Bottom (Nature of) : The composition or character of the bed of an ocean or other body of water (e.g., clay, coral, gravel, mud, ooze, pebbles, rock, shell, shingle, hard, or soft)
Intergovernmental Oceanographic Commission IOC technical series 37, Tsunami Glossary (A glossary of terms and acronyms used in the tsunami literature - English), , United Nations Educational, Scientific and Cultural Organization UNESCO, Paris, France 1991. http://unesdoc.unesco.org/images/0008/000885/08853 8eb.pdf, (ND/ Tsunami Sci - Brit) {590}