THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 33 



side there are worm-tracks and arenaceous Foraminifera, together with 

 some egg-like white capsules. The flat side is, therefore, in this case the 

 upper one. 



Station 4685, 10th December, 1904. Lat. 21° 36.2' S. ; long. 94° 56' W. ; 

 depth, 2205 fathoms. 



Numerous pieces of manganese slabs and a few manganese nodules 

 were brought up at this station. The slabs, which may be as much as 

 six inches in length and one and one-fourth inches in thickness, are essen- 

 tially cakes of volcanic ash more or less impregnated with the oxides of 

 manganese and iron, with formation of an actual crust of the oxides on 

 both surfaces. The volcanic ash is made up of particles of augite, some 

 of which belong to the violet variety, of basic felspar, and of volcanic 

 glass, more or less decomposed. The particles have a diameter of 0.01 to 

 0.02 mm., and are often even smaller. 



The nodules are not so abundant as the slabs. They are discoidal, 

 their shape recalling that of a broad bean, and their diameter is from one- 

 half of an inch to three-fourths of an inch. They sometimes occur in 

 clusters of two or three individuals. The structure is scaly, due to the 

 concentric arrangement of the layers ; the centre of the nodule is occu- 

 pied by a nucleus formed of an aggregate of loose mineral particles, at- 

 taining a diameter of 0.08 mm., which are the same as those occurring 

 in the slabs, i. e. a great quantity of augite, with volcanic glass and 

 plagioclase. Magnetite is also present. There is no marked transition 

 between the nucleus and the body of the nodule proper, so that it is 

 difficult to say what is the relative proportion of the diameter of the 

 nucleus to that of the nodule ; yet it appears to be not more than about 

 one-fifth in the case of a typical nodule. 



Station 4711, 31st December, 1904. Lat. 7° 47.5' S. ; long. 94° 5.5' W. ; 

 depth, 2240 fathoms. 



The Globigerina Ooze from this station contains numerous typical 

 manganese nodules (see PI. 2, fig. 4.), some of which rival those from 

 Station 4658. About half a dozen are of very large size, one measur- 

 ing six inches in diameter. As they all have a distinctly mammillated 

 structure, the mammillae breaking off easily, many of the smaller nodules 

 must be considered as having formed part of the larger ones. 



