IxX PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



of a kind leading us to infer that the resistances to the force, let it 

 have been what it might, were somewhat uniform, so that the great 

 flexures, however far they were removed from that force, preserved 

 an miiformity of character during their range. 



The hypothesis advanced by the Professors Rogers to explain the 

 facts observed is, as you have been some time aware, that the solid 

 crust of the earth, resting on liquid matter, having been exposed to 

 excessive tension, was ruptured along great lines ; that the sudden 

 relief of this tension produced in the liquid mass beneath two receding 

 sets of huge waves of translation, one on each side of the line of frac- 

 tured crust, which threw the crust into corresponding undulations, 

 and at the same time pressed and partially carried forward the two 

 pulsating zones, in the direction of the advancing waves. The crust 

 beneath each concave bend is supposed to have cracked and opened 

 downwards, during this wave-like motion, so that molten matter be- 

 neath rushed in, filled the rents thus formed, partially congealing in 

 wedge-shaped masses, which assisted, in combination with other pres- 

 sures, in preventing the mass from again flattening out, and thus the 

 temporary flexures were braced into permanent arches. 



In the first stage of their formation the flexures are supposed to 

 have been broad and gently curved ; even then, however, the arches 

 steeper on the forward sides of the waves. A succession of similar 

 waves of translation, starting from the same or parallel lines of rup- 

 ture, are considered to have acted on the flexures already formed, con- 

 tracting their horizontal width, increasing their curvature, and aug- 

 menting the diff'erence in the anticlinal dips, even to the inversion of 

 the forward side, with the production of parallel folding. The minor 

 folds and contortions are referred to the crumpling of the softer beds 

 on the bends of the principal flexures. 



With respect to this view you will observe, that it is to waves of 

 translation frequently repeated, and starting from the same or parallel 

 lines of rupture, that the final highly crumpled and contorted state of 

 the parallel bands is attributed ; and hence that the tension of the 

 rocks and their rupture have also to be repeated, so as to produce 

 these waves. If we should admit, which we confess we should have 

 great difliculty in doing, that the external crust would conform, in the 

 manner supposed, to the undulation of the waves produced in the fluid 

 mass beneath by the rending of this crust in long lines, in consequence 

 of tension, we have to reproduce similar conditions to cause similar 

 eff'ects ; that is, to obtain each set of pulsations we must have the 

 needful tension and fracture. We have thus to infer that the rent, 

 which so long as it existed would give way before any repetition of 

 the force that caused the first tension, was cemented up in such a 

 manner as again to permit tension of a kind and order similar to the 

 first, and so on. It is supposed that at every pulsation the beds were 

 crumpled up and driven aside from the original rent, or others parallel 

 to it, so that unless the superficial area of that part of the earth were 

 diminishing, each impulse would drive the once continuous beds further 

 from each other, the intervening space gradually increasing, and re- 

 quiring to be filled up by the hquid matter from beneath to an altitude 



