The continental margin is that part of the ocean floor at the edges of the continents and major islands where, just beyond the shoreline it tapers gently into the deep sea. The continental margin is made up of the continental shelf, the continental slope, and the continental rise.

The continental shelf begins at the shoreline. It is flat and its width varies. For example, off the Arctic coast of Siberia it is 800 miles (1,280 kilometers) wide. However, there is no shelf off southeastern Florida. Rich sediment (particles of soil and decaying matter) from rivers that flow to the sea filters down to the shelf. Over time, deposits of these sediments may become many thousands of feet...