232 EEPOET OF NATIONAL MUSEUM, 1899. 



the mineral as of three varieties, pisolitic, compact, and earthy. The pisolitic 

 variety does not differ in structure from the iron ores of Tranche Comte" and Berry, 

 although the color and composition are different. It occurs in highly tilted beds 

 alternating with limestones, sandstones, and clays, belonging to the upper cre- 

 taceous period, and in pockets or cavities in the limestone. The limestone con- 

 taining the bauxite and that adjacent thereto is also pisolitic, some nodules being as 

 large as the fist, and the pisolitic bauxite has sometimes a calcareous cement, and at 

 others is included in a paste of the compact mineral. M. Coquand supposed that 

 the alumina and iron oxide composing the bauxite were brought to the ancient lake 

 bed in which the lacustrine limestone was formed by mineral springs, which, dis- 

 charging in the bottom of the lake, allowed the alumina and iron oxide to be dis- 

 tributed with the other sediment. In some cases the discharge occurred on land, 

 and the deposit then formed isolated patches. He refers to other similar deposits 

 of bauxite of the same period in France. Sometimes the highly ferriferous mineral 

 predominates over the aluminous (white), at others diaspose is found enveloping 

 the red mineral, while in other cases it is mixed with it, predominating largely, and 

 sometimes manganese peroxide replaces ferric oxide. In some places the ground 

 was strewed with fragments of tuberous menilite, very light and white. 



M. Ang6 [Bull. Soc. Geolog. de France, XVI, 1888, p. 345] describes the bauxite 

 of Var and HeVault and gives analyses of it. Over 20,000 tons were being mined in 

 this region annually at the time of writing his report [1888]. In the red mineral of 

 Var druses occur with white bauxite running as high as 85 per cent. Al-jOj, and 15 

 per cent. H 2 O, corresponding to the formula A1 2 O S +H 2 O. He refers to the prevail- 

 ing theory of the formation of bauxite, according to which solutions of the chlorides 

 of aluminum and iron in contact with carbonate of lime undergo double decomposi- 

 tion, forming alumina, iron oxide, and calcium chloride. Other deposits in the 

 south of France, in Ireland, Austria, and Italy, he says, confirm this view, because 

 they also rest upon or are associated with limestone. The bauxite deposit in Puy 

 de Dome which he studied could not, however, be explained by this theory because 

 it was not associated with limestone, but rested directly upon gneiss and was partly 

 covered by basalt. The geological sketch map of the deposit near Madriat, Puy de 

 Dome, which he gives shows gneiss, basalt, with uncovered bauxite largely predomi- 

 nating, and patches of miocene clay, while a geological section of the deposit near 

 Villeveyrac, Herault, shows the bed of bauxite conformably following the flexures 

 of the limestone formation when covered by more recent beds, and when exposed 

 and denuded occupying cavities and pockets in the limestone. This occurrence is 

 substantially the same as that of the neighboring Baux. M. Ang6 agrees with M. 

 Coquand in attributing the bauxite to geyserian origin. He uses as an illustration 

 of the contemporaneous formation of bauxite the deposits from the geysers of the 

 Yellowstone Park, which is evidently due to a misunderstanding. He made no 

 petrographical examination of the bauxite of Puy de Dome, nor did he attempt to 

 trace any genetic relation between the latter and the accompanying basalt, The 

 occurrence is, however, noteworthy, and an examination might show that it is 

 another instance of the direct derivation of bauxite from basalt, which is maintained 

 in the two following instances, somewhat imperfectly in the first to be sure, but with 

 greater detail in the second. 



The first is a paper by Lang [in the Berichte der Deutschen Chemischen Gesell- 

 schaft, XVII, 1884, p. 2892]. He describes the bauxite in Ober-Hessen, which is 

 found in the fields in round masses up to the size of a man's head, embedded in a 

 clay which is colored with iron oxide. The composition varies very widely. The 

 petrographical examination showed silica, iron oxide, magnetite, and augite. The 

 chemical composition and petrographical examination shows the bauxite to be a 

 decomposition product of basalt. By the weathering of the plagioclase feldspars, 

 augite, and olivine, nearly all the silica had been removed, together with the greater 



