The Huronian sediments, which stretch almost unbroken from the western end of Lake Superior to a line between Killarney and Lake Temiskaming, end abruptly against an area of gneisses.
This area of gneisses, previously thought to be of pre-Huronian age, is now known to be composed in part of rocks younger than the Huronian sediments and known as the Killarney intrusives, in part of remnants of conglomerate, quartzite, and calcareous amphibolite belonging to the Bruce series, and in part of highly metamorphosed gneisses of granitoid composition, also of Huronian age.2
These rocks display certain characteristics of regional contact metamorphism which are unusually well developed, deserving special description and discussion. They include good examples of the mixed rocks, hybrid between igneous and sedimentary rocks, called by Sederholm “migmatites.”3
The general geology of this district recently has been discussed in some detail elsewhere 4 and needs little further general description.
This . . .