412 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



lithosphere. I do not refer to movements connected with vulcan- 

 ism. On the contrary, the best examples of the kind in mind are 

 found in areas but rarely or not at all affected by vulcanism. These 

 differential movements indicate actual elevation of one area, while an- 

 other near by was sinking, and a reversal of the movement in a succeed- 

 ing time. The phenomenon might be likened to a platform supported 

 in the middle and tilted alternately to the east and west, and at other 

 times to the north and south. The condition is recognized by the alter- 

 nate absence and presence of sediments on opposite sides of the tilting 

 platform. Excellent examples are found in comparing sections of Ordo- 

 vician bands met in crossing the Appalachian valleys from east to west. 

 It is thought advisable to cite as many instances as the space available 

 will permit, first, so that the principle of tilting movements may be 

 established, and, second, because it brings out the kind of evidence on 

 which beds hitherto believed to be contemporaneous are shown to be of dif- 

 ferent ages. Additional examples are discussed in the review of the prin- 

 ciples of correlation by diastrophic movements (see pages 535 to 569). 



The varying composition of the Chambersburg limestone in southern 

 Pennsylvania, described in an earlier part of this paper (page 321), shows 

 this kind of oscillation in a very satisfactory manner. In the western 

 belts of this formation, passing through the vicinity of Mercersburg, the 

 lower 100-200 feet of the Chambersburg consists of a subcrystalline 

 limestone (correlated with the upper Chazy) that is entirely absent in 

 the eastern belt, which passes southward from the town of Chambers- 

 burg, Pennsylvania, through Maryland, and thence on into Virginia. 

 The succeeding Black Eiver zones, the first and second of which (Low- 

 ville limestone and Echinosphaerites bed) are widely distributed in south- 

 eastern America, are present in both the eastern and western belts, 

 though subject to considerable variation in thickness, character, and 

 faunas. But the overlying last beds of the Chambersburg are developed 

 only in the eastern belt. The next following argillaceous limestone and 

 shale of the Martinsburg formation again overlaps from the east over 

 the western (Mercersburg) bands. 



Oscillation in the southern Appalachian Valley. — The same type of 

 oscillation prevailed in the southern part of the Appalachian Valley. 

 In northeast Tennessee, for instance (see map and figure 9, page 414), 

 the Canadian deposits hitherto included in the Knox are wanting in the 

 Eopaleozoic bands in the middle and western parts of the valley, but are 

 very strongly developed on the east side. Before that the great Ozarkian 

 Copper Eidge division of the Knox had been excluded from the east side 



