648 N'BW YORK STATE MUSEUM 



Niapira, nor of any later Sihirir ap' in rast Tcnncssoo, iinlessi 

 the Niajrara is roprcst'Uted in the extrenu' m^jcr part of the 

 Kockwood formation, tlie shah's and sandstones of this forma- 

 tion being: as ii ruk^ succeeded in this area hy the Devonic <'hat- 

 tauoo«?a shale. The existence of a hmd surface, extending west- 

 ward from the protaxis across east Tennessee to the western 

 slojje of the middle Tennessee dome, therefore is assumed as 

 siiuric land filling the interval between the clos<* of the Clinton or early 



in Tennessee 



«nd Kentucky Niagara to the middle Devonic. The Cincinnati dome also was 

 above sea level at the same time, and connected with the east 

 Tennessee land in such a manner that a broad bay was left 

 between the two domes. Neither of tht» latter was ever covered 

 entirelv bv Siiuric strata, these being laid down only on their 

 gently sloping shores and in embayments produced by slight 

 warping of their surfaces. The succession of the deposits in. 

 these embayments shows very clearly that the emergence at 

 the close of the Clinton was soon checked, and that gentle 

 subsidence [jrevailed in later Niagara time. 



Throughout Cayugan time, on the contrary, the Mississippian 

 sea was growing shallower, the floor of the sea having risen 

 almost gradually till, at the close of the Rondout, the whole 

 interior of the continent west of the Helderbergian barrier had 

 become land. This important emergence, for which we propose 



Cayugan tlic uauic ('(ii/uoan, coutiuued from Waterlime to Onondaga time^ 



emergence 



when the Mississii)i)ian sea again came in from the southwest, 

 spreading far and wide in the United States. In its eastward 

 progression this invasion (Onondaga) did not reach middh* and 

 east Tennessee till near the close of the Black shale, which is 

 commonly coi related with the Oenesee. The southern Black or 

 Chattanooga shale, however, may really rejjresent late Devonic 

 time only. sinc<' in complete sections the shale in question seema 

 to jKiss very gradually into und(Milited basal Mississi]»pian (Car- 

 bonic) shales. 

 Helderbergian While botli the Oswcgau subsid«*nce and the following Cayu- 



invaaion 



gan ('mergence wer<' atT<Mting the area to the west of the Ilelder- 



