PENNSYLVANIAN. 



453 



SOTTTHERN APPALACHIAN REGION. 



The southern portion of the Appalachian coal field falls in the geographic unit I 16, and 

 lies mostly in Alabama, though it cuts the northwest corner of Georgia. At the northern line, 

 opposite Chattanooga, the residual area of the Pennsylvanian is less than 30 miles wide. From 

 this it expands to a width of 85 miles along its southern exposure. On the east, where the 

 longitudinal folding, locally accompanied by overthrusting, is stronger, the coal field is gashed 

 by several anticlinal valleys, while farther east several synclinal areas are wholly detached. 

 The three most important of the latter are the liighly elevated Lookout Mountain syncline, 

 extending south from Chattanooga; the deeply set Coosa field, a complex synclinorium south 

 of Lookout Mountain, lying farthest east of the three; and the Cahaba syncline, ranging through 

 nearly the same latitude, about midway between the Coosa and the main Warrior field on the 

 west. Overthrust faulting, not uncommon along the eastern margins of the synclines, is 

 especially notable along the eastern border of the Cahaba field and the Warrior field south 

 of Birmingham, where Cambrian strata are thrust on beds of the middle Pottsville. The 

 Walden Plateau, east of the Sequatchie Valley, extends into Alabama as Raccoon Mountain, 

 and the Cumberland Plateau, continuing as a plateau though ruptured by several anticlines, 

 is called Sand Mountain in northern Alabama. Subordinate folds produce oblique lobes or 

 branches of the eastern synclines. 



In passing westward the folds die out and the beds rise gradually northwestward to fringe 

 the main field with irregular lobes and isolated patches, comparable to those along the western 

 and northern borders of the great Appalachian basin; but to the south and west in Alabama 

 the Pennsylvanian disappears beneath a Cretaceous mantle in the great Gulf embayment. 

 How far the coal measures extend beneath this southward-thickening cover has not been 

 ascertained. It is nearly certain that on the west they blend with the Pennsylvanian of the 

 eastern interior lobe. It is probable that at the stage of Kanawha (upper Pottsville) encroach- 

 ment union with that lobe occurred in Tennessee or perhaps in Kentucky. 



We have seen that in southern Tennessee the lower Pottsville, perhaps slightly thinner than 

 it is farther north, appears not to expand eastward as rapidly as the middle Pottsville, but in 

 Alabama we find a marked southeastern expansion of the lower as well as of the middle division. 



The general characters of the Pennsylvanian in the greatly elevated and much eroded 

 northern region are shown in the Ringgold and Stevenson quadrangles, geologically mapped by 

 Hayes, and in the Gadsden quadrangle, which, lying southwest of the Stevenson, cuts three of 

 the eastern synclines, including the south end of Lookout Mountain. 



TMckness, in feet, of Pottsville formations in northwestern Georgia and northeastern Alabama. 



Walden sandstone : Coarse sandstones, sandy shales, good coals, and clays 



Lookout sandstone: Sandstones, conglomerates, sandy shales, and interbedded 

 coals; has heavy cliff, usually conglomerate, at top 



Ringgold 

 quadrangle. 



930 

 [eroded] 



200-550 



Stevenson 

 quadrangle. 



500+ 



300-400 



Gadsden 

 quadrangle. 



500+ 



60-570 



It will be noted that the Gadsden quadrangle is nearly "in strike" with the Ringgold, 

 which explains the similarity in the thiclcness of the Lookout. The highest fossils collected in 

 the Lookout Mountain syncline, from beds reported as about 600 feet above the Lookout, sug- 

 gest the basal horizon of the middle Pottsville. It is therefore very doubtful if any upper 

 Pottsville is present in these quadrangles, which contain the highest beds in this northern sec- 

 tion of the State. '^ 



" For detailed sections outside of the folios cited, see McCallie, S. M., The coal deposits of Georgia: Geol. Survey 

 Georgia, 1906; McCalley, H. B., Coal measures of the Plateau region: Alabama Geol. Survey, 1891; Spencer, J. W., 

 Paleozoic group: Geol. Survey Georgia, 1893; Hayes, C. W., Twenty-second Ann. Rept. U. S. Geol. Survey, pt. 3, 

 1902, PI. XIV. For discussions of sections see Stevenson, J. J., Bull. Geol. Soc. America, vol. 15, p. 126. 



