48 MINERALOGY AND LITHOLOGY. 
exists in most of the bog ores of iron, as is proved by treating them with 
hydrochloric acid. In some of our bogs this ore can be seen in process 
of formation. A sluggish stream, flowing perhaps from a chalybeate 
spring, runs into a marshy spot, and the top of the water is seen covered 
with an iridescent slime,—a result of the oxidation of the iron in solution 
to the insoluble sesquioxide,—while the bottom is covered with a yellow 
deposit of sesquioxide of iron. 
Limonite is a common constituent of rocks. Sometimes it exists as 
an original constituent, as where it forms the cementing material of con- 
glomerates; or, again, it results from the hydration of other oxides of 
iron, under which circumstances it appears as a yellow, semi-transparent 
substance surrounding an opaque, unaltered core, if the decomposition 
is incomplete. 
I would refer to a number of analyses of hydrous iron ores in Jack- 
son’s report; but, as they have no mineralogical significance, they are 
not reproduced here. 
35. PSILOMELANE, Wap. 
Impure, hydrous manganese oxides. Wad is found in many of the 
deposits of bog iron ore. Sometimes it is sufficiently compact and pure 
to be called psilomelane, but most of it is very impure, being much con- 
taminated with iron oxides, organic matter, and other impurities. It is 
recognized as a manganese oxide by its black color, and its manganese 
reactions before the blow-pipe. Psilomelane is fonnd at Winchester, 
with the other manganese minerals. 
36. Motyzspire [Mo 03]. 
This mineral is a result of the oxidation of the sulphuret of molyb- 
denum or molybdenite, and occurs in connection with it. It is found in 
the cavities of the veins of molybdenite in Westmoreland in considera- 
ble amount, and less abundantly with the other deposits in Landaff and 
Franconia. As it occurs in our state, it is an earthy, yellow mineral, 
filling cavities or incrusting the sulphuret. 
This mineral is easily recognized by heating it with the blow-pipe upon 
a piece of charcoal, when it is volatilized, coating the coal with a white 
sublimate, which, when touched for an instant with the reducing flame, 
is changed to a beautiful blue color. 
