ORES OF THE AZOIC BELT ON LAKE SUPERIOR.
The iron ores of this region are truly wonderful in extent, and though but partially developed, enough ore is known to exist to supply the entire demands of the United States—if available—for many centuries to come. In fact, the ores of the great basin, if only confined to the Azoic belt, seem to be on a scale of equal magnificence with its inexhaustible beds or fields of coal. But when we come to consider the ore deposits of the succeeding rocks, the Valley limestones, the Devonian formations, and the stratified beds of the Carboniferous periods, we may be surprised at their combined magnitude, and exult in the future greatness to which our country may attain with such unlimited resources at command.
There is much diversity of opinion among geologists as to whether the great magnetic deposits should be denominated veins or beds. Some contend that they are the direct results of volcanic agencies, and that those "veins" of magnetic ores were ejected from the bowels of the earth in a fluid and molten state; while others contend that all pro ductive magnetic ores are stratified in beds.
It is scarcely possible that we could expect the same uniformity of strata among the deposits of the Azoic rocks, which are often distorted and recline at all angles in rela tion to superstructure among themselves. But, to a certain extent, it appears evident
that most of the productive magnetic masses are the results of precipitation, as described in the commencement of this chapter; and the order of stratification in which the beds of Lake Superior exist seems to confirm this view.
Figure 170 represents the order in which the ores of this region exist, evincing as plainly as possible a uniform stratification. The rocks which are intercalated with the ores are of volcanic origin, and though not now reposing in the form of dikes, they are true volcanic rocks, disintegrated by coming in contact with water while in a molten condition.
It may be noticed that the ores of this region are various, and consist of black oxides, specular ores, red.oxides, brown hematites, &c. The brown hematites appear, however, to be the upper ores, and resulted, undoubtedly, from the oxidization of the lower ores, and the contact of hot water holding carbonic acid and other chemical agents in solution.
This region lies in the Azoic belt, and the ore beds exist in its upper limits, near the base of the Potsdam sandstone, the position being geologically and lithologically the same as the magnetic range of North Carolina and New Jersey and cotemporary with the same belt in Missouri and Sweden.