54 B. N. A. BOUNDARY COMMISSION. 
ally irregular, and with no very determinate direction. They are also 
common among hornblendic and altered rocks surrounding the intrusive 
masses ; and the latter, in such places, are probably not far below the sur- 
face, and have supplied the materials filling the veins. They have been 
seen to cut across granitic dykes, which are probably outlying spurs 
of the main masses. The granite and granitoid rocks of the southern 
part of the lake were also observed to be penetrated by the very 
large coarse-grained diorite dykes already described. These were 
not sufficiently well exposed to warrant any very definite statements 
concerning them, but appeared to have general east and west courses, 
and may very probably be among the oldest of the intrusions. 
Other diorite dykes, very hard and compact, cut both the granitic out- 
bursts, and altered Laurentian rocks, with a general bearing of north- 
east and south-west. These are specially frequent in the vicinity of 
Flag Island. 
Occurrence of Minerals of Economic Value. 
111. Minerals of economic importance, though carefully looked for 
throughout the district, were not observed to occur in any quantity. 
The existence of a vein with at least traces of copper, has been already 
mentioned, and I have been shown specimens of copper pyrites from 
several parts of the lake which I had not time to visit, which give 
ground for believing that workable and valuable deposits of this ore may 
yet be found. Small quantities of molybdenite were observed in connec- 
tion with the altered rocks in one place. Slaty rocks, though abundant, do 
not assume the character of true roofing-slate in any part of this region 
which I have visited. It is not always possible to ascertain how much 
of the cleavage of the rocks is due to bedding, and how much to true 
superinduced slaty-cleavage. The Huronian rocks are so closely pressed 
together, that the two seem often to coincide; and I did not observe any 
clear instance of slaty structure forming a considerable angle with the 
bedding. Of soap-stone, though not actually observed in place, I have 
seen specimens from localities in the south-eastern part of Clear-water 
Lake. Small quantities of magnetic iron sand are found along the 
shores of the southern part of Sand-hill Lake, but this mineral is 
known to be disseminated in small crystals through many parts of the 
Laurentian. 
112. Rocks of similar age and character to those here called Huronian, 
and which occupy the whole of Clear-water Lake, are known to be metal- 


