382 SECTIONAL TRANSACTIONS.—C. 
9, Prof. M. B. Baker.—Metallogenesis and the Pre-Cambrian of Canada. 
Pre-Cambrian rocks occupy more than half the land area of Canada, and 
present a peneplained surface, developed during pre-Cambrian times. There 
were at least two great orogenic movements, developing mountain ranges not 
unlike the rocky ranges of Western Canada to-day. Both of these systems of 
mountains were eroded and base-levelled to a depth sufficient to expose enormous 
batholithic bodies of plutonic rocks. 
The main topographic features of the country, the major courses of the 
streams, the longer axes of the lakes and main deflexions, the axes of the anti- 
clinal and synclinal folds, and the general occurrence and shape of most of the 
intrusive bodies of igneous rocks, are.all directly the result of the rock structure 
of the country, the general trend of all being in a north-easterly and south- 
westerly direction. 
Formations that occupy so large an area, and that are so highly metamor- 
phosed as to destroy most evidences of superposition, and all traces of fossil 
contents, will be open to many interpretations. There is a general agreement, 
however, that three great eras of time are represented, which may be referred 
to as the lower, middle, and upper pre-Cambrian, with two long periods of 
erosion that produced very great unconformities. 
Each of the three eras was brought to a close by a period of marked igneous 
activity. It is noteworthy, however, that whereas the igneous intrusions that 
closed the upper pre-Cambrian era were accompanied by some of the greatest 
deposits of copper, nickel, silver, cobalt, and iron that the world has known, and 
that similarly some of the richest gold deposits yet found accompanied the 
igneous activity that closed the middle pre-Cambrian era, the igneous rocks 
that mark the close of the lower pre-Cambrian era show no evidence of metalli- 
ferous content, at least of economic value. 
As the igneous rocks of all three periods cut through country rocks of both 
sedimentary and igneous origin, and which vary in all degrees of basicity, it is 
evident that these marked differences in ore deposition cannot be due to the 
country rocks, but must be explained by the character of the intrusions them- 
selves. The intrusions that closed the middle and the upper pre-Cambrian eras 
show striking evidences of differentiation, the well-known Sudbury batholith 
being the world’s classic example of this process. The igneous rocks reported 
as closing the lower pre-Cambrian era show no evidence of differentiation. They 
are described as grey to pinkish granite (gneisses). 
Since differentiation of rock magmas, the development of sub-magmas, and 
the expulsion of mineralisers during the crystaliisation of igneous rocks, are 
looked upon as the controlling influences in ore-deposition, it would appear that 
the economic future of the pre-Cambrian areas of Canada depends on the general 
delimitation of those highly differentiated igneous rocks that mark the close 
of the middle and upper pre-Cambrian, followed by an intensive and careful 
exploration of their contacts with suitable country rocks. 
10. Assoc.-Prof. ALEXANDER MacLnan. -— -The Structural Features of 
the Kirkland Lake Gold District. 
11. Dr. J. M. Bext and Asst.-Prof. Extis Toompson.—The Effect of 
Deep-seated Alterations upon the Mineralogical and Geological 
Features of the Keeley Mine. 
The Keeley Mine is situated in the district of South Lorrain, about sixteen 
miles south-east of Cobalt. The Keeley, both in the nature of its general 
geology and in the details of its vein-structure, is very similar to Cobalt, but 
it is noteworthy at the Keeley that the veins occupy pronounced faults, while 
those of Cobalt are ordinarily in joint-like cracks, in which there has been little 
or no displacement. The most interesting differentiation, however, is to be 
found in the extent to which weathering is effective at the Keeley, as compared 
with Cobalt proper. This unusual alteration at fhe Keeley is associated with 
a zone of pronounced and radiating faulting, which is believed to have connec- 
tion with the major faults of the district. The latter are occupied by such 
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