Fossiliferous Devonian Limestone - The Window on Iowas Ancient Tropical Seas. The corals and sponges that dominate the fauna of local limestones belong to biological groups living today only in the shallow marine tropics. Diverse evidence shows that these limestones formed 375 million years ago in shallow warm water seas. The limestone here was donated by River Products Company of Iowa City, Iowa just upstream from where you are standing today.
Plaque on the right reads:
In 1866 workers exposed coral formations while digging the foundations for the woolen mill near the dam. The same year Louis Agassiz traveled by train to Iowa City, the end of the rail line, to study the Midwestern glacial deposits. He was scheduled to lecture on "Glaciers" to the university community. However, the afternoon before the lecture, he was taken upstream on the Iowa River to view the local limestone. That evening he surprised his audience by lecturing on the "Coral Reefs of Iowa City." One week after the lecture on December 19, 1886, the formal name of "Coralville" was documented in the State Press of Iowa City, "A new town was born into this winter weather last week, up at the woolen mills, and was christened "Coralville."