Hanging Rock: A Relic of Ancient Seas (GM-12)
In the Great Lakes region of North America, a belt of marine reefs was developed in the Silurian seas more than 400 million years ago. Many of these reefs are 100 to 400 feet thick and as much as a mile in diameter.

Hanging Rock, 84 feet above the Wabash River about a mile southeast of Largo, is a remnant of a huge reef.

Reefs in several Hoosier counties in the Wabash Valley contain the only rock suitable for high-quality aggregate. In many places outside Indiana where buried reefs are uncased in impermeable strata, oil and gas are found within the porous reef rock, but in Indiana all petroleum produced to date from reef-induced traps has been found in permeable strata above the reefs.

Pioneer studies of reefs, internationally recognized, were done in Indiana in the 1920's by E.R. Cummings and Robert R. Shrock, and the Indiana Geological Survey is currently active in reef research.

Our Hoosier State Beneath Us: Geomorphology


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