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Origin of Iron Ores Recent studies of the origin of the iron formations of the Lake Superior region, including those of Collins, Gruner, Hawley, and others yet unpublished, tend, on the whole, to show that the iron formations are inorganic chemical precipitates, that organic agencies have played a relatively small part, that volcanic sources have made notable contributions, and that normal processes of weathering have likewise been effective. All of these factors have been previously recognized, but now they can be more specifically identified. The studies of secondary concentration of the iron ores themselves have not changed earlier concepts of the processes. Correlations It has long been agreed that the Animikie of the north shore and the Gogebic iron-bearing series (“Upper Huronian”) are the same. In the past this has been correlated with the uppermost of the Huronian series in the remaining districts of the south shore, but it now . . .

THE PROBLEM From the beginning of history, nations have differed in their physical environments and therefore in their economic opportunities. Their activities have been influenced and limited by climate, soil, topography, and accessibility. Only in the last century have mineral resources loomed as an important element in man’s environment because they were not used on a large scale until the Industrial Revolution. The world’s mineral supplies are large enough for all if they were equally distributed among the nations, but unfortunately they are not. Nations favored by their possession of mineral supplies necessary for industrialization are the ones which in modern times have taken a commanding position in world affairs. Military power is coming more and more to be measured in terms of guns, ships, automobiles, and airplanes, rather than by man power alone, and these implements are in turn limited by the capacity of the industrial plants and the . . .

From abstract: Detailed knowledge of the geology of the pre-Cambrian rocks of the Lake Superior region has been greatly augmented since the publication of Monograph 52 by the United States Geological Survey in 1911. The authors have attempted in the present report to assemble as much of this new information as possible, and to give the reader a birdseye view of the geology as seen in the light of all studies made there up to the present time. Detailed descriptions are not presented, and the emphasis is placed upon the major problems of correlation. A revised map of the region, with cross sections, accompanies the report, bringing up to date a knowledge of the areal geology of the region, which otherwise could be gained only by consulting some 150 maps contained in almost as many separate local reports, many of which are unpublished.

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rT HE quest of iron and copper and flint for use as weapons, and of gold and silver and precious stones for adornment, runs far back into history and is associated with many stirring events of exploration and war. But they were used on a relatively small scale and served only as a minor factor in the environmental conditions controlling human activities. With the advent of the industrial revolution of England, a century ago, began the real exploitation of earth materials in a way to in fluence essentially our material civilization. In this short time, at an ever accelerating rate, minerals have become the fundamental basis of industrialism, to be ranked with soil, climate, and other major influences on our activities. In these hundred years the output of pig iron has increased ioo-fold, of mnineral fuels 75-fold, and of copper 63-fold. In the last fifty years the per capita con sumption of minerals in the United States has multiplied fifteen times. By harnessing up the power from coal, gas, and water we have multiplied our capacity for work. The acceleration of the rate of mineral exploitation may be realized from the fact that the world has exploited more of its resources in the last twenty years than in all preceding history. In appraising the effect of this new element in human environ ment we have no historical precedent to guide us, for the change is too recent, too all-pervasive, for us to understand all its signif icance. Yet a few clear tendencies are beginning to be discernible. The rising use of mineral resources has naturally led to an in tensive search of the earth for adequate supplies, which is just beginning to give us some realization of their ultimate geographic distribution. Changes will still be made by discovery, usually in expected fields, but the main outlines are now pretty well fixed. The curve of geographic discovery is falling. The great discoveries of the future will in the main relate to better methods of recovery and use. As the insatiable appetite for minerals has risen, many sources of supply which formerly were adequate are beginning to look relatively small. As the demand multiplies, the sources known to be capable of meeting it become proportionally fewer. In short, it is being realized that nature has concentrated the really big sources of supply, adequate to meet present and future