CHANGES IN ORE SINCE DEPOSITION. 239 
This analysis shows that the lead at least, which is the most conspicu- 
ous metallic constituent, is contained in the oxidized form both as sulphate 
and as carbonate, chiefly the latter. 
Sulphate of magnesia——)n the walls of abandoned drifts in the mines there 
form under favorable circumstances long, silky, and hairlike masses of 
crystals, sometimes several inches long. These are in places very abundant 
and beautiful. They have a bitter taste, and analysis shows them to be 
composed essentially of hydrous sulphate of magnesia, probably epsomite. 
On the walls of quarries or open cuts in the ore a drier white coating forms, 
which is composed of sulphates, chiefly the sulphate of magnesia. This 
sulphate probably originates from the decomposition of sulphides, the 
products of which form sulphate with magnesium solutions. 
Sulphur—At Lenado, on the dump of the Leadville mine, a thin crust 
of yellow sulphur was noted forming on the outside of the sulphide ores. 
There was also a noticeable smell of sulphur dioxide given off, and at the 
same place certain white sulphates were found. 
Bog manganese in caves —In the Best Friend mine, in Tourtelotte Park, there 
is evidence of a fissure which at some recent time existed along the Contact 
fault, and which locally opened out into considerable caves. In one of 
these caves, which was originally over 20 feet high, and which was subse- 
quently filled by cave sediments, the lowest layer of material is very fine 
grained and black, and a sample gave on analysis 45.86 per cent of 
manganese oxide, with 12.83 per cent of iron oxide. This manganese was 
evidently introduced by surface waters, and was precipitated by essentially 
the same process as that which forms manganese in bogs at the surface. 
The ores of silver and lead contain small amounts of manganese, the 
analysis of polybasite ore by 8. H. Pearce’ showing an average of 
1.03 per cent of manganese carbonate, while that of the oxidized ores 
in Tourtelotte Park by Dr. Stokes gives only a trace. It is probable, 
therefore, that the manganese is leached out of the ores in the pro- 
cess of oxidation, and that it may be precipitated in a concentrated 
form under favorable conditions, such as the bottom of this cave 
presented. 
Formation of gypsum—Qn the northeast side of West Aspen Mountain there 
is an extensive alteration of the Weber limestone to gypsum. Tunnels 
1Am. Jour. Sci., July. 1892, 3d series, Vol. XLIV, p. 17. 
