INTRODUCTION. 
69 
presented the features it now does, of valleys extending to the Lower 
Pakeozoic beds, with cliffs 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 efleets 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 
