344 
THE VOYAGE OF H.M.S. CHALLENGER. 
Statiou 157, 1950 fathoms. — Among the stones dredged at this station were numerous 
glaciated fragments, the largest weighing over 20 kilogrammes. Some of them were 
only partially imbedded in the Diatom Ooze, the depth to which they were imbedded 
being marked by a sharp line. The portions above the surface of the deposit had a slight 
coating of the black oxide of manganese, and this substance was most abundant just at 
the line marking the separation between the deposit and the superincumbent water. In 
the same deposit some fragments of Hexactinellid spicules had a rather thick coating of 
manganese peroxide.^ 
Station 160, 2600 fathoms. — The trawl at this station contained about 16 litres of 
manganese nodules, pumice stones, earbones of Cetaceans, and sharks’ teeth. With 
respect to their form the nodules may be arranged into three groups : first, more or less 
pyramidal or irregularly grape-shaped ; second, spheroidal or ellipsoidal ; third, flattened, 
mammillated, and irregular in form. A typical example of the first group is represented, 
natural size, in PI. II. fig. 3. It measures about 5 cm. in longest diameter ; its funda- 
mental form may be compared to a triangular wedge, with a curved surface at the superior 
part. The surface is entirely mammillated, but the rounded rugosities are not very pro- 
nounced, being much softened down, and but slightly projecting, with a diameter of 
5 to 6 mm. Upon one face the mammillae are much more abundant than on the other. 
Animals are usually attached to the smoother face, and we are inclined to believe that 
this face projected above the surface of the deposit, while the rougher one was imbedded 
in the clay. The figure represents the smoother face of this nodule, and shows more 
or less pronounced reliefs in two directions, following which the fracture usually takes 
i»lace with the greatest facility. The first is parallel to the lateral edges of the wedge 
along the radii ; the second is more or less parallel to the superior surface of the figure, 
and follows a curved direction, answering to the disposition of the layers in the interior 
as represented in fig. 3a, showing a section of a nodule similar to that of fig. 3. The first 
direction answers to the fracture running from the periphery to the inferior point of the 
wedge. This form may indeed be compared to a fragment of a more or less regular 
.spherical body, where the fractures had taken* place along the radii, thus leaving a 
triangular solid terminated in one aspect by the primitive peripheral face. Fig. 3a 
shows the internal structure of this type of nodule, and it will be observed that parallel to 
the curved superior surface there are alternating zones, sometimes yellowish white, some- 
times black-brown, the hist having the character of earthy manganese. These internal 
curved bands follow very regularly the external curved surface, and liave a thickness of 
about 2 mm. Notwithstanding their homogeneous appearance, microscopic examination 
shows that the light-coloured bands are traver-sed by fine arborescences or dendrites of 
manganese. The existence of these dendrites is also shown by attacking the nodule 
with hydrochloric acid, and examining the skeleton wdtli a lens ; a portion of a nodule so 
* Murray, Scot. Ueogr. Maij., vol.,v. p. 427, 1889. 
