MINERALS AND GEOLOGY OF CANADA. 119 
neous geological age, appear to be exceedingly rare. Many of the 
granitoid and quartzose veins seen amongst the gneissoid strata, are 
considered, by those who ‘have had the best opportunities to study 
them, as veins of segregation rather than true eruptive matters. The 
most important example of undoubted eruptive origin, is the great 
mass of syenite described by Sir William Logan as occupying an area 
of about thirty-six square miles in the townships of Grenville, Chatham, 
and Wentworth, near the left bank of the Ottawa. This consists of 
red or white potash-feldspar, with black hornblende, and a small 
amount of quartz; but here and there it contains a certain amount of 
mica also, forming the variety generally known as syenitic granite. 
This eruptive mass cuts a series of greenstone dykes belonging to a 
still earlier eruption ; and is in itself traversed by another series of 
porphyritic dykes of a necessarily more recent origin. The greenstone 
dykes, according to Sir William Logan, exhibit a well-marked columnar 
structure, and vary in width from a few feet to a hundred yards: 
These three eruptive formations are also intersected by a fourth series 
of dykes, supposed to be of Palzeozoic age. (See Report for 1853. 
Also the Revised Report on the Geology of Canada). As the more 
northern and uncleared districts within the vast area of our Laurentian 
region become opened up ox more thoroughly explored, other eruptive 
masses of an analogous character will, in all probability, be brought to 
light. 
4. Economie Materials:—In addition to good building stones of 
gneiss, &c., obtainable generally throughout the region occupied by our 
Laurentian rocks, the following are the more important economic mate- 
rials discovered in these strata up tothe present time: * (a) Lron 
Ores ; (6) Lead Ore; (c) Sulphide of Molybdenum ; (d) Graphite ; 
(e) Mica; (f) Ornamental Feldspars ; (g) Marbles ; (h) Sulphate of 
Baryta; (¢) Millstones. 
(a) Lron Ores.—These comprise Magnetic Oxide of Iron ; Specular 
Iron ore (or Red oxide of Iron); and Titaniferous. Iron Ore. The 
magnetic ore occurs principally at the following localities :—(1) Bel- 
mont Township (the Marmora mine): several beds, lying between 
crystalline limestone and gneiss, and mixed with layers of serpentine, 
talcose slate, &c. Total thickuess of the ore beds, over 400 feet.—2, 
Madoc Township: Bed of ore of excellent quality, 25 feet thick, in 
* These various substances will be found described in full, as regards mineral characters, 
composition, &c ,in Part II. of this Hssay. 
