OF THE APPALACHIAN CHAIN. 497 



which, for a short distance, serve to mark the irregular progress 

 of the fault. At length, the dislocation attains what may be called 

 its maximum intensity ; the slate, and not unfrequently, the lime- 

 stone of the valley, resting in an inverted attitude, with a gentle 

 southeast dip, directly vipon the southeasterly dipping gi-its and 

 shales of the formation next beneath the carboniferous limestone, 

 here constituting the southeastern slope of the Brushy mountain. 

 The seam of semi-bituminous coal, generally embraced between 

 these strata, is, in virtue of the dislocation, made to assume the 

 anomalous condition of passing under the valley limestone at a 

 distance of only a few hundred feet, dipping in the same direction 

 with that rock. ^ 



Preserving these features, with but little variation, throughout 

 its whole course to the southwest, this extraordinary fault extends, 

 in an almost perfectly straight line, along the southeastern slope 

 of the Brushy mountain, from near the head of the Catawba 

 creek, to the vicinity of Smyth court-house, a distance of more 

 than eighty miles. At no point, in this line, are the rocks which 

 originally formed the counterpart to the strata of the Brushy 

 mountain, and which are, in fact, represented by those of the 

 Little North mountain, in the northern part of the line, even par- 

 tially restored to the surface ; so that this stupendous dislocation is 

 to be viewed as having actually swallowed up the rocks of the 

 southeastern half of a large synclinal basin, of which the Brushy 

 mountain remains as the other half. 



4th. Of the distribution of the axes in groups. Wherever, in the 

 Appalachian chain, we become minutely familiar with the undu- 

 lations of the strata, we find it impossible to resist the conclusion, 

 that the axes arrange themselves in natural groups, the individual 

 flexures showing a close agreement in their length, mutual dis- 

 tance, straightness, or curvature, and in the extent and style of the 

 arching. In those districts which are crowded with normal axes, 

 such as the Susquehanna and Juniata divisions, many such groups 

 attract our notice. Each of these assemblages of axes being gen- 

 erally distinguished by some special character, we are inclined to 

 regai'd the comparison and analysis of their several features as of 

 the very highest importance, in those investigations of geological 



