436 E. S. MOORE 
the iron will be transported or left as a residual deposit will depend, 
not only upon the presence of solvents for the iron, but also upon 
the presence or absence of precipitating agencies. He agrees with 
Dr. Leith, however, in not regarding the pre-Cambrian iron- 
formations as laterites in sitw, although certain portions of them, 
especially those portions consisting largely of limonite or hematite, 
argillaceous materials, and silica, may very reasonably be regarded 
as lateritic, mechanical sediments more or less assorted. The 
constituents of the granular portions of the iron-formation and the 
iron carbonate must certainly have been carried in solution, probably 
as colloids, and through the aid of carbon dioxide and other agents. 
In the case of the ferric and siliceous granules in the Keepalloo 
iron-formation the presence of calcareous granules suggests that 
they were the primary granules, and that the iron and silica replaced 
them on the floor of the body of water in which these sediments 
were laid down. ‘This is the principle of deposition advocated by 
Cayeux" for some of the odlitic iron ores of France. There may 
also have been some primary iron-oxide and iron-silicate granules, 
as advocated by Hayes? for the Wabana ores of Newfoundland, and 
it seems probable that the concretionary character of the ore may 
be due to the action of low forms of life. The work of Harder’ and 
previous writers has shown that the iron bacteria are the important 
agents in precipitating iron compounds. These bacteria were 
found by Harder to be present in almost all iron-bearing waters, 
Spirophyllum and Gallionella, the latter, often mentioned among 
the algae by previous writers, being found even in underground 
workings of mines to a depth of several hundred feet. Harder 
found further that some solutions were kept under anaérobic condi- 
tions by passing carbon dioxide through them. In some solutions 
ferric hydroxide was precipitated, while in others there was no 
precipitate. The precipitation took place from either ferrous or 
ferric salts by oxidation. 
*L. Cayeux, Les minerais de fer odlithique de France. Ministere des Trav. Pub., 
Paris. 
2 A. O. Hayes, ‘“‘Wabana Iron Ore of Newfoundland,” Can. Geol. Surv. Memoir 78, 
Ottawa, IgIs. 
3 E. C. Harder, ‘‘Iron Bacteria,” Science, N.S., XLII, No. 1079, pp. 310-11. 
