EARLE, INTERBEDDED IRON ORE DEPOSITS 121 



found in a very fragmental condition and have been wholly or partly re- 

 placed and coated and cemented with iron, or a mixture of iron oxide and 

 calcite cement. 



The oolitic ores (Plates X, XX, XXI) are composed of oolites of hema- 

 tite cemented together like the fossil ores, but containing the peculiar 

 oolitic structures which have often been referred to as resembling fish roe. 

 The oolites are made up of a nucleus of quartz or other mineral, coated 

 in concentric rings or spheres with iron, usually in the form of red oxide. 



The flaxseed or "seed" ore is really oolitic ore and has the same pecu- 

 liar structure. In some cases, however, the term refers only to a smaller 

 grained oolite, such as that in Ohio and Wisconsin. 



Dyestone ore is the name given to the Clinton red hematite of Ten- 

 nessee and some other regions because of the fact that it has long been 

 used as a paint or dye ; and even in very early times it was mined in a 

 small way by near-by inhabitants for such purposes. 



The red flux beds refer to a lean seam or seams of fossil ore in northern 

 New York, the highest iron-bearing seam of the New York Clinton 

 formation, and found typically at Clinton, New York. 



Soft and hard ore are names used particularly for southern deposits, 

 to denote the difference between unaltered ore and that which, as a result 

 of weathering and a loss of soluble materials like calcite, has left a resi- 

 due rich in iron oxide and high in silica; the resulting soft ore being 

 rather more porous than the hard, and found at or within a few hundred 

 feet of the surface. The hard ore, on the other hand, is called hard, not 

 because of its actual hardness, but because it runs high in lime and has 

 not been affected by surface changes due to weathering. If we were to 

 dissolve the lime from hard ore, the result would be a residue rich in 

 iron and silica and precisely like the soft ores. Because of the value of 

 lime in fluxing iron ores, the hard ores of lower grade are much sought 

 and extensively mined. The soft ores, originally supposed to be the only 

 valuable ores, have been for the most part worked out ; and the old open- 

 cut mines have given way to the underground hard ore mines. 



EXTENT OF DEPOSITS 



One of the most interesting problems to be solved in a study of the 

 origin of these iron ores is how any single theory of origin can account 

 for a line of deposits extending over such an enormous area. Following 

 the shoreline of the old Silurian land areas bordering the epicontinental 

 sea, we find deposits intermittently all along the line (Plate VII). 



In Wisconsin, the ore occurs in Dodge County, attaining its greatest 



