42 GEOLOGICAL BIOLOGY. 



Ontario, Canada, into Tennessee, marks a contemporaneous 

 disturbance. Evidence of the same revolution is seen in un- 

 conformability between Ordovician and Silurian rocks in Nova 

 Scotia and New Brunswick, The revolution is not sharply 

 distinguishable in the rocks of the more southern or western 

 regions. 



Acadian Revolution. — The second of these lesser revolutions 

 is expressed most sharply in elevation and unconformity ter- 

 minating 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 period upon their eroded surfaces. 



Appalachian Revolution. — The Appalachian revolution 

 closed the Paleozoic time and left the great part of the east- 

 ern half of the continent above sea-level. It forms the 

 natural interval between the Carboniferous and the overlying 

 system, whatever that may be. Its characteristics have 

 already been described (p. 40). 



Palisade Revolution. — A revolution which affected the 

 rocks along the eastern border of the continent during or 

 closing the period in which the Triassic sandstones were 

 being deposited may be called the Palisade revolution. 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 faulting of the underlying red sandstone 

 and shale, and the resulting unconformity with the succeeding 

 formations. The evidences of the revolution are not widely 

 extended, nor is the time-relation of the termination of the 



