GEOLOGICAL NOTES IN THE GEEAT EXHIBITION. 
387 
operation is slovrer in the case of the labradorite there is no greater amount 
of mechanical contrivance required than for marble, and that slabs could 
be prepared for chimney-pieces and other articles of furniture at a cost 
beyond that of marble not greater than is proportionate to the superior 
beauty and durability of the material. The foot square of gneiss ought to 
be looked upon with reverence, as a sample of the oldest stratified (?) rock 
on our globe ; a piece of the floor in reality of the great superstructure of 
the earth's crust. Mr. O. Donnell, C.E., of Quebec, sends a specimen of 
the gneiss used for building the reservoir of the Quebec Waterworks on 
the St. Charles river. It is hornblendic and composed of translucent 
colourless quartz, white orthoclase (the feldspar predominating over the 
quartz), and black hornblende, all running in irregular parallel planes, 
showing the gneissoid structure very distinctly, and having at a little dis- 
tance a general grey colour. The rock splits in almost any direction by 
means of wedges, but most easily on that of t!ie gneissoid layers, particu- 
larly where these are even. The layers are however occasionally affected 
by undulations and contortions, but these do not materially affect its divi- 
sion by wedges. The rock splits and dresses with most difficulty at right 
angles to the gneissoid layers. It is capable of receiving fine smooth 
faces, giving sharp edges and corners. Masses of almost any size can 
be blasted out from the rock. From Grenville we have a specimen 
of porphyroid orthoclase gneiss, which forms great mountain-ranges 
among the Laarentian rocks, rising into the highest peaks of the ortho- 
clase region, and generally constituting the main body of the rock sepa- 
rating One important band of limestone from another. These masses 
appear to attain several thousand feet in thickness, divided however at 
unequal intervals by thinner and less feldspathic bands, in which the strati- 
fication is more distinct. 
The intrusive masses of the Laurentian series consist chiefly of syenite 
and dolerite. These occur in many parts of the country, but their relative 
ages have been ascertained almost altogether by the investigation of the 
counties of Ottawa and Argenteuil. What appear to be the oldest are a set 
of dykes of a rather fine-grained dark greenish-grey greenstone or dolerite, 
varying in thickness from a few feet to 100 yards. Their general bearing 
appears to be E. to W. These greenstone dykes are interrupted by 
an intrusive syenite, a mass of which occupies an area of 36 square miles 
in the townships of Grenville, Chatham, and Wentworth ; specimens of 
this S3'enite are exhibited, as also from a mass of a similar character occurring 
between Kingston and Gananoque. In Grenville the syenite is penetrated 
by dykes of a porphyritic character. These masses belong to what has 
been called felsite porphyry, hornstone porphyry, or orthophyre, having 
for its base an intimate mixture of orthoclase and quartz, coloured by 
oxide of iron, and varying in colour from green to various shades of black. 
Throughout the part which is homogeneous and conchoidal in its fracture, 
are disseminated well-defined crystals of a rose-red or flesh-red feldspar, 
apparentl}'- orthoclase, and less frequently small grains of a nearly colourless 
quartz. All these intrusive masses are cut by another set of dolerite dykes, 
which probably belong to the Silurian period or perhaps to the Devonian. 
Two specimens of granite arc exhibited, one from St. Joseph Beauce, 
\^here the band of granite — about 50 or 60 feet thick — has been worked 
for millstones. It has a considerable proportion of quartz, and would be 
a strong and durable stone for building. It runs with the stratification 
near to a band of serpentine, and is supposed to be an altered and not an 
intrusive rock. It occurs in the Quebec group of the Lower Silurian. 
An intrusive granite of Devonian age occurs in considerable abundance in 
