542 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



great lens of Athens sandstone described by Hayes^^ as occurring in the 

 body of the Athens shale in Polk County, Tennessee, is due to some local 

 cause. No similar change in deposition, from black shale and limestone 

 to sandstone, is known to have occurred at this time in any other part of 

 the Appalachian A^alley. It may ])ossibly be contemporaneous with 

 movements and consequent displacements of the strandline in more in- 

 terior regions, but we have no means of proving such connection. 



Thin sandstones in the late Chazy to middle Black River sections in 

 the Ottawa Eiver Valley may also have only local significance, but it is 

 thought likely that they bear genetic relationship to movements in the 

 middle and northern Appalachian Valley that opened the way for trans- 

 gressions of the Lowville sea. 



The transition from the Everton limestone to the Saint Peter sand- 

 stone in northern Arkansas, as descril)ed on page 479, is perhaps the best 

 example of the rare phenomenon of sandstone deposition following lime- 

 stone without interruption of the process of sedimentation. In the great 

 majority of cases in which a clastic deposit succeeds a pure limestone 

 cessation of deposition intervened. 



(13) Differential effect on strandline in continental tilting. — Elevation 

 and consequent sea withdrawal, whether due to orogenic or epeirogenic' 

 movements, may occur on one side of a continent while the opposite side 

 is subsiding. Hence in such cases emergences and stratigraphic hiatuses 

 on the former side are to be correlated with submergences and resulting 

 deposits on the latter. This condition may have obtained occasionally if 

 not commonly with respect to the east and west sides of a continent, but 

 the reasons why it might are not so convincing and the stratigraphic 

 facts on which the demonstration of the proposition must chiefly rely are 

 not so clearly expressed as in the case of the north and south sides. The 

 theory is explained on page 406 and its operation illustrated by figure S. 

 The stratigraphic evidence on which it is founded is brought out in 

 discussing the distribution of Ordovician and Silurian formations and 

 faunas which invaded alternately from the north and south (see pages 

 367 to 371 and 558 to 561). This extremely important principle applies 

 mainly to correlations implying broad continental tilting. The next 

 following is concerned more particularly with relatively local oscillations. 



(14) Correlation implying local tilting and warping. — Differences iri 

 the stratigraphic sequence on opposite sides of structural domes or in 

 neighboring troughs, also local peculiarities in sequence, generally denote 

 differential oscillation and warping of the earth crust and consequent 



71 C. W. Hayes : Geol. Atlas U. S., Cleveland folio, 1895. 



