i68 ^ S. W. McCALLIE 



granites have been intruded. The series is supposed to be largely 

 of igneous origin, though sediments undoubtedly occur in certain 

 localities, as shown by the graphitic schist, quartzitic schist, and 

 schistose conglomerate. 



The Roan gneiss is a series of basic igneous rocks including horn- 

 blende schist, hornblende gneiss, and schistose diorite. These 

 rocks occur in belts varying from a few feet to hundreds of rods in 

 width and often cut the Carolina gneiss, into which they have been 

 intruded at rather high angles. Less abundant and only locally 

 developed are pyroxenites, dunites, and serpentine belonging to 

 the same series. 



The granites are widely distributed and in places cover areas of 

 many square miles. They are prevailingly biotitic and generally 

 show gneissic structure. In age they are supposed to be largely 

 pre-Cambrian, though the more massive varieties, such as Stone 

 Mountain near Atlanta, are probably younger. The granites 

 unquestionably represent two or more periods of intrusion. 



CAMBRIAN SYSTEM 

 ALTERED CAMBRIAN 



The Cambrian system is divided into the altered and unaltered 

 Cambrian. The altered or metamorphic Cambrian rocks, so far 

 as known, are mainly confined to an irregular belt, varying in width 

 from eight to twenty-five miles, in the northwestern part of the 

 state. The belt lies immediately west of the Archean rocks and 

 embraces in its northern extension a greater part of the Appalachian 

 Mountain physiographic division of the state. These rocks belong 

 to the Ocoee group of Safford and were long regarded as of Algon- 

 kian age. However, fossils of Lower Cambrian age are found as 

 far down as the middle of this group of strata in Tennessee and 

 North Carolina, and the strata below the fossil-bearing beds are 

 conformable and not materially different in character. In addi- 

 tion to this main belt there is a narrow belt known as the Brevard 

 schist entering the state from South Carolina northeast of Gaines- 

 ville and stopping about five miles west of Atlanta. It seems quite 

 probable that the metamorphic Cambrian originally overlay the 

 Crystallines as far east as Atlanta and possibly beyond. 



