A glacier covered the land bordering an ocean. Sand, mud, and boulders were deposited by the glacier. Over time, the climate grew warmer and the area became part of a beach. Layers of sand were deposited. Then, the sea level began to rise, and the area became a shallow part of the ocean. A coral reef formed on top of the older sediment. Sediment made mostly of the shells of marine organisms was deposited. When the sea level rose even further, the area became part of the deep ocean and mud was deposited.