i6o Bulletin of Laboratoties of Denison University. [Voi.xii 



bly, but the quantity of chert admixed with the clay is always 

 large. It is by means of its residual material, especially the 

 chert nodules and masses, that the Knox dolomite is olten 

 traced, for exposures of the fresh rock are seldom seen except 

 along the stream-courses. 



The magnesian limestone has an estimated thickness of 

 3000 to 5000 ft. As a producer of manganese-ores, the Knox 

 formation is, perhaps, of less importance in the immediate Car- 

 tersville district than either the Weisner quartzite or Beaver 

 limestone. Excepting the Cartersville district, the Knox dolo- 

 mite is one of the most important ore-producing formations in 

 the Georgia Paleozoic area, as the extensive accumulations of 

 bauxite and a part of the iron- and manganese-deposits are as- 

 sociated with it. 



The numerous chemical analyses made from specimens 

 collected from the Knox formation over many localities in 

 Georgia show its composition to vary within the following 

 limits : 



SiOi, 3.75 to 7.25; AI2O3 and Fe20i, 1.24 to 1.76; CaCOs, 

 34.07 to 53.44; and MgCOs, 36.32 to 55.74 per cent. 



The Older Crystalline and MetamorpJiic Rocks of the Cartersville 

 District on the East Side of the Cartersville Fault. 



Several types of crystalline, metamorphic rocks are repre- 

 sented which show wide variation in composition and, probably, 

 in age. Of these, the Corbin granite-area, which occupies the 

 middle eastern portion of the map (Fig. 3), is the most exten- 

 sive. As mapped, this granite mass is a roughly oval-shaped 

 area extending from Stamp Creek P. O. on the north to the 

 line of the Western and Atlantic railroad on the south, and 

 continuing eastward into Cherokee county. The granite is a 

 coarse-grained porphyritic rock, presenting a distinct augen- 

 gneiss facies in the border-portions. It is composed of large, 

 microcline phenocrysts imbedded in a ground-mass of blue 

 quartz, plagioclase feldspar, augite and mica. Its composition 

 is shown in the following analysis, made by Dr. H. N. Stokes, 



