Small hills found only in the deep sea which rise from the ocean basin floor with heights ranging from 10 to over 500 feet and widths from a few hundred feet to a few miles. They are found along the seaward margin of most abyssal plains and originate from the spreading of mid-ocean ridges. As such, they usually form two strips parallel to mid-ocean ridges. They generally decrease in height as one traverses away from the ridges as they gradually become covered with sediment and are replaced by abyssal plains.