in Eastern North America. 407 



the one closing the Paleozoic. The appended graphs (see 

 Figs. 1-5) show that the Pennsylvanian in many places 

 was a time of marked crustal instability. In eastern 

 North America and in western Europe this instability is 

 apparent in the Mississippian or Lower Carboniferous, 

 but it is in the Pennsylvanian that the crustal unrest be- 

 comes marked. The graphs show that in a given province 

 there may be only two orogenies during this period ( Ap- 

 palachian while in others there are three (Llano) or four 

 (Acadia and Europe), if we count those at the very begin- 

 ning and close of the Pennsylvanian. On the other hand, 

 these deformations are not all synchronous, and it there- 

 fore appears that in eastern North America there are 

 six times of crustal movements. Such marked crustal 

 instability we see in no other period of the Paleozoic. 

 Before the middle of the Permian had passed, there 

 was another time of mountain-making, but in general the 

 closing period of the Paleozoic was a time of high lands, 

 cool and arid climates, and a crustal instability more like 

 the periods of pre-Carbonif erous times. During the Per- 

 mian, the marine organic world, although still dominantly 

 Paleozoic, was slowly changing toward the aspect of the 

 Mesozoic, but the life of the lands, facing far more stren- 

 uous environmental conditions, was rapidly taking on the 

 expression of the medieval world. 



If diastrophism were to be the sole or even the dominant 

 criterion for delimiting the eras, we would be obliged, in 

 Pennsylvania and West Virginia, to close the Paleozoic 

 with the fresh-water Dunkard formation of earliest Per- 

 mian time, because in these states there are no later Pale- 

 ozoic deposits. In eastern Canada, the Paleozoic would 

 be closed at about the same time or possibly a little later. 

 On the other hand, in Texas, New Mexico, and Arizona, the 

 dominant orogeny falls in the later Pennsylvanian, and 

 if we take this movement as our sole guide in Historical 

 Geology, then some of the latest Pennsylvanian and all of 

 the Permian goes into the Mesozoic era. The marine 

 faunas, however, are not of the medieval type, and are a 

 standing protest against such a reference. 



Let us examine into another critical period, the oro- 

 genies of the Laramide revolution, and here again the 

 evidence appears to lead to other conclusions than the 

 accepted ones of our text-books. The Laramide revolu- 

 tion as such began in Laramie time. Then there was a 



