Ch. 28] IRON OXIDES AND HYDROXIDES 517 



originally in the powdery or oolitic form or that the hematite replaced 

 the carbonates long after deposition. 



The Wabana ores are similar in many respects to the Clinton de- 

 posits. The hematite is in the form of oolites, but according to Hayes 

 (1915, p. 25) considerable siderite and chamosite are present. Fossil 

 fragments are abundant, but they have not been replaced by hematite. 

 Ripple markings, cross-bedding, and worm burrows are excellently 

 preserved in the ore ; they indicate shallow, marine conditions of deposi- 

 tion. There are six iron-bearing beds of which three have been worked 

 commercially. The Dominion bed normally ranges in thickness from 

 12 to 20 feet but locally reaches a thickness of 35 feet. The ore 

 averages about 9 cubic feet per ton. The iron ranges from 20 to 57 

 percent, the alumina from 3 to 6 percent, the phosphorus from 0.7 to 2 

 percent, the lime from 1 to 3 percent, the silica from 6 to 50 percent, 

 and the sulphur is very low. 



The oolitic Minette limonites occur as lenticular bodies interbedded 

 with shales, limestones, and sandstones. Seven ore horizons occur, 

 ranging in thickness from a few inches to 25 feet. The ore is soft, 

 earthy, oolitic limonite and hematite with some siderite and chamosite. 

 The limonite has been generally regarded as a primary deposit, but 

 Cayeux (1909, p. 284) concludes that calcite oolites were replaced by 

 the iron oxides. The ore averages 30 percent iron and contains 0.5 to 

 1.8 percent phosphorous, 5 to 12 percent lime, and 7 to 20 percent 

 silica. 



The Bavarian and Wurttemberg oolitic ores of Germany are mainly 

 sedimentary limonites but contain some siderite and hematite. The 

 high-phosphorus Salzgitter ores occur in thin beds and contain about 

 30 percent iron and 25 percent silica. 



Bog Deposits of Limonite 



Bog iron ores are formed in swamps, lakes, and sluggish streams. 

 They consist of dark-brown, cellular, or oolitic masses of limonite with 

 some hematite. Iron silicates, iron sulphides, iron phosphate, siderite, 

 organic matter, and clay or sand occur in the ore in variable amounts. 

 Plants and roots are often replaced by limonite. Deposits of this type 

 are thin and have a very limited lateral extent. The ores are usually 

 mixed with clay and sand and rarely contain as much as 50 percent 

 iron. Silica, alumina, and phosphorus are usually present in relatively 

 large quantities, but sulphur is normally low. Bog iron ores are now 

 of slight importance to the mining industry because of the small size 

 and the impurity of the deposits. Bog deposits have been mined at 

 many localities throughout the world. It is of interest to note that 



