430 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



out completely in the vicinity of N'ashville. In the opposite direction, in 

 the depression between the Nashville and Cincinnati domes, doubtless an 

 even greater development of limestone of this age is concealed by later 

 deposits ; and by "greater development" I mean not only greater thickness, 

 but also more continuous deposition of Cannon limestone and an earlier 

 beginning of its post-Bigby part. (See figure 11, page 417.) 



Dome tilting illustrated in the peninsula of Florida. — In a searcli 

 of geological maps for recent instances of dome structure suggest- 

 ing differential oscillation like that of the interior uplifts described on 

 preceding pages, at least one reasonably satisfactory case was found in 

 the peninsula of Florida. As will be seen from the accompanying map, a 

 semi-dome of outcropping Oligocene formations, the lower of which 

 (Vicksburg) has a diameter exceeding 100 miles, occurs in the north- 

 western quarter of this peninsula. It will be observed further that, 

 while the semicircular outline of the eastern half of the dome shows on 

 the land, the whole of the western half is submerged beneath the waters of 

 the Gulf. In other words, the western half of the dome has been tilted 

 downward beneath sealevel and is now receiving a load of sediment, while 

 the eastern half has been elevated above sealevel and is being eroded by 

 subaerial agencies. 



Should this dome be completely emerged, the deposits now being laid 

 down would be found to overlap from the west and cover only its western 

 side. Further, as these recent deposits rest on the Vicksburg, the contact 

 would be unconformable and contain a stratigraphic hiatus occupied in 

 part by the Appalachicola, Choctawhatchee, and Jacksonville formations 

 on the east side. In short, the' distribution of the successive stratigraphic 

 units would be found to alternate in directions of overlap essentially as 

 has been shown of the Paleozoic formations on the flanks of the Cincinnati 

 and Nashville domes. 



Possibly the whole of the peninsula is comparable to the Cincinnati 

 geanticline, namely, the formations as mapped on the southern ex- 

 tremity of Florida suggest another low periodically tilted dome that might 

 be likened to the Nashville dome. If so, the northern or Ocala dome, as 

 it might be called, would be comparable with the Cincinnati dome. 



Causes of differential oscillations of continental seas and interior land 

 areas. — Two distinguishable though closely allied causes seem chiefly 

 concerned in bringing about the local oscillations briefly described in 

 the foregoing sections. The first and, more particularly in the Appa- 

 lachian Valley, perhaps more important of these causes I conceive to be 

 the pulse-like inland transmission of oceanic thrusting of largely ex- 



