STRAND-LINE DISPLACEMENTS 497 



younger measures passed in transgression over the abraded surfaces of the 

 folds into which the earlier measures had been thrown" (Suess, IT: 248, 

 249). 



Appalachian revolution (see maps, plates 84, 85). — Beginning in the 

 early Devonic, North America underwent one great transgression of long 

 duration which culminated late in the Hamilton, and was followed by 

 what may be called an uncertain emergence of long continuance. This 

 emergence was marked by two minor and one major transgressions — the 

 Fern Glen, Saint Louis, and Pottsville. During this vast period of time 

 enormous quantities of material had been transferred from the lands into 

 the subsiding continental seas, filling them beyond the limit of their 

 capacity. The neighboring lands were again mainly featureless, and a 

 long period ensued in which the eastern half of the United States was a 

 vast region of aggrading marshes producing luxuriant floras not much 

 unlike those of Europe. The loading areas spasmodically and irregularly 

 subsided, for short intervals letting in the marine waters, but these always 

 yielded the same fauna of enduring hardy species. The seas were slowly 

 but haltingly withdrawn. This is the history of nearly all late Paleozoic 

 continental seas. Tt is therefore concluded that not only were the oceanic 

 basins subsiding, but at irregular intervals the continental loading areas 

 as well, and thus was developed an oscillatory negative strand-line. 



The concluding Paleozoic withdrawal of the seas began early in the 

 Pottsville in the southern Appalachian sea, later in the northern area of 

 this same trough, and finally throughout the northeastern portion of the 

 Mississippian sea. This was about the time of the latest Pennsylvanic, but 

 to the north, west, and southwest of Missouria the sea remained for a short 

 interval ; then during the early Permic the waters gradually passed away 

 southward, leaving red clays and vast quantities of gypsum in their wake. 

 The Sonoran and Californian seas retreated less slowly, and in the later 

 Permic the only continental sea remaining was the restricted Sonoran sea 

 of Guadalupian time. Even it finally vanished, and the American Paleo- 

 zoic sedimentary record is at an end. According to the maps, the per- 

 centages of marine inundations are as follows : 



North America. United States. 



Upper Pottsville 27 per cent 36 per cent 



Upper Pennsylvanic 18 " " 31 " " 



Lower Permic 3 " " 25 " " 



Late Permic 1 " " 1 " 



This gives the history of slowly but constantly subsiding oceanic areas, 

 with the withdrawal of the continental waters. Through this subsidence 

 the border region of eastern North America was once more thrown into a 



