SOUTHERN AND CENTRAL APPALACHIANS 



109 



: ig. 8.14. Major structural features of the Cumberland overthrust block (upper map). Area 

 )f fensters ruled and shown in more detail in smaller map (lower). The area of fensters is now 

 an oil field and is known as the Rose Hill district. Reproduced from Miller and Fuller, 1947. 



the anticlinorial belt is as shown in Fig. 8.25. These recent interpretations 

 of the structure show no important thrusts along the inner side of the 

 Blue Ridge belt, but rather folded normal sequences. Southward, espe- 

 cially south of the James River, reverse faults are numerous and thrusting 

 Jbecomes dominant, as will be seen in the following discussion of the 

 Great Smokies. 



The old Precambrian crystalline complex is composed of granite, 

 granodiorite, and gneiss. Cutting through it are basic dikes believed to 

 be feeders of the overlying basaltic Catoctin greenstone. The whole 

 Catoctin mass has undergone low-grade metamorphism, and a slaty or 



schistose cleavage pervades it, which dips southeastward as shown in tin- 

 sections just referred to. A distinct lineation occurs along the general 

 boundary of the Precambrian and Paleozoic rocks, and in northern Vir- 

 ginia, Maryland, and Pennsylvania, the cleavage in which the lineation 

 lies extends into the Beekmantown beds according to Cloos ( 1957 ) and 

 into the Martinsburg shale according to Nickelsen (1956). See Fig. 8.24. 

 Lineation and cleavage is limited to the Precambrian from Roanoke 

 southwestward where thrusting has brought the basement rocks into 

 abrupt contact with the unaltered Paleozoic rocks. 



The shear type of deformation accompanied by thickening along the 

 fold axes and thinning along the flanks is most characteristic of the Blue 

 Ridge, and sets it apart from the Valley and Ridge structures. 



Only one deformation has been detected from the lineation north of 

 the Potomac River in the South Mountain anticlinorium. Since the Pre- 

 cambrian Catoctin greenstone as well as the Cambro-Ordovician lime- 

 stones and shales of the Great Valley are affected and since the lineation 

 is remarkably regular along the Blue Ridge from Pennsylvania to the 

 French Broad River in North Carolina, Cloos ( 1957) thinks that this one 

 deformation is post-Ordovician, and therefore either Taconian or Acadian 

 in age. These orogenies will be described presently. 



Great Smoky Mountains 



South of the French Broad River the Blue Ridge belt loses its weltlike 

 form, and a broad, high, and geologically complex terrane sets in. Along 

 the Tennessee-North Carolina boundary between the cities of Knoxville 

 and Ashville are the Great Smoky Mountains where 16 peaks rise above 

 6000 feet. The general expansion of the Blue Ridge in this region is shown 

 on Fig. 8.22, and a geological map by P. B. King is presented in Fig. 

 8.26. A small-scale cross section is part of Fig. 7.2, and a more detailed 

 section is given in Fig. 8.27. Most of the Great Smokies is a thrust com- 

 plex of the Ocoee Late Precambrian series. 



This is a body of terrigenous clastic sedimentary rocks, which has minor 

 intercalations of limestone and dolomite but no volcanic components or known 

 fossils. The series is probably 30,000 feet or more thick. It lies unconforniahly 

 on a basement of earlier Precambrian granitic and gneissic rocks, and on the 



