386 MORLEY E. WILSON 
PRINCIPLES OF PRE-CAMBRIAN CORRELATION 
Since pre-Cambrian rocks are generally unfossiliferous, their 
correlation must be based on either their lithological similarity, 
their similar stratigraphical relations or their similarity of structure. 
The criteria of pre-Cambrian correlation may thus be enumerated 
as follows: (1) stratigraphical relations; (2) lithological character; 
(3) degree of folding and metamorphism; (4) relationship to igne- 
ous intrusions. These will accordingly be used as the basis of the 
correlations suggested in the following pages. 
LAKE HURON—-LAKE TIMISKAMING-LAKE MISTASSINI REGION 
The earliest stratigraphical investigation of the pre-Cambrian 
rocks occurring in the Lake Superior—Lake Huron region was that 
of Logan and Murray on the north shore of Lake Huron, where 
they found a great series of slightly folded sediments resting un- 
conformably on a basement complex consisting chiefly of granite 
and gneiss. To the rocks of the first group the name Huronian 
was given, while the granite and gneiss were correlated with the 
similar Laurentian granite and gneiss occurring in the vicinity of 
the Ottawa farther to the eastward. From this classification it is 
apparent that, theoretically at least, Logan recognized the divisi- 
bility of the pre-Cambrian into a Huronian system and an older 
complex, although both he and his successors in the later recon- 
naissance work carried on in other districts included greenstones, 
green schists, and other rocks in the Huronian which are now 
known to belong to the basement complex. 
It was not until about ten years ago, when detailed geological 
work was begun in the Timiskaming region, that it was found that 
in this district as on the north shore of Lake Huron a series of 
slightly disturbed sediments rested in striking erosional and struc- 
tural unconformity on a basement complex... This complex con- 
tained a large proportion of volcanic rocks which were then called 
Keewatin on the assumption that they were the equivalent of 
similar rocks occurring in the Lake of the Woods region 500 miles 
to the westward. In this way it became customary to divide the 
older complex of the Timiskaming region into two divisions, (1) the 
tA. E. Barlow, Ann. Rep. G.S.C., XV, 127a, 1903. 
2W.G. Miller, Ann. Rep., Ont. Bur. of Mines, Pt. II, 1905. 
