Reinhardt Thiessen pioneered the thin-section method of coal petrography in the United States as well as the application of spores to the correlation of coal beds. His scientific career, mainly with the U.S. Bureau of Mines, spanned three decades during which he investigated the petrographic and botanical composition of American coals and conducted related research on peat and oil shale. He was the first in North America and, perhaps, worldwide to relate the macroscopic bands in coal to a microscopic classification of coal. Thiessen’s published record of about 82 items and the Thiessen coal thin-section slide collection, which consists of...