THE NONTVIETALLIC MINERALS. 



235 



Tho Connasauga is between 2,000 and 3,000 feet in thickness. It 

 consists at tho base of fine abuninous shales; tho iippor portion is 

 more cali-areous, and locall^^ passes into heavy beds of blue seamy 

 limestone. 



Above Connasaiio'a shah> is the Knox dolomite, the most uniform 

 and persistent formation <>f the southern Appalachian region. It con- 

 sists of from H.OOO to 4,000 feet of gray, semicrystalline, siliceous 

 dolomite. The silica is usually seo-regatod in nodules and beds of 



Fig. 0. 

 MAP SHOWING THE GEOLOGICAL RELATIONS OF GEORGIA AND ALABAMA BAUXITE DEPOSITS. 



After C. W. Hayes. 



chert. These remain upon the surface, and with the other insoluble 

 constituents form a heavy residual mantle covering all the outcrops 

 of the formation. It is associated with these residual materials that 

 the extensive deposits of limonito and bauxite are found. The geo- 

 logical structure of the region is complicated and for its details the 

 present reader is referred to Dr. Hayes's original paper. 



Subaerial decomposition has progressed for a long period, and the 

 surface is deeply covered with a mantle of residual material, consisting 

 of the more insoluble portions of the original rock masses. This 



