MINERALS AND GEOLOGY OF CANADA. 125 
occasionally into syenitic gneiss or syenite—according as to whether the 
rock be regarded as of sedimentary or eruptive origin. 
2. Associated Intrusive Rocks, Mineral Veins, §e :—The intrusive 
rocks which break through the Huronian series, and belong apparently 
to the same geological period, consist of numerous dykes of dark 
greenstone, varying in breadth from less than a foot to two hundred 
feet or more; and of some large masses and veins of red granite, 
frequently of an epidotic character. An exposure of the latter occurs 
in force on the north shore of Lake Huron, associated with Laurentian 
strata, but is regarded by Sir William Logan as most probably of 
Huronian age from its agreement in mineral characters with similar 
veins which traverse the deposits of that period at neighbouring 
localities. Some of the greenstone dykes are older, and others newer, 
than the granite masses. The vein-fissures filled with copper pyrites, 
&c., which are so abundant amongst these Huronian strata, are of still 
later formation, since they cut many of the greenstones and granites, 
and often break the continuity of these and the surrounding beds, 
causing upthrows or downthrows of greater or less extent. An enor- 
mous fault caused by a dislocation of this character, has been traced out 
by Mr. Murray in the valley of the Thessalon and adjoining district. 
In one place, a downthrow of nine thousand feet is attributed to this 
fault. (See the Report for 1858. Also Canadian Journal, vol. V, p. 463.) 
Finally, it may be observed that several large anticlinals extend across 
the Huronian strata of this region generally. The axis or summit of 
one of these, crosses the workings of the Bruce Mines. 
3. Heonomie Materials :—The more important substances of this 
class obtained from the Huronian rocks, comprise: copper ores; 
quartzose sandstones suitable for glass making purposes; hones of good 
quality ; and (as ornamental stones) the jasper conglomerates mentioned 
above. The copper ores belong chiefly to copper pyrites, purple cop- 
per pyrites or erubescite (the “horse flesh ore’’ of the miners), and 
copper glance: minerals which have been fully described in Parr II. 
These occur on the north shore of Lake Huron in veins or lodes, 
varying in thickness from about two to ten feet. The gangue or 
veinstone consists essentially of quartz, and the average yield of metal 
is said to be from six to eight per cent: amounting, however, in the 
dressed ore to about eighteen or twenty per cent. The principal 
workings are at the Bruce Mines (Cuthbertson location), Wellington 
Mines (Keating location), and at the Copper Bay Mines; but ore has 
