THE STRATIGRAPHY AND STRUCTURE OF THE MESABI RANGE, MINNESOTA.

By David A. White '50. Minneapolis: University of Minnesota Press, 1954(Minnesota Geological Survey Bulletin 38.)92 pp. $2.50.

Since 1892, when iron ore was first shipped from the Mesabi, this northern Minnesota range has been one of the wellsprings of American prosperity and the largest iron-producing district in the world. Approximately two billion tons of Mesabi ore, averaging more than 50% iron, have been fed through the blast furnaces of Pittsburgh and Cleveland. This represents about 55 percent of the nation's entire production in the period since 1891. Reserves of high-grade ore are, however, virtually depleted, and the district faces a crucial period of conversion to the 5 billion tons of siliceous low-grade ore, or taconite, still remaining. Dr. White's book is a study of the geologic relations in the district, aimed at interpreting its geologic structure and history, and economic future, in terms of their relations to these remarkable Pre-Cambrian deposits.

After a description of the various rock units underlying the region, the knotty problem of the genesis of the iron ores is taken up. Consideration of the available evidence indicates that the iron ores were originally deposited in a marine environment, at some distance south of the deeply weathered regions and ancient shoreline which lay to the north. An understanding of the ancient geography makes it possible to predict that more ore may yet be discovered toward Lake Superior, but that areas to the west and north are generally unfavorable.

The detailed distribution and structure of the iron formations, which have been tilted southward subsequent to deposition, are shown on a series of eleven map sheets which have been constructed on the basis of detailed field mapping, and a study of more than 3000 drill holes. The economic value of these maps is obviously immense.

Dr. White has presented an excellent factual and interpretive study of an important mining region. Dartmouth shares, to some extent, in reflected glory, because, as the first sentence of "Acknowledgments" states, "The research on which this report is based was made possible by successive grants from Dartmouth College...."