AGE OF THE KILLARNEY GRANITE. 
5 
rocks in question. Accordingly, attention is now directed to the 
great thicknesses of the Bruce and Cobalt series, to the number 
of formations constituting each and their order of succession; 
also to such characteristic formations (horizon markers) as the 
Bruce and Espanola formations in the Bruce series, and the 
extraordinary association of boulder conglomerate, laminated 
greywacke conglomerate, etc., in the Gowganda formation of 
the Cobalt series. For these are the criteria by means of which 
the Huronian is distinguished from other Pre-Cambrian sedi- 
mentary rocks on the north shore. 
A peculiar and distinctive feature of the Bruce series, of 
especial recognitive value, is found in the Espanola greywacke, 
Espanola limestone, and Serpent quartzite. These formations 
are intersected by dykes of quartzite (Plate I). Dykes of this 
kind are rare occurrences in geological history. They have not 
been found in any qther horizon of the Pre-Cambrian, either in 
this district or elsewhere in northern Ontario. They, therefore, 
constitute a particularly effective means of identifying the mem- 
bers of the Bruce series which they intersect. 
DEFORMATION OF THE HURONIAN. 
The successive steps which led to the age-determination of 
the granite at Killarney are described below in the order in which 
they were actually taken. This arrangement has the disad- 
vantage of presenting the weakest evidence first; but, on the 
other hand, the relation of one step to the next is more apparent. 
The first obvious peculiarity of the Huronian on the north 
shore is its unusually intense deformation. Elsewhere in 
northeastern Ontario and the adjoining part of Quebec (the 
Timiskaming region or sub-province of Museum Bulletin No. S) 
the Huronian is not much disturbed. Around Lake Timiskam- 
ing and Larder lake the Cobalt series in few places dips more 
than 20 degrees and very few faults have been observed. There 
are several thousand square miles near Gowganda and Lake 
Timagami in which the average dip of the Cobalt series is from 
20 to 30 degrees; and as far north of Lake Huron as the writer 
has worked in the north shore district — 25 miles — the Huronian 
strata are notably little disturbed. They do not in many cases 
