THE OROGENIC EPOCHS IN NORTH AMERICA 643 



laid down. It is now generally agreed that the climax of that dis- 

 turbance came near the close of the Permian period. If these 

 correlations are correct, we must then recognize two separate 

 orogenic epochs. There is apparently ground for correlating the 

 Arkansan crumpling with that which produced the Armorican and 

 Variscian systems of western Europe, which Haug' assigns to the 

 opening of the Stephanian (upper Pennsylvanian) epoch. 



Appalachian orogeny {late Permian). — This epoch of folding 

 was the first to be well recognized in America and is without doubt 

 the one now best known to students of American geology. Its 

 effects have been traced from Alabama to New York and from 

 southern New England to Newfoundland. The southeast limit of 

 the area affected is everywhere concealed either by the ocean or by 

 much younger undeformed deposits. To the northwest the limit is 

 rather sharply defined where the folds give way to the horizontal 

 strata of the Cumberland and Alleghany plateaus. There are, it is 

 true, some broad gentle swells in these apparently horizontal beds, 

 and those flexures were probably produced at the same time as the 

 Appalachian folds. In western New England and adjacent parts 

 of New York and Canada, the limits are less easily ascertained 

 because little now remains but pre-Devonian or even pre-Silurian 

 strata, and those had been already folded either in the Brunswick- 

 ian or the Taconic epoch or both. Available evidence, although 

 meager, indicates that the crumpling and overthrusting at the close 

 of the Permian were even more intense in the Piedmont and New 

 England regions than in the Appalachian Mountains themselves. 



Reasons have been given above for beheving that the Ouachita 

 region was not deformed at this time. If this conclusion is correct 

 it may be said that the western three-quarters of North America 

 was not affected by the Appalachian orogeny except that there 

 were, over large areas, mild epeirogenic movements which made 

 notable changes in the relations of land-masses and seas. 



Nevadian {late Jurassic). — -The folding of the rocks in the 

 Sierra Nevada at the close of the Jurassic was established by 

 Whitney and his associates about half a century ago, but it seems 

 to be less widely understood that the entire west coast of North, 



• Emile Haug, Traiie de Geologic, II, Part I (1910), p. 829. 



