SOUTHERN AND CENTRAL APPALACHIANS 



103 



but in part are in the Great Valley. Modern interpretations show a num- 

 ber of fensters and klippes. See sections 4, 10, and 12 of Figs. 8.13, 8.16, 

 and 8.17, respectively. 



In northeastern Tennessee and southeastern Kentucky, the Appalachian 

 front is characterized by an unusual thrust. Elsewhere the Appalachian 

 front is one of fairly sharp folds that start abruptly from the flat-lying 

 plateaus sediments. As seen in Figs. 8.14 and 8.15, an extensive block of 

 the flat plateau strata has been torn loose and thrust, with only gentle 

 deformation, toward the stable interior. The great, basal fault is known 

 as the Pine Mountain and the two lateral tears as the Jackson and Russell 

 Fork. Although the large mass is a thrust sheet, the strata from Pine 

 Mountain to Cumberland Mountain are so flat that an arborescent drain- 

 age has developed and the region is considered geomorphically part of 

 the plateaus province. The thrust mass is known as the Cumberland block 

 and is 125 miles long and 25 miles wide. Its displacement has been cal- 

 culated as 5.8 miles (Miller and Fuller, 1947). Along the Powell Valley 

 anticline in the thrust sheet, erosion has cut several small fensters, and 

 the Rose Hill oil field has been developed in the underlying beds with 

 production from the Moccasin limestone. 



Structural Characteristics in the Virginias, Maryland, and Pennsylvania 



The southern part of the Appalachian belt, characterized by thrust- 

 ing, is narrow; but toward the north in west-central Virginia a number 

 of folds begin to show and the belt broadens. Sharp asymmetrical folds 

 and mild metamorphism characterize the Great Valley, strong upright 

 ! folds the main Valley and Ridge province, and very gentle folds, a 

 western belt. See index map, Fig. 7.1. The folds of the westernmost zone 

 are so gentle that the region is considered part of the Plateaus province, 

 and the Appalachian structural front here is regarded as the western 

 boundary of the zone of sharp folds. The plateaus generally stand in relief 

 above the valleys and ridges of the strongly folded belt, and the eastward- 

 facing escarpment is called the Allegheny front, which is a geomorphic 

 feature, whereas the Appalachian front is a structural feature. 



The chief faults are the Pulaski and North Mountain overthrusts. They 

 may be parts of one great thrust which extends from southern Penn- 



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I \ P / 





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Fig. 8.6. Basins of deposition in middle and late Ordovician time and in Silurian time in the 

 Pennsylvania-New York region. After Kay, 1942. 



