3o4 
THE VOYAGE OF H.M.S. CHALLENGER. 
auy case was very small compared with the larger indications in the clays at other 
stations where the deposit is of a dark chocolate colour. The surfaces of many of the 
nodules were covered with Rhizopod tubes and the stolons of Hydroids. 
Station 253, 3125 fathoms. — The small dredge, as well as the tow-nets attached to it, 
contained clay and manganese nodules. One of the nodules was of large size, and flat or 
slab-like in form. It measured 31 x 20 x 6 cm. ; a fourth part of this nodule is shown in 
PI. IX. fig. 1. There was a great difference in appearance between the upper and lower 
surfaces ; the lower surface, that which rested on the deposit, or was immersed in it, is 
very rough and uneven, consisting of numerous closely-set mammillae ; these mammillae 
are more numerous near the outer edges of the block, and the whole under surface has a 
scoriaceous aspect. The upper surface, on the other hand, has relatively few mammillae, 
and these are smooth, rounded, and softened, when compared with those of the under 
surface. Small pieces of pumice appear to have fallen on the upper surface of this block, 
and to have been cemented to the upper surface of the nodule by subsequent depositions 
of peroxide of manganese. In the same way a Nodosarian Foraminifer and worm-tubes, 
that lived attached to the upper surface, have become imbedded by the successive additions 
of manganese. Attached at different parts of the surface of this nodule were four living 
specimens of a Hydroid (Stephanoseyphus), a Tubularian, two small Aetinians, a Serpu- 
larian, two Polyzoons, and the whole surface had a reticulated appearance from the 
presence of Rhizopod tubes or the stolons of the Hydroids. An Annelid with a muddy 
tube was attached to the under surface. Fig. la shows a portion of a section of this 
nodule, from which the manganese has been removed to show its structure. The whitish 
coloured irregular nueleus is surmounted by successive layers of manganese 3 to 4 cm. in 
thickness, while beneath this nucleus the layers are only about 1 cm. in thickness. It will 
be observed that many of the layers above the nucleus terminate rather abruptly towards 
the periphery, which structure seems to suggest that this nodule was once a part of a larger 
ma.ss that had subsequently been fractured and surrounded by the external layers. 
The nucleus is irregular and of an elongated form, and in its centre are hollow spaces 
filled with clay ; it is very hard and compact, but can be scratched with a knife. When 
examined in thin slices this nucleus is yellowish and finely granular, the grains being 
about O'OOl mm. in diameter. The whole mass is streaked with colourless lines, 
resembling in some respects certain microliths ; it is isotropic, some colourless fragments 
being birefrangent ; it did not present cleavages nor crystallographic contours. Two or 
three fragments of felspar and some elongated fragments, which appear to be mica, 
were observed, as well as some prismatic sections of zeolites. The nucleus is penetrated 
by dendrites of manganese in many directions. In all probability this nodule projected 
about an inch above the general level of the deposit when at the bottom of the ocean. 
In addition to this large nodule was another with a diameter of 8 to 9 cm., re- 
sembling in many respects the nodules dredged at Station 252. The mammillae are. 
