The metaphor used for the title of this column could read, "A Window Into the Past" or "An Encyclopedia of Ancient Fossil Plants."
This is a story about coal balls. They are found at the entrances to some coal mines, oftentimes discarded. There is hardly any coal in a coal ball, and therefore it would not burn with the expected results.
By chance, a geologist picked up one out of curiosity and examined it with a magnifying loupe. He found remnants of ancient plants in the coal ball. He brought three or four of them, about the size of softball up to the size of a basketball, back to the geology lab. He broke off pieces to macerate and look at them with a more high-powered microscope.
Another method of research is to saw the coal balls into slices and smooth the surface with varying grades of emery paper. This led to the process known as "peel," which involves three types of acid - one to remove limestone, one to remove sandstone and one to remove other extraneous material.
This last acid, hydrogen fluoride, is so powerful that if a large enough drop were to touch an unprotected hand, it could not be stopped from burning all the way through. Obviously, great care is taken and rubber gloves are worn. Also, the fumes from these acids could be harmful to the lungs of the researcher, so the process is carried out under a hood with an exhaust fan while wearing a protective breathing mask.
The process leaves the specimen with a smooth surface of exposed organic material. The coal ball slice is then flooded with water to remove the acid. One side of the slice is then bathed in acetone liquid and covered with a thin leaf of clear acetate, which is placed on the surface very carefully without any bubbles or wrinkles. After a specified period of time, the leaf is removed from the specimen. It will have lifted from the specimen a thin layer of the fossilized plants that were contained in the coal ball. This is then positioned on a slide for examination under a microscope.
This peel method was a giant break-through in the research in ancient plants. It first occurred nearly a hundred years ago.
From this research, plant parts as small as spores were identified. They came from a time before flowering plants existed. Fragments from as small as spores to as large as segments of the lepidodendron tree, which grew as tall as 100 feet, were found. This was evidence these plants and others, such as tree ferns, made up the great coal fields of the Pennsylvania Period.
These trees grew in a shallow swamp before the Allegheny Mountains were formed. They died in due course and fell into the water. Because the water was shallow and slow moving, it had little oxygen in it, so they did not decay but were fossilized as they were covered with layers of sediment. The location of what is now Pennsylvania and Ohio was at that time below the equator, where it was hot. This provided the environment for the lush growth of the trees that became the coal that is mined in this area today.
In the mountain-building caused by the movement of the European and African continents from what we now know as East to West, new layers of earth were moved across the seams as if giant bulldozers were pushing them, rolling up balls of incompletely coalified material. Today, these coal balls are found where those layers of earth meet the coal seams.