GEOLOGICAL J^OTES IN THE GREAT EXIlIBITIOIf. 
385 
A considerable portion of the rocks of the Quebec group in tlieir meta- 
morpliic condition consists of chloritic slates, which appear to occupy a 
higher stratigraphical position than the magnesian strata just noticed. 
Magnesian mica, or phlogopite, occurs abundantly in small scales in tlie 
crystalline limestone of the Laurentian sj^stem, but sometimes also in 
crystals sufficiently large to be economically available. Among its asso- 
ciated minerals are commonly quartz, pyroxene, and feldspar, and occa- 
sionally tabular spar, apatite, spheric iron pyrites, idocrase, garnet, tour- 
maline, zircon, and corundum. In Grenville crystals of mica have been 
obtained, giving sheets measuring 24 by 14 inches. In North Burgess, 
where it has been mined, the mica is embedded in a soft pyroxenic rock 
and limited by a band of quartzite on the south side. The mica there ap- 
pears to run for 75 yards in tolerablj^ regular bands, and some of the 
sheets after being dressed are as much as 20 inches square ; some have 
been obtained measuring 20 b}" 30 inches. The crystalline limestones of 
the Laurentian system are marked almost universally by the occurrence 
of graphite or plumbago in small scales, which are often so thickly disse- 
minated in particular bands of the rock -as to give them a black or dark 
grey colour, distinctly marking the stratification. Plumbago also occurs 
in beds, of sufficient purity and quality to be economically available. The 
workable beds are chiefly on the north side of the Ottawa, and occur in 
many localities at considerable distances from one another, but several of 
the exposures are probably repetitions of the same bed, or at any rate of 
beds approximately equivalent in repetition of the same band of Laurentian 
limestone. The whole Laurentian series is so corrugated that the outcrop 
of one of these bands of limestone in the counties of Argenteuil iind Two 
Mountains, followed through all its windings in an area of fifty miles by 
twenty, measures up\A ards of two hundred miles. Abed of pure graphite 
occurs in the augmentation of Grenville township, and has been traced at 
intervals for a distance of three miles. One of these exposures has been 
mined by Messrs. Eussell & Co.. and at the opening of the excavation the 
graphite showed a thickness of ten inches ; but the pure substance was 
found to form a lenticular mass, separated from other masses of the same 
character by intervals in which the graphite became mixed with the lime- 
stone. It is probable that a number of these lenticular masses running 
through the rock at the same horizon may represent the general character 
of the workable beds. Asbestos, generally a fibrous serpentine or chryso- 
lite, occurs in veins cutting the serpentine of the Quebec group in the 
Eastern Townships (St. Joseph Seigniory). A friable sandstone in the 
Potsdam formation occurs at Pittsburgh, twenty feet thick, and is much 
in demand for protecting the sides and bottoms of iron foundries, it is sup- 
plied to those at Montreal and Toronto, at distances of a hundred and se- 
venty miles in opposite directions. 
Of the minerals applicable to common or decorative construction it 
would be perhaps of no great service to English geologists to give ver)-- 
minute details. Still however the characters of the samples, as indicative 
of the nature of the rocks constituting the formations to which they belong, 
will be at least interesting. We begin with a sample from one of the bands 
of crystalline limestone of the Laurentian series from the Lac des Chats. 
Another building-stone comes from Phillipsburg (St. Armand) ; the rock 
is compact and crystalline, and of considerable strength. A few obscure 
fossils show the formation to be the Calciferous of the Quebec group. 
There are specimens of building-stones from Caughnawagu, St. Dominique, 
and East Hawkesbury, all from the Chazy formation, which in those dis- 
tricts is composed of massive beds yielding blocks of stone fitted for canal 
VOL. Y. 3 D 
