THE KONMETALLIC MINERALS. . 233 



part of the lime and magnesia; the iron had been oxidized and hydrate of alumina 

 formed as shown by its easy solubility in hydrochloric acid. The residue of the 

 silica had crystallized as quartz in the pores of the mineral. 



The more detailed account of the derivation of bauxite from basalt is given in an 

 inaugural dissertation by A. Liebreich, abstracted in the Chemisches Centralblatt, 

 1892, p. >4. This writer says that the well-known localities of bauxite in Germany 

 are the bouthern slope of the Westerwald near Miihlbach, Hadamar, in the neigh- 

 borhood of Lesser Steinheim, near Hanau, and especially the western slope of the 

 Vogelsberg. Chemical analyses show certain differences in the composition of 

 bauxite from different places, the smaller amount of water in the French bauxite 

 referring it to diaspore, while the Vogelsberg mineral is probably Gibbsite (hydrar- 

 gillite) . The bauxites of Ireland, of the Westerwald, and the Vogelsberg, show by 

 certain external indications their derivation from basalt. The bauxite of the Vogels- 

 berg occurs in scattered lumps or small masses, partly on the surface and partly 

 imbedded in a grayish white to reddish brown clay, which contains also similar 

 masses of basaltic iron ore and fragments of more or less weathered basalt itself. 

 Although the latter was associated intimately with the bauxite, a direct and close 

 connection of the two could not be found, but an examination of thin sections of the 

 Vogelsberg bauxite showed that most specimens still possessed a basaltic (anamesite) 

 structure, which enabled the author to determine the former constituents with more 

 or less certainty. The clays from different points in the district carrying basalt, 

 basaltic iron ore, and bauxite were examined, some of which showed clearly a sedi- 

 mentary character. Some of the bauxite nodules were a foot and a half in diameter 

 and possessed no characteristic form. They were of an uneven surface, light to dark 

 brown, white, yellowish, and gray in color, speckled and pitted, sometimes finely 

 porous and full of small colorless or yellowish crystals of hydrargillite. The thin 

 sections showed distinct medium-granular anamesitic structure. Lath-shaped por- 

 tions filled with a yellowish substance preponderated (the former plagioclases) and 

 filling the spaces between these were cloudy, yellow, brown, and black transparent 

 masses which had evidently taken the place of the former augite. Laths and plates 

 of titanic iron, often fractured, were commonly present and the contours of altered 

 olivine could be clearly made out. The anamesitic basalt of the neighborhood 

 showed a structure fully corresponding with the bauxite. Olivine and titanic iron 

 oxide were found in the clay by washing. The basaltic iron ore also showed the 

 anamesite structure. 



But two localities in the United States have thus far yielded bauxite 

 in commercial quantities. These are in Arkansas and the Coosa Valley 

 of Georgia and Alabama. 



According to Branner the Arkansas beds occur near the railway in 

 the vicinity of Little Hock, Pulaski County, and near Benton, Saline 

 County. "The exposures vary in size from an acre to 20 acres or 

 more, and aggregate something over a square mile." This does not, 

 in all probability, include the total area covered by bauxite in the 

 counties mentioned, for the method of occurrence of the deposits leads 

 to the supposition that there are others as yet undiscovered by the 

 survey. 



In thickness the beds vary from a few feet to over 40 feet, with the 

 total thickness undetermined; the average thickness is at least 15 feet. 



These Arkansas deposits occur only in Tertiary areas and in the 

 neighborhood of eruptive syenites ("granites 71 ) to which they seem 



