Day: July 14, 2021💾

Michigan has small deposits of coal, although many of our coal deposits are in thin seams, and not economically valuable for that reason.

The swamp forests of the Pennsylvanian stored many forms of usable wealth. The sands at the bottom of the swamp, now hardened into the Parma sandstone, are a prominent reservoir for fresh water in central Michigan counties; in a small area natural gas has been obtained from it. The trees of the forest died, were buried, and became the coal of the Saginaw valley, Grand Ledge, Shiawassee, Ingham, and Jackson counties. The coal is a bit difficult to use in the ordinary furnace, but with the proper type furnace and proper firing methods, it burns well.

What was the Pennsylvanian environment, during which these coal deposits formed, like? Slow, gentle crustal movements caused the Mississippian seas to almost retreat from Michigan, leaving a shallow pool in the central part of the basin and cut off from the outside sea. The time was the Pennsylvanian, the last 45 million years of the Carboniferous, and the time of the great coal swamps. Sedimentation was partly marine, partly fresh or brackish water in swamps. A layer of sparkling sand was first spread over the last Mississippian limestone and above this in the shallow waters a luxuriant swamp forest flourished --- but the trees were quite unlike our modern trees. They were giant fern trees, ground pines, and horsetail rushes that grew to 10 meters or more in height. No birds or butterflies or flowers were there, but dark loathsome amphibians and the earliest known reptiles crawled in the muds; giant scorpions and dragonflies flew about. The climate was warm and moist. The swamp vegetation died and fell to the swamp floor, layer upon layer of plant remains accumulated, changed to peat, were buried under a blanket of dark muds which slow streams brought from forest covered lands. Thus protected from oxygen, they have become the coal beds and shales of the central counties.