The region under consideration has been termed the Northern Sub-province of the Lake Superior pre-Cambrian. It is largely contained on the Kenora Sheet, Map No. 266A of the Geological Survey of Canada, though its natural boundaries lie outside the map limits. These might be considered to be the Mesabi Range on the south, the Lake Superior and Lake Nipigon basins on the southeast and east, the heavy cover of Quaternary clays and silts of the Lake Agassiz plain on the west, and an arbitrary line along Parallel 52, which separates approximately the area of more-detailed mapping from that of reconnaissance and exploratory surveys (Pl. 1). The region thus outlined is slightly larger than the State of Illinois. The bedrock, so abundantly exposed as a result of Pleistocene glaciations, consists, in the main, of granite, granite-gneiss, and related rocks, volcanic flows and pyroclastics, and sediments of . . .