Wisconsin. Chief Geologist / Geology of Wisconsin. Survey of 1873-1879 ...
Volume IV (1882)
Chapter II. Theoretical deductions, pp. -553 PDF (13.0 MB)
CHAPTER II. THEORETICAL DEDUCTIONS. The characteristic facts relating to the associated lead, zinc, iron and copper deposits of southwestern Wisconsin, having been now de- scribed, it remains to consider what theoretical views can be held con- sistently with the facts, what explanations can be offered for the special phenomena presented, and what practical inferences may be drawn. While there may not be, at the present time, any marked disposition among competent geologists to differ widely as to the origin of these ores, a somewhat greater diversity of views was entertained by earlier investigators; and, among parties financially interested in these resour- ces, a still wider rangoe of belief yet prevails. It is felt to be obligatory therefore, to briefly consider such views as are rejected, and assign reasons for so doing. I. REJECTED HYPOTHESES. 1. Rypothesis oJ sublimnation. According to this theory the ores in question were deposited by heated vapors rising from below. Its advocates appeal to the fact that galena is sometimes found in the crevices of smelting furnaces and similar situations, where, it is claimed, with undoubted correctness, that it must have been formed fromn the penetration of gases; and to the wider range of facts ob- served in connection with volcanic vapors and steam vents. That ores are formed, in certain situiations, fron vapors is admitted as scarcely debatable in the present state of knowledge. But the vital' question is, whether those under consideration were so formed - whether the whole assemblage of facts now before us, will sanction such a view. It is essential to an affirmative answer to suppose (1.) that the whole group of mingled ores were vaporized, (2.) that this was done to somne considerable extent simultaneously, (3.) that these hot vapors arose through all the strata lying between their present situation and their source in rocks heated to the temperature necessary to volatiliza- tion, (4.) that they were then condensed in the manifold forms and
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