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THE

JOURNAL OF GEOLOGY

FEBRUARY-MARCH, 1893.

AN HISTORICAL SKETCH OF THE LAKE SUPERIOR REGION TO CAMBRIAN TIME.^[1]

(WITH PLATE I.)

The ancient formations south of Lake Superior may be grouped into five great divisions: the Basement Complex, the Lower Huronian, the Upper Huronian, the Keweenawan, and the Lake Superior Sandstone. These five divisions are separated by unconformities of great magnitude, two of them at least being of the first order. According to the classification adopted by the United States Geological Survey, the Basement Complex is Archean; the Lower Huronian, Upper Huronian and Keweenawan constitute the Algonkian for this region; and the Lake Superior Sandstone is Cambrian.

The Basement Complex.—The characteristic rocks of the Basement Complex are (1) light colored granites and gneissoid granites, and (2) dark colored finely foliated or banded gneisses or schists. These are cut by various basic and acid intrusives, many of which are not different from eruptives

↑ In this very general article no attempt will be made to give references to the many authors from whom facts are taken. To give full credit for all information used would required citations from scores of papers. The writer gives a summary of the literature of the Lake Superior Region in Bulletin 86 of the U. S. Geol. Survey.

Many of the problems considered have no definite answers as yet. The aim of the article is to give a summary of the very limited knowledge available on a subject that has not before been considered, because the data were not at hand upon which to base any reliable conclusions.

Vol. I.—No. 2.

[1] In this very general article no attempt will be made to give references to the many authors from whom facts are taken. To give full credit for all information used would required citations from scores of papers. The writer gives a summary of the literature of the Lake Superior Region in Bulletin 86 of the U. S. Geol. Survey.

Many of the problems considered have no definite answers as yet. The aim of the article is to give a summary of the very limited knowledge available on a subject that has not before been considered, because the data were not at hand upon which to base any reliable conclusions.

[1]