https://en.wikipedia.org/wiki/Canadian_Shield https://en.wikipedia.org/wiki/Canadian_Shield: "Glaciation has left the area only a thin layer of soil, through wh

https://en.wikipedia.org/wiki/Canadian_Shield https://en.wikipedia.org/wiki/Canadian_Shield: "Glaciation has left the area only a thin layer of soil, through which the composition of igneous rock resulting from long volcanic history is frequently visible."