385 HYDROGRAPHIC MANUAL PaGE 306 



Beyond the above zone to approximately 200 miles from land, the ocean bottom 

 deposits are still considerably influenced by the nature of the adjacent coast, and in 

 these deeper areas, down to about 1,000 fathoms, which we may consider on the conti- 

 nental slope, the deposits consist principally of blue, green, and red muds formed by 

 the deposition of the finest clays which have been carried to the sea by rivers. The 

 shells of marine animals are also found m these deposits. The different colors residt 

 from the presence of various mmerals. Fine bluish-black or blue muds are most fre- 

 quent, although green mud also occurs frequently. Red muds are relatively rare. 



In oceanic areas remote from land, the deposits consist principally of the 

 remains of organisms living in the ocean, in which are to be found small quantities 

 of wind-carried volcanic debris and very fine terrigenous materials. The principal 

 types are: 



Glohigerina Ooze occurs at an average depth of 2,000 fathoms, most commonly within the range 

 from 1,200 to 2,200 fathoms, although it has been found from 400 to 3,000 fathoms; it is the char- 

 acteristic deposit in the Atlantic Ocean. It consists principally of the debris of the minute calcareous 

 shells of the Foraminifera, especially the globular form Glohigerina of characteristic shape. It is 

 dirty-white in color when dried. 



Radiolarian Ooze is abundant in the Pacific Ocean, occurring at an average depth of 2,900 fathoms, 

 most commonly within the range from 2,000 to 5,000 fathoms. It is not found in the Atlantic Ocean. 

 It is nothing but red clay containing a large number of the minute siliceous skeletons of Radiolaria, 

 a group of the Protozoa. It is frequently mixed with the principal constituent of glohigerina ooze, 

 but this latter is rarely found in deposits in the greater depths. Its color is red or dark brown; it is 

 less plastic than red clay alone. 



Diatom Ooze is found at an average depth of 1,500 fathoms, in a range from 600 to 2,000 fathoms. 

 It is found extensively in the Antarctic Ocean and in the North Pacific Ocean." It consists of the 

 siliceous remains of a primitive group of microscopic plants, with which clay and Radiolaria are 

 commonly found. It is white in color. 



Red Clay is the most characteristic and widely distributed oceanic deposit, occurring in depths 

 greater than 2,225 fathoms and in the greatest depths of the oceans. It is formed almost entirely 

 of insoluble residues, consisting of wind-blown dust, generally of volcanic origin, which by a long 

 process of decomposition form red clay. In the North Atlantic the color is brick-red, owing to the 

 presence of iron oxide. The calcareous and to a large extent the siliceous materials, which charac- 

 terize the oozes, are gradually dissolved as they sink slowly to the ocean bed and so are rarely present 

 in these depths. 



385. Descriptive Report and Coast Pilot Notes 



It is obvious that satisfactory Descriptive Reports of hydrographic surveys cannot 

 be written from memory after the completion of the survey, nor by a person who was 

 not in charge of the actual field work, 



A daily journal shall be kept by each hydrogi-apher in which a complete set of 

 notes is made concurrently with the progress of the survey. The notes* should include 

 information about the various items required in Descriptive Reports (see 842), but in 

 no case should they take the place of remarks and miscellaneous entries properly 

 belonging in the Sounding Record (see 815). 



In some cases extenuating circumstances may justify the omission of a sounding 

 Hue, a deviation from standard methods, an apparently incomplete development, etc. 

 A complete record should be made of such circumstances by the hydrographer while 

 they are fresh in his mind. 



Occasionally, for one reason or another, it is impracticable for the hydrographer to 

 write the actual Descriptive Report, or the hydrographic smooth sheets may have to be 

 plotted under the supervision of some individual who did not have personal knowledge 



