DISTRIBUTIOX AND GEOLOGIC STRUCTURE. 41 



for details beyond those given here. It should be remembered in this 

 connection that while the general trend of the Appalachian chain is 

 from north-northeast to south-southwest, yet the system describes many 

 curves, so that in some portions of its course the trend is almost east and 

 west, a fact exceedingly important in ifs bearing upon the value of com- 

 parisons made along certain lines. 



Immediately beyond the South mountain or Blue ridge is the Great 

 valley which, with many names, extends almost unbroken from New^ 

 England to Alabama and is bounded on its northwesterly side by a 

 monoclinal ridge known in Pennsylvania as Kittatinny or North moun- 

 tain, but by many names in its course through Virginia. 



GEOLOGIC STRUCTURE. 



The first coal-bearing area is the somewhat complex region lying be- 

 tw^een the Kittatinny and the Alleghany mountain, the latter an irregular 

 ridge traceable from Luzerne county southward almost to the Maryland 

 line, Avhere it betjomes an anticlinal with the Cumberland or Potomac 

 coal field at its easterly foot. In a general way, disturbance was much 

 greater within the valley than within this second area, for Cambrian and 

 Silurian rocks prevail in the former, whereas those rocks are deeply 

 buried in much of the latter. In its northward extent, the latter is, 

 comparatively speaking, a broad, gently folded area, in which rocks older 

 than the Devonian are rarely shown and the Coal Measures have been 

 preserved in deep synclinals known as the anthracite fields. Southward 

 the plication is greater; new and abrupt folds make their appearance, 

 so that in the central and other counties of Pennsylvania almost to the 

 Maryland line, the Lower Silurian is present in broad spaces and Upper 

 Silurian is a striking feature of the scenery. Still further southward, 

 faults, for the most i)art insignificant in this portion of Pennsylvania, 

 become more and more numerous until in southwest Virginia they are 

 tlie characteristic structural features. 



ANTHRACITE STRIP. 



As the result of this increasing plication southward, the Southern and 

 possiblv the iSIiddle anthracite fields have no representatives in the 

 southern counties of Pennsylvania, but the synclinal of Licking moun- 

 tain in Fulton countv, just fails to hold the Coal Measures ; it is where 

 the 'representative of the Southern field should be. The Northern or 

 AVyoming-Wilkesbarre field is represented in Huntingdon, Fulton and 

 Bedford counties by the Broad Top coal-field, while still further south- 

 westward and almost 20 miles nearer the Alleghany mountam is the 



