Lycopsida (club mosses, scale trees)
Scale trees (lycopods), related to the modern club mosses or ground pine in Kentucky, also grew to be trees over 100 feet tall. They are called scale trees because their bark looked like the scales of a snake. Modern lycopods seldom reach over 1 foot in height.
Stumps and roots of the scale trees, like the one above, are very common fossils in the coal fields; the roots go by the scientific name Stigmaria.
Fossil stumps are common in the roofs of some deep coal mines, where they are called kettlebottoms by miners. Kettle bottoms are a hazard to miners because they sometimes fall out of the roof of the mine after the coal has been removed.