34G 
THE VOYAGE OF H.M.S. CHALLENGER. 
incut of the nodule is well seen. One of these nodules, about 4 cm. in diameter, had 
attached to it two Ascidians and a Brachiopod (see Fig. 34), so that a portion of the 
nodule probably projected above the mud when at the bottom. 
A great many nodules belonging to the third, flattened, mammillated, or irregular 
variety were present. They vary greatly in size, contour, and internal structure, some 
resembling the first, others the second, varieties above described. Those resembling the 
first variety are mammillated on the exterior, while the 
interior is friable, sometimes mottled, or with ill-defined 
black and whitish bands, but not concentric. Those re- 
sembling the second variety are less mammillated, are 
generally compact throughout, with fine concentric layers, 
and, when cut in section and rubbed with a chamois 
leather, give a fine black shining submetallic surface. 
Sometimes they have a volcanic fragment, or a fragment 
of bone, for a nucleus, and then the external form of the 
Fio. 34 .— Manganese Nodule with two Tuni- nodule resembles closely the shape of the enclosed frag- 
catea (Styda squamosa and Styela bythia) _ i i i i i 
and a Brachiopod attached. Station 160, ment. Frequently the nucleus appears to be pseudo- 
2600 fathoms. Southern Indian Ocean. j^oT^hosed by manganese, especiaUy when it consisted of 
carbonate or phosphate of lime. Sharks’ teeth and earbones of Cetaceans also give a 
form to the nodules when forming the nuclei. 
Two or three nodules, or fragments of nodules, merit a special reference. They 
appear to be fragments of the spherical variety, and we have every reason to believe that 
the nodules of which they once formed part were broken while yet at the bottom of the 
sea. The structure and angular form, as well as the radial and concentric fractures, of 
one piece, leave no doubt that it once formed part of a large spherical nodule. The 
surfaces of the broken part are covered with fine rugosities, indicating a deposition of 
manganese over the fragment after its separation from the original nodule, and upon 
these same surfaces of fracture two Brachiopods and a Hydroid have subsequently attached 
themselves. Another and smaller fragment, with concentric structure, in which a portion 
of the palagonitic nucleus is still to be observed, is wedge-shaped, and has been formed 
by a fracture following the direction of the rays of the original nodule. That the nodule 
had been broken while yet at the bottom of the sea is proved by the fact that the fragment 
is entirely surrounded by a new concentric deposit of manganese about 0‘5 mm. in 
thicknes.s. This fragment must then be regarded as having been separated from the 
original nodule at the bottom, and to have subsequently become the nucleus of a new 
nodule. 
About twelve of the nodules contained nuclei of basic volcanic glass or of palagonite. 
In some the unaltered gla.ss was surrounded by coloured bauds of palagonite or altered 
material, similar to the sjjccimen represented in Bl. XIX. fig. 3 from Station 293. In 
