32 THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 



the nodule was at the bottom of the sea, as both sides are coated with a 

 thin film of clay. 



Station 4676, 5th December, 1904. Lat. 14° 28.9' S. ; long. 81° 24' W. ; 

 depth, 2714 fathoms. 



About half a dozen manganese nodules were brought up at this station, the 

 largest being two and one-half inches in diameter. Their shape is somewhat 

 spherical, but with a very rough surface, the mammillae being very sharp- 

 pointed and acute. On the surface remnants of living organisms, such as 

 siliceous Sponges, are to be seen. The nodules are far from being formed ex- 

 clusively of the oxides of iron and manganese ; the general appearance of a 

 section made across a nodule shows it to be also partly made up of the clay 

 itself, with a good many small mineral particles. Many of the latter are 

 decomposed and cannot be determined, but felspar, volcanic glass, and 

 probably augite, can still be recognized. 



A section made across a nodule did not reveal the presence of any hard 

 nucleus, and there is no trace of concentric structure, the nature of the con- 

 cretion being the same throughout, excepting towards the periphery, where 

 the clayey element is more conspicuous. A powdered portion of nodule, 

 treated with hydrochloric acid, leaves a residue quite similar to the clay 

 itself, with the only difference that mineral particles are there a little 

 more numerous, though very small, averaging 0.005 mm. in diameter, only 

 a few being as much as 0.02 mm. Of these, augite and felspar are the 

 only particles recognizable. 



Station 4681, 8th December, 1904. Lat. 18° 47.1' S. ; long. 89° 26' W. ; 

 depth, 2395 fathoms. 



The nodules from this station vary in shape, from slabs two and one-half 

 inches in diameter to flat, elliptical, bean-shaped nodules. The more strictly 

 nodular forms (one inch in diameter) have a rather large nucleus, composed 

 of palagonite mixed with clay proper; concentric structure is hardly 

 noticeable, affecting only the outer zone. Both surfaces are structurally 

 identical, though the one is generally more soiled with clay than the other. 

 In both cases the surface is not shining, but finely granulated. 



The slabs have the same structure ; the internal layer contains more 

 mineral particles than the outer ones. Both surfaces are also finely granu- 

 lated, but one is nearly flat, whilst the otlier is maramillated. On the flat 



