Temagami Greenstone Belt phases of volcanic activity. These two sequences, known as the Older and Younger volcanic complexes, consist of volcanic rocks ranging in composition from felsic to mafic. The Older Volcanic Complex is composed mainly of felsic lava flows and pyroclastic deposits with smaller amounts of mafic volcanic rocks. It underlies a large portion of northwestern Strathy Township and is penetrated by mafic intrusions, although the Kanichee Intrusion consists of peridotite and pyroxenite, which are ultramafic rocks. Just to the southeast, the Younger Volcanic Complex consists mainly of mafic volcanic rocks that form four geologic formations. The Arsenic Lake Formation is composed
Ringing rocks that retained the olivine and pyroxene crystals (OPM) is extremely resistant to weathering and is the material which forms the tors. The altered rock (AM) conversely is very weak and readily breaks down to a coarse soil. The inner felsic core is a medium grained quartz monzonite that gradually grades into granite at the center. The transitional unit between the mafic zone and the felsic core units is completely obscured, and is represented by distinctive low-lying swales. A series of radial dikes punctured the mafic units, beginning in the felsic zone and terminating at the outer border of the intrusion.