EARLE, INTERBEDDED IRON ORE DEPOSITH 125 



interested in the financial success of the various properties naturally 

 lean for the most part to the theory that will best support their conten- 

 tion that the richness of the ore body will not diminish with depth. The 

 views maintaining this contention seem to be well sustained in certain 

 places by some of the facts developed in the course of actual mining 

 operations. In other localities, however, data appear to contradict this 

 view to some extent. 



A theory which would apply to all of the Clinton deposits must ac- 

 count for the oolitic character of some ores and the fossiliferous charac- 

 ter of others, for the occurrence of the ores in conformable strata, for the 

 difference in lime and silica content in the various ore beds and within 

 the same bed, for the presence of waterworn pebbles and grains of sand, 

 for the soft and hard ores so common in the southern localities and for 

 the compact and cleavable ores of some of the northern deposits. To 

 find a theory that will reconcile all of these variables has thus far been 

 impossible, and most writers have admitted that to a limited degree 

 other theories besides their own may have some value. 



Three principal hypotheses have been advanced to account for these 

 Clinton ores: (1) the theory of original deposition, which has been 

 referred to as the sedimentary theory; (2) the residual enrichment 

 theory; (3) the replacement theory. Of these theories, the first has the 

 greatest number of advocates. It has the merit that depth would not 

 affect the value of the deposits. 



PRIMARY DEPOSITION 



The advocates of the primary deposition theory believe that the Clin- 

 ton ores were deposited contemporaneously with the inclosing rocks, in 

 the form of chemical precipitation at the bottom of the sea. Some 

 claim that the iron was originally dissolved from the ancient crystalline 

 and metamorphic rocks of Appalachia Land. The ferruginous waters 

 were carried into inclosed or partly inclosed shallow seas or basins. The 

 iron salts were slowly oxidized and precipitated gradually, fonning con- 

 centric layers of iron about particles of sediment on the sea bottom. As 

 the sediments varie'd in kind and texture in different places and at dif- 

 ferent times, the nuclei about which the iron concretions wore formed 

 differed. In some layers, the oolitic structure surrounded grains of well- 

 rounded quartz sand ; in other layers, broken fragments of fossils such as 

 crinoid stems, brv'ozoans, brachiopods or corals were inclosed in iron 

 concretions. It is claimed by some that where calcareous fossils were 

 present, some replacement occurred, but only while the process of original 

 sedimentation was in progress. 



