GEOLOGICAL NOTES IN THE GEE AT EXHIBITION. 



887 



0|)eration Is slower in tlie case of tlie laljrndoi'ilc (licro is no j^^realer amount 

 of mcdianieal contrivance required tlian for marble, and liiat 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 sam])le of the oldest stratified (?) rock 

 on our globe; a piece of the floor in reality of tlie great superslriicturc of 

 <]ie earth's crust. Mr. O. Donnell, C.E., of (Quebec, sends a s))ecimen 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 ])redoTninating over the 

 quartz), and black hornblende, all running in irregular parallel planes, 

 showing the gneissoid structure very distinctl}^ 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 the 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 hue 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 Laurentian rocks, rising into the highest peaks of the ortho- 

 clase region, and generally constituting the main body of the rock sepa- 

 ]-ating 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 a]:>pear 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 

 ai)pears to be E. to W. These greenstone dykes are interrupted by 

 an intrusive syenite, a mass of wliicli occupies an area of 36 sqiuire 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 Gauanoque. In Grenville the syenite is penetrated 

 b}'' dykes of a porphyritic character. These masses belong to what has 

 been called felsite porphyry, hornstone ])orpliyry, 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 felds])ar, 

 apparently orthoclase, and less frequently small grains of a nearly colourless 

 quartz. All these intrusive masses arc cut by another set of dolerite dykes, 

 which probably belong to the Silurian period or ])erhaps to the Devonian. 



Two specimens of granite arc exhibited, one from St. Joseph Beauce, 

 v,hovc the band of granite— about 50 or GO 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 serix-ntine, and is supposed to be an altered and not an 

 intrusive rock. It occurs in the Quebec group of. the Lower Silurian. 

 An intrusive !;i'anile of Deviuiian a^e cH'i'urs in ('onsiderabK> abundaiice in 



