1) However, the floor of the Atlantic is becoming fairly well known as a result of special surveys since 1920.
2) The topography of the ocean floors is none too well known, since in great areas the available soundings are hundreds or even thousands of miles apart.
3) A broad, well-defined ridge-the Mid-Atlantic ridge-runs north and south between Africa and the two Americas.
4) Numerous other major irregularities diversify the Atlantic floor.
5) Closely spaced soundings show that many parts of the oceanic floors are rugged as mountainous regions of the continents.
