MINERALS AND GEOLOGY OF CANADA. 431 
‘tines occur in Tuscany and elsewhere. In some cases, however, mas- 
sive serpentines of this kind may have been derived from the altera- 
tion of trap and greenstone rocks. The serpentines which occur in 
Canada, are considered to belong entirely to the Metamorphic series, 
and are described, consequently, under that division. 
6. Granites.—These rocks possess normally a crystalline aspect 
and strongly-marked granular structure, whence their name. They 
are also especially characterized by the presence of free silica, or 
quartz, as an essential component. They occur in irregular, unstrati- 
fied masses (often breaking through and tilting up the surrounding 
rocks), or in tortuous branching veins. Some are of very ancient 
date ; whilst others are of comparatively recent formation, at least 
in a geological point of view. Hence the obvious objections which 
apply to the use of the terms ‘ Primary” or “ Primitive,’ often 
bestowed indiscriminately on all granitic rocks, as well as on strata of 
metamorphic origin—these latter, like the granites, and all other 
rocks, indeed, being of various periods of formation. Under a subse- 
quent section, it will be shewn that the age of a rock is in no way 
indicated by mineral characters or composition. Where two granitic 
or other veins intersect, the intersected vein (which is generally 
displaced moreover, one portion being thrown up or down) will, of 
course, be the older of the two. In like manner, where a granitic or 
other eruptive rock underlies another rock of any kind, this latter will 
necessarily be the older of the two if veins pass into it, or if it be 
altered by chemical or mechanical action. 
The more important rocks of this section, comprise granite and 
syenite 
Granite, properly so-called, is composed of three minerals : Quartz, 
Feldspar, and Mica, full descriptions of which are given in Part II. of 
this Essay. The quartz is colourless and vitreous; the feldspar, 
usually white or flesh-red, with smooth and somewhat pearly cleavage 
planes; the mica, white, grey, brown, black, or sometimes green, in 
scales, specks, or folie, of a pearly-metallic aspect. In the fine- 
grained granites, these component minerals become so intimately 
blended as to be individually undistinguishable. When crystals of 
feldspar are distinctly imbedded in a fine or coarse-grained granitic 
mass, a variety termed Porphyry, or better, Porphyritiec Granite, is 
produced. The term “porphyry” (from zopdupa) as the name 
would indicate, was originally applied to rocks of this kind in which 
