REPORT OP THE STATE PALEONTOLOGIST 1901 647 



of relaxed lateral pressure; and then occurred adjustments, 

 largely by gravitation.'^ Certainly this is true in this instance, 

 for after the subsidence had commenced it continued nearly 

 through all Siluric times. 

 The Oswegan subsidence or invasion, as it may be called, be- oswegan 



^ ' "^ ' invasion 



gan with the Oneida and continued with little interruption to 

 the close of the Salina age. In New York these deposits thin 

 out eastward, and one after the other formation overlaps the 

 older, so that in the region south of the Mohawk river the Euryp- 

 terus bearing Waterlime, which is the uppermost division of the 

 Salina, appears not to have reached the eastern side of the 

 Helderberg mountains. The Clinton, Niagara and Salina also 

 pinch out one after another west of the Helderberg mountains. 

 To the south, the equivalent deposits transgress even less toward 

 the Appalachian protaxis, the eastern line in middle Pennsyl- 

 vania swinging westward to the vicinity of Altoona. From 

 this point southwestward the line, judging from the data 

 available, seems to have run about parallel with the general 

 trend of the Appalachian folds into West Virginia, and it prob- 

 ably swung eastward again toward the Appalachian valley fold 

 before passing through that state. This westwardly bent 

 line has great significance, because it corresponds with the course 

 of a barrier defining the western limit of another basin, the 

 Cumberland basin, that was occupied by an Appalachian Cumberland 



basin and 



Mediterranean, with a fauna very different from that of Heiderbergian 



•^ basin 



the contemporaneous Mississippian sea. We mention this 

 a little out of the regular order of our description, so that the 

 reader may understand why the Siluric deposits east of the 

 Helderbergian barrier just located are not regarded as con- 

 tinuations of the sediments of the Mississippian sea. 



In the southeastern portion of the Mississippian sea the Oswe- 

 gan invasion was limited by the Rome barrier, and besran with ^°^f barrier 



•^ ' » m Siluric 



a shale instead of conglomerate and sandstone. This character 

 of deposits continued with occasional interruptions of thin, fer- 

 ruginous, fossil limestones, and locally heavier beds of sand- 

 stone, to the close of the Clinton. There are no deposits of 



