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A Geological Map of Wisconsin

Increase A. Lapham

Beneath the Surface
The first fully detailed map of Wisconsin’s geology reveals the structures that formed Door County’s limestone cliffs—and, far off this map, Niagara Falls.

Increase A. Lapham, a noted Wisconsin naturalist, scientist and conservationist, produced and signed this map. It was based in part on the work of U.S. geologist David Dale Owen, who had published a geological survey of Wisconsin and other states earlier in the century. However, Owen’s work only showed the position of certain geological features; he did not attempt to connect these features nor show the bedrock of the state under every point, as does this map.

Lapham’s map illustrates the Niagara Escarpment (light blue), a dominant feature of the otherwise gently sloping Lake Michigan shoreline. In Wisconsin, it is most evident in the exposed limestone cliffs of Door County before it dips underground further south along the Lake Michigan shore. Those cliffs supplied the stone for many a harbor improvement. Probably the most famous outcropping of the escarpment bedrock is the spectacular 193-foot-high Niagara Falls, where waters from Lake Erie plunge toward Lake Ontario.