Guidebook 3. Field Trip Guide Book for Precambrian North Shore Volcanic Group Northeastern Minnesota

Abstract

Detailed mapping of the 85th Minnesota shore of Lake Superior began with A. E. Sandberg's study (1938) of the section between Duluth and Two Harbors. Grout and Schwartz (1939) and Gehman (1957) studied the intrusions and flows in eastern Lake County; Grogan (1940) mapped the lakeshore between Two Harbors and Split Rock River; Schwartz (1949) studied the Duluth area; and Grout and others (1959) mapped most of Cook County. James Kilburg (1972) has recently mapped the wedge of lavas just west of Duluth. Most of the data reported in this account derive from studies by the writer who, starting in 1965, has mapped the shoreline between Silver Bay and Grand Portage, with considerable reconnaissance inland and to the southwest (Green, 1966; 1968a; 1968b; 1970). The report does, however, also lean considerably on Grout and others (1959) and, for the Duluth-Two Harbors area, on Sandberg (1938). The field studies have been supported by the Minnesota Geological Survey, and most of the laboratory studies have been .supported by the National Science Foundation (Grant No's GP-5865 and GA-134ll). Sincere gratitude for this support is extended to both agencies. The writer's ideas have benefited from discussions with many other geologists concerned with Keweenawan rocks, especially including Bill Bonnichsen, D. M. Davidson, Jr., H. Hubbard, G. B. Morey, W. C. Phinney, P. W. Weiblen, and W. S. White. Trip will leave Duluth and head up-section in the southwestern limb of the basin.