350 
THE VOYAGE OF H.M.S. CHALLENGER. 
of mangauesc, and to the outer surfaces were attached Ascidians, Brachiopods, Hydroids, 
aud Rhizopods. The appearance of these fragments of pumice is represented in PL I. 
figs. 1-4. Fig. 1 shows (one-fourth natural size) a characteristic specimen of the light, 
porous, filamentous variety of liparitic pumice ; the form is rounded or egg-shaped, many 
of the pores and areolar spaces are filled with the deposit, and the whole surface of the 
fragment has undergone a slight alteration into a clayey or earthy substance. A few 
crystals are visible to the naked eye projecting from the surface, and large portions of 
the surface are discoloured by the peroxide of manganese. Fig. 2 represents a rounded 
specimen (natural size) of the same variety as the preceding, to which several deep-sea 
organisms are attached. The surface is coloured brownish or black by the hydrated 
oxides of manganese and iron. Fig. 3 exhibits a similar specimen, with a segment 
removed to show the discoloured altered zone towards the periphery, and the light- 
coloured, less altered, internal parts. Fig. 4 represents a similar and smaller specimen 
cut in section to show the discoloured altered zone towards the periphery. 
Station 248, 2900 fathoms. — The trawl contained a large number of manganese 
nodules and many pumice stones, together with a Lamna tooth, 2 cm. in length, and 
many other sharks’ teeth of smaller size. Some of the pumice stones had but a slight 
coating of manganese, while others were surrounded by concentric layers of this substance 
over 9 cm, in thickness. Some of the manganese nodules were 2 to 3 inches in diameter, 
composed almost entirely of dense, black, concentric layers of manganese, surrounding one 
or more small nuclei. PI. II. fig. 1 represents one of the most characteristic, as well as 
one of the most abundant, forms of nodule at this station, about thirty nodules more or 
less resembling this one in shape and in size being procured. The general form is 
round ; the mammillae are not prominent, but run the one into the other without forming 
marked reliefs. Two surfaces of these nodules present a marked difference of aspect ; the 
inferior surface, which we believe to have rested in or on the clay, is represented in the 
figure, and is seen to be covered with an immense number of little rugosities, or rounded 
points, about 1 to 2 mm. in diameter, and the same in height ; these asperities, being 
scattered over the whole of the surface, render the nodule rough to the touch and some- 
what like shagreen in appearance. On the other, or superior, surface of the nodule, which 
appears to have projected above the surface of the clay, the asperities are not nearly so 
numerous, and the mammillae are smoother, larger, and less pronounced than on the 
surface here represented. PI. IX. fig. 4 shows the internal structure of these large 
round nodules, the left half of the figure giving the appearance of a nodule when cut in 
section and polished, the right half showing a similar surface after the manganese has 
Ijccn removed by steeping it for some time in strong hydrochloric acid. In both these 
nodules the nuclei may be referred to fragments of pumice which have undergone profound 
alteration. Around these nuclei undulate fine alternating zones of manganese peroxide, 
sej)anited by other lighter coloured zones in which this material is less abundant. These 
