Notes on the Geology of Georgia

Abstract

The geological history of Georgia begins with the ancient Crystalline 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 northeastern 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: Carolina 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 Baltimore gneisses of Maryland and the Stanford and Fordham gneisses of New York. The most abundant, widespread, and typical rocks of the Carolina formation are schists, largely micaceous and garnetiferous, and biotite gneiss. In addition there occur in more or less restricted