OF THE APPALACHIAN CHAIN. 517 



as usual from the southeast. The latter, originating last, with a 

 more northern strike, would converge upon the former as the 

 waves advance northwestward, and coming in contact with 

 the eastern extremities of the previous flexures, would encounter 

 a retardation at their southwestern ends, while their remote or 

 northeastern extremities would be free to advance with their whole 

 velocity. The natural tendency of this species of resistance, 

 would be to break the retarded wave, and to give the northeastern 

 portions a more northerly strike. The whole movement may be 

 likened to the march of a platoon of soldiers in what is called a 

 right oblique order, wherein the advanced files slightly wheel 

 upon the left. 



The hypothesis we have advanced, seems also to explain the 

 important fact, that the whole undulated surface, estimated by the 

 average change of level of any given sti'atum traced across the 

 chain, rises in a regularly inclined plane southeastward, or towards 

 the quarter where we find, by other evidence, that the uplifting 

 and undulating action was most powerful. This circumstance, 

 of a progressive rise of the whole belt towards the side which 

 anciently lay near the shore of the Appalachian ocean, accords 

 entirely with the belief, that under the now rent and dislocated 

 margin of the chain, there was a vast accumulation of fluid rock, 

 charged with compressed gaseous matter, which exerted on the 

 crust an enormous disrupting tension. 



On THE Identity of the Undulations which produced the 

 Axes, with the wave-like Motion of the Earth in Earth- 

 quakes. 



That the undvilatory movements which we suppose to have 

 been the primary cause of our Appalachian axes, and generally 

 of all other parallel flexures, were strictly analogous to well-known 

 phenomena of the present day, is apparent, when we examine the 

 nature of that tremendous agitation of the crust, which we call 

 an earthquake. A wave-like undulation of the ground is of such 

 common occurrence during great earthquakes, that we are inclined 

 to consider it as their essential condition. On this subject, we 



