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ment with hydrochloric acid. It is situated in the midst 
of shales, and most of the small fissures for some distance 
beneath it are filled with black oxide of manganese. 
The oxide of manganese occurs in many other fissures in 
and around Ratcliffe Wood, but nowhere so abundantly as 
in the sections referred to. in this paper. The most widely 
spread form is a thin black film, not sufficiently thick to 
exhibit to the unassisted eye any pellet-like structure, as is 
the case with the mineral described above. Such a film is 
to be seen in some of the fissures in almost every section in 
the wood, and the fact that the oxide does not occur in 
larger quantities cannot be owing to the circumstance that 
there are no cracks exposed so large as those in which it is 
found in pellets, miniature columns, and threads, but in 
consequence of its scarcity in the stratum from whence it 
was derived ; for in one quarry there are two faults which 
produce cavities and fissures of a much larger size, and yet 
these are well filled with brown iron ore with a com- 
paratively small amount of MnO a . 
In the Triassic strata, on the E. side of the Red Rock 
Fault, this mineral occurs not only as an infiltration-product, 
but also as a part of the cementing material of certain thin 
beds of the sandstone. 
V . — References to Descriptions of Deposits of Hydrated 
Mn0 2 . 
On referring to Bisch off’s “Chemical Geology”* an 
enumeration of instances recorded before 1854 of the 
occurrence of deposits of hydrated oxide of manganese is to 
be found. Here no less than six cases are mentioned. 
During the repair in 1840f of a water channel hewn 
in the rock in the neighbourhood of Nurnberg, an immense 
mass of hydrated oxide of manganese was discovered. A 
spring near the Cape of Good Hope, whose waters have a 
temperature of 110°F., is said to deposit in the discharge 
* Yol. I., pp. 160, 161, Edit. 1854. f Journal fur prakt. Chem., Yol. 21. 
