In 1916 I attempted 2 a correlation of the pre-Cambrian of the various districts that had been studied between Rainy Lake and the Adirondacks on the basis of the hypothesis that throughout this region there had been two, and only two, distinct periods of granitic irruption in the earth's crust.3 For the earlier of these two periods the term “Laurentian” was retained, in accordance with long usage, and the later was called the “Algoman,” a term which since has been widely adopted. The two plutonic upheavals are widely separated in time.
The Huronian rocks rest on the peneplained surface of the Laurentian granite and are cut by the Algoman granite. The Algoman granite was in turn deeply eroded and certainly peneplained before the deposition of the Animikie rocks of Thunder Bay. This alternation of granitic invasions and peneplanations, if general throughout the region referred . . .