54 THE ORIGIN OF MOUNTAINS. [V. 



the eastern and central parts of Xorth America is directly con- 

 nected with the greater accumulation of sediment along the 

 Appalachians. He has further shown that so far from local 

 elevaDion being concerned in the formation of these mountains, 

 the strata which form their base are to be found beneath their 

 foundations at a much lower horizon than in the undisturbed 

 hills of the Mississippi Valley, and that to this depression chiefly 

 is due the fact that the mountains of the Appalachian range do 

 not, like those hills, exhibit in their vertical height above the 

 sea the whole accumulated thickness of the palaeozoic strata 

 which lie buried beneath their summits 



The lines of mountain-elevation of De Beaumont are, accord- 

 ing to Hall, simply those of original accumulations, which took 

 place along current or shore lines, and have subsequently, 

 by continental elevations, produced mountain-chains. " They 

 were not then due to a later action upon the earth's crust, 

 but the course of the chain and the source of the materials 

 were predetermined by forces in operation long anterior to 

 the existence of the mountains or of the continent of which 

 they form a part." (p. 86.) 



It will be seen from what we have said of Buffon, De Mont- 

 losier, and Lesley, that many of the views of Mr. Hall are not 

 new, but old ; it was, however, reserved to him to complete the 

 theory and give to the world a rational system of orogrupliic 

 geology. He modestly says : " I believe I have controverted 

 no established fact or principle beyond that of denying the 

 influence of local elevating forces, and the intrusion of ancient 

 or plutonic formations beneath the lines of mountains, as ordi- 

 narily understood and advocated. In this I believe I am only 

 going back to the views which were long since entertained by 

 geologists relative to continental elevations." (p. 82.) 



The nature of the palaeozoic sediments of North America 

 clearly shows that they were accumulated during a slow pro- 

 gressive subsidence of the ocean's bed, lasting through the 

 palaeozoic period, and this subsidence, which would be greatest 

 along the line of greatest accumulation, was doubtless, as Mr. 

 Hall considers, connected with the transfer of sediment and 



