Coal Studies in Archaeology

John G. Jones, Ph.D.
Senior Paleoethnobotanist

From time to time, we find coal in archaeological contexts. Through careful analysis, coal can provide clues to plant evolution as well as information that helps to illuminate the past. In the mid 1980s a Revolutionary War-era vessel was found in the York River in Virginia. All that remained was the lowermost portion of the ship’s hull. The vessel was thought to have been intentionally scuttled in an effort to block the river, though by whom and for what purpose was not known. The interior of the ship contained coal fragments representing former cargo/ballast in the ship’s bilge. Would an analysis of the coal provide any insights into the origin of the vessel?
Spores were extracted from the coal in an effort to determine the coal’s origin. We reasoned that if the coal was of Welsh origin, then the vessel was probably a British ship. Likewise, if the coal originated in Pennsylvania, then perhaps it was an American vessel. Nice theory, but when the organics making up the coal were deposited in Pennsylvanian age swamps about 306 million years ago, Wales and Pennsylvania were right next to each other and the coals contained nearly identical flora. One spore called Reinschospora, originating in a wide-ranging fern, contained a coronal fringe—short in length in coals from Wales, and longer in Pennsylvania coal. The short fringe on the Rienschospora identified the coal as being from Wales, suggesting the vessel was probably of British origin, intentionally scuttled to block the river in an attempt to keep the Continental Army away from the Yorktown area.
Coal on the coast of Oregon is constantly being washed up on the beach, though its origin had long been a mystery. An examination of the spores in the coal revealed a plant assemblage known as the Triassic age Ipswich Flora, a unique flora limited in extent to a couple of mines in the Perth area of Western Australia. But what was the coal doing on the coast of Oregon? Research revealed that on Valentine’s Day 1908, a vessel named the Emma G. Rose (apparently named after a Portland area prostitute of some renown) en route to Portland, ran aground on the coast spilling her cargo of, evidently, coal. Coal is fairly common in the Pacific Northwest, so why in the world would anybody carry coal from Australia when it can be had easily and cheaply from local sources? Our research revealed the vessel had been working in Australia and was re-positioning back in Portland. The vessel had no registered cargo, and perhaps coal was not of such worth that it was even considered as cargo. However, coal would have served as ballast, making the Pacific Ocean crossing a bit easier and more stable. Evidently, the vessel picked up a load of coal in Perth before the Pacific Ocean crossing, making it almost the whole way home before it wrecked near Lincoln City, spilling its cargo, some of which is still tumbling around in the surf today.
Finally, a recent examination of sediments from the Chaco Canyon area of New Mexico, revealed a bizarre fern-filled flora unlike anything I had ever seen before. The presence of rare tiny oak grains, tupelo-like grains representing a swampy habitat, and other anomalies indicated that many of the grains in the samples were actually re-worked Cretaceous age palynomorphs, eroded out of locally abundant coals. The Cretaceous age forests contained a large number of pines, fortunately very distinct from the pinyon and ponderosa pine pollen found in the area today.
Phytoliths of geological age are also commonly encountered in archaeological sediments. Samples from south Texas often contain abundant palm phytoliths of three different types, along with distinctive phytoliths from Heliconia, a tropical relative of the ornamental bird-of-paradise plant. Native palms are present in extreme southern and coastal Texas, but the nearest naturally occurring Heliconia is in tropical central Mexico, so we knew we were dealing with an exotic assemblage. Many of the rocks in south Texas are composed of Oligocene age sandstones containing abundant phytoliths deposited with the silts and sands 30 million years ago, and it is these phytoliths that are found in our archaeological samples. The Oligocene age phytoliths can be distinguished from recent age phytoliths because they have turned a slightly darker color, readily visible under the microscope.