150 Bulletin of Laboratories of Deiiison Universitv. [^'"i. -^i^ 



indicated by the solid black areas. The map further shows the 

 outline of the areas covered by the Crystalline and Paleozoic 

 rocks, and the extreme northwestern part of the Coastal Pl.iin 

 along- the fall-line. That part of the Coastal Plain indicated on 

 the map has its greatest width in a north-south direction along 

 the eastern margin, extending south from Augusta. 



The manganese-deposits of the two geologically different 

 areas are best considered separately under I. The manganese- 

 deposits of the Paleozoic area ; and II. The manganese-deposits 

 of the Crystalline area. 



I. The Manganese-Deposits of the Paleozoic Area. 



Resume of the Geology of the Paleozoic Area. 



Position. — The position of the Paleozoic area is shown on 

 the accompan3ing map (Fig. i). 1 he area includes the ten 

 northwest counties of the State, and is separated on the east 

 ai^d south from the Crystalline area by the Cartersville over- 

 thrust fault. It forms a part of the southern extension of the 

 great App.ilachian valley soulhweslward into Alabama. 



Topography. — The region as defined above is a long, nar- 

 row belt in which the valley-type predominates, and the axis of . 

 which has a general northeast-southwest trend. When viewed 

 in detail, it is observed to be composed of numert)us subordi- 

 nate valleys, separated by more or less extensive parallel ridges, 

 whose axial directions are coincident with the general trend of 

 the valley province. This ridge valley type of topography 

 bears a definite relation to the rock-structure of the area. The 

 ridges mark the lines of more resistant rock, while the valleys 

 are etched out of the soft shales and hmestones. Acc(^rding to 

 the character of the rocks composing the ridges, and the posi- 

 tion of the beds with respect to the honzon, the ridges are 

 high or low, rather broad and fl.it topped or narrow, and sharp- 

 crested. The Knox dolomite, one of the most persistent for- 

 mations in the area, and of intermediate hardness, forms a pla- 

 teau of moderate elevation (between 900 and 950 ft. above mean- 

 tide level) whose surface is g< ntly undulating, usu.illy not 

 marked by any sharp ridges or peaks. 



