REPORT OF THE DIRECTOR I917 99 



Of course there is no direct evidence that these manganese deposits 

 are of organic origin but it is very possible that the humic sols may 

 have played an important part in the decomposition of manganese- 

 bearing silicates in the rocks underlying the drainage basin of the 

 bogs. As manganese hydroxide has been found on the walls of the 

 iron bacteria, it is highly probable that bacteria may cause the 

 manganese to be precipitated from the sol humates which take the 

 humates up in the carbonate form and precipitate it in their bodies 

 as the hydroxide. Further investigations along this line have still 

 to prove how great and how general such action is. 



Assuming then that the manganese exists in the bog waters in 

 some soluble form, possibly in that of the bicarbonate, its precipita- 

 tion must have taken place through the oxidation of the same or as 

 the result of the presence of calcareous bicarbonate. As a precip- 

 itate, it is very possible that manganese exists as a colloidal hydroxide 

 quite as much as the hydroxide of iron does after its chemical changes 

 from the soluble to the solid form. Whether the precipitation takes 

 place in the fresh-water bogs as in the deep sea free from clayey 

 admixtures or subsequent to absorption by the clay, is a problem; 

 though it would seem to the writer that the clayey solids etc., do 

 act as absorbents as they do with the hydroxide of silica, iron and 

 alumina (12 1288). 



The assumption of the nodular and concretionary forms seems to 

 the writer to be a purely physical matter, the result of the tendency 

 of substances in mobile state to collect in bodies of smallest surface 

 area in proportion to mass. The centrifugal force or the accommo- 

 dating of the interior mass to the dimensions of the outer envelop 

 appears to be a characteristic of many minerals, especially those of a 

 calcareous, siliceous, ferruginous or manganiferous nature. Deep 

 sea nodules (11), and Cambrian manganese of Newfoundland 

 (3 : 450) illustrate this principle of surface tension as well as nodules 

 of the Columbia county manganese bogs. 



Bibliography 



1 Beck. Mineralogy of New York. Albany, 1842 



2 Beyschlag, Vogt, & Krusch. The Deposits of the Useful Minerals and 



Rocks. Translation by Truscott. 191 6. v. 2 



3 Dale, N. C. The Cambrian Manganese Deposits of Conception and Trinity 



Bays, Newfoundland. Am. Phil. Soc, 1915, 54:371-456 



4 Dale, T. N. Geology of the Hudson Valley between the Hoosic and the 



Kinderhook. U. S. G. S. Bui. 242. 1904 



5 ■ ■ ■ The Rensselaer Grit Plateau in New York. U. S. G. S., 13th 

 Ann. Rep't, 1894, p. 297-540 



4 



