OF THE APPALACHIAN CHAIN. 499 



Another well characterized belt of flexures fills the Lewistown 

 valley in Pennsylvania ; applying this name to the whole of the 

 long, natural valley, which extends from the Susquehanna to the 

 Juniata, southeast of Jack's mountain. In a breadth of about six 

 miles, there are here usually from five to six long, parallel, 

 and gently curving anticlinal axes, ail of them of the normal 

 form, resembling each other very nearly in the steepness of the 

 dips, or average degree of flexure. The lowest rocks, which they 

 lift to the surface, are the variegated shales, (F. V, Clinton group,) 

 and the highest, which their intermediate troughs have retained, 

 are the sandstone (F. VII,) and the overlying slates of F. VIII. 



A third very natural gi'oup of flexures is to be noticed in 

 the eastern part of the middle anthracite coal-field of Pennsylva- 

 nia. The axes in question separate that region into an assemblage 

 of small, parallel coal basins, of which the Beaver Meadow basin 

 is one. Lilve the previous gi'oups, these axes are characterized 

 by their remarkable parallelism, their similarity in length, their 

 exact equidistance, and then' gentle gradation, approaching to 

 equality, in the degree of the flexure. They aU of them bring to 

 the surface the conglomerate which next underlies the coal, and 

 the troughs, which they form, contain about the same moderate 

 depth of coal measures, growing shallower, however, to the north- 

 west. This collection of axes, unlike the two groups before de- 

 scribed, belongs to a straight system. 



If it were desirable, we might extend the enumeration of the 

 groups of axes to every part of the Appalachian chain ; but abun- 

 dant evidence has been furnished, to show that our anticlinal 

 axes are not irregularly distributed, but maintain relations with 

 each other, which requue that they should be classified and stud- 

 ied collectively. Their generic resemblances examined, they will 

 be found to exhibit general laws and analogies, that cannot fail to 

 lead to some highly curious results concerning the forces, which 

 from time to time have thus undulated the earth's crust. That 

 this curious and most instructive department of geological dy- 

 namics has escaped, until lately, the attention of the best investi- 

 gators, we can only attribute to the fact, that in Europe, no belt 

 of axes, equal in extent to the Appalachian system, has come 



