282 



PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



Samples from Marquesas Lagoon. 



Specimen 98 is from the east side of Marquesas Lagoon (see plate 95). 

 The dimensions of Marquesas Atoll between sea fronts are 4 nautical miles 

 along a line from northeast to southwest and 3 nautical miles from northwest 

 to southeast. The width of the rim ranges up to about 0.625 nautical 

 mile on the northeast side, which is a crescent bowed against the northeast 

 winds. There are entrances to the lagoon in the southeast, southwest, and 

 northwest quadrants. 1 The maximum height of the rim is about 10 feet 

 above low tide. The depths outside the rim range up to about 15 feet 

 within a mile of the shore; within the lagoon the water except along tidal 

 channels is usually less than 3 feet deep, along the channels it is as much as 

 9 feet in a few places. The bottom of the lagoon is limy mud resting on a 

 floor which lies at a strikingly uniform depth of about 12 feet below low-tide 

 level; one place was found where the depth of mud is 15 feet, below which is 

 rock. The floor underlying the mud is indurated oolite. The lagoon has 

 been filled with mud to an average depth of about 9 feet. 



The first cultures Drew made of denitrifying bacteria to ascertain if they 

 would precipitate calcium carbonate were from specimens obtained in 

 Marquesas Lagoon, and Kellerman used specimens from there in his work on 

 the same subject. 



I have collected samples at many stations within the lagoon, and have 

 had several mechanical analyses made, but only one chemical analysis. The 

 results of the mechanical analyses of specimens from Marquesas Lagoon 

 (made by U. S. Bureau of Soils) are herewith presented (for graphic repre- 

 sentation see plate 94). 



Mechanical analyses of bottom samples from Marquesas Lagoon. 



No., 



U.S. 



Bureau 



Soils. 



27250 

 26467 

 26871 

 27251 

 27252 

 27253 

 27254 



No., 



T. W. 



V. 



63 

 98 

 98 

 106 

 no 

 "5 

 "7 



Description. 



SW. quadrant (surface) 



SE. quadrant (surface) 



...Do 



...Do 



SE. quadrant (9 feet below surface) 



SE. quadrant (surface) 



Outside SE. entrance, water 5 feet deep 



2 to 1 

 mm. 



1 to 

 0.5 



mm. 



3-1 



6.4 



6.9 



24.1 



4-3 



17-4 



17-9 



0.5 to 

 0.25 

 mm. 



17-5 



0.25 

 to 0.1 

 mm. 



17-3 

 19.8 

 19.8 



9-1 

 18.2 

 32.0 

 38.6 



0.1 to 

 0.05 

 mm. 



24.8 

 25.6 

 24.2 



6.6 

 16.5 

 13.0 



7.8 



0.05 



to 



0.005 



mm. 



33-3 

 27.4 

 22.0 



'7-3 

 26.5 



9-7 

 6-5 



0.005 

 to o 

 mm. 



16.3 

 12.6 

 19.9 

 16.4 



28.1 



14-3 

 11. 7 



The analyses of the surface material indicate an appreciably greater coarse- 

 ness than that of the muds from South Bight and from off the west side of 

 Andros Island. Only hypothetical explanations can be advanced for this. 

 These are: (a) there is greater outwash of fine material; (b) bacteria are less 

 abundant. Drew found 800 b acteria per cubic centimeter in a sample sent 



'For description of the Marquesas, see Vaughan, Carnegie Inst. Wash. Pub. 182, pp. ^7-68, 1914; and 

 \aughan and Shaw, Carnegie Inst. Wash. Year Book No. 14, pp. 232-238, 1916. 



