 Elongated lakes lie in many of these depressions.To the south near Lake Superior, rock strata of the Duluth and Beaver Bay complexes are interspersed with and underlie the extrusive rock of the North Shore Volcanic Group.The Beaver Bay Complex occupies the center of the North Shore Volcanics, and is slightly younger in age than the other mafic rocks of the Duluth Complex, dating from c. 1096 mya.