A series of pre-Cambrian metamorphosed sedimentary rocks extends from Rainy Lake, in western Ontario, eastward about 150 miles to the vicinity of Lac des Mille Lacs. The age of this series has been in dispute since the time of the early descriptions by Lawson (1887) and McInnes (1897). During the last decade the contributions of Grout, Bruce, Tanton, Hawley, and Gill have thrown new light on this perplexing problem, although the added facts and interpretations regarding the stratigraphic position of the sedimentary series often appear incongruous.

The sediments have been termed Seine and Coutchiching in age, depending upon whether they were believed to be stratigraphically above or below the Keewatin lavas. Inasmuch as the Keewatin is considered by most students of pre-Cambrian geology to represent the base of the pre-Cambrian column in the Lake Superior region, the determination of the stratigraphic position of the sedimentary and the volcanic series . . .

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