes 

 of any of our Appalachian groups. Such a supposition would, 

 doubtless, account for the simple features of a symmetrical flex- 

 ure ; but it would afford no clue to an explanation of those beau- 

 tiful relations, which prevail between the form of the flexures and 

 their position in the groups, to which they appertain, or to the 

 fact of their assemblage into groups ; and these are among the 

 most interesting general facts, which a theory of flexures is called 

 upon to explain. How could a merely vertical force, applied to 

 the interior surface of the crust, either along a narrow line, or 

 over an elongated elliptical, narrow zone, produce that oblique 

 form of the anticlinal arch, which we find to be its normal con- 

 figuration ; or how could it give rise to the regular horizontal 

 bending of the axis-line, as seen in the curving districts of the 

 chain. Again, in what way can it explain the occuiTcnce of the 

 great lines of fault only on the northwestern side of the axes, or 

 the close oblique foldings, in all the southeastern side of the belt. 

 But, apart from all these objections, on what principle or analogy 

 are we entitled to assume, that the supposed successive shifting 

 of the upward force woiild be in parallel lines. Should the ele- 

 vation theory be modified so as to suppose the upward force to 

 have been exerted simultaneously along all the present anticlinal 

 lines, but not in the manner of an undulation, the equally formid- 

 able difficulty arises of accounting for the production of any 

 flexures ; since, by the close contiguity of the parallel lines of 

 upward pressure, the sole effect would be a nearly uniform dif- 

 fused bulging of all that portion of the crust, upon which the 

 tension was exercised. 



Of the Origin of the supposed Subterranean Undula- 

 tions, AND OF the Manner in which the Strata became 

 permanently bent and dislocated. 



The parallel flexures of the crust, so strikingly exhibited in the 

 Appalachian chain, and recognizable, we believe, in nearly all 



