12 



BULLETIN 55, UNITED STATES NATIONAL MUSEUM. 



interior of the shells, even to the minute foramina. These casts are 

 also noted twice in volcanic mud (stations 991 and 1065). Doubtless 

 examples of these casts might be found in many other samples of 

 globigerina ooze. 



Diatom ooze. — Diatom ooze is the name given to a deep-sea deposit 

 of which the principal constituent is the siliceous f rustules of diatoms. 

 Previous to this survey such a deposit had not been found in any 

 tropical waters, and was supposed to be " confined to the Southern or 

 Antarctic oceans, or to the northern parts of the North Pacific." 

 Unexpectedly, therefore, many distinct patches of characteristic diatom 

 ooze were found on the line, especially between Guam and Luzon, 

 latitude 11° 28' to 11° 50' north, and longitude 136° to 130° 30' east. 

 Along this tract, about 300 miles in length, diatom ooze was recovered 

 at stations, as follows: 



Diatom ooze. 



Between Guam and Midway Islands diatom ooze of the same nature 

 appears at stations 559, 1710, and 1724. Also at stations 314 and 350 

 broken f rustules of Ooscinodiscus rex are noted. 



As may be seen from the above table, the depths varied from 2,432 

 to 3,658 fathoms. In appearance the typical examples are greyish- 

 white in color, shading off to a pale yellowish-brown wherever the 

 fine red clay mud is present in any considerable proportion. In con- 

 sistence it is mucilaginous, but is readily disintegrated by shaking with 

 water. Radiolaria are generallj^ rather numerous in this deposit. 

 Mineral fragments are few. In all the specimens examined the 

 diatoms belong almost exclusively to a single species identified by 

 Professor Mann as Ooscinodiscus rex Wallich. This is one of the 

 largest diatoms known, having a diameter of about 0.8 millimeter, 

 and is plainly visible to the naked eye. In form it resembles a minute 

 pill box, with slightly rounded corners. The two valves (bottom and 

 cover) are held together by a broad circumferential band. The valves 

 are extremely thin and fragile, and the markings exceedingly delicate. 



