The lignite of North Dakota occupies part of an area that is shared by the neighboring states of Montana, Wyoming, and South Dakota, and by Assiniboia on the north. The total area of this lignite field in the United States alone is 70,000 square miles, apportioned as follows: North Dakota 31,500, Montana 25,000, Wyoming 9,000, and South Dakota 4,500. It is probable that all of this field does not contain lignite beds of workable thickness, but studies carried on in North Dakota and Montana during the past summer indicate that thick beds are very general, and that often a series of four or five are separated by relatively thin strata of clay. Some of the beds are very thick, one which out crops near the Little Missouri in southwestern North Dakota measuring forty feet, while twenty-foot beds are not uncommon.
Proceedings of the Iowa Academy of Sciences
©1902 Iowa Academy of Science, Inc.
Wilder, Frank A.
"A Possible Origin for the Lignites of North Dakota,"
Proceedings of the Iowa Academy of Science, 10(1), 129-135.
Available at: https://scholarworks.uni.edu/pias/vol10/iss1/24