Low-Sulfur Coal (CO-10)
Coal is Indiana's most important fossil fuel. It is the product of vegetation accumulated in the vast swamps between river channels on ancient deltaic plains during Pennsylvanian time (320 million to 280 million years ago). Many ancient deltas were similar to modern deltas, such as the delta of the Mississippi River.

Geologists at the Indiana Geological Survey have noted that the place where coals were deposited within the deltaic plain profoundly affected its composition and thickness. In Indiana, low-sulfur coals are generally found in the fresh-water areas of the ancient deltaic plains; thicker coals are found close to the river channels within the deltas. Regional mapping of the coal gives information about the origin of Indiana coal and the factors that determine its quality and marketability.

Our Hoosier State Beneath Us: Coal