400 E. C. HARDER AND R. T. CHAMBERLIN 



of which in nature oxidation of the carbonate with the resulting 

 hydrolysis is perhaps the most likely possibility. But such a 

 reaction should necessitate a notable quantity of iron compound 

 in solution. Van Hise and Leith object that river and sea-waters 

 do not contain the requisite amount of iron.^ Their suggestion 

 that the iron in the various iron formations of the Lake Superior 

 region has come from associated basaltic lavas, either from the 

 magmatic waters or from chemical reactions between the hot 

 basic lavas and the sea-water,^ hardly seems applicable to the 

 Brazilian iron formation, since nothing in the nature of basic 

 lavas has been found within the sedimentary series of the iron-ore 

 district with the exception of the serpentinized remains of one 

 small flow near Cattas Altas. This is very insignificant in extent 

 in comparison with the iron formation, and furthermore extensive 

 lenses of iron formation occur higher up within the Piracicaba 

 schist with which there are no igneous rocks associated. In chemi- 

 cal precipitation there is likewise to be considered the fact that 

 chemical reactions would be likely to produce other precipitates 

 in addition to ferric hydroxide, such as aluminum hydroxide and 

 calcium compounds, which would result in the formation of impure 

 deposits of iron ore rather than in thick beds and lenses of pure 

 ferric hydroxide. 



The other possibility is that the ferric hydroxide was thrown 

 down by organic action. It is now known that much of the bog 

 iron ore being formed in lagoons at the present time is the result 

 of the activity of a certain group of bacteria known as the iron 

 bacteria. The iron bacteria include many individual species, of 

 which the thread bacteria Chlamydothrix, Gallionella, Spirophyllum, 

 Crenoihrix, and Clonothrix, and the coccus form Siderocapsa have 

 perhaps been most carefully studied.^ While the different species 

 have individual morphological peculiarities of their own, the type 



' C. R. Van Hise and C. K. Leith, "The Geology of the Lake Superior Region," 

 Mon. §2, U.S. Geol. Surv. (1911), pp. 503-6. 



= Op. cit., pp. 506-18. 



3 Hans Molisch, Die Eisenbakterien, p. 10, Jena, 1910; D. ElHs, "A Contribution 

 to Our Knowledge of the Thread Bacteria," Centralbl. fur Bakt., Abt. II, Bd. 19 

 (1907), p. 502; Abt. II, Bd. 26 (1910), p. 321. 



