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 mammille 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 mammille, where there is no relation 
between the last layer and the mammille surmounting it. It appears as 
if on some smooth nodule, with only faintly outlined mammille, a new 
generation of mammille 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 mammille 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 mammille 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. 
