662 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Subdivision of the Appalachian and Allegheny geos^'nclines by trans- 

 verse axes. — According to information now in hand, the Appalachian 

 Valley trough and the adjacent Allegheny basin between southern New 

 York and central Alabama are each divisible into five parts by four sub- 

 parallel and relatively unstable transverse axes. The most northerly of 

 these broad axes passes in a northwesterly direction across the valley 

 between Chambersburg and Lebanon, Pennsylvania, toward Niagara 

 Falls. For present purposes it may be called the Harrisburg axis. The 

 next to the south intersects the valley of Virginia between Staunton and 

 Harrisonburg. The third or Wytheville axis passes across southwestern 

 Virginia and may be a continuation of the Wabash axis of Indiana. 

 The fourth axis crosses the Appalachian A^alley in a northerly direction 

 through the belt lying between Eome, Georgia, and Gadsden, Alabama, 

 and presumably continues in a general northwesterly direction to the 

 Nashville dome and thence on to southeastern Missouri. For convenience 

 in reference the depressed areas separated by these axes may be named 

 as follows: The northeastern Pennsylvania hasin to the north and the 

 Maryland hasin to the south of the Harrisburg axis, the central Virginia 

 hasin to the north and the Tennessee hasin to the south of the Wythe- 

 ville axis, and the Alahama hasin to the south of the northeastern Ala- 

 bama or Gadsden axis. 



These transverse axes do not cross the longitudinal troughs in con- 

 tinuous direct lines. On the contrary their course zigzags within the 

 varying limits of a broad band so that the northern head of a bay in 

 one trough may extend 50 miles or more beyond the latitude of the 

 southern head of another bay in an adjacent trough. The band is wide 

 enough and was always low enough so that regional tilting occasionally 

 permitted overlap of edges of formations transgressing from opposite 

 directions. Often the axis formed an efficient barrier in one trough and 

 was much less effective or seems to have failed entirely in another. Most 

 of the latter cases, however, are indicated by formations that are not 

 contemporaneous. Sometimes again, a bay connected with waters occupy- 

 ing another trough in which the submergence extended across the trans- 

 verse belt which, while limiting the submergence in the first, failed to 

 do so in the second. Such a case seems to have been the Holston, which 

 sea was limited in the Knoxville troughs on the north by the Wytheville 

 axis but not in the troughs to the west of these. In one of the latter the 

 sea apparently extended northward to some point in Virginia between 

 Staunton and Fort Defiance. 



As a rule the southwardly overlapping formations in the Allegheny 

 troughs west of the Appalachian belt of overthrust faulting extend much 



