The Keweenawan lavas of the Lake Superior district form the inner border of the Lake Superior syncline. They crop out over an area of several thousand square miles, and in one section on Keweenaw Point, Michigan, form a series with a minimum thickness of 15,000 feet (the lower horizons not being known because of faulting). Individual flows vary from gushes a few inches in thickness to The Greenstone flow with a maximum known thickness of 1300 feet. Hundreds of flows are known in various sections, some of them having marked characteristics which enable them to be identified and traced for forty miles or more along the strike and which present, as A. C. Lane suggests, strong evidence for the correlation of individual flows from Keweenaw Point on the south limb of the syncline to Isle Royale on the north limb, a horizontal distance of over fifty miles. Little evidence . . .