247 



features of this region as evidence of a deposition of the strata 

 during- a long-continued upward movement of the ancient sea- 

 floor. 



Anotlier consideration opposed to this view is the great aggre- 

 gate t/iicl'ness of the marine deposits exhibited in the middle and 

 southern portion of the Appalachian area, and the known fact 

 that even the older and lower of these formations, where brought 

 to view by anticlinal structures, present a composition and surface- 

 markings bespeaking a comparatively shallow ocean at the time 

 of their accumulation. As, therefore, the ancient sea of this re- 

 gion could have had no great depth at the commencement of 

 these deposits, it seems clear that, in order to receive the whole 

 series of more than twenty thousand feet of successive strata, its 

 original floor, instead of rising during this period, must have 

 undergone aji enormous amount of depression. 



Looking to the series of carboniferous rocks forming the upper 

 portion of this vast succession of deposits in our Appalachian 

 basin, the evidences of such a subsiding movement are too obvi- 

 ous to be questioned. Each of the nearly horizontal beds of 

 vegetable matter forming an incipient coal-seam must have been 

 deposited at or a little above the ancient sea-level, and must then 

 have been depressed and covered in by sediments forming the 

 sandstones and shales, often with marine fossils, which now over- 

 lie it. Thus, stage by stage, with long pauses, in which the 

 materials of successively newer coal-seams were accumulating by 

 vegetable growth, the sea-bed was depressed until it had received 

 the entire thickness of the carboniferous rocks, with their in- 

 cluded strata of coal. 



On either hypothesis, that of a subsiding or of a rising ocean- 

 bottom, the features of the land, as first presented on the comple- 

 tion of its formation, w^ould be far from corresponding with its 

 present topography. This existing configuration has undoubtedly 

 been the work of subsequent denudation, of which extensive and 

 unmistakable evidences are apparent throughout the paleozoic 

 area. The theory of an uplifting movement during the depo- 

 sition does not, as has been supposed, dispense with the neces- 

 sity of such a further agency for remodelling the surface. On 

 the contrary, in this case, the depth of denudation required to 

 carve out the profile of the region in question, so as to make it 



