The Precambrian Shield
The surrounding rock formation is among the oldest of the Earth's crust. Formed between one and two billion years ago, it is part of the Precambrian Shield, which occupies two-thirds of the surface area of Ontario. Unsuited to agriculture, the Shield impeded early settlement, yet it contained the economic potential from which much of Ontario's wealth is derived. Beneath its surface lies the greater part of the province's mineral resources, while on it grows most of its timber and pulpwood. Thousands of lakes were carved in the Shield by the ice-sheets of the last glacial period and these, with its forests, offer unparalleled facilities for vacationers and sportsmen.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.