MINERALS AND GEOLOGY OF CANADA. 433. 
METAMORPHIC ROCKS. 
The rocks thus named are stratified rocks of a more or less granitic,. 
trappean, or crystalline aspect, and of various periods of formation. 
It has been already stated, that where a dyke, vein, or erupted mass 
of trap or granite traverses other rocks, these latter are very generally 
altered in character, and, to some extent, in composition. Earthy or 
common limestones are thus near the points of contact transformed, 
in some localities, into hard marbles or crystalline limestones, and are 
frequently filled with crystals of garnet, tourmaline, hornblende, and 
other minerals. In like manner, sandstones are changed in colour 
and texture, and are often converted into quartz-rock; whilst clay- 
slates are transformed into gneiss, mica-slate, tale-slate, and other so- 
called ‘‘ crystalline schists.”’ Although analogous effects are some- 
times produced artificially in the walls of smelting furnaces, these 
metamorphic results, as seen in Nature, are probably due not so much 
to the simple agency of heat, as to that of various gases and heated 
vapours accompanying the protrusion of the eruptive mass. In many 
localities, on the other hand, these effects appear to have been pro- 
duced without the direct intervention of eruptive rocks, in which case 
the alteration or metamorphism has probably proceeded from steam 
and gases transmitted from below, from heated chemical solutions 
percolating the altered rocks, or from other causes more or less imme- 
diately dependent on the presence of subterraneous heat. Be this as 
it may, it is now universally conceded that the crystalline stratified 
rocks are altered sedimentary deposits—sandstones, slates, limestones, 
and so forth. In Canada (as explained more fully in Parr V.) there 
are two distinct series of metamorphic rocks. One, including the 
Laurentian and in part the Huronian series, belongs to the Azoic 
Age, and constitutes the most ancient group of rocks of this conti- 
nent. The Laurentian series is made up of vast beds of gneiss, crys- 
talline limestone, and other rocks described below, and it extends 
over almost the entire northern portion of the Province. For geo- 
graphical limits, geological and other characters, see Part V. of this 
Essay. The Huronian rocks of the north shore of Lake Huron, &c., 
are also in part metamorphic, and include, amongst other more or 
less altered deposits, some remarkable quartz and jasper conglome- 
rates. The other series of metamorphic strata are of more recent, 
although still of ancient, date. They belong to the Silurian and 
