510 OF THE PHYSICAL STRUCTURE 



gradual and prolonged pressure, exerted northwestward. Con- 

 ceiving the various degrees of inflection witnessed in different 

 parts of the chain to have resulted from a long-continued pres- 

 sui'e, we should be compelled to admit, that the southeastern side 

 of the tract had had impressed upon it successively all the different 

 gradations of flexure met with throughout the chain, and thus we 

 should have to suppose, that the closely folded, crowded axes of 

 the gi-eat valley were slowly developed by a force that, in its 

 earlier stages, produced every where only wide and gentle arches. 

 Yet, if such was the case, why do we not recognize a yet more 

 uniform or gradual transition in the dimensions of the axes, than 

 our Sections show. If the steepness of the flexures measures thus 

 then- age, why, it may be asked, are those of the same group so 

 various in this respect, while their intimate relations to each other, 

 in respect to parallelism, gradation of distance, and dip, plainly 

 prove them to have had a contemporaneous origin ? If a long 

 period was consumed in their production, why did there not take 

 place, by virtue of the simultaneous denudation and deposition 

 which must have been in progress, a constantly unconformable 

 superposition of the new deposits, as the axes slowly rose above 

 the level of the water ? 



But, while the observed variety in the magnitude and steepness 

 of the flexures thus makes it incumbent on the advocates of such 

 a theory of the gradual formation of axes, to admit, that the folded 

 and closely crowded ones have arisen out of broader and normal 

 curves, the general tenor of then* doctrine of progressive and cu- 

 mulative actions, implies, that the short and narrow flexures were 

 produced first, and that some of them were enlarged into the vast- 

 ly bolder and longer axes, which abound in many parts of the 

 same region. This, however, seems an insuperable difficulty, 

 since, if we suppose the breadth and length thus steadily to in- 

 crease, a great number of intervening flexures and foldings would 

 be necessarily obliterated or reversed. 



But, quitting the theory of a gradual horizontal pressure, an- 

 other hypothesis suggests itself, as likely, in the present stage of 

 geological speculation, to be offered in explanation of the 

 structural laws we have described. It may be urged, that a 



