


LAKE OF THE WOODS—GENERAL CONCLUSIONS. 53 
rived from the degredation of comparatively unaltered Huronian rocks. 
From the occurrence of nacreous schists, and other points of resemblance 
to the rocks of the Quebec group, the latter supposition may probably 
prove to be the correct one, and these rocks be classed as nearer in age 
to the Quebec group than the true Huronian. Mz. Selwyn, in treating of - 
similar rocks explored by him north-west of Lake Superior, writes: “As 
regards the age of these so-called Huronian rocks, the evidence is not of 
the most satisfactory kind. While stratigraphically they rest directly 
upon highly crystalline and typical Laurentian gneisses, mineralogically 
they resemble as closely the chloritic, epidotic, and dioritic strata of the 
altered Quebec group, as they do those which on the shores of Lakes 
Huron and Superior are referred to the Huronian series.” * All that can 
be definitely said with regard to the age of these rocks in the region of 
the Lake of the Woods, taken by itself, is that they are newer than the 
typical Laurentian, there largely developed, and older than the little 
altered and nearly horizontal Lower Silurian limestones of Fort Garry 
and Lake Winnipeg. 
109. Numerous localities present opportunity for the study of the na- 
ture of metamorphism experienced by the rocks of the green slate series, 
when approaching intrusive masses. The chloritic, talcose, and nacreous 
slates, are observed, when nearing such a centre of alteration, to become 
harder and less finely fissile, and to assume green and grey-green colours 
from the formation of crypto-crystalline hornblende, and possibly also of 
epidote. They next become still harder and more compact, changing to 
a green altered rock, characterized by hornblende, and in which the ori- 
ginal bedding can sometimes scarcely be distinguished. Where imme- 
diately in contact with the eruptive rock, this is generally still further 
changed to a grey soft gneiss, by the appearance of mica in place of 
the hornblende. The conglomerates generally show a tendency to pass 
from hard green altered rock, to rocks of a roughly gneissic character, 
which still exhibit remains of the component fragments on fractured 
surfaces. 
110. A tableshowing the character and directions of all the dykes and 
intrusive masses is appended. The granitoid gneisses and intrusive gran- 
ites are universally cut by veins of red orthoclase felspar, associated with 
white quartz. These appear to be true segregation veins, formed by a 
re-arrangement of the materials of the rocks themselves in cracks, gener- 


* Report of Progress Geol. Surv. Canada., 1872-73. 

