NOTES ON THE GEOLOGY OF GEORGIA 175 



in narrow outcrops with a linear distribution coextensive with the 

 Rockwood formation. The Armuchee chert, which consists of 

 bedded chert and thin beds of reddish-brown sandstone, is confined 

 to a few small areas north of Rome. 



CARBONIFEROUS SYSTEM 



The Fort Wayne chert is the lowest member of the Mississippian 

 group of the Carboniferous system and unconformably overlies 

 the Chattanooga black shale. It consists essentially of siliceous 

 limestone, with layers and nodules of chert made up in places largely 

 of crinoid stems. The formation in the western part of the Appa- 

 lachian Valley occupies narrow belts, while north of Rome it covers 

 large, irregular areas. 



The Floyd shale and the Bangor limestone, which also belong 

 to the Mississippian group are probably stratigraphically equiva- 

 lent, though one is largely shale and the other limestone. The 

 former is best developed along the narrow valleys at the base of 

 Lookout and Sand mountains, while the other occurs in numerous 

 narrow belts in Floyd County and the adjacent counties both north 

 and east of Rome. 



The Pennington shale unconformably overlies the. Bangor 

 limestone and forms the uppermost series of the Mississippian 

 group. It consists largely of shale, with sandstone in the upper 

 portion. Its linear distribution is coextensive with the Bangor 

 limestone. 



The Lookout formation and the Walden sandstone are both mem- 

 bers of the Pennsylvanian group. They are best developed in 

 Lookout and Sand mountains, which constitute what is known as 

 the Cumberland Plateau physiographic division of the state. They 

 consist of sandstones, conglomerates, shales, and a number of com- 

 mercial coal seams. 



CRETACEOUS SYSTEM 



The Cretaceous system, which rests unconformably on the old 

 crystalline rocks, is confined to a narrow, irregular belt traversing 

 the middle portion of the state in a southwest direction from 

 Augusta to Columbus by Milledgeville and Macon. The total 

 area covered by this system of rocks is approximately 250 square 



