This collection is useful to non-professionals who simply wish to learn more about the geology of the county. It is not intended to be a one-stop, comprehensive collection. It is useful to anyone with an interest in earth science or the county.

The rock outcrops in northern St. Louis County expose a part of the earth’s crust that is considered to be an Archean (2.7 billion-year old) greenstone belt. Greenstone belts contain the products of ancient volcanism, deep ocean deposition and igneous (granite) intrusion. The area has a rich history of geologic investigation. Because the rocks are well exposed, the geology of the area has been the model against which other greenstone belts in Canada and elsewhere have been compared. The exposures allow geologists to make detailed interpretations of how the rocks were deposited and how they were deformed.

St. Louis County, Minnesota Bedrock Collection.

It can be argued that nowhere else in the state is geology such an integral part of the natural landscape as along the rocky North Shore of Lake Superior. Southeastern St. Louis County is where it all starts. Both the St. Louis Bedrock Collection and the Cook County Gunflint Trail Collection are intended to give an introduction to that geology.

The rocks of the southeastern part of the county tell the story of an aborted attempt by the North American continent (Laurentia) to break apart about 1,100 million years ago. Some of the layers of lava deposited at this time are known as the North Shore Volcanic Group. Macro photos of secondary minerals that fill large cavities in those lavas are to the left.