114 A POPULAR EXPOSITION OF THE 
tian series, which forms the lower and more largely developed portion 
of the Azoic group, is chiefly characterised by its highly crystalline 
condition, and (as regards Canada) by the great beds of iron ore which 
it contains. The Huronian series includes many conglomerates and 
partially-metamorphosed slates amongst its strata, and is traversed 
by numerous quartz veins holding copper pyrites and other copper 
ores. Iron ore is also associated with this series, but not abundantly 
in Canada. The semi-crystalline condition of its rocks (as compared 
with the highly crystalline gneissoid strata of the Laurentian series) 
and the marked prevalence of slaty conglomerates, constitute its 
more distinctive characters. 
Laurentian Series.—These strata, the oldest series of deposits re- 
coguised on the American continent, are regarded as sedimentary 
accumulations, originally collected together by the action of water, 
and converted subsequently into a crystalline condition by the agency 
of metamorphic forces. (See under the head of “ Metamorphic 
Rocks” in Part II). Their absolute thickness cannot be ascer- 
tained, but it must be very great, embracing many thousands of feet ; 
and their exposed area in Canada, as estimated by Sir William Logan, 
covers a surface of about 200,000 square miles. It will be convenient 
to consider these Laurentian rocks under the following heads :— 
(1) Mineral characters; (2) Structure; (3) Associated intrusive 
rocks ; (4) Economic materials ; and (5) Topographical distribution. 
Mineral characters of the Laurentian strata ;--The stratified rocks 
of Laurentian age consist essentially of vast beds of micaceous and horn- 
blendic gneiss ; interstratified with subordmate beds of quariz-rock‘ 
mica-slate, hornblende-rock, crystalline limestone and dolomite, and 
oxidized iron ores ; and associated with thick beds of feldspar rock or 
anorthosite. In addition to these, a few quartzose conglomerates 
(shewing the metamorphic character of these deposits), thin layers of 
serpentine, beds and layers of a taleose character (Renselaerite or pyral- 
lolite: see Parr Ii.), and others composed in large part of Wollasto- 
nite, are interstratified with the limestones, or with the gneissoid beds, 
of particular localities. These different kinds of metamorphic rocks 
have been described already in Parr III.; but a few additional re- 
marks on some of their more special characters are necessary here. 
Viewing our Canadian formations, of this age, im their broader features, 
we may subdivide them conveniently, and to some extent naturally, 
