In Michigan the western limb of Lake Superior is a sequence of rock layers. with mostly black lava flows (a formation called the Portage Lake Volcanics) underlying a layer of reddish sedimentary rocks. These rocks are the dark colored ones on this diagram.
The idea of a syncline comes from observed features in geology--like the one in the picture to the right, from a photo by Kimberley Motz in the Canadian Arctic. In the Keweenaw we cannot see the whole syncline--far from it! We just see the rocks dipping toward the North at Copper Harbor and those dipping to the South on Isle Royale. In between is how geologists earn their money!
Do you believe there is a syncline between Isle Royale and the Keweenaw? There are some ways to test this idea:
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1.Are the layers the same on each side?
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2.Is there any evidence that the layers connect?
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3.Is it reasonable that a syncline would form?
Implications of this Hypothesis: 1. Layers of rock extended from the Keweenaw to Isle Royale, apparently filling a basin. 2. Something caused the basin to subside. 3. The basin has influenced the formation of Lake Superior. 4. The basin may continue beyond the lake. 5. Its importance could extend much farther than explaining the tilting.
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Syncline
