568 E. O. ULRIGH — REVISION OF THE PALEOZOIC SYSTEMS 



to attain their maximum thickness in Clinch Mountain, Tennessee, 

 though the development here does not greatly exceed that seen at McCon- 

 nellsburg, Pennsylvania. Except that the closing Cincinnatian deposits 

 in the valley proper are less generally distributed in the south and the 

 deposits on the whole thinner, their distribution is much the same as that 

 of the middle and late Eden shales. Extraordinary thicknesses were 

 attained by the late Ordovician Oswego (Bald Eagle) and Juniata sand- 

 stones in central Pennsylvania. 



Sea-shifting largely due to localized surface warping and torsion. — 

 While continental tilting may be partly responsible for the sea-migrations 

 cited in illustration of this principle, the chief cause no doubt lies in 

 more localized surface warping. This is shown by the described shifting 

 of the point of maximum continuity of submergence and deposition from 

 one to another of the five Appalachian basins. Also by occasional emer- 

 gence of the median troughs of a basin, while the troughs on either side 

 are subjected to submergence. This condition is indicated by the middle 

 Stones Eiver-Lenoir line in the table facing page 545. The same table 

 brings out also the opposite condition of median submergence and mar- 

 ginal emergence which prevailed during the Holston. 



Still another phase of warping is shown in the Appalachian Valley. 

 This suggests torsion of the valley tract, so that the point of greatest 

 deposition moved eastward in one basin while westward shifting was 

 going on in another. For instance. Stones Eiver deposits are often partly 

 and sometimes wholly absent in the eastern and middle troughs of the 

 valley in the central Virginia and Tennessee basins and along the Eome 

 barrier in the Alabama basin. So far as known, they are absent also in 

 both the middle and eastern troughs in the northeastern Pennsylvania 

 basin. On the other hand, the Stones Eiver is fully developed in the 

 middle and eastern troughs — that is, in the troughs to the east of the 

 Eome barrier, in the Maryland basin toward the north, and in the Ala- 

 bama basin at the south. 



Almost directly opposite torsion of the valley tract had occurred when 

 the next succeeding deposit, the Holston, was laid down. At this time 

 the Tennessee and west central Virginia basins were largely submerged 

 and slightly tilted eastward, while emergence and westward tilt prevailed 

 in the Alabama basin and in the Maryland basin. As described on page 

 335, sedimentation at this time occurred in the Mercersburg belts of the 

 Maryland basin and not in the Chambersburg trough. 



Torsion is clearly exhibited also by the Oriskany and probably by other 

 formations in the Appalachian Valley, but details remain to be worked 

 out. Indeed, stratigraphers should class these movements among the 



