7824 HYDROGRAPHIC MANUAL PaGE 736 



(2) The sounding, with legend "lik" appended, should be used in all cases, where the depth 

 on the rock is known, and where the rock, at the sounding datum, is covered 1 foot or more on 

 the Atlantic Coast or 2 feet or more on the Pacific Coast. 



(3) The abbreviation "Rk" may be appended to the sunken-rock symbol where there is 

 risk that the latter may be overlooked or mistaken for a defect in the paper. 



(4) Under no circumstances shall both the least depth and the symbol be used to represent 

 the same rock. 



d. Accuracy of location. — Any specific rock (bare, awash, or sunken) which has been accurately 

 located by a rod reading, a three-point sextant fix at the rock, or sextant or planetable cuts forming 

 a good intersection at the rock, shall be encircled by a dotted line to distinguish it from those rocks 

 whose positions are estimated, or are from generalized symbolization. 



If a rock is so located by the topographic survey, the dotted line shall be in black ink. If located 

 by the hydrographic survey, the dotted line shall be left in pencil to be inked in red after the smooth 

 sheet is verified in the Washington Office (see fig. 169). 



It is to be noted that the dotted line is not to be used around rocks located by estimated dis- 

 tances from a sounding line. 



7824. Reefs and Ledges 



A reef is a rocky or coral elevation dangerous to surface navigation, which may 

 or may not be above the sounding datum in elevation. A rocky reef is always de- 

 tached from shore, but a coral reef may or may not be connected with the shore. A 

 ledge is a rocky formation connected with and fringing the shore, and is generally 

 above the sounding datum in elevation. These terms should always be so used in the 

 Sounding Records, and will be construed in accordance with these definitions, unless 

 information from other sources indicates otherwise. 



These features when bare or awash at the sounding datum must be clearly marked 

 on the smooth sheet to show their nature and extent. They may be represented by 

 symbol or by broken line and legend depending on which method will show the 

 feature correctly and clearly with the least amount of work. A small reef or ledge, 

 for example, might be sho^vn b}'- symbol but a large reef or ledge extending a consider- 

 able distance along the shore may be indicated more economically by a broken line 

 with an appropriate legend. 



There is no distinctive symbol for a submerged reef or ledge, and where the limits 

 have been determined they should be indicated by a broken line, enclosing sunken- 

 rock symbols or an appropriate legend (see 7826). 



No distinction is made between the symbol for a rocky reef and a ledge. Where 

 a reef is continuous at the sounding datum, the standard rocky-ledge or coral symbol, 

 as the case may be, should be used (see fig. 189, part II), but where the reef is generally 

 submerged and projects only in spots above the sounding datum, rock-awash symbols 

 should be used to represent the protuberances and sunken-rock symbols, the depressions. 



From their very nature, the exact delineations of reefs and ledges are sometimes 

 unobtainable from a single source. Therefore, in plotting such features on the smooth 

 sheet, their limits and extent shoiUd be based on all available information from the 

 Sounding Records, the boat sheet, and the topographic survey. Care should be taken 

 to distinguish between positions outlining a reef, and those outlining a sandy low-water 

 line interspersed with rocks awash. 



7825. Elevations and Notes 



All notes and elevations relative to rocks should be referred to the precise datum 

 planes applicable, and not to a generahzed one. For example, "uncovers 2 ft at MLW" 



