Those which lie below all the stratified rocks, and exhibit no marks of sedimentary origin. They contain no fossils, and are oldest or lowest strata known. Granite, hornblende, quartz, and some slates belong to this division.

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[Source: "Glossary of Miners'&Mineral Terms" in St. John, John R. A True Description of the Lake Superior Country ... (New York, W. H. Graham, 1846).]