80 
THE PRINCIPAL FLOOR. 
The bog-iron ore is an interesting variety of limonite formed 
in low marshy ground from the decomposition of other iron 
ores. It always contains a large proportion of impurities, 
phosphoric acid being often present to a considerable extent. 
The lake ores of Sweden, -Norway, and Finland, are concre- 
tionary forms of brown iron ore formed, by organic agency, at the 
bottom of shallow lakes, whence they are obtained by dredging. 
Brown iron ore appears in many cases to have resulted from 
the alteration of the carbonate of iron, to which species we now 
pass. 
This valuable mineral, called indifferently Spathose iron ore , 
chalybite, siderite, and sparry iron ore, frequently occurs 
crystallised in rhombohedral forms, which commonly present 
curved faces, well seen in the fine specimen from Dauphine ; 
whilst the large crystals from Hiittenberg in Carinthia exhibit 
the change of this mineral into brown iron ore by the elimination 
of carbonic acid and the absorption of oxygen and water. 
Immense beds of spathose ore are found in Styria, forming part 
of the Erzberg, a mountain from which it was probably dug by 
the Romans. In Carinthia an excellent ore of this kind exists, 
from which iron and steel of the first quality are produced. 
Valuable deposits of spathose ore occur in the Devonian rocks 
in the neighbourhood of Siegen in Rhenish Prussia, including 
the celebrated Stahlberg, near Musen, where it has been worked 
since the fourteenth century. 
The remainder of this Case is occupied by iron ores of far less 
importance than those already mentioned. Among these may 
be noticed the Elban silicate of iron, called Ilvaite or lievrite ; 
the common arsenio -sulphide of iron, or Mispickel ; and the 
rarer arsenide of iron, from Reiclienstein, termed Lotingite, the 
treatment of which for the separation of gold will be noticed at 
p. 97, The large pentagonal dodecahedrons of Iron pyrites from 
Elba, and the fine bronze-coloured crystals of Pyrrhotine or 
magnetic pyrites, from Brazil, also deserve attention ; and these, 
with a small collection of Chrome iron ores, complete the series. 
Manganese, Bismuth, &c. 
Case 20. — Examples of the rarer oxides of manganese called 
Hausmannite and Braunite are placed by the side of the oxides 
known as Pyrolusite, Manganite , and Psilomelane (p. 70), 
minerals which are largely raised in Spain, Nassau, Thuringia, 
and the Hartz. With these oxides are grouped specimens of the 
pale pink carbonate of manganese called Diallogite, or manganese 
spar, and of the rose-red silicate termed Rhodonite ; whilst the 
sulphides are represented by samples of Alabandine or 
manganese blende, and by the rare mineral Hauerite, from 
Hungary and Sicily. 
The minerals of the somewhat rare metals which follow need 
but slender description. A few ores of Bismuth are introduced, 
principally from the cobalt mines of Saxony ; and with these are 
