The rocks of western Ontario have been more or less carefully examined by several geologists, such as Bigsby, Bell, and Dawson, but the first detailed mapping of the region was done in 1883 and succeeding years by A. C. Lawson, who laid an excellent foundation for the future study of the Lake of the Woods and Rainy Lake districts.* Since then adjoining districts have been mapped by W. H. C. Smith and W. McInness, and special portions have been studied by H. L. Smyth, Winchell and Grant, and the present writer. The general conclusions reached by Lawson have been commonly accepted by those who have followed and will be made use of largely in the present paper, though most of the facts employed have been observed by the writer while engaged in field work for the Ontario Bureau of Mines.
Classification of the . . .