408 G. Schuchert — Paleozoic Crustal Instability 



long pause, during which the Lance, Ft. Union, and equiv- 

 alent fresh-water deposits were laid down, with their in- 

 cluded Mesozoic mammals and dinosaurs. Following this 

 time of deposition, came the post-Laramide orogeny of 

 Epi-Mesozoic time, one that apparently was even more 

 marked than that of the Laramide movement. On these 

 mountains glaciers appeared, and in the valleys was de- 

 posited the Wasatch series with its modernized mammals, 

 clearly of Cenozoic time. The question now arises, which 

 one of these two periods of orogeny shall delimit the 

 Mesozoic? The writer seems to be gradually working 

 toward the second one, in which case all of the Lance, Ft. 

 Union, and their equivalents will go into the Mesozoic. 

 If this is done, it will seemingly solve many of our field 

 and f aunal perplexities, but our botanical friends and pos- 

 sibly other stratigraphers will continue to have different 

 views. 



In this connection, we should also draw attention to 

 the Nevadian deformation closing the Jurassic, when 

 mountains were made all along the Pacific states, appar- 

 ently from Lower California into Alaska. Some years 

 ago Lawson pointed out this marked time of orogeny and 

 said that it had the import of those at the close of eras. 

 Certainly it is by far a more marked deformation than 

 any of those which are usually ranked as disturbances, 

 though one can not yet grant that it has the same import- 

 ance as the Appalachian and Laramide revolutions. If 

 we follow Lawson in his interpretation of the significance 

 of this crustal movement, the Triassic and Jurassic will be 

 of one era, and the Comanchian and Cretaceous of an- 

 other. In this event we would be adopting a classification 

 useful for America, but not applicable everywhere. That 

 we can not follow Lawson in this is plain, because no Euro- 

 pean would think for a moment of relegating the Jurassic 

 to an era that would not also embrace the Cretaceous. 

 However, what we want more especially to point out here 

 is that while most of the orogenies can be classified into 

 disturbances and revolutions, yet the Nevadian deforma- 

 tion has not the significance of a revolution, because the 

 majority of continents are not in movement in late Juras- 

 sic time, as they are during the Appalachian and Lara- 

 mide revolutions. 



Another case similar to the Nevadian orogeny is the 



