REPORT ON THE DEEP-SEA DEPOSITS. 
347 
other cases the whole of the glass had been converted into palagonite, and these nuclei, 
when freshly taken from the sea, might be cut with a knife like new cheese. In other 
cases, again, all that remained of the nucleus was a patch of white matter, soft to the touch, 
easily cut with a knife, and having an argillaceous aspect, resembling some of the 
outer palagonitic zones of other nuclei. Again, in some of the nodules all trace of the 
nucleus seems to have disappeared, but the centre is composed of very compact, black, 
shining, highly-oxidised manganese. This centre recalls, by its form and aspect, a 
fragment of volcanic glass, which, in the first instance, had become transformed into 
palagonitic material, and subsequently a replacement of palagonite by manganese had 
taken place. There is nothing improbable in this supposition, when we remember the 
pseudomorphism of hydroxide of manganese upon calcite, fluorite, pharmacosiderite, &c. 
The Carcharodon and Lamna teeth, as well as their broken fragments, and the 
earbones and other bones of Cetaceans, were sometimes covered with but a slight coating 
of manganese ; at other times they were surrounded by concentric layers of manganese 
fully 1 cm. in thickness. One of the deeply embedded earbones is shown in Id. VIII. 
fig. 11, which represents in section a tympanic bulla of Mesoplodon The earbone 
determines the external form of the nodule ; the manganese enveloping the bone breaks 
up radially and concentrically, and can be easily detached, the layers presenting all the 
physical and microscopical characters already described. The bone itself is penetrated 
by dendritic ramifications of manganese, and some portions of the substance of the bone 
appear to have been wholly removed. The specimen represented in PI. VIII. fig. 10 
resembles the petrous bone of a Glohiocephadus. It has but a slight coating of oxides of 
manganese and iron, but in some places it is much penetrated by dendrites of those sub- 
stances. A large compact fragment of bone, about the size of a cricket- ball, appears to 
have been the earbone of a Balaenid or Balaenopterid. The external form of the bone has, 
however, been quite lost ; much of the substance seems to have been removed, and dendritic 
ramifications of manganese penetrate the surface in all directions. The interior is very 
compact, the bluish colour, cherty aspect, and the fracture, recalling what is observed in 
some fossil phosphates ; it has not, however, the hardness of chert, nor any of its physical 
properties, but merely presents a strong analogy of aspect. The microscopic structure is 
identical with that of recent earbones, but most of the organic matter seems to have 
been removed. 
In many nodules a structure was observed indicating that the nuclei were originally 
portions of bone, which have subsequently been entirely removed, and replaced by 
manganese depositions. 
Among the nodules were over a dozen rounded pieces of pumice, from 0‘5 to 2‘5 cm. 
in diameter ; some belong to the felspathic, and others to the basic, varieties. While the 
interior of these fragments presented a fresh aspect, the surface to the depth of 1 or 2 mm. 
had undergone profound alteration. At the periphery the pumice is transformed into 
