150 ANNALS NEW YORK ACADEMY OF SCIENCES 



admit that these fragments and grains are corroded, we must also admit 

 that solvent waters were present at some time in these artesian runways. 



We are not dependent, however, upon this one bit of evidence. The 

 penetration of iron for short distances into slightly porous contact layers, 

 with a progressive thinning out of the iron (Plate XX, fig. 3), until 

 within a short distance from the line of (Toi^tact penetration and precipi- 

 tation altogether ceased ; the filling of the seams caused by cross-bedding, 

 mudcracks (Plate XVIII), sand streaks in the shale, fractures and places 

 of weakness, all point to precipitation from penetrating solutions. Cav- 

 ernous consolidation in loose sand layers (Plates XI, XII, XIII), filling 

 of corrosion embayments in nuclei (Plates XVI, XX, XXI), widespread 

 replacement in all stages of completeness of calcite and in some cases of 

 quartz by iron, and the secondary calcite, iron and to some extent silica 

 cementation of the iron-coated fragments, all add to the certainty of the 

 filling of these retaining layers or catch basins with artesian waters. 



Thus we must conclude that all the factors necessary for complete 

 artesian conditions existed in the Clinton strata; that much evidence has 

 been adduced that these natural artesian runways were well filled with 

 ferruginous solutions, and finally that these solutions were responsible 

 for the present mineral content of the ore seams. 



Ore Conditions Besulting from Aetesian Slopes 



DEPTH of deposits 



The only downward limit under this theory would be the limit of the 

 artesian flow. As artesian wells have been sunk in some cases to more 

 than 4,000 feet, and as artesian conditions would seem to be as perfect in 

 the Clinton strata as could be expected anywhere, it appears to the writer 

 at least that the only limit of ore deposition would be the seaward ex- 

 tremity of the porous strata, and that this limit might well be expected 

 in many places to extend to at least as great depths as any artesian well 

 known at the present time. 



That borings in Birmingham. Alabanui, have demonstrated the exist- 

 ence of good ore at 1,902 feet would appear to bear out the writei-'s con- 

 tention that the iron content of the seams should extend to great depths 

 with little or no change in richness within the hard-ore limits and that 

 this condition would be found wherever the proper artesian factors along 

 the marine slopes existed. In Holt County, Missouri, a borehole 1,885 

 feet showed good ore at that depth and favorable artesian conditions be- 

 cause of the impervious overlying and underlying beds (66, p. 148). 



