GENERAL OBSERVATIONS. 



397 



The mountains of Pennsylvania as well as Virginia are full of such 

 sections. In fact, they present the common features of the Appa- 

 lachians, from Alabama to New Jersey. It is here obvious that not 

 only the Coal-measures but the whole Paleozoic has been forced by 

 some agency out of its originally horizontal condition into this con- 

 torted state. The folds were mountains themselves in extent ; but, 

 through the extensive denudation to which they have since been sub- 

 jected, they have been worn off and variously modified in external 

 shape, until now, as explained on page 96, it is often extremely dif- 

 ficult to trace out the original connections. 



The folds are most abrupt to the eastward ; to the west, they 

 diminish in boldness, and become gentle undulations; yet there is often 

 a sudden transition to these gentler bendings, along lines of great 



Fig. 703. 



Map of Pennsylvania, showing the positions of the axes of the folds in the strata. 



faults. It would be an error to suppose that the number of folds is 

 uniform, through the length of the Appalachians. On the contrary, 

 all along their course, there are folds rising and others disappearing ; 

 they may continue on for a few miles or scores of miles, and some for 



