Term: transition rocks (mining)
Definition:
A series of rocks which lie below the secondary and next above the primary, and are called "transition," because they seem to have been formed at a period when the earth was passing from an uninhabited to a habitable condition, and contain a number o char
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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).]
