Feulner, while mapping the bedrock of Clayton county during the summer of 1951, observed numerous large chert erratics scattered over the landscape west of Strawberry Point. These erratics lie near the edge of the Iowan drift plain just south of the northfacing Niagaran escarpment, which is formed by the erosion of Silurian rocks.
Proceedings of the Iowa Academy of Science
©1956 Iowa Academy of Science, Inc.
Tuttle, Sherwood D.; Fuelner, Alvin J.; and Northup, Richard C.
"A Massive Chert Bed in the Hopkinton Formation and an Associated Boulder Train Near Strawberry Point, Clayton County, Iowa,"
Proceedings of the Iowa Academy of Science, 63(1), 435-438.
Available at: https://scholarworks.uni.edu/pias/vol63/iss1/43