1681 HYDEOGRAPHIC MANUAL PaGE 54 



generally comprise features of specific navigational importance as well as a few coastal 

 and inland features, the terms for which heretofore have been used in a loose, confusing 

 manner. The common terms referring to embayments and streams are often used 

 locally with specific meaning applicable only in that region. From the standpoint of 

 regional uniformity, it is often advisable in specific instances to follow such local or 

 regional usage. 



1681. Primary Features 



a. Marginal continental features: 



BANK. — A detached, broad, and relatively shallow area on the continental shelf or in greater 

 depths, not constituting a danger to navigation in itself, but from which may rise a reef, shoal, or 

 other secondary feature, which is a danger to navigation. (See Bank in 1682.) 



CONTINENTAL SHELF. — The zone, of the submerged continental margin from the coast 

 offshore to the continental slope (in depths of about 100 fathoms). 



CONTINENTAL SLOPE.— The declivity from the offshore border of the continental shelf 

 at depths of approximately 100 fathoms to oceanic depths. It is characterized by a marked increase 

 in gradient. 



INSULAR SHELF. — The zone of the submerged margin of an island or group of islands from 

 their coasts offshore to the insular slope (in depths of 50 to 100 fathoms). 



INSULAR SLOPE. — The declivity from the offshore border of the insular shelf at depths of 

 50 to 100 fathoms to oceanic depths. It is characterized by a marked increase in gradient. 



6. Deep-sea depressions: 



BASIN. — A large submarine depression of a general circular, elliptical, or oval shape. 



DEEP. — The well-defined deepest area in a submarine depression. 



DEPRESSION. — A general term signifying any depressed or lower area in the ocean floor. 



DEPTH. — The maximum sounding measured in a deep. 



FOREDEEP. — A deep, elongated depression fronting a mountainous land area. (A geologic 

 term which can include a submarine trench or trough.) 



TRENCH. — A long and narrow submarine depression with relatively steep sides. (Converse 

 of ridge.) 



TROUGH. — A long and broad submarine depression with gently sloping sides. (Converse of 

 swell.) 



c. Deep-sea elevations: 



PLATEAU. — An elevated feature having an extensive flat top, usually with rather steep side 

 slopes. 



RIDGE. — A long and narrow elevation with steeper sides than those of a swell. (Converse of 

 trench.) 



SEAMOUNT. — A submarine mountain rising more than 500 fathoms above the ocean floor. 

 (See Knoll in 1682.) 



SWELL. — An extensive long and broad elevation which rises gently from the ocean bottom. 

 (Converse of trough; supersedes former term rise.) 



1682. Secondary Features 



a. Embayments (application of specific terms varies with locality) : 



BAY. — An extensive arm of the sea which is usually smaller than a gulf. 



BIGHT. — A small open bay formed by an indentation in the coast; a minor feature which 

 affords little protection for vessels. 



COVE. — -A small sheltered recess in a shore or coast, generally inside a larger embayment. 



HARBOR. — A natural or artificially improved body of water providing protection for vessels, 

 and generally anchorage and docking facilities. 



INLET. — An arm of the sea, comparatively long with respect to its width and not restricted at 

 its entrance, which may extend a considerable distance inland; or a relatively narrow passage con- 

 necting a virtually enclosed body of water with the sea. 



