A MULTIYEAR STUDY OF HISTORIC MILLSTONES IN OHIO

Millstones are key geological components of material culture. They are also the most commonly preserved elements of the thousands of historic gristmills which once dotted North America. Building on previous observations by Hannibal and Saja (GSA abstracts, 2009), between 2009 and 2013 we examined millstones at approximately 60 sites (historic mills, historical societies, parks, roadsides, and backyards, some with more than one millstone) in northern and northeastern Ohio, as well as dozens of additional millstones in other areas of Ohio. Most of this work has taken place in summer, utilizing college summer interns and high school students.

Millstones which we have examined are made of granitic rock, metaconglomerate, sandstone, conglomerate, and chert. Granitic and metaconglomeritic millstones are almost certainly derived from glacial boulders. Jasper metaconglomerate millstones at two sites appear to be composed of glacial boulders derived from the Lorrain Formation of the upper Great Lakes. Use of granite boulders for millstones in Ohio is noted in historic works. Most chert millstones we have examined in Ohio are made of certain (based on the presence of charophyte gyrogonites belonging to the genus Gyrogona and freshwater snails), or probable, French buhr (chert from the Tertiary of the Paris Basin), but some are derived from the Vanport limestone of Ohio. Sandstone and conglomerate millstones are, or probably are, made of stone from the Paleozoic of Ohio.

Seriation curves for the better documented millstones studied in Ohio’s Western Reserve (an area of northern and northeastern Ohio for which we have the most data) show that granitic rocks were used exclusively between 1790 and 1810, and that metaconglomerate, sandstone, and conglomerate were used in the 1810s along with granite. Before 1825 the dominant stone used in the Western Reserve was granite. Chert (French buhr) was first used in the Western Reserve in the 1820s, and its use increased over time. After 1825 the dominant stone was chert and it replaced, for the most part, other stone types by at least the 1860s. These changes in stone use for millstones were due to the construction of the Erie Canal and to the international reputation of French buhr as being the finest type of stone available for use as millstones.