666 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



siderable part transmitted by folding to adjacent portions of the Alle- 

 gheny region. 



Application of the principle. — Applying the principle of rliythmic 

 shifting of the area of maxiimim deposition to systems in the Appa- 

 lachian Valley^ it appears that the area in which deposition continued 

 longest was in the Tennessee basin during the Cambrian, in the 

 central Alabama basin during the Ozarkian, in central and northern 

 Pennsylvania during the Canadian, in east Tennessee again during the 

 Ordovician, in the Maryland basin during the Silurian, in the northern 

 Pennsylvania basin during the Devonian, in the central Virginia basin 

 during the Waver lyan, and in the central Virginia and Alabama basins 

 during the Tennessean and Pennsylvanian systems. 



Applied to parts of systems in which considerable oscillation occurred, 

 we find that during the Ozarkian period deposition in the Appalachian 

 basins was at first confined to central Alabama troughs. Next the area 

 of deposition was shifted to the Maryland and northeastern Pennsylva- 

 nia basins, where the Conococheague and the Allentown formations were 

 laid down. This was followed by the typical Knox, which, though 

 strongly represented in Alabama, attained its maximum development in 

 Tennessee. Northwardly the Copper Eidge divisions of the Knox ex- 

 tends to Eoaring Spring, Pennsylvania, where it pinches out, presumably 

 by overlap. Late middle Ozarkian, represented by the Chepultepec, is 

 confined in the valley proper to the Alabama basin, but it must have 

 extended northwardly in the Allegheny basins, since the fauna is recog- 

 nized in Pennsylvania and New York. In the closing Jefferson City 

 stage of the period none of the Appalachian basins seems to have been 

 submerged. 



Shifting of Ordovician seas. — North-south oscillations in the valley 

 occurred very frequently during the Ordovician. Indeed, with the pos- 

 sible exception of the Silurian, sea-shifting seems to have attained its 

 maximum on the American continent in this period. However, the oscil- 

 lations were more gentle and the results more varied than in the Ozark- 

 ian. Space is lacking to point out the minor shiftings. Besides, most 

 of them affected the basins of the Appalachian region in east-west direc- 

 tions and many of these have been referred to on other pages of this 

 work. (See pages 321 to 328 and 544 to 557.) For present purpose, 

 then, it will suffice to add a few words concerning the distribution of the 

 larger subdivisions of the system. 



During the Stones Eiver epoch the volume of sediments and the time 

 consumed in their deposition were not greatly different in the Alabama, 



