564 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Formations limited by the Staunton barrier. — Tlie Staunton or Fort 

 Defiance axis prevented southward extension in the Appalachian Valley 

 of the Elbrook limestone, the Conococheague formation, the Stones Eiver, 

 and the Chambersburg, all limestone formations of the Maryland basin. 

 It prevented also northward extension of the Murat limestone, the Athens 

 shale, and the Liberty Hall limestone, three of the valley formations in 

 central Virginia. Whether it exerted any well marked effect on the 

 distribution of later formations west of the Allegheny Front is unknown. 



The Wytheville axis as a barrier. — The principal formations which 

 failed to extend across the Wytheville axis are the following : The Stones 

 Eiver and the Liberty Hall lapping out from the north ; the upper Cam-» 

 brian formations, the Knox, the Holston, and the Tellico from the 

 south in the eastern troughs of the Appalachian Valley proper ; the mid- 

 dle divisions of the Clinton, the Sneedville, the Helderbergian, the middle 

 and upper Devonian, late Tennessean and early Pottsvillian formations 

 from the north; the Brassfield Clinton, the typical Chattanooga, and 

 the Fort Payne from the south in the eastern part of the Allegheny 

 basin. In the western troughs of the Appalachian Valley the upper 

 Cambrian formations, the Copper Eidge chert, and the Murat Limestone 

 part of the Holston extend northward from the Tennessee basin into 

 the central Virginia basin. In the eastern — Athens — trough the Cana- 

 dian Jonesboro limestone similarly extends across the Wytheville axis. 



The Gadsden barrier. — The northeast Alabama axis vitally influenced 

 the distribution of many Paleozoic formations. As noted on page 549, 

 the Ozarkian has three formations in Alabama beneath and another, the 

 Chepultepec, above the typical Knox that are not seen in Tennessee. The 

 Alabama basin has also a thick Canadian limestone, the Frog Mountain 

 Oriskany sandstone, the Tennessean Floyd shale, and considerable Potts- 

 villian deposits, all of which formations were cut off on the north l)y this 

 axis. The Stones Eiver limestones also have a development to the east 

 of the Eome barrier that is much greater along the strike of the rocks 

 than is seen to the north of the axis. Finally, the deposits of Black 

 Eiver age to the east of the Cahaba coal field, as seen in the vicinity of 

 Pelham, Alabama, differ greatly in character and thickness of beds and 

 in their faunas from beds of the same epoch in east Tennessee. 



The list of formations developed in the Tennessee basin east of the 

 Eome barrier and which do not extend into the central Alabama basin 

 comprises the Lenoir limestone, the Holston marble, the Tellico sand- 

 stone, the Ottosee formation, and the Waverlyan Grainger formation 

 along the foot of Chilhowee Mountain. It may be added that in places 



