Common RocJcs of the British Frovinces. 197 



quartz, rose quartz, ferruginous quartz, violet quartz, or amethyst, according 

 to its structure or appearance. 



The most certain metliods of deciding as to whether a particular 

 specimen is quartz or not is to try it with glass and steel. If a fragment of 

 mineral be white or transparent, and it will scratch glass and give sparks to 

 steel, it may be pretty safely labelled as quartz. 



Felspar somewhat resembles quartz in external appearance, being often 

 white, and sometimes semi-transparent. It is however of an inferior degree 

 of hardness and may be scratched with the point of a well tempered knife, 

 while quartz is so hard that, steel makes no impression upon it. It is of 

 various colours, white, grey, yellow, blue, green, or red. It has generally a 

 pearly lustre, and breaks up into rhomboidal fragments, a form never assumed 

 by quartz in its fracture. Among the Laurentian rocks, and in the boulders 

 derived from this formation specimens of felspar may be readily procured 

 in this shape, and by frequently observing these, the eye will soon become 

 familiar with the external appearance of the mineral with respect to its lustre, 

 forms of cleavage, &c. When felspar and quartz of the same colour, however, 

 are confusedly mixed together in small grains, they cannot be distinguished 

 unless by an experienced eye without resort to other methods which we shall 

 notice hereafter. 



31ica is easily recognised. It is a mineral remarkable above all others 

 for the facility with which it may be divided into thin leaves. It is often, 

 though improperly called Isinglass. It is generally of various shades of 

 yellow and brown. Yery thin flakes are transparent. Large sheets of it 

 are used by the Russians for windows in their ships, the advantage being, 

 that while by reason of its transparency it serves the purpose of glass, yet, 

 03 it is exceedingly tenacious, it cannot be broken by the concussions 

 resulting from the discharges of heavy artillery. It is also used for lanterns, 

 and as heat does not destroy it, for stove doors. This mineral occurs in the 

 gneiss and limestone of the Laurentian rocks in small scales or specks, or in 

 crystals from one eighth to several inches in diameter, preserving however 

 its lamellar character. 



Hornblende is dark bottle-green or brownish green, or brown approach- 

 ing to black, but when pulverized, of a greenish grey. Its lustre is vitreous 

 or glassy, and it yields pretty easily to the knife. When in considerable 

 masses it is tough, and is not easily broken like the brittle species. It is a 

 very abundant mineral, being an essential ingredient of various species of 

 rocks and is found in most countries. 



The above four minerals by their combinations constitute a vast propor- 

 tion of all the harder kind« of rock in Canada. Some idea of their abun- 

 dances may be formed by ti.king a general view of the geographical extent 

 of the Laurentian formation. This great system of rocks constitutes an 

 irregular belt from one hundred to three or four hundred miles in width 

 extending from Labrador to the country lying north of Lake Superior, a 

 distance of more than a thousand miles. In its course it makes a deep bend 

 towards the south and sends out a projection which crosses the St. Lawrence 



