1916. United States. Bureau of Chemistry and Soils and University of Minnesota. Agricultural Experiment Station. Cartographic Details: Scale approximately 1:49,000. Not "1 in. = 1 mi." (W 93°30 ª--W 93°00 ª/N 45°25 ª--N 45°00 ª). Enlarged reproduction. "Soils ... Snyder & Black (New York).