deepest point in the Atlantic Ocean, lying at a depth of 27,493 feet (8,380 m) about 100 miles (160 km) northwest of the island of Puerto Rico. It lies within a submarine depression called the Puerto Rico Trench, located at the southern edge of the North American Basin, between the Puerto Rico Ridge (north) and the North Antillean Arc (south); it is about 7,000 feet (2,100 m) deeper than the adjoining basin floors. The Milwaukee Depth is named after the first ship that sounded it. Its bottom is covered with mud, sand, rock, and shells.