34 THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 



As regards shape, the nodules do not appear to have been built ac- 

 cording to a definite type. They are angular, and have roughly the same 

 diameter in all directions. They are all mammillated, the mammillae being 

 very prominent, each standing apart. A section across a nodule shows it 

 to be compact and homogeneous, in spite of a distinct concentric arrange- 

 ment, the different layers being in close contact with each other, and 

 there is no softer material between each consecutive layer. The trans- 

 verse section of the various layers does not form a regular line, but is 

 sinuous, each layer espousing the contour of the preceding, till one ap- 

 proaches the root of the external mammillte, where there is no relation 

 between the last layer and the mammillae surmounting it. It appears as 

 if on some smooth nodule, with only faintly outlined mammillae, a new 

 generation of mammillae had been grafted, independently of the original 

 protuberances. 



Many nodules exhibit, though to no very great extent, an upper and 

 an under surface ; that is to say, in one case the mammillae are larger and 

 smoother than in the other, where they are rougher and more distinctly 

 separated from each other. This could perhaps have been seen on all 

 the nodules, if during the process of collecting the mammillae had not 

 been often destroyed. 



Though a section across a nodule shows a concentric arrangement, still 

 no material playing the part of a nucleus can be seen. They are also 

 very free from foreign admixtures; in the parts less rich in oxides the 

 microscope shows only the presence of some kind of chloritic mineral, with 

 augite and microlites of felspar. Palagonite, so often met with in similar 

 formations, appears to be absent. Magnetic particles are likewise absent. 



Station 4717, 13th January, 1905. Lat. 5° 10' S. ; long. 98° 56' W. ; 

 depth, 2153 fathoms. 



A few small manganese nodules accompanied the Globigerina Ooze 

 from this station. They are flat in shape, and the diameter of the largest 

 one does not exceed three-fourths of an inch, its thickness being about 

 one-fourth of an inch. Both surfaces are identical, with a granulated ap- 

 pearance. Internally there is no concentric arrangement, the external 

 granular portion alone forming a differentiated layer. 



These nodules are coal-black, quite hard, and must be considered perfect 

 nodules, although the deposit is a typical Globigerina Ooze. 



