i882. 7 Trans. N. Y. Ac. Sci. 



and coincidence with the bedding planes, separate the ore bodies of 

 crystalline character from recent deposits formed in this way. 



7. Derivation from deep-sea deposits. — The form and structure of 

 the nodules in the ooze differ widely from those of the ores under dis- 

 cussion, while the strata associated with the latter are evidently shal- 

 low-water deposits. 



8. The metamorphism of ancient bog-ores. — This theory, now com- 

 monly accep^ted and taught in all the text-books, is unsatisfactory, from 

 the absence of evidence, within the crystalline strata, of any terres- 

 trial or subaerial surfaces on which such bogs or marshes could have 

 rested ; all the surfaces appear to be submarine. 



Two theories of mechanical origin remain yet to be considered : 



9. Violent abrasion and transport, by volcanic agencies combined 

 with powerful currents. — To this it has been properly objected that 

 the results of such violent agencies would be altogether conglomentic. 



10. Concentration and metamorphism of iron-sands. — Abundant 

 instances of such concentration are shown along our coasts, and the 

 deposits found along the St. Lawrence often contain but five or six per 

 cent, of siliceous impurity. As the loose sands so concentrated 

 consist at various localities of quartz, garnet, chrysolite, menaccanite, 

 magnetite, etc., so we find in the metamorphic rocks their indurated 

 counterparts, quartzyte, garnetyte, dunyte, menaccanyte, magnetyte, 

 etc. The intermixture of garnet with magnetite, or its intercalation 

 in separate alternating beds, is as common in the rocks as in the pres- 

 ent oceanic sands. The thin interlamination of magnetite, martite or 

 hematite with jasper, in the Huronian jasper-schist, corresponds to the 

 still more frequent association now found along our sea-beaches. The 

 abundance of ore beds of pure magnetite, free from apatite, in the strata 

 of the Lower Laurentian of Ontario, and of menaccanite, more or less 

 mixed with the other ore, in those of the Upper Laurentian of Quebec, 

 Canada, appear to correspond with the general distribution of magnetite 

 grains through the gneisses of the former, and grains of menaccanite 

 through the anorthosites and traps of the latter formation. In bog 

 ores no concentration of titanic acid has ever been found ; its abun- 

 dance in the form of menaccanite seems to necessarily involve a me- 

 chanical origin, and a vast source of that mineral is presented in its 

 form of fine distribution through the rocks mentioned. 



DISCUSSION. 



, Dr. J. S. Newberry said that he would not claim that the chemical 

 theory best explained the origin of all bodies of iron ore, but, he 

 thought, it was applicable to most. It was not limited to mere terres- 

 trial deposits like bog ores, but equally well accounted for marine 



