The park area sits astride the crest of the Cincinnati Arch, a convex tilting of bedrock layers caused by an ancient upheaval • Younger rocks lie both east and west of this crest where some of the oldest rocks in Ohio are exposed • The sedimentary limestones and shales tell of a sea hundreds of millions of years in our past which once covered the state • The park's excellent fossil finds give testimony to the life of this long vanished body of water