286 THE JOURNAL OF GEOLOGY. 



Several lesser, more or less local, revolutions have left their 

 permanent mark in the grander structure of the rocks or in con- 

 spicuous geographical features of the restricted region of the 

 continental area. The first of these was the Green mountain rev- 

 olution which separated the (Lower Silurian) Ordovician from 

 the (Upper Silurian) Silurian, for the eastern part of North 

 America. The elevation, disturbance and metamorphism of the 

 rocks of the Green Mountains stand forth as monuments of this 

 event. The revolution is not sharply distinguishable in the 

 rocks of the more southern or western regions. The second of 

 these lesser revolutions is expressed most sharply in eleva- 

 tion and unconformity terminating the Devonian formations of 

 Maine, New Brunswick and Nova Scotia, and may therefore be 

 called the Acadian revolution. In the continental interior 

 it may be indicated by the remarkable thinning out of the 

 Devonian rocks toward the southwestward. In Tennessee, 

 Alabama and Arkansas they are represented by a thin sheet of 

 black shale, a few feet thick, or by but little more than a 

 line of separation between the rocks of the Silurian below and the 

 Carboniferous beds resting scarcely unconformably upon them. 

 This seems to indicate an elevation of the region still further 

 south toward the close of the Devonian, sufficient to produce 

 extensive erosion, uncovering the Lower Silurian rocks which 

 were again depressed to receive the marine deposits of the early 

 Carboniferous upon their eroded surfaces. 



The Appalachian revolution closed the Palaeozoic time and 

 left the great part of the eastern half of the continent above sea- 

 level. It forms the natural interval between the Carboniferous 

 and the overlying system, whatever that may be. Its character- 

 teristics have already been described. 



The Palisade revolution, along the eastern border of the con- 

 tment, marks the division between the Jura-Triassic part of the 

 Mesozoic time and its closing Cretaceous age. It is expressed 

 by the trap ridges in the Connecticut valley, the Palisades and 

 other similar tracts distributed inside the coast from Nova Scotia 

 to North Carolina, and by the uptilting and in some cases fault- 



