NOTES ON THE GEOLOGY OF GEORGIA 



S. W. McCALLIE 

 Atlanta, Georgia 



ARCHEAN SYSTEM 



The geological history of Georgia begins with the ancient Crys- 

 talline rocks, the greater part of which are supposed to be of Archean 

 age. These rocks form a northeast-southwest belt about 125 

 miles wide traversing the northern part of the state and are a part 

 of the great belt of ancient Crystallines extending from north- 

 eastern New York to eastern Alabama (Fig. i). The areal extent 

 in Georgia is about 15,000 square miles, or approximately one-fourth 

 of the state. They occupy all of the physiographic division known 

 as the Piedmont Plateau, and a part of the Appalachian Mountain 

 division. To the northwest they are limited by the metamorphic 

 Cambrian rocks and to the south by the Tertiary. The latter 

 boundary is sharp and distinct, while the former is ill-defined. 

 These rocks are here described under the following names: Caro- 

 lina gneiss, Roan gneiss, and granites. 



The Carolina gneiss, so called from its wide distribution in the 

 Carolinas, where it has been studied by Keith and others, is the 

 prevailing rock of the ancient Crystallines of Georgia (Fig. 2). 

 Broadly speaking, the formation may be correlated with the Balti- 

 more gneisses of Maryland and the Stanford and Fordham gneisses 

 of New York. 



The most abundant, widespread, and t3^ical rocks of the Caro- 

 lina formation are schists, largely micaceous and garnetiferous, 

 and biotite gneiss. In addition there occur in more or less restricted 

 areas graphitic schist, quartzitic schist, and schistose conglomerate. 

 The most persistent character of these rocks is the schistose and 

 bended structure due to the segregation of the component minerals 

 along definite lines. They are the oldest rocks of the state and may 

 be considered the country rock into which the Roan gneiss and 



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