Hard Canadian shield, metamorphic rock with large, sharp fractures but few cracks. Brittle but strong.
Highway 11 north of Toronto for 6 hours. Left down Temagami Lake access road. Park, take a boat to the western shore at the portage trail to Skunk Lake. Paddle across Skunk Lake then portage to Gull Lake. Paddle north through the choke. Cliffs on east side of lake.