THE QUALITY OF THE BOTTOM 



Various kinds of charts are compiled to describe, in one way or 

 another, the type or quality of the ocean bottom. The commonest type 

 is a chart which shows the relative size of the particles that maJte up 

 the bottom sediments. For this purpose the U. S. Navy Hydrographic 

 Office uses the standard categories of mud, sand, gravel, and rock. 

 The two additional sediment categories used are shell and coral; 

 however, these do not relate directly to size but indicate origin and 

 chemical composition. Other charts of a nnore specialized nature may 

 be made in addition to the standard bottom sediment chart, such as 

 charts showing the presence or proportion of calcium carbonate or the 

 distribution of globigerina. 



The chief sources of data used in compiling bottom sediment charts 

 are navigation charts. To use these sources effectively, one needs to 

 know (with as much precision as possible) the meaning of the various 

 abbreviations used on these charts to indicate the type or quality of 

 the bottom. This glossary was compiled to meet this need. 



The following list is based on the International Hydrographic Bureau, 

 Glossary of Cartographic Terms, 1951 and the U. S. Navy Hydrographic 

 Office Chart No. 1, "Nautical Chart Symbols and Abbreviations," 1957. 

 The definitions herein are based, for the most part, on "Websters New 

 Collegiate Dictionary," 1954, "The Glossary of Geology and Related 

 Sciences," American Geological Institute, 1957, and H. O. Pub. No. 

 220, "Navigation Dictionary," 1956. 



Often some indication of the type or quality of the bottom is given 

 by Icindforms of the adjacent coast and by other notations not usually 

 classified under the general heading "Quality of the Bottom." Such 

 symbols can be found in H. O. Chart No. 1, page 1, "The Coastline" 

 and page 12, "Dangers." 



The abbreviations and terms are listed in the order given in the 

 H. O. Chart No. 1, rather than in alphabetical order. On nautical charts 

 the initial letter of the abbreviation of names is in capitals and the 

 initial letter of the abbreviation of adjectives is in small letters. When 

 these abbreviations appear on a chart, they may or may not be followed 

 by a period depending on the date of the chart. 



