Complex sentence: Saint Anne's Shrine is located on the island, which is known for its quarries of gray or black fossiliferous limestone from the Late Cambrian and Ordovician Chazy Formation, the oldest known coral reef on Earth.
Split into simpler sentences: Saint Anne's Shrine is located on the island. The island is known for its quarries of gray or black fossiliferous limestone from the Late Cambrian and Ordovician Chazy Formation, the oldest known coral reef on Earth.