For nearly forty years the so-called Coutchiching problem has been discussed by geologists working in the boundary area between the United States and Canada west of Lake Superior. The question has been the existence of any great mass of sedimentary material beneath the volcanics, to which Lawson gave the name of Keewatin in his report on the Lake of the Woods district. In most cases the arguments have dealt with accuracy or inaccuracy of field observations. In the heat of discussions it seems generally to have been forgotten that both the sediments, which all geologists agree are present, and the lavas of the generally accepted Keewatin series are formations individual members of which could not be expected to have a great lateral extent, since the sediments are terrestrial in character and since a single lava-flow can necessarily not extend to any great distance from the vent. If these facts . . .