434 A POPULAR EXPOSITION OF THE 
Devonian periods of the Palzeozoic Age (see the close of this Parr, 
and also Part V.), and they occur in the Eastern Townships and ad- 
joining district south of the St. Lawrence. On the edge of this 
latter metamorphic region, the passage of the unaltered into the 
altered strata may be traced in many localities. 
The following are the more important metamorphic rocks of Cana- 
dian occurrence : 
Gneiss.—This crystalline rock only differs (lithologically) from 
granite and syenite by occurring in beds or strata. It is of two kinds: 
micaceous or ordinary gneiss, and syenitic or hornblendic gneiss. The 
former consists of quartz, feldspar, and mica; the latter, of quartz, 
feldspar, and hornblende. When the mica or the hornblende predo- 
minates, and the feldspar diminishes in quantity, these pass into mica 
slate and hornblende slate (or hornblende rock), respectively. Gneiss- 
oid rocks of this kind prevail everywhere amongst the Laurentian 
strata, and sometimes contain garnets and other minerals. They con- 
stitute, moreover, the greater number of the boulders scattered so 
abundantly over the surface of Canada (see Parr V.) Gneiss may 
generally be distinguished from granite, even in hand specimens, by 
its striped or banded aspect, the colours being usually various shades 
of grey and red. 
Mica Slate——This rock consists normally of quartz and mica. It 
is more or less fissile or schistose, somewhat pearly or silvery in as- 
pect, and usually of a white or greyish colour, though sometimes 
almost black. It passes into gneiss on the one hand, and into clay- 
slate on the other. It is often called mica schist. It occurs more or 
less, throughout the Laurentian formation (Lake Huron, north shore ; 
French River; Baie St. Paul, &c.) 
Feldspar Rock.—This is a mixture of various feldspars. It is 
usually of a greenish-blue or slightly-shaded white colour; or, other- 
wise, pale reddish, greenish, brownish-yellow, &c. Fine-grained and 
porphyritic varieties occur. In the latter, the enclosed, grey, cleave- 
able masses sometimes present the green and other reflections peculiar 
to the characteristic examples of labradorite. (See Part II.) At 
other times, these enclosed masses or crystals are of a red, lavender- 
blue, or brownish colour. Hypersthene, also, in laminar masses of a 
brown sub-metallic tint, is frequently present, forming the variety 
sometimes called Hypersthene Rock. Mica, augite, garnet, titanife- 
rous iron, and some other minerals, are likewise of occasional oceur- 
