5o6 REVIEWS 



Iron Depositing Bacteria and Their Geological Relations. By 

 Edmxtnd Cecil Harder. United States Geological Survey, 

 Professional Paper 113, 1919, Government Printing Ofl&ce, 

 Washington. Pp. 85, pis. 12, figs. 13. 



Geology, probably more than any other science, occupies an apical 

 position in the pyramid of the natural sciences; its function is not so 

 much to enunciate the more fundamental theories not based on the 

 concepts of other branches of knowledge, as to weld together the contri- 

 butions of its sister-sciences and apply them to its own purposes. From 

 this point of view a work such as that under review is especially illumi- 

 nating; it demonstrates conclusively the hitherto only partially appreci- 

 ated breadth of scope of the "science of rocks and minerals." 



The paper begins with a careful description of the living iron- 

 depositing bacteria, both those of the higher and those of the lower type. 

 Not only the more common forms, such as Leptothrix, GaHonella, and 

 Spirophyllum are mentioned, but a brief review of the classification, 

 morphology, and physiology of essentially all relevant forms known to 

 date is given. The iron-bearing algae also are named. From the early 

 work of Cohn and Zopf, who thought iron accumulation in bacterial 

 sheaths essentially a mechanical process, through that of James Campbell 

 Brown, who considered the deposition of ferric hydroxide to be merely 

 incidental to the extraction of the organic constituents in the water 

 affected, to the studies of Lieske, which demonstrated conclusively that 

 the carbonate radicle of ferrous carbonate is extracted by the bacteria, 

 leaving the insoluble hydroxide, the increasing importance of bacterial 

 metabolism has come to be recognized. It is probable, in fact, that 

 some bacteria require ferrous bicarbonate; that others can use it inter- 

 changeably with other soluble iron compounds; while still others, 

 notably the lower groups, can use only the organic salts of iron. 



Mr. Harder himself prepared and studied cultures of various forms. 

 Crenothrix was obtained from city water of Madison, Wisconsin, which 

 contained large amounts of magnesium and calcium carbonates. Cul- 

 tures of Leptothrix ochracea were grown from the water of a chalybeate 

 spring near Madison, the water bearing much ferrous iron in solution, 

 probably as the bicarbonate; this form was also brought up from a low 

 level of a Cuyuna District mine, where ferric hydroxide is being pre- 

 cipitated in large amounts. Cultures of Galionella ferruginea from the 

 Federal Mine of Wisconsin and from the Kennedy Mine of central 

 Minnesota are also reported; in both of these localities a brown, gelat- 

 inous scum occurs on the walls of the tunnels and in little pools in the 

 drift-floors. Spirophyllum ferrugineum appears in the waters of the 



