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Stop 1. Thomson Dam. Rocks exposed at Thomson Dam include slates and greywacke of the Thomson Formation (Animike Group) which is about 1.9 billion years old. You will also see cross-cutting dikes of Keeweenawan age (1.1 billion years old). Sedimentary structures that we may see include concretions, soft-sediment deformation, graded beds, and cross-beds. Igneous structures include dikes which show columnar joints and chilled margins. Other structures we will see are anticlines, foliations, lineations and pseudo ripple marks.

Stop 2. Mission Creek. Here we see rocks of the Fond du Lac Formation. They are red shales and sandstones that are about 800 million years old. They are a result of sediments filling in the Mid-continent rift area after volcanism ceased. Here we will see cross-beds, ripples, shales and sandstone.

Stop 3. Bardon Peak. Rocks of the Duluth Complex are exposed at Bardon Peak. They consist of ophitic gabbro and layered troctolite with cross-cutting pyroxenite. The contact with the North Shore Volcanic Group is exposed at the far west side of the stop.

Stop 4. Lief Erickson Park, Duluth. Basalts, dikes, and interflow sedimentary rocks of the North Shore Volcanic Group. Basalts vary from porphyritic to massive, non-porphyritic.Tops of flows are recognized by sheeting joints, amygdules (with epidote and calcite), and rubbly weathering. Flow bottoms are massive and may contain pipe vesicles. In several places flows are separated by interflow sedimentary sandstone which varies from less than two inches thick to one unit that is 116 feet thick. This latter sedimentary rock displays trough cross-bedding. Dikes tend to be massive and very fine-grained and weather out in positive relief.

Stop 5. 42nd Avenue East, Lakeshore Lutheran Home. Contact between an icelandite flow and a pyroclastic flow which is a rhyolite in composition. Good sheeting joints seen on the top of the icelandite. The rhyolite shows pumice fragments. Both rocks are variably altered and are either a red in color or dark grey. Color is probably due to Fe oxidation and reduction.

Stop 6. 75th Avenue East, Lakewood Township Stop. A series of lava flows showing the contact between a vesicular rholite and a basalt. Structures seen include: vesicle cylinders, polygonal joints, vesicles, pipe vesicles, ropy lava and a small interflow sedimentary rock.