120 
composition, have assumed a reddish or unnatural brownish 
colour ; others, in a later stage, exhibit minute patches of 
the black oxide studding their surface, appearing as if 
affected by a black mildew ; others are almost entirely 
covered with the incrusting mineral ; while, in the final 
stage, the whole of the organic matter has disappeared. In 
short, the rootlets are completely pseudomorphosed into 
hydrated dioxide of manganese by the action of the decom- 
posing plant tissue upon a solution of some manganese salt. 
These facts are interesting as showing that the deposition 
of oxide of manganese is still taking place, or, at least, did 
take place until the section was opened. There is now 
no perceptible percolating water, even in the most rainy 
weather, but the mineral is at all times moist. 
With regard to these oxide of manganese pseudomorphs, 
it appears that very few cases of the alteration of organic mat- 
ter into this mineral have been recorded. This oxide is not 
mentioned in Phillips’ Mineralogy,* in the list of minerals 
said to occur as petrifactions, but is referred to in the 
“Erster Nachtrag zu den Pseudomorphosen,” by Blum. 
Wiser has described a fossil consisting of black oxide of 
manganese, which he stated, in 184 2/ f to be the first in- 
stance on record of this mineral occurring in a petrifaction ; 
and again, in 185 1 ,|| he mentioned a fragment of an Am- 
monite from Gonzen, near Sargans (Switzerland), which was 
fossilized in the same manner. Neither of these cases, how- 
ever, can be regarded as quite similar to the pseudomorphism 
of the rootlets, since it was not the truly organic matter 
that was mineralised, but the surrounding chiefly-inorganic 
shell. 
The mineral itself, as found in the bed of rock in the 
section at Ratcliffe Wood already described, is of a bluish- 
black colour when freshly obtained, but assumes a browner 
* Edit. Brooke & Miller, 1852. 
f Jahrbuch fur Mineralogie, &c. || Ibid. 
