North Dakota lignites occur in the Fort Union and upper part of the Lance Formations. Individual seams vary from a few inches to over forty feet in thickness. The lignite horizons are quite continuous over large areas, but the individual seam representing a particular horizon is commonly lenticular and of limited extent horizontally.Underclays are conspicuously absent. The lignite is woody in character and brown in color. Ash is low, and sulphur conspicuously so, and moisture is high. There is indication of cyclical sedimentation.

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