490 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



its climax about Louisville time. The waters abounded in life, especially 

 corals. This transgression was described by Ulrich and Schuchert as the 

 Oswegan invasion (1902, 647), for which the preferable name Niagaran 

 transgression is here substituted. The amount of inundation is shown by 

 the following figures : 



North America. United States. 



Medina-Edgewood 5 per cent 9 per cent 



Early or Ohio-Clinton 5 " " 11 " 



Middle Clinton 14 " " 14 " " 



Rochester-Osgood 34 " " 29 " 



Louisville 35 " " 35 " 



The deposits of the Appalachian sea are mainly clastic, being derived 

 from rejuvenated Appalachia. West of the Cincinnati axis, however, 

 most of the material is organic in nature, being chiefly limestone in the 

 Oklahoma and Indiana basins, while in the Ohio and Iowa basins, under 

 the dominant influence of the very shallow Hudson sea, the deposits are 

 dolomites. 



An examination of the maps showing the variations in this transgres- 

 sion in eastern America will draw attention to the fact that the invasion 

 was at first controlled by slight movements of Appalachia, for the seas lay 

 on its inner side in the renewed syncline and on each side of the Cincin- 

 nati axis, which also has the strike of the eastern land. In other words, 

 the inward movement of Appalachia accentuated not only the synclines 

 occupied by the continental seas, but likewise affected the parmas Alle- 

 ghania, Cincinnatia, and Kankakeia. Finally, between the thrusts of the 

 Atlantic and the Pacific was produced the low land Siouxia, the barrier 

 preventing the intermigration of the faunas of these two realms. The 

 original nucleus of the Xorth American continent, however, was not influ- 

 enced by the oceanic subsidences, but remained as an unmoved continental 

 horst. Only the Arctic waters again became widespread on its western 

 side. However, the writer has no intention of conveying the idea that 

 these parmas and the land Siouxia were directly and wholly bowed up 

 by the tangential thrusts of the Atlantic and Pacific. It is probable that 

 the tangential forces were the primary cause of this action, but that dur- 

 ing these movements isostatic compensation was the direct force in bring- 

 ing about these flexures through vertical movements immediately below 

 the arches. 



That in Acadia the greater part of the submergence was marked by 

 extensive volcanic activity is proved by the statement made by members 

 of the Federal Survey to the writer, showing that in southeastern Maine 

 not less than 46,000 feet of material were deposited during this interval, 

 by far the smaller amount of which was of clastic marine origin. 



