GGO • NEW YORK STATE MUSEUM 



likely to be opposed, we do not doubt that it will prevail in the 

 end because it will have a natural basis. 



Depth of Mississippian sea. With the possible exception of the 

 Beekmautown, we fail to see anything even approaching deep 

 sea conditions in any of the sediments of the Mississippian sea. 

 On the contrary, there is abundant evidence that during 

 Paleozoic time the " shift of relative level " of the sea and 

 land was never great outside of the area of the barriers de- 

 scribed. Sometimes the sea was so shallow as to form tidal 

 flats, in other cases the land was so near sea level that erosion 

 was practically nil, but in other cases again, the land was high 

 enough to be subject to erosive agencies, the effects of which 

 are now more or less obviously preserved in unconformities of 

 stratification. These unconformities however, are in but few 

 cases so clear that the stratigraphic discordance may be recog- 

 nized in any given exposure, but their recognition depends in 

 most cases on the absence in a section of a zone or formation 

 observed in other sections. Sometimes, as on the west flank of 

 Cincinnati axis in middle Tennessee, where Upper Devonic or 

 even Lower Carbonic may rest on Middle Trenton, the evidence 

 of unconformity is so slight that without fossils it would 

 scarcely be detected. 



Principal submergences and emergences. The first pronounced 

 Paleozoic submergence in North America resulted in what we 

 have called the St Croix invasion. It embraced nearly all of that 

 part of the Algonkian continent lying between the Rocky moun- 

 tain protaxis and the Appalachian protaxis south of the Cana- 

 dian shield. This subsidence gave birth to the Mississippian 

 sea, and the movement accentuated a Precambric fold under 

 the Lower Cambric sea extending from Alabama to Gaspd. The 

 northern part of this fold we call the Green mountain barrier, 

 while its southern half is termed the Chilhowee barrier. 



The submergence inaugurated by the St Croix invasion cul- 

 minated in Beekmantown or " Calciferous " time, when more 

 of the continent was under water and the sea probably deeper 

 than at any subsequent period. 



