APPALACHIAN MOUNTAINS 



95 



... in southern Ohio the Mississippian rocks on the western margin of the 

 Allegheny Plateau form cuestas rising to the full height of the plateau. The 

 prominence of these cuestas diminishes toward the south, but they continue 

 to form a narrow belt included in the plateau as far as latitude 37° 30', beyond 

 which the Mississippian rocks (all except the uppermost) spread widely to the 

 west at a lower level and belong to a different province. Farther south the strong 

 conglomerates or sandstones at the base of the Pottsville (Rockcastle group) 

 underlie and support the margin of the plateau. All beds here dip slighdy to 

 the east, and the strong basal formations are to some extent stripped, leaving 

 at places a decided eastward dip slope. As the stripped belt widens toward 

 the south, and the province narrows, the entire width of the Cumberland 

 Plateau in Tennessee and Alabama comes to be on the strong formations here 

 | known as Walden and Lookout sandstones. 



For nearly 200 miles along the median line of the province in Tennessee and 

 Alabama, runs the straight Sequatchie anticline, broken on the west by a thrust 

 fault. If left uneroded, it would form a range of mountains, as it still does at 

 its northern end where the Crab Orchard Mountains are in line with the perfect 

 anticlinal valley which marks the rest of the uplift. Like the more extensive 

 and complex Allegheny and Cumberland Mountains, this anticline represents 

 the propagation into the plateau of the compressive stress by which the Valley 

 and Ridge province was folded. Parallel to this feature, and 15 miles to the 

 east is the similar Wills Creek anticline, marked by the valley west of Lookout 

 Mountain (Fenneman, 1937). 



Valley and Ridge Province 



The folded and thrust-faulted Appalachian structural system is the 

 geomorphic Valley and Ridge province, which as already stated consists 

 of parallel or subparallel ridges and valleys of 1000 to 2000 feet local 

 relief. It has been spoken of as the newer Appalachians in contradistinc- 

 tion to the older Appalachians which would include the Blue Ridge and 

 | Piedmont provinces. 



The Valley and Ridge province can readily be divided longitudinally into a 

 northwestern section, in which high ridges alternate with valleys of moderate 

 width (the "Valley and Ridge" section), and a broad southeastern lowland 

 section (the "Great Valley"). This division is more or less apparent throughout 

 the length of the province. 



Except for a short distance in New York, the entire northwestern boundary 

 of the province is an erosional escarpment formed on gendy dipping or horizon- 



i tal sediments of the Appalachian Plateau. From southern Pennsylvania to 

 Alabama, the southeastern boundary is formed by the resistant rocks of the 



1 Blue Ridge, towering above the Great Valley. This boundary is erosional in 

 origin, weaker Paleozoic sediments having been stripped from the Precambrian 



surface (in some places from resistant Cambrian quartzites) on which till 

 were deposited. In other localities the contact of weak Paleozoic sediments with 

 resistant crystalline rocks takes place along a low-angle thrust fault, and erosion 

 has lowered the sediments northwest of the Fracture plane. 



The rocks of the province are Paleozoic sediments ranging in age from Cam- 

 brian to Pennsylvanian. Their resistance to erosion varies gready and has a very 

 important effect upon the topograph}'. The broad low land composing the Great 

 Valley is due to the weakness of the Cambro-Ordovician limestones (Kittatinnv 

 and other formations) and Ordovician shales (Martinsburg). The ridges of the 

 Valley and Ridge belt are composed of very resistant middle and upper Paleo- 

 zoic sandstones and conglomerates, particularly the Tuscarora quartzite and 

 conglomerate (Silurian), the Pocono sandstone (Mississippian), and the Potts- 

 ville conglomerate (Pennsylvanian). 



At the end of Paleozoic time the sediments in the Newer Appalachian 

 province were subjected to strong pressure from the southeast and folded into 

 great anticlines and synclines, in places overturned toward the northwest. 

 Reverse faults were also commonly developed in the zone of greatest pressure, 

 the horizontal attitude of the beds was scarcely disturbed. The region of 

 undisturbed rocks today forms the Appalachian Plateau; the folded area has 

 become the Newer Appalachians. In the latter province the structural trends 

 are northeasterly, and owing to the remarkable development of subsequent 

 streams the topographic features trend in the same direction (Fenneman, l937). 



Blue Ridge Province 



The Blue Ridge province rises in southern Pennsylvania as the Carlisle 

 prong and continues southwestward in accordance with the general trend 

 of the Appalachian systems to northern Georgia. It stands conspicuously 

 above the Great Valley section of the Valley and Ridge province on the 

 northwest and the much lower Piedmont province on the southeast. The 

 province takes its name from the Blue Ridge in Virginia, which is a rela- 

 tively narrow mountainous ridge that extends from the Potomac River 

 200 miles southwestward to Roanoke. It has an altitude of about 1000 feet 

 near the Potomac, but attains an elevation of more than 1000 feet to the 

 southwest. Southwest of Roanoke, the Blue Ridge province is a rolling 

 plateau, about 10 to 65 miles wide ami with an average elevation of 

 3000 feet. Its bounding escarpments are 1000 to 2000 feet high. This part 

 of the province includes the Great Smokies which are the highest land 

 east of the Rockies. Mount Rogers, near the northwestern escarpment 

 in Virginia has an altitude of 5719 feet, and Mount Mitchell in North 

 Carolina has an elevation of 6711 feet. 



