224 ECONOMIC GEOLOGY 



where the calcium compounds in the dolomite produced alumina 

 amd calcium sulphate. The aluminum compound which was 

 light and gelatinous was carried upward into spring basins on the 

 surface where it finally settled. 



(3) The bauxite deposits of the Tennessee district are situated 

 near Chattanooga, on the southeast slope of Missionary Ridge. 

 They came into prominence in 1907. According to H. Hies they 

 represent the northward extension of the Georgia-Alabama 

 district. 



(4) The bauxite deposits of Arkansas are confined to a small 

 area in Pulaski and Saline Counties. These ores have been care- 

 fully studied by C. W. Hayes, J. C. Branner, and J. F. Williams, 

 who state that the ores are found in Tertiary areas in the neighbor- 

 hood of irruptive syenites and in a region free from limestones. 

 There are two varieties of the ore. The one is granitic, and the 

 other pisolitic. The granitic variety shows the structure of the 

 syenite from which it was probably derived. The pisolitic variety 

 was doubtless deposited from solution. The three authorities 

 agree in tracing the genesis of the bauxite back to the action of 

 waters upon the heated syenite. Hayes believes that these 

 waters were either alkaline or saline, that they dissolved out the 

 silica and the alkalis and deposited alumina in their places. 

 Fourche Mountain, which constitutes one of the bauxite areas, is 

 the home of elaeolite syenite and both diaspore and gibbsite are 

 recognized as decomposition products of elaeolite and sodalite. 



According to F. W. Clarke, bauxite is intermediate between 

 diaspore and gibbsite and represents an admixture of the two 

 hydrates, sometimes approaching one in composition and some- 

 times the other. The granitic type above referred to very closely 

 conforms to gibbsite, while the pisolitic type may more nearly 

 represent A1 2 O 3 ,2H 2 O. One variety of the bauxite is high in silica 

 and low in iron, while the other has been worked as an iron ore 

 on account of its high percentage of iron. 



(5) Bauxite deposits occur in the vicinity of Silver City, New 

 Mexico, which appear to have been derived from a basic volcanic 

 rock in situ. These ore bodies are some distance from the rail- 

 road and therefore are not extensively worked. 



The type locality for bauxite is the town of Baux in the south- 

 ern part of France. It is from this district that the mineral de- 

 rives its name. At Baux the ore occurs in irregular masses in 

 Cretaceous limestones where it has been deposited through the 



