148 THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 



then comes a thin layer of palagonitic tuff, identical with that of the 

 nucleus, but only on one side of the nodule, so that in transverse section 

 it forms a half circle midway between the nucleus and the surface. It 

 looks as if a relatively small nodule had been covered on one side with 

 palagonite, and as if the concretionary process had still gone on afterwards, 

 enveloping it as it enveloped the nucleus. The heavy manganese-iron 

 oxide layers contain a certain proportion of palagonite in the shape of 

 small grains irregularly distributed, and not forming individualized layers. 

 Pounded nodules showed the absence of magnetite and magnetic spherules. 



The slabs differ from the nodules in shape only, and may be considered 

 as flattened nodules, not as fragments detached from larger masses; the 

 largest one measures 18 by 12 by 2i cm. Just as in the case of the nodules 

 proper, a large flat nucleus is enveloped by manganese-iron oxides, having 

 a finely mammillated structure all over, without any signs of fracture. All 

 that can be said is that the shape of the slab follows the shape of the 

 nucleus, but why the latter is flattened cannot be satisfactorily explained. 



Station 174, 4th November, 1899. 

 Lat. 18° 28' S. ; long. 147° 11' W. ; depth, 2087 fathoms. 

 Two small manganese nodules, each about 15 mm. in diameter, form 

 the only material obtained at this station. The one is oblong in contour, 

 with nucleus of red palagonite, the other subspherical, harder than the first, 

 with nucleus of whitish volcanic glass, the decomposition not being so far 

 advanced. 



