From New York to Michigan to Wisconsin, Minnesota and down to the south in Iowa, Indiana, Kentucky and Ohio (and many more) we find deposits that are the remains of ancient tropical seas. Within these deposits, one can find corals. Solitary and colonial corals were abundant then much as they are in coral reefs today. Fossilization of these ancient corals is pretty particular but where they can be found fossilized, they exhibit outstanding detail.
Mother nature exposes these deposits as does the action of humans, building roadcuts, digging foundations etc. Even the last succession of Ice Ages has scoured the earth exposing vast deposits of fossils. People often ask where do I go in my state. I suggest joining a local rock club and getting a book for your state – Roadside Geology of ______. Get out and have fun……..not now most of the Midwest is under snow !!!!