ABSTRACT

Investigations of heavy minerals in tills peripheral to the Canadian Shield indicate the following characteristics: the Grenville tills contain more garnets, tremolite-actinolite, and hypersthene than the Superior tills, which are richer in chlorite-serpentine, clinopyroxenes, and epidotes. Epidotes dominate in some Superior tills northwest of Lake Superior. Hornblende is very abundant in all tills, but particularly along the Grenville-Superior boundary north of Lake Huron.

The Huron lobe tills contain more heavy minerals than the Erie tills. The heavy mineral content in the Huron tills of southwestern Ontario derive principally from the Superior province, with some admixture from the west end of the Grenville, while typical Grenville minerals dominate in the Erie tills.

Comparison of heavy mineral content between successive tills and recessional moraines reveal a shifting of ice flow in both lobal areas during Wisconsin time. First each lobe entered its lake depression from north-northeast. Later the major flows drifted apart, the Huron lobe assuming a more north-south, and the Ontario-Erie lobe, a northeast-southwesterly direction. The space between them became occupied by minor but tributary ice-flows.