THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 49 



patches ; placed in water it becomes plastic, but is coherent when dried. 

 Numerous pebbles, from 1 to 15 mm. in diameter, are scattered in the mass. 

 Calcium carbonate : per cent. 

 Residue : 100 per cent : — 



Siliceous Organisms (80 per cent) constitute by far the greater portion 

 of the deposit, but as they are mixed with a certain proportion of fine 

 amorphous clayey matter it is difficult to estimate the actual percentage. 

 It is also impossible to draw the line between those that should be included 

 under the heading of " fine washings." Yet it may safely be assumed that 

 quite 80 per cent of the deposit is formed of the remains of siliceous 

 organisms. Diatoms are the most abundant, and are accompanied by 

 Eadiolaria and minute Sponge spicules. 



Minerals (traces) ; exclusive of the rock fragments, mineral particles are 

 few in number, are all angular, none showing rounded edges, and are very 

 variable in size (from less than 0.01 mm. to 0.2 mm. in diameter). They were 

 probably not all derived from the same source, as is indicated by the nature 

 of the rock fragments. The following are represented : magnetite, oxi- 

 dized at the surface, oligoclase, quartz, the products of the decomposition of 

 some ferro-magnesian mineral, also rather large flakes of what appears to 

 be decomposed biotite, splinters of volcanic glass, and a few very small 

 grains of glauconite. The numerous rock fragments are represented mostly 

 by a limestone, which is the same as that constituting the large angular 

 blocks. No. 3. These small fragments of limestone are sometimes rounded, 

 sometimes angular, and have all undergone surface decomposition. There 

 is also a pebble, 15 mm. in diameter, of a compact black rock, apparently 

 of volcanic origin, much rounded, smooth, and worn. 



FineWas/niiffs (20 per cent); the amorphous clayey matter is brownish 

 green and is irregularly distributed. The mottled appearance of the deposit 

 is due to this unequal distribution of the amorphous matter, or rather of 

 the substance giving it its brownish green color. 



(2) The cakes of consolidated deposit, labelled " Siliceous earth " on 

 board ship, are greenish gray, extremely light, and coherent. They differ 

 in no way from the material in the bottle, being mainly made up of the 

 debris of siliceous organisms, in which a species of Coscinodiscus is conspic- 

 uous. The mineral particles belong to the same species as those enumerated 

 above, and are very scarce. Particles of what appears to be glauconite were 

 also detected. 



