OCEANOGKAPHY OF THE PACIFIC. 13 



In some instances complete f rustules are found, but usually the valves 

 are separated and often much broken. A peculiar feature of this 

 deposit is the strict limitation of the patches. Nearl}^ pure diatom 

 ooze may be recovered from one station, and at the next, five miles 

 away, not a diatom appear in the desposit. 



Radiolarian ooze. — No well-marked example of radiolarian ooze has 

 been found in the specimens examined. Though radiolaria are noted 

 in most of the samples, nowhere do thej^ appear as a dominating con- 

 stituent of the deposit. They are most numerous in the diatom oozes, 

 where they are generally conspicuous bj" the number of individuals, 

 but the number of species represented is not great. 



Volcanic mud. — This is a deposit found in the neighborhood of 

 volcanic islands or submarine volcanic peaks. Its characteristic con- 

 stituents are pumice, glass, ashes, and the debris of volcanic rocks. 

 It is often mixed with a considerable proportion of f oraminifera when 

 taken from depths less than 2,000 fathoms. Most often it is dark gray 

 in color, and is readily disintegrated by shaking with water, being 

 devoid of the sticky quality of red clay. This deposit is noted about 

 the islands-of Oahu and Guam, and nearly the whole distance from 

 Guam to Yokohama, where the route passes along nearly parallel to 

 the Ladrone and Bonin groups of volcanic islands, and at no great dis- 

 tance therefrom. The most conspicuous mineral constituent of this 

 deposit is volcanic glass. It appeals in various forms, the most fre- 

 quent being the fibrous or filamentous variety. This has the appear- 

 ance of having been drawn out when in a plastic state, sometimes into 

 long, extremel}^ fine threads, more commonly into larger threads or 

 ribands, furrowed longitudinall}^, broken into short pieces, and alwa}- s 

 colorless and transparent as the finest artificial product. Another 

 form is more massive, ragged in outline, dark brown, translucent, 

 with numerous large, rounded cavities, and not so conspicuously sug- 

 gestive of having been drawn out while cooling. A third variety 

 consists of very fine, angular, perfectly transparent ;md colorless 

 fragments, which often make up the bulk of the washed sediment. 

 Red palagonite, coating fragments of other minerals is more fre- 

 quently present in this deposit than in an}^ other. 



Blue mud. — Blue mud is the deposit generally found in inclosed or 

 partially inclosed seas, and in the waters bordering continental land. It 

 is composed for the most part of the debris carried out from the land 

 by rivers or other currents. The few specimens collected by the JSfero 

 are blue-black in color, on the sides of the vial exposed to the light of 

 a dark steel-blue with metallic luster, and iridescent. The color is 

 said to be due to the presence of organic matter and iron sulphide. 

 The odor of hydrogen sulphide is evident in all the well-corked vials 

 of this mud. Except in deep waters foraminifera are more or -less 

 numerous. Radiolaria and diatoms are generally present, sometimes 



