saddle—a low part, resembling in shape a saddle, in a ridge or between contiguous seamounts. 
seachannel—a continuously sloping, elongated depression commonly found in fans or plains and 
customarily bordered by /evees on one or two sides. 
seamount—an elevation rising generally more than 1,000 meters and of limited extent across the 
summit. 
shelf—a zone adjacent to a continent (or around an island) that extends from the low water line 
to a depth at which there is usually a marked increase of slope towards oceanic depths. 
shelf valley—a valley on the shelf, generally the shoreward extension of a canyon. 
shoal—a hazard to navigation with a depth of 20 meters or less, composed of unconsolidated 
material. 
sill—the low part of a gap or saddle separating basins. 
slope—the slope seaward from the shelf edge to the beginning of a continental rise or the point 
where there is a general reduction in slope. 
spur—a subordinate elevation, ridge, or rise projecting outward from a larger feature. 
tablemount (or guyot)—a seamount having a comparatively smooth, flat top. 
lerrace—a relatively flat horizontal or gently inclined surface, sometimes long and narrow, 
which is bounded by a steeper ascending slope on one side and by a steeper descending slope 
on the opposite side. 
tongue—an elongate (tongue-like) extension of flat sea floor into an adjacent higher feature. 
trench—a long, narrow, characteristically very deep and asymmetrical depression of the sea floor, 
with relatively steep sides. 
trough—a long depression of the sea floor characteristically flat bottomed and steep sided, and 
normally shallower than a trench. 
valley—a relatively shallow, wide depression, the bottom of which usually has a continuous gradient. 
(This term is generally not used for features that have canyon-like characteristics for a 
significant portion of their extent.) 
The terms arch and arrugado have not been incorporated in the above list, but they do appear in 
the names Hawaiian Arch and Guadalupe Arrugado which have been approved by the BGN on the 
basis of the names’ established usage. The two names have not been given designations in this gazet- 
teer. Hawaiian Arch is a low bulge around the southeastern end of the island of Hawaii, and 
Guadalupe Arrugado is an area of subdued corrugations. 
Name proposal form 
Undersea name proposal forms are provided in this publication to facilitate submittal and expedite 
approval and promulgation of names. Anyone may propose a name for an unnamed undersea feature 
that has been adequately identified as to type and geographic location. 
Users are encouraged to submit a separate form for each name proposed, copying the form if 
necessary, and filling in all the blanks that are pertinent. They should give coordinates of latitude and 
longitude taken at the approximate center of the feature and read closely enough to sufficiently identify 
the feature. Additional coordinates for extremities of large features are helpful. 
For “‘kind of feature,’’ use the appropriate term from the list of terms and definitions in this gazet- 
teer. This term should be used also as the generic term in the name. If the feature is of a kind not 
covered by these terms or definitions, explain in a supplementary note. 
1x 
