490 C. 11. Smyth. Jr. — Clinton Iron Ore. 



• the layers of silica and iron are often so dense and impervious 

 that hydrochloric acid cannot dissolve all of the iron present. 



Further, it is difficult to account for the present chemical 

 condition of the ore on the substitution theory. This theory 

 postulates that the iron is taken into solution in the overlying 

 rocks by circulating waters containing organic matter. The iron 

 would thus be brought to the limestone in the form of carbon- 

 ate and would be precipitated in that form. In highly tilted 

 strata it is easy to see that currents of water coming more 

 directly from the surface, along the dip, might contain oxygen 

 instead of the products of organic decomposition and thus cause 

 the precipitation of the iron as hydrated oxide, or convert to 

 that form a previously precipitated carbonate, as described by 

 Professor Yan Hise in his paper on the Marquette ores.* 

 But when, as in New York State, the strata are horizontal, 

 such an explanation will not suffice. Yet in no case has there 

 been seen anything to indicate that the ore was once a carbon- 

 ate. If this ore was once a carbonate, what agent has so com- 

 pletely altered it to the peroxide ? 



The character of the overlying rocks presents another stum- 

 bling block in the way of replacement. Both shales and 

 sandstones are very calcareous. It is difficult to understand 

 why meteoric waters should dissolve iron from some calcareous 

 strata and deposit it in others lower down. The two actions 

 are incompatible. As a matter of fact, the waters that soak 

 through these overlying ' rocks are so heavily charged with 

 carbonate of lime that they deposit it wherever there is an 

 opportunity, and layers of calcite are abundant on outcrop- 

 ping ledges and in small veins. How can such water be the 

 bearer of iron salts that are supposed to be precipitated by 

 lime carbonate at a lower level ? There is nothing to indicate 

 that the percolating waters have not always been thus charged 

 with carbonate of lime. 



The character and relations of the so-called " bottom tier " 

 are of interest. If it be a substitution product, the iron must 

 have passed through the two-foot bed of rich ore and the one 

 to two feet of shale separating the two beds. This shale is so 

 hard and dense that it would seem almost impervious to water. 

 Any iron-bearing solution which may have passed through 

 this rock must have done so very slowly and the conditions for 

 the complete replacement of calcite were most favorable, and 

 yet there is some five per cent of calcite still present and no 

 indication of replacement. The " bottom tier " ore is quite 

 lean, about thirty per cent iron, but this is due to an increased 

 percentage of silica, rather than of lime. It is, in fact, a fer- 



* C. R. Yan Hise : The Iron Ores of the Marquette "District of Michigan : this 

 Journal, III, xliii, p. 116. 



