182 



TRANSACTIONS OF THE 



remarkable deflection in that river, obvious to all who 

 cast a glance at the map of its course, in the same man- 

 ner as the first anticlinal line occasions a corresponding 

 deflection of ten miles, higher up the same river, between 

 Alexandria and Williamsburg. 



We have also a solution of the originating cause of a 

 remarkable group of contorted rocks which line the banks 

 of the Juniata along a space of thirty miles in Mifflin 

 county. From among many sketches of flexuous strata 

 occupying the sides of this river, I have selected one 

 which has been exposed by the excavations for the 

 Pennsylvania canal. PI. 7, fig. 4. In a previous com- 

 munication, p. 11, I have adverted to these twisted 

 rocks as forming a characteristic feature in the geology 

 of the Juniata valley, for which I w^as then unprepared 

 to account. I there observed that here was displayed 



a continued series of contorted stratified masses, rolling 

 and heaving like the waves of a stormy ocean." 



A reference to the sketch of part of this trough of the 

 Juniata, pi. 4, fig. 6, and of its transverse section, fig. 

 7, exhibiting the converging of the oppositely inclined 

 masses, will save unnecessary repetition here. 



Having subsequently examined a wider range of this 

 central area, and traced its geological features in connec- 

 tion with this portion, the circumstance which produced 

 this crushing and twisting of the rocks, in the line of 

 junction of two vast disrupted planes, now becomes suf- 

 ficiently intelligible. All that on the present occasion I 

 mean to convey, as the result of much local examination, 

 however inadequate to the perfect elucidation of the 

 whole, is — 



That within a breadth of seventy miles, forming the 

 western zone of the transition rock series, and indepen- 

 dent of innumerable minor disturbances of their separate 

 parts, there are two great anticlinal lines, (that is longi- 

 tudinal lines, from which descend the strata on either 



