494 C. H. Smyth, Jr.-— Clinton Iron Ore. 



of the pebbles of the latter. The conclusion seems inevitable 

 that the ore was in its present condition when the limestone 

 was deposited upon it. 



If these ores are altered limestones, it is as difficult as with 

 the oolitic variety to account for their complete oxidation. 



These facts suggest that the calcareous remains were subject 

 to the action of waters containing iron and silica resulting in 

 a replacement of the calcite, before the fragments were ce- 

 mented into rock form. Such an action would take place only 

 near shore, and that it was near shore that they were deposited 

 is shown by the fragmental and rounded character of the fos- 

 sils. This substitution may have taken place partly while the 

 fragments were being rolled about on the bottom, and partly 

 after they were massed together and covered with thin layers 

 of mud or sand. Under these conditions ferrous carbonate 

 formed would be quickly oxidized. Associated with this 

 material would be a varying amount of iron oxide deposited 

 from suspension. The coarser particles would supply the 

 scales seen in the ore, while the finer portions might enter into 

 the replacement, being cemented by the silica. Let such a 

 layer as this be covered by other strata and be cemented by 

 calcite, partly derived from a foreign source and partly from 

 solution and crystallization of unaltered shells, bryozoa, etc., 

 and the result would be the non-oolitic Clinton ore. When an 

 ore formed in this way is elevated and inclined at such an 

 angle that surface water may work down through it, there is, 

 of course, a solution of the calcareous cement while the iron is 

 untouched and as a result the amount of iron is relatively 

 increased. Thus, above drainage level the ore becomes soft, 

 porous, and rich, while below, it remains hard and calcareous. 

 The character of an ore then depends, first, upon the amount 

 of iron originally deposited, and secondly, upon the amount of 

 lime removed by leaching. In many, perhaps in most, cases 

 where the ore is said to run into limestone below drainage 

 level, the limestone is decidedly ferruginous and is, in fact, a 

 lean ore, requiring only the removal of its lime to make it 

 available for working. 



Samples taken at the Eureka mine, Oxmoor, Ala., illustrate 

 well this relation. The ore at the surface is soft and porous, 

 while a specimen taken 158 feet down the dip is hard and 

 compact, showing cleavage faces of calcite. Subject the latter 

 sample to the action of water containing carbon dioxide, and 

 the result would be an ore indistinguishable from the surface 

 piece. When the ore is in a horizontal position, as in New 

 York and Wisconsin, and covered by a mass of rocks more or 

 less calcareous, it would seem doubtful if there has been even 

 this relative increase in iron. For by the time surface waters 



