The Meter Reader: Early magnetic studies in the Lake Superior region

Abstract

In the mid-19th century, the quality of life in the United States was improving rapidly with widespread electrification of the nation and growth in the industrial revolution. These advances were dependent on the increasing availability of copper for instruments and electric wires and iron ore for the production of iron and steel. Accordingly, reconnaissance geologic investigations in the Lake Superior region of North America that discovered copper and iron-rich rocks in the 1840s rapidly attracted the attention of prospectors and mining companies. However, ore deposits were a challenge to find in this region because of superimposed geologic events and limited rock exposures due to the widespread cover of unconsolidated sediment deposited from Pleistocene glaciation, the abundant lakes, and, locally, the cover of Phanerozoic sedimentary rocks. Limitations to surface geologic mapping were evidenced by the few outcrops of iron formation in the iron ranges and the even fewer ore exposures. As a result, geologic mapping was restricted to locating regions for constructing test shafts and pits and drilling that would lead to identifying favorable mining sites.