INTRODUCTION. • 73 



plateau of the west, we have a much greater proportion above the level 

 of the sea. 



So far, therefore, as our observation extends, we are able to deduce 

 some general principles in regard to the production of this mountain 

 range. To explain its existence, we are to look to the original accumu- 

 lation of matter along a certain line or zone, the direction of which 

 will be the direction of the elevation. The line of the existing moun- 

 tain chain will be the course of the original transporting current. 

 The minor axes or foldings must be essentially parallel to the great 

 synclinal axis and the line of accumulation. The present mountain 

 barriers are but the visible evidences of the deposits upon an ancient 

 ocean bed ; while the determining causes of their elevation existed long 

 anterior to the production of the mountains themselves. At no point, nor 

 along any line between the Appalachian and Rocky mountains, could the 

 same forces have produced a mountain chain, because the materials of 

 accumulation were insufficient ; and though we may trace what appears 

 to be the gradually subsiding influence of these forces, it is simply in 

 these instances due to the paucity of the material upon which to 

 exhibit its effects. The parallel lines of elevation, on the west of the 

 Appalachians, are evidenced in gentle undulations, with the exception 

 of the Cincinnati axis, which is more important, extending from Lake 

 Ontario to Alabama, and is the last or most western of those parallel 

 to the Appalachian chain. 



In this connection, we come now to the consideration of the important 

 phenomenon of the metamorphism of strata composing a large part of 

 the Appalachian range. Approaching from the west, and crossing the 

 successive low parallel undulations of the strata, we find their incli- 

 nation becoming more and more extreme. Coincident with this there 

 is a gradual and almost imperceptible change in the condition of the 

 strata. The shale appears as if partially crushed or pressed, and shows 

 striae and smooth shining surfaces which are not parallel to the line of 

 bedding : it breaks or separates into small, irregular fragments, with 



[ PALiKONTOLOOY III.] 10 



