EARLE, INTERBEDDED IRON ORE DEPOSITS 155 



iron-bearing waters, deriving the necessary solutions from the old grani- 

 toid and schistose rocks, found their way down these natural runways. 

 The water probably contained considerable carbon dioxide (CO2) and 

 thus, because of its own nature, aided by increasing pressures and tem- 

 peratures, became an active solvent, until it reached the saturation point; 

 it then became a depositional agent and began to deposit. The iron salts 

 were probably the first ingredients to be given up; then followed other 

 constituents, such as secondary calcite and silica which form a prominent 

 part of the final deposits. 



The solid particles which were not entirely dissolved from the original 

 constituents of the porous layers, and which included in many cases large 

 numbers of quartz grains, became centers for the segregation of iron. 

 These quartz grains were therefore first corroded to a varying extent and 

 then protected from further corrosion by layers of iron and in some cases 

 secondary silica. Finally, the remaining pore space was filled in by sec- 

 ondary calcite, sometimes mixed with iron. In a large number of cases, 

 the iron replaced both calcite and quartz. This is well shown where the 

 iron has worked its way into microscopic cracks and gradually clouded 

 the quartz and other nuclei and in many cases actually replaced it. 



The artesian contacts are fairly clean, as would be expected, the shales 

 and clays furnishing the cleanest of the contacts except those forming 

 along fractures. Where such breaks occur in the inclosing layers, they 

 are filled with streaks of iron ore. The iron appears to follow fractures 

 and other such planes of weakness as lamination or stratification planes. 

 Iron also fills mud cracks and other holes and porous places left in the 

 shales and other contact layers. 



"Where iron has penetrated a short distance into the inclosing layers, it 

 appears as though much pressure had been exerted upon the solutions. 



Depth, extent along the dip, wide distribution, differences in composi- 

 tion, texture and richness, all can be accounted for under this theory 

 without the necessity of appealing to special conditions, unique for this 

 particular period. Under the artesian theory, deposits were probably 

 made with the usual deliberateness characteristic of natural processes of 

 deposition. It is entirely posssible that the time consumed in the com- 

 plete filling of these artesian runways with ore was many times longer 

 than. the time taken for the deposition of the sediments that composed 

 the original Clinton layers. 



Finally, imder the Artesian Eeplacement Theory-, the genesis of the 

 iron ores shows an interesting similarity in many ways to that of origin 

 of the Lake Superior hematites and magnetites. 



