178 A POPULAR EXPOSITION OF THE 
in thin pieces; H. 1.0-2.0; Sp. gr. about 2.0. Inalterable before 
the blow-pipe. It occurs in small scales disseminated more or less 
throughout our Laurentain formation, and more especially im the 
crystalline limestones of that series; but its principal Canadian 
localities are the townships of Grenville (Addington County,) and 
Fitzroy (Carleton County,) on the Ottawa. At the former locality it 
constitutes several veins, each of an average thickness of about 
five inches ; and is associated with garnets, zircon, feldspar, and other 
minerals. Graphite when of fine granular structure and dark colour, 
is extensively employed, under the popular name of Plumbago or 
‘«< Black-Lead,” in the manufacture of the so-called black-lead pencils. 
It consists, however, simply of carbon (or of carbon mechanically 
mixed with oxide of iron,) and does not contain a trace of lead. Our 
Canadian graphite is unfortunately too coarse and not sufficiently 
intense in colour for pencils, but, according to Sir William Logan, it 
may be used in the manufacture of refractory crucibles. Some 
samples that we have seen, might be employed also when ground to 
powder, as a polishing material for grates and stoves. 
Molybdenite :—This substance much resembles graphite, but is of a 
lighter colour; and whilst it leaves a black trace on paper, it makes a 
dull greenish streak on smooth porcelain. It occurs chiefly in small 
scaly masses of a lead-grey colour. Like graphite it feels somewhat 
greasy, and it is also flexible. H. 1.0-2.0; Sp. gr. 4.4-4.8. In- 
fusible, but it colours the blow-pipe flame pale-green, and volatilizes 
very slowly, depositing a white crust of molybdie acid on the 
charcoal. One hundred parts consist of: sulphur 41, molybdenum 
59. It is not uncommon in small quantities amongst our Laurentian 
rocks generally, and in the intrusive granites of that formation. As 
special localities, we may cite from the Reports of the Geological 
Survey: Jerome, C. E.; Mud Turtle Lake, north of Balsam Lake ; 
the River Doré near Gros Cap; and a granite vein on the west side 
of Terrace Cove, Lake Superior. Molybdenite is the principal source 
of molybdenum compounds, used in porcelain painting, and as a re- 
agent in certain chemical experiments, &e. 
To this section belong also, Pyrolusite or Black Manganese Ore, and Sulphide 
of Antimony or Grey Antimony Ore. The former (a compound of oxygen 36.7, 
manganese 63.8) occurs chiefly in radiating fibrous masses of a black or dark 
steel-grey colour, and is quite infusible. We have received a specimen said ;to 
