THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 35 



Station 4721, 15th January, 1905. Lat. 8° 7.5' S. ; long. 104° 10.5' W. ; 

 depth, 2084 fathoms. 



The trawl brought up a fair quantity of manganese nodules, although 

 the deposit is a Globigerina Ooze with 75 per cent of calcium carbonate. 

 These nodules have a peculiar appearance, being generally of low specific 

 gravity, somewhat slaggy looking, with a dull, not shining surface. They 

 have a very irregular shape, mostly flattened, and the diameter of the 

 largest does not exceed three inches. As regards structure, there is no 

 concentric arrangement round a central nucleus, the substance being equally 

 distributed throughout. They are not formed of pure iron and manganese 

 oxides, but contain a large amount of palagonite, in grains averaging 1 mm. 

 in diameter ; the grains are visible in the nodules themselves, but can be 

 best seen after removing the oxides with hydrochloric acid. Fresh, unde- 

 composed minerals are very few. The oxides very often form a coating 

 round each grain of palagonite, the whole nodule having then a granular 

 structure. 



Besides actual nodules there are also deposits of manganese-iron oxides 

 round what were originally siliceous Sponges, and in two cases the shape 

 is well preserved ; the siliceous skeleton has not disappeared, and can still 

 be seen on fractures, with a magnifying glass (see PI. 3, fig. 5). 



Generally speaking, one may say that at this station manganese and iron 

 oxides impregnated either Sponges or fragments of palagonite, these being 

 possibly the only solid bodies present. But in no case is concentric arrange- 

 ment round one central nucleus to be seen. 



Station 4740, 11th February, 1905. Lat. 9° 2.1' S., long. 123° 20.1' W. ; 

 depth, 2422 fathoms. 



Three small manganese nodules were brought up at this station. These 

 call for no special description, but it is interesting to note their presence in 

 a typical Globigerina Ooze. 



Palagonitic Tuffs. 



In addition to the cakes of volcanic ash described under Station 4685, 

 palagonitic tuffs were brought up at two other stations : — 



Station 4736, 23rd January, 1905. Lat. 19° 0.4' S. ; long. 125° 5.4' W. ; 

 depth, 2289 fathoms. 



Several large cakes of palagonitic tuff from this station were mixed with 



