164 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



luster it is often waxy, and thin edges frequently are translucent. The, bedding is quite irregular, 

 small lenses between the beds being very common. * * * 



The upper portion, in those parts where it is aU present, is much thicker than the lower. 

 It consists of layers of novaculite the most common thickness of which is from 1 to 6 inches, 

 interpolated by layers of shale that is very black and soft when unaltered. ■ - When weathered, 

 this shale is brown to green in color, producing a banded effect. The novaculite layers usually 

 are dark to black but hthologicaUy are not otherwise very different from the massive novaculite 

 beds of the lower part of the formation. This part of the formation is frequently and sometimes 

 wholly removed, as a result of an unconformity between it and the Carboniferous rocks that 

 rest upon it. 



The Fork Mountain slate, when present, lies at the top of the Arkansas novaculite, and is 

 about 125 feet thick. On account of the unconformity above mentioned, it is only locaUy 

 present, having in many places been removed by erosion. * * * 



This formation consists of gray to greenish and chocolate-colored slates, containing thin 

 layers of quartzite in the lower part. 



I 16. ALABAMA, GEORGIA, AND SOtTTHEASTEBN TENNESSEE. 



The classification and synonymy of the Ordovician worked out by Hayes *" in 

 the southern Appalachian region is: 



Ordovician rocks in southern Appalachian region. 



The stratigraphic relations and distribution of the formations are described 

 in the Stevenson, Gadsden, and Chattanooga folios of the Geologic Atlas of the 

 United States, according to the divisions which have been carefully worked out 

 as lithologic units. Recent paleontologic studies by Ulrich and Bassler, not yet 

 published, appear to lead to the discrimination of several paleontologic facies and to 

 correlation with the Stones River and other established horizons of the Mississippi 

 Valley and New York sections. 



A recent study of the Birmingham district'"^ has resulted in the following 

 lithologic distinctions : 



reet. 



Silurian: Clinton (Rockwood) formation 250-500 



Unconformity. 



Ordovician: Chickamauga (Pelham) limestone 200-1,000 



Unconformity. 



Cambro-Ordovician : Knox dolomite (includes at base Ketona dolomite member, 600 feet) . . 3,300 



Cambrian: 



Conasauga (Coosa) limestone 1,000 



Uome (Montevallo) formation (great thickness) . 



