524 OF THE PHYSICAL STRUCTURE 



manent flexures or other disturbances of the crust occurred, to 

 interrupt this continuous and amazingly prolonged succession 

 of parallel deposits. 



In thus confining the era of the principal movement which 

 elevated the Appalachian chain to a comparatively short period, 

 at the very close of the carboniferous formation, we are far from 

 implying that a few local elevations, and many minor oscillations 

 of the surface, unattended by permanent flexures, did not occur 

 previously to this final,'and, beyond all comparison, most energetic 

 effort of the subteiTanean forces. The unconformable superposi- 

 tion locally, of the Helderberg sti-ata,upon the Hudson river slates, 

 in the vicinity of the town of Hudson, is a sufficient evidence 

 that even at an early period in the history of the Appalachian 

 formations, this part of the region was disturbed by a considerable 

 movement of the strata ah-eady deposited ; and there are indica- 

 tions that similar agitations of the Appalachian territory, but to a 

 much feebler extent, were experienced at the same and at other 

 periods, during the progress of these formations. But, with the 

 single local exception spoken of, none of these disturbances 

 appear to have inten-upted, however partially, the perfect general 

 conformity of the strata throughout the whole Appalachian sys- 

 tem. The occurrence oi feeble movements, from time to time, in 

 the earlier ages of the long Appalachian period, is clearly proved 

 by the presence of fragments of older strata, enclosed in the next 

 succeeding beds, and also by the coarseness of the materials of 

 which some of the formations largely consist. The phenomena 

 of the coal-measm"es, at the same time, go to show, as one of us 

 has attempted to argue in another paper, that these movements 

 continued to increase in frequency and power, as the Appala- 

 chian period drew near its termination ; the entire coal-formation 

 being the result of alternate quiet accumulations, and sudden 

 paroxysmal movements, terminating in that stupendous train of 

 actions, which lifted the whole Appalachian chain from the bed 

 of the ancient sea. 



The obvious agreement in point of date, between this, which 

 was incomparably the most energetic and extensive change in the 

 physical structure of North America, and the wide-spread revolu- 



