REVIEWS 509 



Carpathian and Harz Mountains, and in Westphalia; the sedimentary 

 origin of some of these beds, however, is still in doubt; more typically 

 sedimentary are some of the oolitic pyrite beds of Wabana. Ferrous 

 sulphide is common in the limans of the Black Sea. The general expla- 

 nation offered for these deposits is that of Doss, who believed that the iron 

 is carried as a carbonate, upon which bacteria may act directly or 

 indirectly to yield colloidal ferrous sulphide or ferric hydroxide, which 

 in turn is converted into ferrous sulphide. 



Various facts of importance to students of sedimentation are brought 

 out in a discussion of the origin of the separate iron deposits ; for instance, 

 the experiments by Spring and Ruff on the conditions favoring and 

 opposing the derivation of limonite from ferric hydroxide. It is shown, 

 also, that primary deposits of ferric hydroxide may be readily altered 

 to the carbonate, especially in the presence of large amounts of organic 

 matter. 



From a discussion of the inorganic causes for the precipitation of 

 iron compounds as sediments, the writer returns to a consideration of 

 organic causes. Here, especially in connection with the precipitation 

 of ferric hydroxides, the line is not readily drawn between oxidation, 

 taken as the purely inorganic process, and bacterial action; the latter, 

 however, is surely of much importance, whether actually preponderant 

 or not. The conditions under which iron-bearing bacteria are active 

 vary between wide limits. Temperature, if too high or too low, may be 

 inhibitory, as may also be a reduction in the amount of organic matter 

 present. 



To present in detail all the significant facts of this interesting paper, 

 would necessitate a review as long as the original publication; it must 

 be read to be fully appreciated. It displays both the clear thought and 

 the technical skill of Mr. Harder in original work and his ability to join 

 his observations to those of other investigators of the subject. All in 

 all, it is a most admirable contribution to experimental geology. 



C. H. B., Jr. 



Helium-Bearing Natural Gas. By G. Sherburne Rogers. United 

 States Geological Survey, Professional Paper 121. Washing- 

 ton, 192 1. 

 This report comes from the press many months after the accidental 

 death of its author in South America. It reflects so zealous a spirit of 

 scientific research in the public service that it stirs anew the sorrow of 



