30 The American Gcoloi^isl. jniy, looi. 
stone. The silica is dislrilnitcd ihroug-h the hniestonc in the 
form of segregated nodules and lenses of chert. The lime- 
stone yields upon weathering a highly siliceous clay, and the 
residual mantle attains considerahle thickness over the entire 
region, leaving only scant outcrops of the fresh limestone ex- 
posed to view. The Connasauga shale (Cambrian) is next 
below the Knox dolomyte with an approximate thickness of 
2,000 to 3,000 feet. The shales belong essentially to the 
aluminous type, containing as shown by analyses 20 to 30 per 
cent, of alumina. (See page 43.) 
In the Georgia area the ore-bodies are confined principally 
to the Knox dolomyte and appear not limited to any particular 
or definite horizon in the formation, but are rather associated 
with all parts of it, and have therefore a somewhat wide 
stratigraphic rang'e. So far as mining operations extend the 
Georgia bodies are inclosed in the heavy mantle of siliceous 
residual clays derived from the Knox dolomyte. For reasons 
subsecjuently given in this paper, the bauxite is shown not to 
be a residual product, as the previous sentence might imply, 
but its origin has been entirely different from that of the resid- 
ual clays. 
Associated Minerals. 
The trihydrate of aluminum, gibbsite, and the silicates, 
halloysite and clay or kaolin, are intimately associated with the 
bauxite. Gibbsite is found in many of the deposits amount- 
ing to scarcely more than traceable quantities, incrusting or 
lining the cavities of the bauxite, not exceeding one-eighth of 
an inch in thickness and is readily recognized by its mode of 
occurrence. -Halloysite is a more frequent associate than 
gibbsite, and occurs in the form of hard, pure white, procel- 
laneous small nodules and lenses, irregularly distributed 
through the ore-bodies. It is oftentimes striated and slicken- 
sided from subsequent movement probably due to settling of 
the deposits. Vari-colored white to red mottled clay or 
kaolin is always found in large quantity inclosing the Ore- 
bodies, and in the form of clay horses and dikes cutting the 
bodies in various directions and attitudes. The pisolitic struc- 
ture of the bauxite passes by imperceptible gradations into the 
surrounding masses of structureless bauxitic clavs and kaolins. 
