504 OF THE PHYSICAL STRUCTURE 



which they terminate at their opposite extremities, and they are 

 demonsti'ably of the same age with the rectilinear flexures, with 

 which they there alternate. But the different sections of the chain, 

 thus referred to one general succession of elevatory movements, 

 differ from each other in their strike as much, in some instances, 

 as forty or forty-five degrees; and, if we include systems 

 of axes not contiguous, but the sameness of whose date is 

 equally demonstrable, — as when we compare the Vermont and 

 the Holston axes, — the difference in direction is even as much 

 as sixty degrees. Here are extensive mountain belts, each up- 

 wards of two hundred miles in length, possessing unequivocally 

 the same epoch, differing in the direction of the elevatory move- 

 ment much more than some of the European systems of widely 

 different geological age. It is obvious, then, that the general- 

 ization of M. de Beaumont, if in accordance at all with nature, 

 is only so as it relates to the general dii-ection of entire moun- 

 tain systems, and not to the course of special groups of axes, how- 

 ever extended. 



Description of a Series of Sections across the Chain. 



Section A, (PL XVIII.) This Section extends from the South 

 mountain, in Berks county, Pennsylvania, through the anthracite 

 basins, to the Allegheny mountain, in Luzerne county, and ex- 

 emplifies the usual features of structure prevailing in the Sus- 

 quehanna division of the chain, showing the folded and inverted 

 condition of all the rocks in the South mountain and great 

 valley, also the steepness of the northwestern sides of the flex- 

 ures in the rest of the belt, and the beautiful grouping of the axes, 

 especially in the middle anthracite region, combined with a gen- 

 eral progressive reduction in tlie abruptness of all the curves and 

 dips. It likewise shows, that the hypogene strata of the South 

 mountain are included in the same general system of flexures with 

 the Appalachian strata. 



Section B, (PI. XIX.) This extends in a west-northwest di- 

 rection, from the South mountain, in Cumberland county, Penn- 

 sylvania, through the Broad Top coal-field, to Chestnut ridge, iq 



