Every continent has a core of very ancient metamorphic rocks.
The Superior Upland Province is the southern extension of the Laurentian Upland Province, part of the nucleus of North America called Canadian Shield . The basement rocks of the Laurentian Upland Province were metamorphosed about 2500 million years ago in a mountain-building collision of tectonic plates called the Kenoran orogeny. If we could strip away all of the younger rocks deposited on top of buried Precambrian basement, you would see a landscape of low relief. The topography of the Precambrian rocks is very subdued, with barely 500 feet difference between the highest point and the lowest. Clearly, this region was exposed to a very long period of erosion in the very distant past which beveled the original mountainous surface to a gently undulating surface.