DEVELOPMENTS IN PRE-CAMBRIAN STRATIGRAPHY 389 
both in its lithological character and in the stratigraphical succession 
of its members, and like the Cobalt series rests on the trunkated 
surface of a basement complex.' Throughout the intervening 
distance between Lake Timiskaming and Lake Chibougamau, no 
outcrops of the Cobalt series have been described, but the Abitibi 
group and the Laurentian are typically developed throughout 
the whole interval. From these facts it may be concluded that 
the pre-Cobalt series erosion plane, the Abitibi group and the 
Laurentian extend eastward to the Chibougamau district. 
From the evidence already cited it might be inferred that the 
pre-Cobalt series erosion plane is also the equivalent of that which 
underlies the original Huronian rocks on the north shore of Lake 
Huron, but since a large part of the conclusions of this paper are 
based on the correlation of these two planes, it is important that 
the evidence be stated in full. In support of their correlation it 
might first be pointed out that the Cobalt series and the two original 
Huronian series are structurally and lithologically very similar, 
even to the presence of a sea-green quartzite containing pebbles 
of jasper and quartz. It is true that until recently, it was thought 
that the limestone was absent in the Cobalt series, but as that 
series is traced southward it changes somewhat in character, and 
limestone beds have been found to be present in the district north- 
east of Sudbury.? Not only are the original Huronian rocks similar 
to the Cobalt series, but there is no other series in the Timiskaming 
region which resembles them either in lithological character, 
structure, or relationship to batholithic intrusions. The basement 
complex which underlies the original Huronian rocks has not been 
studied in detail, but like that beneath the Cobalt series, it consists 
in the main of metamorphosed volcanic flows intruded by granite 
and gneiss. Thus in both districts an older complex occurs which 
is separated from the overlying slightly disturbed sediments by 
erosion planes, which would coalesce if projected across the interval 
which intervenes between the known occurrences of the Cobalt 
series and the original Huronian. 
From the foregoing discussion it follows that throughout the 
* Rep. on the Geol. of the Chibougamau Region (Dept. of Mines, Que.), pp. 134-38, 
IgIl. 
2W. H. Collins, Sam. Rep. Geo. Surv. Dept. of Mines, Can., 1913. 
