INVESTIGATING MIDWESTERN MILLSTONES: DISTRIBUTION AND CHARACTERIZATION OF MILLSTONES MADE OF LOCAL CHERT IN OHIO

Ohio was a major producer of chert millstones made of local chert in the early to mid-1800s. In the 1830s, geologists with the first Ohio Geological Survey noted occurrences of chert quarries and suitable sites for additional quarries. Preferential rates of canal transportation encouraged local production. Until recently, however, few millstones have been identified as being made of Ohio chert, and only one study has illustrated fossils in these millstones. That study listed only four Ohio chert millstones, clustered near quarry areas in central and southern Ohio.

As part of a multiyear study of Ohio millstones that located millstones in 58 of 88 Ohio counties, fifteen millstones (out of close to 200 studied) were identified as being made of, or partially made of, Ohio chert. Our study shows that such millstones were widely distributed throughout Ohio, with the exceptions of northwestern and northeastern Ohio. The former includes the last area of Ohio to be settled intensively; the latter consists of the Western Reserve of Connecticut. Lack of use of Ohio chert in the latter is more certain as this was our most intensely sampled region. More than half of the millstones made of Ohio chert were found in counties that were crossed by canals, suggesting the importance of canal transportation for millstone distribution; however this does not explain the lack of Ohio chert millstones in other areas crossed by canals.

Fossils were found in almost all chert identified as being from Ohio, and were sparse to abundant in number. Paleozoic fossils in Ohio chert millstones examined included marine forms such as: bryozoans; fusulinids; pelmatozoan columns; brachiopods, included an athyrid (?Composita). Some brachiopods show silicified spiralia. Coloration of the chert millstones identified as being from Ohio varied, with darker colored, or mottled darker-and-lighter colored, chert outnumbering those made of lighter-colored chert. Fusulinids were common only in lighter colored stones.

Fossil content of only one other type of chert used for millstones in North America has been adequately characterized, that of French buhr from the Paris Basin, which eventually dominated the market in Ohio. Local chert quarried in about 13 other states remains to be adequately characterized, although that is in progress at one millstone quarry in Kentucky.