INTRODUCTION. «9 



presented the features it now does, of valleys extending to the Lower 

 Palaeozoic beds, with cliflFs of the height represented by the actual 

 thickness of the beds which there constitute the entire series. 



The gradual declination of the country westward is due primarily 

 to the thinning out of all the formations which have accumulated with 

 such great force in the Appalachian region. It is also susceptible of 

 proof, that no beds of older date have contributed to elevate the later 

 ones, or to form a part of the mountain chain. 



We have in the east one example where the conditions of elevation 

 correspond with those in the Mississippi valley. The Catskill mountains 

 are composed almost entirely of strata in a horizontal or very slightly 

 inclined position ; the Hudson-river group, which constitutes a few feet 

 of their elevation at the base, is disturbed, and the succeeding beds lie 

 upon this unconformably. These mountains, therefore, rising to a height 

 of 3800 feet above tidewater, mark in their altitude simply the ver- 

 tical thickness of the strata. 



At this point of our inquiry, several questions of importance present 

 themselves : First, what has been the cause of this folding and plica- 

 tion of the strata ; secondly, having been thus folded and plicated, what 

 influence has this action exerted upon the elevation of the parts, or of 

 the whole ; and thirdly, what effects are due to the metamorphism 

 which accompanies this mountain chain ? 



It has been long since shown that the removal of large quantities of 

 sediment from one part of the earth's crust, and its transportation and 

 deposition in another, may not only produce oscillations, but that che- 

 mical and dynamical action are the necessary consequences of large 

 accumulations of sedimentary matter over certain areas. When these 

 are spread along a belt of sea bottom, as originally in the line of the 

 Appalachian chain, the first effect of this great augmentation of matter 

 would be to produce a yielding of the earth's crust beneath, and a gradual 

 subsidence will be the consequence. We have evidence of this subsi- 

 dence in the great amount of material accumulated ; for we cannot 

 suppose that the sea has been originally as deep as the thickness of 



