Early industrial geology of western Pennsylvania and eastern Ohio: Early gristmills and iron furnaces west of the Alleghenies and their geologic contexts
Published:January 01, 2011
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Joseph T. Hannibal, Tammie L. Gerke, Mary K. McGuire, Harry M. Edenborn, Ann L. Holstein, David Parker, 2011. "Early industrial geology of western Pennsylvania and eastern Ohio: Early gristmills and iron furnaces west of the Alleghenies and their geologic contexts", From the Shield to the Sea, Richard M. Ruffolo, Charles N. Ciampaglio
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Even before 1800, geological resources such as chert, iron, limestone, and coal were being utilized from the Pennsylvanian rocks of eastern Ohio and western Pennsylvania. These materials were of great interest to the early geologists of the region. This field trip discusses these products in the context of early grain milling, iron furnaces, and allied industries of Ohio and Pennsylvania in the late eighteenth and early nineteenth century, with a focus on two publicly accessible sites: McConnells Mill Park in western Pennsylvania, and Mill Creek Park in eastern Ohio. These parks contain publicly accessible gristmills and iron furnaces, and outcrops. We also provide new observations on cultural materials related to these industries, especially iron-furnace slag and millstones.
American colonists began to move westward beyond the Allegheny Mountains at the end of the French and Indian War in 1763. The first industries were typically sawmills and grain mills, with products of the sawmills used to build the mills for grinding grain. Local stone was utilized for the manufacture of millstones, key components of the grain mills. Iron furnaces followed soon after, where there was a suitable source of iron ore, limestone for flux, and trees suitable for making charcoal. By the early 1800s, coal was beginning to be used to stoke these early blast furnaces.
In western Pennsylvania and eastern Ohio, the same, or adjacent, Pennsylvanian rock units from the Pottsville and Allegheny Groups (Fig. 1) could contain buhrstone for manufacturing millstones, iron ore suitable for blast furnaces, clay and sandstone for use in bricks and as building stone for construction of furnaces, lime for flux, and coal for fueling the furnaces (Rogers, 1836; Hildreth, 1838; Mather, 1838). The geologists of the first Pennsylvania and Ohio geological surveys paid special attention to buhrstone for millstone, iron ore for blast furnaces, and other resources.
Mills and iron furnaces were key components—and sources of wealth—along the frontier (Harper, 1991, p. 50–53). In this guide, we provide an overview of earlier and ongoing geological and archaeological investigations of some of these early industries in western Pennsylvania and eastern Ohio west of the Allegheny Mountains, with a concentration on mills, millstones, and iron furnaces, placing recent archaeological work in its geological context. We define the Allegheny Mountains as being bordered on the east by the southwest side of the Appalachian Mountains and on the west by the Allegheny Plateau, that is the general high-elevation area delineated as the “Allegheny Mountain Section” by Way (1999) which is similar (at least on its western border) to the “Allegheny ‘Mountains’” section of Murphy and Murphy (1937, fig. 4).
Western Pennsylvania and eastern Ohio have much in common. Both are on the Appalachian Plateau, both have Pennsyl-vanian bedrock, and portions of these areas between 41 and 42 degrees north latitude were once claimed by the state of Connecticut. The two major parks discussed in this guidebook chapter are similar in many respects, but have complementary geological and cultural features that recommend a visit to both.
Mills, Millstones, and Buhrstone
Mills were established early on as Euro-Americans moved across the Alleghenies, and so, along with sawmills, were the first industries in western Pennsylvania and eastern Ohio. Mills were constructed where there was a drop in water along a stream, typically at a waterfall or where such a drop could be engineered. In eastern Ohio and western Pennsylvania, waterfalls, typically formed by resistant beds of sandstone, provided the necessary drop to turn a waterwheel, especially when aided by a dam. The waterwheel provided the power to turn pairs of millstones that actually ground the grain. Millstones in the region actually predated water-powered mills, however, as hand mills (querns) utilizing local stone were used from an early date along with tree-stump mortars and wooden pestles.
Stone millstones used in the eighteenth and nineteenth centuries produced nutritious flour that contained some bran and midlings (Fletcher, 1950, p. 326). Newer, more efficient types of mills invented in the mid- and late-1800s, along with finer bolting cloths, resulted in whiter flour minus bran, wheat germ, and other unwanted material. This resulted in less nutritious flour for people and some nutritious midlings for cattle and pigs. Stone-ground flour has continued production, however, to this day, and has come into greater prominence with the renewed interest in healthful breads in the later decades of the twentieth century. In addition to processing grain, millstones were also used for other purposes, including crushing calcined lime at lime kilns.
A variety of stones have been used for millstones in Ohio and Pennsylvania. The best overall references to date on these and other millstones of the United States are the compilation of papers on millstones by Ball and Hockensmith (2007) and the recent book on the millstone industry by Hockensmith (2009a). In this paper, we provide additional information on millstones in western Pennsylvania and eastern Ohio.
The bedrock of western Pennsylvania and eastern Ohio is composed of sedimentary rock, but some early millstones were fashioned from granitic glacial boulders (Saja and Hannibal, 2009). There are a number of mentions of such usage in the historical literature. Fletcher (1950, p. 325) noted that early millstones in Pennsylvania “were made of native granite and were three to seven feet in diameter.” The millstones seen at the ruins of McConnells Mill (Stop 1) confirm this statement. Work in northeastern Ohio (Saja and Hannibal, 2009) shows that the situation was similar there. The oldest millstones used for Youngstown’s 1845 Lanterman’s Mill (Stop 4) are said to have been granite (Melnick, 1976, p. 235). Early millstones in Shenango Township, Pennsylvania, have been described as being composed of “country stone” (Durant and Durant, 1877, p. 112), which may or may not have been granite. Elsewhere in Pennsylvania, the term “country stone” has been used in contrast with “burrs” (Hazen, 1908, p. 299). Leung (1981, p. 38), in a study of mills in Ontario, noted country stone as being granite or conglomerate.
Conglomerate, along with sandstone, has been widely used for millstones in Europe and the United States (Safford, 1880; Tucker, 1984; Hockensmith, 2009a). This use gave rise to the old European and American rock-strata name “Millstone grit.” The nineteenth-century term “millstone grit” (lower case) referred to a coarse sandstone or a pebbly sandstone, presumably intermediate in grain size between a conglomerate and sandstone (Dana, 1884, p. 426). As a rock-unit name, Millstone grit was used synonymously with the Pottsville conglomerate (Chamberlin and Salisbury, 1909, p. 620, 641). Apparently influenced by European models, many early millstones in the United States were also made from conglomerates and conglomeritic sandstones. There is a reference to conglomerate and millstones in one of the early Ohio Geological Survey reports (Whittlesey, 1838, p. 58), but that reference notes that the local conglomerate (now known as the Sharon Formation) was not good for millstones. This is an unusual statement that seems to imply that someone was using, or attempting to use, this conglomerate for millstones. Indeed they were (Hannibal and Saja, 2009); a millstone found along Mill Creek (Stop 4) at the Lanterman’s Mill site in Youngstown is an example of such a conglomerate millstone. Berg (1986) also documented a millstone quarry in the Olean Conglomerate in Tioga County, north-central Pennsylvania. In addition, Hockensmith (2009b) documented, in detail, six conglomerate millstone quarries in Powell County, Kentucky.
The advantages of conglomerate millstones appear to be their heterogeneity and, perhaps, by the presence of hollows created by plucked-out pebbles. These hollows retained, or appeared
to retain, sharp edges as the stone was ground down through use. In this way conglomerate was like French buhr, the most desirable of millstones, which was made of chert. Conglomerate millstones tended to glaze after repeated use (C.D. Hockensmith, December 2000, personal commun.), however, so this comparison of conglomerates with French buhr may not hold true.
Chert Millstones (Buhrstone Millstones), Especially French Buhr
The premier material for manufacture of millstones in the eighteenth and nineteenth centuries was the rock traditionally known as buhrstone (also spelled burrstone, or burstone, and sometimes known simply as buhr). This term was used typically for siliceous rock that is suitable for manufacture of millstones (Arkell and Tomkeieff, 1953, p. 16). The term has been used in geological literature (e.g., Stout, 1927, p. 256) and by those who study millstones (Hockensmith, 2009a, p. 215). Buhrstone is typically a light-colored chert. The name buhrstone continues to be used for this rock today, but the term is also known as part of the name of “buhrstone ore,” an iron ore associated with buhrstone. The term buhrstone has also been used for millstones made of buhrstone (e.g., Lepper et al., 2001, p. 55).
The best known buhrstone by far is French buhr, that is, buhrstone from France. Classic descriptions of this Cenozoic French stone quarried in the Paris Basin go back to Cuvier (e.g., Cuvier, 1815, p. 308–311) and the stone was well known in North America being prominently noted in publications such as Hughes’ (1851) classic book, The American Miller and Millwright’s Assistant, which went through many editions. French buhr was long quarried in La Ferté-sous-Jouarre and vicinity in France (Ward, 1993) and exported to Britain, the British colonies, and the United States. In many of the larger cities in the United States, manufacturers imported blocks of the French buhrstone, which were then assembled into complete millstones at their workshops. City directories show that French buhr was being used by millstone manufacturers in Cleveland (Mac Cabe, 1837; Fig. 2) and Pittsburgh (Harris, 1837; Hockensmith, 2009a, p. 97–98; Fig. 3) in the 1830s. Newspaper advertisements indicate that by April 1825, composite French-buhr millstones were being produced in Cleveland (Fig. 2). Pittsburgh City Directories in the middle decades of the 1800s show that William W. Wallace was also one of the Pittsburgh manufacturers who sold Chesnut [Chestnut] Ridge and Laurel Hill millstones as well as French-buhr millstones in Pittsburgh.
In southern Ohio, the earliest millstones were French buhrs and millstones from Redstone and Laurel Hill, Pennsylvania (Garber, 1970, p. 77–78). The Laurel Hill, Pennsylvania, stone has been mistakenly referred to as granite (Garber, 1970, p. 11; this is not the only case of misidentification of chert millstones as being composed of granite!) and as “Laurel sandstone” (Melnick, 1976, p. 248), but was a cryptocrystalline chert quarried from the Pennsylvanian rocks near Brownsville in Fayette County, western Pennsylvania. By 1790, Laurel Hill stones were sent by flatboat to Marietta, Ohio (which was founded only in 1788) via Pittsburgh (Garber, 1970, p. 11). The Laurel Hill material was used early on in the Pittsburgh area as Pittsburgh was downriver from Brownsville on the Monongahela River. The stone continued to be available for sale in Pittsburgh well into the nineteenth century (James M’Kinney ad in Harris, 1837; Fig. 3). Laurel Hill millstones were also shipped down the Ohio River to Kentucky, and were in use there by at least 1802 (Hockensmith, 2008).
Historically, buhrstone was produced in Vinton (Raccoon buhr), Muskingum, and Licking counties, Ohio, from greyish or yellowish white micro/cryptocrystalline-quartz rocks of Penn-sylvanian Age. Raccoon buhr, a variety of chert quarried from the Vanport limestone near McArthur, Vinton County, Ohio, was especially well esteemed, although second to French buhr in reputation (Foster, 1838, p. 90-91; Safford, 1880, p. 176). Contemporary advertisements (Figs. 2 and 3) make this ranking clear. Stout (1927, p. 259) described the best stone used for buhrstone in Elk Township of Vinton County as “somewhat cellular but firmly bonded” flint (“cellular” refers to stone that has rounded to subrounded hollows). The Vanport was also quarried at other locations in Vinton County (Stout and Schoenlaub, 1945, p. 75-78) as well as at Flint Ridge (Garber, 1970, p. 80-82; Carlson, 1991, p. 14-16, 65-67; Hockensmith, 2007), Ohio for millstones. Carlson (1991, p. 15) described the Vanport flint used as millstones as coming from the “impure, porous phases.”
The Pennsylvanian cherts from Pennsylvania and Ohio quarried for millstones can presumably be distinguished from the French by their fossil content. The Vanport and other Penn-sylvanian units contain Paleozoic fossils, including fusulinids (Smyth, 1957; Carlson, 1991). The French material is Ceno-zoic in age. However, a direct comparison of material at La Ferté-sous-Jouarre with the material from Pennsylvania and Ohio still needs to be made.
Iron, Iron Furnaces, and Iron Ore in Western Pennsylvania and Eastern Ohio
Early Iron Industry in Ohio and Pennsylvania
Iron was (and is) produced by blast furnaces (Fig. 4) operated by combining three elements (fuel, flux, and ore) to create two (iron and slag). The fuel used in the late eighteenth and early nineteenth century was typically hardwood charcoal, which was readily available by cutting swaths of the virgin hardwood forests of Pennsylvania and Ohio. As these forests were cleared, the fuel switched around the 1850s to coal, which was and still is abundant in Pennsylvania and Ohio. Around 1875, these would give way to coke (White, 1979, p. 4). The fuel provided the necessary heat and reducing power needed to melt the ore inside the furnace. Flux, often limestones such as the Vanport limestone, was added to the furnace to bond with molten iron-ore impurities in the blast furnace. This bonding would create a glassy material, called slag, which would float upon the molten iron at the bottom of the furnace. When the impurities separated from the iron, the slag was removed from the furnace, the molten iron metal would be tapped from the furnace, and the process started again.
The name “blast furnace” comes from the air, or blast, which is forced into the furnace. With the addition of this air, the furnace is able to reach much hotter temperatures and is essential to melting the iron ore (iron melts at around 1200 °C). In the nineteenth century, this blast could be produced by following one of three general methods: using a trompe, bellows, or blowing tubs. A trompe was a crude blast device that used falling water to push air into the furnace. Because the air came directly from the area where the water was stored, it was cold and the pressure was not as great as under other styles. The Hopewell Furnace (Stop 6) originally had a trompe device; however, it eventually was switched to bellows to produce a more efficient blast. The bellows are another way to force a blast into a furnace. In this method, a waterwheel is attached to a shaft with a cam upon it, and this cam operates a bellows or set of bellows that force air into the tuyère opening (see illustration on p. 78 of Bining, 1938). The final method is the use of blowing tubs. In this method, a waterwheel is attached to a set of piston arms which operate two blowing tubs alternatively. The tubs supply their oxygen into a central chamber, known as a plenum, which is connected to a blow pipe that forces air into the tuyère. Later innovations would heat the blast and channel it into the tuyère. Because the hot blast was already several hundred degrees Celsius, it allowed the furnace to operate more efficiently and reach hotter temperatures with less fuel. In contrast to that innovation, furnaces that utilize a trompe, bellows, or blowing tub method are known as “cold blast.”
The early furnaces created a type of iron known as cast iron. Cast iron is an iron which has a high carbon content (3–4.5%). This high carbon content makes it brittle after casting, and it is unable to be worked by a smith after casting. This cast iron was either cast directly into goods or into ingots for transport. Because of the inflexibility of cast iron, it was often cast into ingots, known as pigs, and transported to a bloomery, where it would be rendered into a more workable form, wrought iron. Until its replacement by mild steel in the early twentieth century, wrought iron was the metal of choice for smithing (Light, 2000).
Early Iron Manufacture in Pennsylvania
Pennsylvania’s history of blast furnaces predates the American Revolution. The year 1692 saw the first blast furnace producing iron in the colony and by 1720 there were four blast furnaces there. By the time of the revolution, there would be nearly 60. In 1841, there were well over 200 (Moldenke, 1920, p. 15–16). As settlement moved westward, blast furnaces too moved westward to supply the iron stove pieces, nails, andirons, pigs, and utilitarian products necessary to settling the frontier. Pittsburgh, a city long associated with ferrous metallurgy, saw its first furnace erected in 1792, but it was not successful. In the first half of the nineteenth century, Pittsburgh would be known not for its pig iron production, but for the foundries which converted the cast iron pigs into wrought iron (Moldenke, 1920, p. 18).
Two types of furnace systems existed in Pennsylvania: the plantation and the entrepreneur furnaces. The plantation systems frequently emerged in areas near established populations (White, 1979, p. 5). These plantations were nearly self-sufficient communities, creating even their own food (Schallenberg and Ault, 1977, p. 436). An example of this is the Hopewell Furnace National Historic Site in southeast Pennsylvania. Entrepreneur furnaces were those furnaces that were willing to supply a local market with readily available goods for a finite amount of time. These took advantage of the abundant timber and readily available low-grade iron ore found in western Pennsylvania. When the distances from raw materials or markets became too great, these furnaces would close, and a new furnace would be built that could more profitably produce iron. It would be these entrepreneurial furnaces that would sprout west of the Alleghenies. In Mercer County, Pennsylvania, alone, no fewer than fifteen entrepreneurial furnaces operated (Sharp and Thomas, 1966).
Early Iron Manufacture in Ohio
Like its eastern neighbor, Ohio has a long history of manufacture of ferrous metal. The first blast furnace in Ohio, circa 1802, was the Hopewell (Eaton) Furnace. Its name is now synonymous with metallurgy (White, 1978, p. 391). Before 1820, blast furnaces would be erected in Akron and Tallmadge as the frontier moved ever westward (Moldenke, 1920, p. 27). The furnaces constructed in Ohio in the first half of the nineteenth century would be almost exclusively charcoal furnaces. As the hardwood forests began to disappear, many of these furnaces closed. Some furnaces, such as the Mill Creek (Trumbull), were able to make the switch to fossil fuels (coal) that fueled the furnaces after 1840–1850.
By 1884 (Wright, 1884, p. 129), Ohio ranked second highest in iron manufacture behind Pennsylvania. In that span, iron production in Ohio transformed from many small production furnaces (around two to five tons a day) to massive mill complexes each capable of many hundreds of tons per day. Ohio was fortunate enough to be located near early iron rich ores and hardwood forests essential for early nineteenth century iron production. Following the discovery of iron-rich deposits around Lake Superior in the mid to late nineteenth century and the rise in use of coal due to the depletion of Ohio’s forests, Ohio still had a role as the nexus of where those materials could be inexpensively transported for manufacture. By the mid nineteenth century, the Mahoning Valley, with Youngstown as its center, was leading the entire state in iron manufacturing (Wright, 1884, p. 131).
One of the most important influences on the rise of iron, and later steel manufacturing, was the availability of transportation. Ohio’s industries profited early on (though it would nearly bankrupt the state) by the creation of a number of canals. These permitted goods to find readily available markets both farther from the source of manufacture and also at a fraction of the time and cost previously employed. Lasting for only a generation, these vital waters would be supplanted by railroads, which permitted coals from West Virginia, Pennsylvania, and Ohio to be combined with Lake Superior ores, shipped inexpensively to ports such as Cleveland and Ashtabula on Lake Erie (Wright, 1884, p. 133).
Iron Minerals Used for Iron Ore
The common forms of iron minerals used in the early furnaces were iron carbonates (siderites) or iron oxides (limonite and hematite) that were available near the furnace. These minerals were found near the surface and could be extracted from pits or trenches. Early furnaces were sited near sources of iron ore, limestone (used for flux), fuel (charcoal or coke made from coal) and running water for powering a blast machine.
An iron carbonate (siderite) was one of the earliest types of ore used in eastern Ohio and western Pennsylvania. In this area, this mineral is found as layers, concretions, or nodules. The mineral siderite is a precipitate of iron and carbonate ions which form with other minerals within a soft mud sediment close to the sediment-water interface (Fisher et al., 1998). Siderite forms a dark to medium gray, dense rock which weathers to a reddish brown color. Density of siderite varies from 3.00 to 3.80 depending on the purity of the siderite (Stout, 1944a). All carbonate ores were roasted prior to use in the furnace to drive off water and carbon dioxide (Stout, 1944a). Continuous siderite layers can sometimes be found above a limestone bed as a layer intermixed with varying amounts of calcium and magnesium carbonate and silica. An example of this type of ore is the Buhrstone iron ore which is found above the marine Vanport limestone in western Pennsylvania (Coyle, 2003). The Vanport limestone is an important marker bed for the identification of adjacent rock layers because of its unusual thickness which is greater than 20 ft in Lawrence, Butler and Armstrong counties, Pennsylvania (Berkheiser, 1999). Below the Vanport limestone are typically three other marine limestones, the Upper Mercer, the Lower Mercer, and the Lowellville, of which the Upper Mercer and Lower Mercer are exposed along U.S. Route 422 south of New Castle, Pennsylvania, near the Moravia Street exit.
Layers of siderite can occur above the Vanport limestone, the Upper Mercer Limestone and the Lower Mercer limestone which were used for iron ore. The ore above the Upper Mercer limestone was also known as the Big Red Block ore (Stout, 1944a, p. 116). The ore over the Lower Mercer limestone has been called the Little Red Block ore (Stout, 1944a, p. 64).
Siderite can also be found incorporated into concretions or nodules found in shale beds (Newberry, 1878, section between p. 804 and 805; Willis, 1886), including dark shales above limestone or coal beds. These concretions were referred to as “kidney,” or reniform, ore because they were oval or kidney shaped (Willis, 1886, p. 235; Stout, 1944a, p. 7). This kidney ore, however, is not as heavy and not as iron rich as some of the classic kidney ores of England and the eastern United States. The current Glossary of Geology (Neuendorf et al., 2005, p. 352) defines kidney ore as a variety of hematite, but also as a concretionary ironstone. Thus the definition can include iron carbonate (e.g., siderite) as well as minerals such as hematite. Newberry (1870a, p. 41) described the Ohio kidney ore as an “earthy carbonate of iron” which “generally forms balls or concretions, lying in the shales of the coal formation.” By the time Newberry wrote this, however, its use had been supplanted by other types of ore.
Fossils or shell fragments have been found within concretions or nodules but are not found in all concretions (Pye et al., 1990, p. 325). Concretions can form in shallow sediment, close to the sediment-water interface (less than 10 m) (Fisher et al., 1998, p. 1). Carbonate cement forms in the pore space of the sediment and incorporates clay particles as it grows, eventually forming a spherical or ovoid shape. The original laminations of the clay can sometimes still be seen inside a concretion when broken open. Size of the concretions or nodules vary and can be up to 4+ inches in diameter and irregularly shaped. The concretions can be aligned in layers or occur randomly in a shale. Concretions can have a rind of limonite or hematite which is a yellowish to brownish red iron oxide. Concretions with rinds of iron oxides can be found embedded in shale along the streambed of Yellow Creek, in Struthers, Ohio (Stop 6), where the first iron furnace in Ohio was built. Such concretions have also been collected by archaeologists at furnace sites. Mined buhrstone and siderite nodules can vary in iron content from 25 to 45 percent (Harper and Ward, 1999, p. 29).
Siderite can also be found as black, hard layers within or on top of coal seams where it was called blackband ore. Black-band ore was found just above the Upper Freeport coal seam in Tuscarawas, Carroll, Perry, Stark, Guernsey, and Gallia counties, Ohio (Stout 1944a, p. 181). This blackband ore was a black, bituminous shale impregnated with iron in the form of an iron carbonate (Stout, 1944a, p. 182). The quantity of metallic iron in blackband ore varies from 25 to 40 percent (Stout, 1944a, p. 182). After weathering, the blackband ore breaks down into thin rusty flakes (Stout, 1944a, p. 183). This ore was sometimes overlain by a calcareous layer with nodules of siderite (Camp, 2006, p. 213). Blackband ore is not noticeably denser (its specific gravity ranges from 2.3 to 2.5) and looks like a black shale (Stout, 1944a, p. 189). It was not discovered until 1854 by an English miner, John Lewis, who was familiar with the blackband ore in the Victoria mines in England (Stout, 1944a, p. 29).
The Sharon blackband ore played an important part in the development of iron industry in Youngstown. The Sharon black-band ore is found within the Sharon coal or is found at the bottom of the Sharon coal and is limited to Trumbull and Mahon-ing counties. Within the Sharon coal it occurs as a layer of iron
carbonate in the form of a coal parting. It is banded in brown and black layers and displays a varvelike structure (Stout, 1944a, p. 28). After 1854, the blackband ore began to be used in furnaces in Mahoning and Trumbull counties (Stout, 1944a, p. 29). Slucher and Rice (1994, fig. 2) located a number of siderite beds in their column of the Pottsville Group in Ohio.
Bog-iron ore formed relatively recently in the Quaternary age and has been mined along the beach ridges from Cleveland, Ohio, to the Pennsylvania-Ohio state line (Stout, 1944a, p. 6). It is generally yellow-brown in color and variable in thickness from a few inches to several feet (Stout, 1944a, p. 6). Bog ore is open and spongy in texture and contaminated with impurities such as clay (Stout, 1944a, p. 6). It precipitates in shallow waters such as springs or swamps as a yellow or orange sediment that consolidates into an iron ore (Harper and Ward, 1999, p. 29). Bog iron is a limonite precipitated as nodules or sheets over several acres (Stout, 1944a, p. 6). Bog iron ore was used at the Van Buren Furnace in Cranberry Township, Venango County, Pennsylvania (Harper and Ward, 1999, p. 29).
Iron ores were of special interest to the early geologists of Ohio and Pennsylvania including Ohio’s W.W. Mather (Mather, 1838, p. 7–9) and Pennsylvania’s H.D. Rogers, who even had his own iron furnace (Gerstner, 1994, p. 62,132–133).
Slag and Slag Analysis
Slag from old iron furnaces can be found in many places in western Pennsylvania and eastern Ohio, including places where there have been iron furnaces and places where the slag has been transported by streams, or more often, dumped or reused. Such slag can take on a variety of external forms, ranging from irregular material resembling aa lava to vitrified material that bears a resemblance to obsidian or bottle-glass (Fig. 5). Because it is eyecatching, people pick up pieces of slag and bring it to museums (at least in the United States and Great Britain) for identification. Sometimes those bringing the slag to museums are doing so with the hope of confirming their find of a “meteorite.”
Slag is both the most prevalent object at blast furnaces and also the item that best tells the story of blast furnaces (White, 1979, p. 7). Two of us (H.E. and T.G.) have analyzed a suite of slag samples collected over a period of two years from 36 charcoal furnace sites in Venango, Clarion, Forest, Mercer, and Lawrence counties in western Pennsylvania and Lebanon and Berks counties in eastern Pennsylvania (Fig. 6; Edenborn et al., 2009). Where discernible, representative slag samples, as well as any slag that seemed unusual in terms of color or texture, were collected from each site. In addition, ore, limestone flux, and iron metal samples were collected, if observed.
In the laboratory, the samples were broken open and examined. Pieces with weathered surfaces were discarded and representative pieces with fresh surfaces were crushed in a mortar and pestle. The magnetic susceptibility of crushed slag samples was determined from the ratio of inductance obtained with and without the sample inside of a 2.8 cm inner diameter measuring coil (SI-2 Magnetic Susceptibility and Anisotropy Instrument, Sapphire Instruments, Ruthven, Ontario, Canada). Specific gravity of samples was estimated by fully suspending solid samples of known weight in deionized water (Mursky and Thompson, 1958), and slag color was estimated using the Munsell Rock Color Chart (1991). Powdered (<75 µm) slag samples were analyzed for major and minor elements using a molten salt fusion analysis and inductively coupled plasma–atomic emission spec-trometry (modified ASTM Method D6349). A subset of the slag sample set was analyzed by X-ray fluorescence.
Description of Slag Samples
Slags from these sites were frequently dark green–colored and glassy, reflective of high silica and residual iron content. Slags from specific furnace sites tended to have similar suites of minor trace elements that may be traceable to given ore or flux sources. Magnetic susceptibility tests were able to screen for slags containing small iron prills, likely indicative of inadequately heated furnaces. Short-wave fluorescence was intense in some samples and likely only occurs when correct ratios of activator and quenching elements are present. Lower specific gravity was generally indicative of greater amounts of entrained air or gas in slag, also lightening the slag color.
Two general metallurgical indices can be calculated based on chemical analysis of slags. The refractory index (RI) reflects the amount of alumina in slag relative to lime and silica, high values indicating a more refractory slag that requires a higher furnace temperature to melt. The desulfurization index (DI) is calculated as the ratio of calcium and magnesium oxides to silica and alumina, a high index indicating a greater sulfur-removing capacity.
Analysis of Slag Samples
Preliminary analyses of slag samples from cold-blast charcoal iron furnaces in northwest Pennsylvania suggest the following. (1) Slags from a given furnace site are generally physically similar in appearance and contain similar trace elements. (2) Low refractory indices (RI) suggest that furnace charge materials (ore, flux) were of a composition that permitted relatively low furnace operating temperatures. (3) The desulfurizing capacity (DI) of tested slags was low, but this ability was unneeded where low-sulfur charcoal fuel and ores were routinely used. (4) The principal component analysis (Fig. 7) indicates the presence of two distinct groups: When the control of Axis 1 is plotted against the control of Axis 2, it is clear that the slag samples are chemically distinct from the ore samples. This difference may provide insight to the types of fluxes utilized during smelting.
Pioneering research on the composition of early Ohio and Pennsylvania iron blast furnace slags was conducted by John White (1980), who compared slags from twelve early blast furnaces in Ohio (including the Hopewell [Eaton] and Trumbull), Pennsylvania (Wilroy), and Europe in terms of their metallurgical features and physical attributes. White (1980) was able to show that properties of slag could be used to indicate the likely operating conditions and relative efficiency of the furnaces at the time. An “optimal” slag in an active furnace would demonstrate the following two important metallurgical characteristics: it would be fusible, or easily melted at high temperatures; and be fluid, with a low viscosity, at those temperatures. Additionally, as mentioned previously, the chemical composition of the slag was important in the scavenging of stray sulfur, seldom a problem in charcoal iron furnaces, but a more common problem when coal was used. Many of White’s observations on the characteristics of slag are consistent with recent studies (Edenborn et al., 2009) of a much larger number of additional furnaces in Pennsylvania. Not surprisingly, the metallurgical characteristics of studied slags suggest that blast conditions at small charcoal iron furnaces were seldom optimal, probably reflecting the consistent use of low-grade iron ores, which could be composed of a wide range of ore types and qualities, and technical difficulties maintaining proper blast temperatures. Interestingly, White was able to determine that blast conditions at the Hopewell (Eaton) furnace in Ohio, one of the first to attempt to use both charcoal and coal with a higher sulfur content, probably resulted in the demise of the furnace, due to its inability to fully remove the additional sulfur, which would have resulted in an inferior iron product.
Field Trip Stops
Stops cover parts of western Pennsylvania and eastern Ohio (Fig. 8). These stops were chosen so that sites in both states could be visited during a one-day field trip. The stops may, of course, be visited in a different order. Information on the stop locations is given at the beginning of each stop. Web sites for the two major parks systems visited on this trip contain detailed maps.
Stop 1. McConnells Mill, McConnells Mill State Park, Slippery Rock Gorge, Lawrence County, Pennsylvania
McConnells Mill State Park is located west of Portersville, in southeastern Lawrence County, Pennsylvania. With the exception of the inside of the mill, it is open year-round. This park includes sites related to several early industries, including grain milling, iron production, and the burning of agricultural lime. Visitors to the park should obtain a copy of the Pennsylvania Trail of Geology Moraine and McConnells Mill State Parks guide (Fleeger et al., 2003). Maps of the park are available on the Pennsylvania State Park Web site.
The eastern end of McConnells Mill State Park contains the site of the McConnells Mill (Figs. 9 and 10) itself as well as the ruins (mostly foundation material) of an earlier gristmill. Access to McConnells Mill is from a set of stairs leading from a trail from a parking lot along McConnells Mill Road or from a park road leading downhill to a small parking area by the mill itself. The trail from the upper parking area is recommended as it is scenic and provides good views of a thick sequence of the Home-wood sandstone (Fig. 11). Here the Homewood is composed of coarse-grained sandstone and conglomerate. Joints, crossbeds, and honeycomb weathering can be seen in the unit. (A discussion of the Homewood and a stratigraphic column of McConnells Mill State Park in Skema [2005b], however, shows that identifying a unit as the Homewood is not without its problems.)
McConnells Mill (Forest Mills)
McConnells Mill (Figs. 9 and 10) is located in the eastern part of McConnells Mill State Park, near the entrance to the park off of State Route 422. The mill is open seasonally, closing at the end of October and re-opening in the spring. This mill, also known in the past as the Forest Mills, was one of a number of gristmills constructed along Slippery Rock Creek in this area,
the first of which was constructed in or just after 1825. McCon-nells Mill is the best known and only remaining intact mill here. It was run by Captain Thomas McConnell (1822–1905) and his son James (Durant and Durant, 1877). McConnells Mill was constructed in 1870 on the foundation of an even earlier mill which burned in 1868.
McConnells Mill has its foundation built into the Home-wood sandstone, and it appears to have been built out of blocks quarried from the Homewood. The Homewood has been quarried in other areas of Lawrence County (Stone, 1932, p. 191–192) and across the state border in Ohio as well (Stout, 1944b). Red sandstone in part of the present mill foundation is said to have been reddened by the fire that burned down the predecessor to the current mill. Fire can redden sandstones rich in iron, but we have not verified if this red color was caused by fire or if the stone was originally red.
This mill was once noted for its early use of rolling mills, which utilized steel rollers to crush grain. Despite this, a number of traditional millstones remain in and around the mill.
Two complete French-buhr millstones are preserved here, one inside the mill (Fig. 12) and one outside (Fig. 13). The stone inside the mill is a composite millstone composed of polygonal blocks (known as “panes”) of light-colored chert (yellowish gray 5Y 8/1), 106 cm in diameter. This is a runner stone (the top stone in a working pair of millstones), still with its plaster top (see Hannibal and Evans, 2010, fig. 30, for a view of another runner stone whose plaster is deteriorating because the stone has been left outdoors). Such plaster, typically incorporating stone rubble, was added to finish and balance the runner. (Balance boxes were also used for weights to balance the runner.) The millstone contains a number of rounded to suboval cavities, several of which exceed 3 cm in maximum diameter. Another composite French-buhr millstone outside of the mill has the same coloration and diameter. Microfossils and other particles can be seen in the stone. Cavities range up to 4.5 cm in maximum diameter. One block of this millstone is cut in an unusual manner, showing bedding structures that indicate that its cutting surface was cut to be perpendicular to bedding. Most millstones made of sedimentary rock are cut parallel to bedding. Bedding surfaces with abundant cavities (cells) were typically chosen as the cutting face of millstones (Hildreth, 1838, p. 343).
There are other millstones and related materials in the mill. These include a level used in finishing millstones. A 33 by 48 cm piece of a French-buhr millstone can also be seen inside the mill. Only the cutting surface of this millstone is finely fin-ished. The sides are very rough. There is also a sandstone millstone inside the mill.
The ruins of an earlier mill are located along the Kildoo Trail which follows Slippery Rock Creek to the south from McCon-nells Mill. (From the mill, the trail to the ruins runs along the east side of the stream south past the covered bridge.) The ruins are ~100 ft past the wooden footbridge over the falls. Some sandstone building blocks used for the mill are in place while others are strewn about. Shallow, rectangular depressions used for anchoring wooden beams can be seen in the 5-m-high stone block at stream level.
Three millstones can be seen at the ruins just below the level of the trail. Two of the stones are entire; a third is broken. Two of the stones are monolithic feldspathic stones. The entire stone that is readily measurable is 115 cm across. It has large crystals that delineate some foliation or preferred orientation along which some cracks are developed. The third, broken millstone is a light-colored granitic stone and was presumably monolithic. It is ~105 cm in diameter. Roughly one-third of the stone has broken off at some time, with the break partly along an old 3-cm-diameter, 9-cm-deep, drill hole.
A fourth monolithic millstone (Fig. 14) is leaning against a tree downslope from the trail. This granitic stone, ~109 cm in diameter, is very high in quartz and contains biotite. It has a maximum thickness of 20 cm and has a very irregular bottom.
Stop 2. Hells Hollow, McConnells Mill State Park, Lawrence County, Pennsylvania
Hells Hollow (also known as Big Hollow in the past) is located in the western part of McConnells Mill State Park (Fig. 15), with access from a parking lot along Shaffer Road. A path leads from the parking area downstream along Hell Run, a tributary of Slippery Rock Creek. The trail bifurcates just before the first footbridge over Hells Hollow Run; the trail along the southern side of the river leads to an old quarry area and an old quarry. There are excellent exposures along the trails of the Vanport limestone as well as associated karst features indicated by very evident changes in stream flow over relatively short distances (see Fleeger et al., 2003). Hells Hollow was once known for its disappearing streams and “darksome dells” (Durant and Durant, 1877, p. 115). This site is not the only “Hells Hollow” in western Pennsylvania. The Hells Hollow in McConnells Mill State Park should not be confused with the (equally interesting as far as Pennsylvanian rocks and nineteenth-century industrial geology) Hells Hollow in Mercer County. The Vanport has been widely quarried in this and other areas of Lawrence County because of the access to exposures and the uniformity of the rock (Miller, 1934, p. 482).
The old quarry adjacent to the trail is shallow. If missed, it can be found by backtracking from the lime kiln which is more evident. According to Fleeger et al. (2003, p. 9) this quarry was the source of flux (limestone) and iron ore.
The lime kiln (Figs. 16 and 17) preserved at this stop is unusual as it is completely, rather than partly, built into the limestone and shale bedrock of the hillside. The rock here was carved out and lined with fire brick, with the bricks aligned with their ends facing in. The bottommost part of the kiln is in shale; the top in limestone. This is a vertical (also known as continuous) kiln; the top opening was for raw material, while the bottom opening allowed for removal of the calcined lime.
This kiln was used to produce agricultural lime. Kilns were used to make agricultural lime in the nineteenth century as this method reduced the limestone to smaller pieces that could be readily powdered. Early lime kilns and iron furnaces in the United States had a similar morphology (Hahn and Kemp, 1994, p. 9–11). Lime kilns in western Pennsylvania and eastern Ohio during the seventeenth and eighteenth centuries were typically built to produce agricultural lime and natural cement (a hydraulic cement that could set under water). The calcining process helped to reduce the size of lime particles for agricultural lime. Limestone was further crushed here by a horse (or similar animal) mill (Natalie Simon, October 2010, personal commun.).
Lawrence Furnace, located on private property (“X” on Fig. 15) adjacent to the park property, was built in 1865 or 1866. White (1986, table 1) reported that this furnace was built into limestone bedrock and that slag and a tipple retaining wall are present at the site but his description of the site (his table 1) as being well-preserved indicates that he probably confused the furnace site with what is now interpreted as the lime kiln. This is understandable as there are a number of similarities between early blast furnaces and lime kilns. Both, for instance, are tall, have openings, and are lined with fire-resistant materials.
The first ore used for the Lawrence Furnace was presumably quarried nearby, but already by 1870 on this furnace utilized “red ore” from the iron ore banks of southern Shenango Township (Durant and Durant, 1877, p. 117; the ore banks are also shown on a map between p. 5 and 6). The limestone used for flux has been described as being local, thin, brittle, bluish-gray in color (Durant and Durant, 1877, p. 117), a description which fits the Vanport limestone at Hells Hollow. The iron produced at Lawrence Furnace in the 1870s was sent mainly to Youngstown, Ohio.
Stop 3. Route 422, New Castle Pennsylvania: Allegheny/ Pottsville Outcrops
A spectacular outcrop (Fig. 18) of Pennsylvanian rocks at New Castle, Pennsylvania, along U.S. Route 422 south of New Castle, on the New Castle South topographic quadrangle at latitude N 40° 58’ 6.42” and longitude W -80° 21’ 47.88”, is conveniently located between McConnells Mill Park in western Pennsylvanian and Mill Creek Park in eastern Ohio. This stop is situated along a busy highway and should only be viewed with extreme caution.
The rocks are exposed on the north and south side of the road over a length of 3000 ft. (~914 m). The outcrop extends from
the Martha Street Overpass west to the Moravia Street ramps. Vertical relief is ~200 ft from the upper Pottsville Formation to lower Allegheny Formation. This stop has an abundance of sid-erite (iron carbonate, FeCO3) deposits that were used as iron ore in many early Ohio and western Pennsylvania iron furnaces. The following description of the stratigraphy at this stop is adapted from Skema (2005a).
Rock units at this exposure (Fig. 19) range from the Brookville and Clarion coals of the Allegheny Formation down to the Lowellville limestone horizon of the Pottsville Formation. The north side of the roadcut exposes the Clarion coal at the top to the Flint Ridge coal at the base. On the south side of U.S. Route 422, rocks below the Flint Ridge coal crop out as low as the Lowellville limestone. This outcrop shows: (1) the repetitive nature of coal, limestone, shale, and sandstone deposition during the Pennsylvanian, (2) siderite in various forms, and (3) a channel, incised into preexisting sediment layers, that locally cuts out important marker beds such as the Lower Mercer limestone. Note that the Lower Mercer limestone is missing on the north side of the roadcut whereas it is present on the south side of the road. The Upper Mercer limestone crops out on both sides of the road.
Iron carbonate (siderite) is present as nodules or layers above the marine limestone beds and as concretions or “kidney stones” in the shale above the limestone beds. Siderite is reddish on weathered surfaces and light gray, bluish gray, or dark gray on fresh, unweathered surfaces. If tested with mild acid, it will fizz. The iron carbonate may be siliceous, however, and contain Mg-calcite and/or pyrite, each of which lessens its tendency to fizz under acid. The siderite is finely crystalline and breaks with a conchoidal fracture (Inners, 1999, p. 563). It has a higher specific gravity than the surrounding shale.
A strip mine for the Vanport limestone was located in the hillside above this outcrop. An important iron ore horizon called the Buhrstone ore was mined above the Vanport. It was named for the light bluish-gray chert, or buhrstone, that occurs between the ore bed and the limestone. Rogers (1840, p. 189–190) compared this buhrstone to the classic French buhr. Unweathered buhrstone ore is medium gray, calcitic siderite, locally siliceous, weathers brick red. The buhrstone ore (also known simply as buhrstone,but that term is best used only for the siliceous rock for which the buhrstone ore was named) was mined in the 1800s to supply iron ore to the iron furnaces (Coyle, 2003). The ore in the old mines was generally 6–12 inches thick (Chance, 1880, as stated in Inners, 1999, p. 563). Weathering of the siderite resulted in thick pockets of secondary limonite (Inners, 1999, p. 563).
In the roadcut exposure, more erosion-resistant sandstone and limestone layers stand out from the “softer” claystone or shale. The most prominent layer in the middle of the outcrop is the Upper Mercer limestone (see Fig. 19) (Skema, 2005a, p. 132, fig. 10–3). Just above this limestone is a thin layer of siderite. At the far western end of the outcrop, a layer of siderite is exposed in the bottom of the drainage ditch along the road. This layer of siderite is interesting because faint ripple marks on the bedding surface indicate that the siderite was forming a layer on top of the mud while under water and not formed as a hardpan at the bottom of a soil (Skema, 2005a, p. 132). Concretions are found in the shale above the limestone layers. The photo of the outcrop (Fig. 18) has some of the limestone and siderite layers identified. Loose nodules or concretions that have fallen from the shale may be present on the ground. In this area, nodules with a “lumpy” surface may have barite, a barium sulfate mineral, precipitated within internal fractures. Siderite concretions in the dark shale above marine limestone or coal may have septarian fracturing in the center of the nodules. These fractures may contain cal-cite, barite, and zinc minerals, such as sphalerite and wurtzite, and clay (Skema, 2005a, p. 130). Partial fossils may be preserved within nodules (Skema, 2005b, p. 151) indicating that the fossil may have served as a nucleus for the growth of the concretion. However, there are concretions with no apparent nuclei (Pye et al., 1990, p. 325). Concretions which occur in the shale are disc-like and conform to the surface of the underlying and overlying shale layers. Concretions probably grew within the soft sediment as seen in Recent marsh sediments of the Mississippi River deltaic plain (Moore et al., 1992, p. 357). Siderite nodules (<2 cm in diameter) and clayey tabular siderite accumulations (<5 cm thick) that parallel bedding are common in the lacustrine and back-swamp muds of the southern lower Mississippi Valley floodplain (Aslan and Autin, 1999, p. 803).
A channel cuts into preexisting sediments at the western end of the roadcut. There is a layer of siderite nodules above, but parallel to, the base of the channel. These nodules may have been transported by the eroding stream and then deposited as part of lag gravel along with the clay and sand. Another theory is that this is an example of the siderite precipitating on plants, logs and other carbonaceous lag debris along the edge of the stream channel. The original organic matter would have been completely replaced (Skema, 2005a, p. 132).
Stop 4. Lanterman’s Mill, Mill Creek Park, Youngstown, Ohio
Lanterman’s Mill (Stop 4 on Fig. 20) is a restored gristmill in the valley of Mill Creek, the early industrial heartland of Youngstown, Ohio. The mill (Fig. 21) is located at 980 Canfield Road (Route 62), on the east side of Mill Creek, immediately south of the Canfield Road bridge over the creek, in Mill Creek Park. This park is one of the parks in the Mill Creek MetroParks system. There is a parking area located just to the north of the bridge. The best easily accessible view of the mill (and the best site for photographing the mill) is from the Canfield Road bridge over Mill Creek. The park and area around the exterior of the mill, including an elevated boardwalk along the cliffside of the valley of Mill Creek that extends in a downstream direction, is open all year long except when closed due to extreme weather conditions. The mill itself is open seasonally, typically between May and October.
The mill is located alongside a scenic waterfall formed by a resistant layer of the Pennsylvanian Massillon sandstone (Stephenson, 1933, p. 69–71). (As with the Homewood as noted above, the correlation of the Massillon can be problematical; e.g., see Ruppert et al., 2010, fig. 1; Szmuc, 1957, p. 136) A path from the mill leads to the elevated boardwalk allowing a close look at the rocks along the stream. The Massillon here (Fig. 22) is a coarse-grained, crossbedded, cliff-forming quartz sandstone. Typical Pennsylvanian plant fossils (Sigillaria, Lepidodendron) can be seen in places in the outcrop (Stephenson, 1933, p. 70–71) and as float along the stream. Despite these fossils, the identification and correlation of the Massillon (also known as the Con-noquenessing sandstone; Rau, 1970, p. 79) in this area of Ohio remains problematical (Slucher and Rice, 1994, p. 37).
The earliest mill along Mill Creek was erected by Abraham Powers and his son ca. 1799. According to the Mahoning Valley Historical Society (1876, p. 167), the pair of millstones for this mill were split from a rock ~3 ft in diameter. The same source notes that this rock was found “in the vicinity of where Lincoln Avenue will cross Holmes Street” in Youngstown. This location would have been on the north side of the Mahoning River, just to the northeast of where Mill Creek flows into the Mahoning River. Butler (1921, p. 658) called the material “a native boulder,” and Melnick (1976, p. 235) called the source material “local granite boulders.” This is likely, based on the location of the site, its description in the literature, and other cases of early use of glacial granite boulders in northeastern Ohio for millstones (Saja and Hannibal, 2009).
The present Lanterman’s Mill, the third to stand at this site, was constructed by German Lanterman and Samuel Kimberly between 1845 and 1846 and restored between 1982 and 1984. The mill is built into an outcrop of the Massillon sandstone where more resistant layers of the rock unit form a waterfall. The mill is also built of the Massillon sandstone, which was historically quarried along the Mill Creek gorge at various places. Quarry walls can be seen, for instance, in the Bears’ Den area to the northwest of the mill in Mill Creek Park. The Massillon is a coarse-grained quartz sandstone at the mill. Sedimentary features seen in the stone used for the mill include Liesegang rings. The mill was built at this location to utilize the drop to turn a waterwheel. The present, still functional, waterwheel is located inside the mill structure. The interior of the mill also provides a good look at a bright reddish brown iron precipitate forming at a seep in the natural sandstone forming part of the mill foundation. There are a number of such iron-rich seeps in the Massillon sandstone in this area.
Millstones at Lanterman’s Mill
A number of millstones and millstone fragments can be seen outside and inside of Lanterman’s Mill. Some of the millstones are monolithic, and others are composed of multiple pieces. Millstones at this site are made of conglomerate, granite, and, presumably, French buhr.
A granite millstone (Fig. 23) with a bronze plaque is preserved near the entrance of Lanterman’s Mill. While it is likely that this millstone was fashioned from a glacial boulder, we have not been able to determine its history.
A conglomerate millstone (Fig. 24) is the best documented, as it has long been preserved in the bed of Mill Creek, 155 m (500 ft) south of the downstream edge of the mill and 170 m (~548 ft) from the lip of the falls. By 2009, the millstone had become almost completely covered by typical stream gravel and sediment. The upward-facing surface of the millstone, however, was uncovered during the summer of 2009 and subsequently swept off in 2010. (One year of normal stream deposition had partially covered it again.) The millstone can be seen from the boardwalk, where a sign points it out on the opposite side of the stream. Published sources indicate that this millstone is from the Baldwin Mill, the second (1823) mill at this site. The composition of the millstone is consistent with the identification of Melnick (1976, p. 244), who noted that the millstones here at the mill were made of “‘Pudding stone’ or perhaps Sharon conglomerate.” The millstone is a monolith made of a conglomerate with rounded to angular, white quartz pebbles. The quartz pebbles, as well as the rounded to subrounded cavities (Fig. 24, where clay clasts had broken away) present, are consistent with it having been fashioned from rock from the Sharon Formation. Interestingly, the Sharon (then known as the Carboniferous Conglomerate) was once correlated with the Millstone Grit in Europe (Newberry, 1870b). The Sharon Formation is exposed along the lower reaches of Mill Creek as well as elsewhere in the region. Conglomerates were once a preferred stone for manufacture of millstones in both England and America, but fell out of favor as the popularity of imported French-buhr millstones increased as transportation networks (especially canals) allowed for easy transport to places in western Pennsylvania and eastern Ohio. To complicate things, however, Galaida (1941, p. 10) reported that conglomerate buhrstones from Lisbon, Ohio, were brought to the old Woolen Mill (Pioneer Pavilion) area of Mill Creek Park for use in crushing flax. This type of buhrstone would have been an edge runner, that is, a buhrstone whose edge was utilized as a grinding surface. It is possible, but unlikely, that the stone in the stream by the mill is one of those other buhrstones.
Three multiple-piece chert millstones (Fig. 25) are prominently displayed outside of the mill. They are presumably made of French buhr. Most large millstones sold in the United States that were composed of French buhr are composite. But, as Hockensmith (2009a, p. 71) noted, domestic Ohio chert millstones were also produced in segments by the 1820s. The presence of French buhrstones at this site in the past is indicated by the inclusion of “3 damaged French bur [sic] mill stones” in an 1842 inventory of the personal property of Eli Baldwin (MSS 2097, Container 1, Folder 6, Estate of Eli and Mary Baldwin, 1840–1881, Eli Baldwin papers, Archives of the Western Reserve Historical Society). There are several individual segments of French-buhr millstones (e.g., see Fig. 26) preserved inside the mill. These clearly show that only the grinding surface of the stone pieces was finely finished, with the other sides of the stones finished to various degrees. Also, it is not uncommon for French-buhr millstones to be constructed from blocks of varying thicknesses (C.D. Hockensmith, 2010, personal commun.).
At quite an early date, Hildreth (1838, p. 33–34) explained the basic geologic difference between French buhr and the Ohio millstones: French buhr was Tertiary and contained fresh-water shells; Ohio stone was from the Coal Measures and contained marine forms. Thus, easily identifiable fossils such as fusulinids (all Paleozoic) and horn corals are potential index fossils to the Ohio cherts used for millstones.
Some of the chert millstones at this mill contain molds of trace fossils and low-spired snails, and French buhr was noted as having small fossil shells (Safford, 1880, p. 177; Hockensmith, 2009a, p. 61). A detailed geological and paleontological comparison of the various cherts used for millstones, however, remains to be made to definitively identify the sources of this stone.
Stop 5. Trumbull (Mill Creek) Furnace, Mill Creek Park, Youngstown, Ohio
Trumbull Furnace (Fig. 27; Stop 5 on Fig. 20), also known as the Mill Creek Furnace, is located along Old Furnace Road just to the east of its intersection with Cohasset Drive. This is just to the north of Lake Cohasset. The mill is next to Pioneer Pavilion. The furnace is built into the side of an outcrop of an unnamed Pennsylvanian shale subjacent to the Massillon sandstone.
Originally built as a charcoal-fueled furnace, this furnace later utilized bituminous coal. Butler (1921, p. 177) stated that the furnace began production in either 1826 (p. 177) or 1832 (p. 663) as a strictly charcoal furnace, and that after twenty years it was rebuilt to accommodate both charcoal and bituminous coal. However, competition from other more efficient furnaces drove it out of business some time after that in the 1840s or 1850s. Also, the furnace was located roughly three miles from the Pennsylvania and Ohio Canal (completed in 1848), so both raw and finished materials had to be moved that distance by other means (Williams, 1882, p. 371). The furnace was excavated by archaeologist John R. White in the summers of 2003–2005. A number of innovations over the original Hopewell Furnace were discovered, including stone-lined recesses under the casting floor and an access door to either side of the furnace. The recesses served a dual purpose of removing water from both the casting floor and also the molten iron and of cooling the casting floor from below. The access doorway to the left of the crucible (defined below) extends from the casting floor to the back of the furnace from which it curves around the back of the furnace before emerging on the right of the crucible. This doorway would provide access for the workers to the other side of the casting floor and would be especially useful during those times when the casting floor was covered in molten iron.
The use of the site has changed over time. The furnace was built against the base of a rise, used, and abandoned. Williams (1882, p. 371) revealed that the machinery was stripped from the furnace after it was closed. Some of the blocks from the furnace were scavenged. Also, as the road above the furnace (the aptly named Old Furnace Road) was constructed, the earth from the top was leveled and pushed over the sides and took much of the front of the furnace with it, causing many of the large blocks from the outer shell of the furnace to become jumbled above the casting floor. Additionally, the iron salamander from the furnace came to extend several meters out from the furnace. Sometime following all this, a gas line was laid through the casting floor to reach Pioneer Pavilion. Following 150 years of deposition, only the most superior edges of the top two topmost blocks were visible prior to excavation in 2003. Ironically, because of the burial of the furnace, it was able to endure much longer than otherwise would be the case. Already in the few years since excavation, dangerous cracks have emerged, which, if left untended, threaten to destroy some of the most salient features of the site.
The dominating feature of the furnace is the central inner furnace. The inner furnace can best be thought of as two truncated cones with their widest sections placed back to back, like an inverted hourglass. The point where the inner furnace is widest is known as the bosh and is visible at the Mill Creek Furnace. Just below the bosh (Fig. 4) is the hole where the tuyère was located. (The tuyère is where air, known as blast, was forced into the furnace; see the section “Early Iron Industry in Ohio and Pennsylvania” above for additional discussion.) Below the tuyère opening is a narrower area, now solidified. This is the crucible and would have represented an area where the molten iron and slag congregated. Below that is the point at which the iron would have emerged onto the casting floor, which would have been covered with a dam stone or clay plug. Just outward from the inner furnace is a red layer of brick. This is the inwall and would have consisted of refractory brick used to insulate the inner furnace, some of which is still visible. Another insulating layer composed of loose sand lined the exterior of the brick lining. Finally, just outward from that are the sandstone blocks used as a shell of the furnace. The area in front of the furnace was known as the casting floor and would have been where the iron castings and pigs were
made. The casting floor extends beyond the excavation area. Just in front of the furnace is a large conglomeration of iron and slag, called a salamander or bear. This represented the last batch of iron and slag from the furnace and still remains at the site. White (1980c, table 3) described the slag at this site as green and stony, but also gave a more detailed analysis (1980a) and a greater color range. Samples (now in the University of Youngstown Department of Sociology and Anthropology collections) from this site that have been collected by archaeologists vary from gray to blue-green to green-brown to brownish black in color and range from glassy to vesicular in appearance. White (1980a, p. 59, table 3) noted that the slag found at Trumbull Furnace was high in sulfur in comparison to other early furnaces, hypothesizing that this may have been due to the use of coal.
Pioneer Pavilion, located next to the furnace, was originally constructed in 1822 as a wool carding and fulling mill and operated until 1830 (Butler, 1921, p. 663). It was once a simpler building (Blue et al., 1995, p. 19); additions have been made over time. It is made of locally quarried Massillon sandstone. The stone is coarse-grained and contains nested Liesegang rings. It is likely that the mill race that provided the water power for whatever system the furnace used to force air into the furnace is located between the pavilion and the hillside, possibly under the more recently added restrooms on the southwest side of the pavilion. During construction of additions on the pavilion, pieces of a likely waterwheel were recovered; however, whether that wheel belonged to the carding mill or the blast furnace remains unknown. Both the carding mill and furnace likely used the same mill race to supply their hydropower needs.
Source of Iron for Trumbull Furnace
It is likely that the source of iron for this furnace was local. Charles Whittlesey showed (1838, cross-section between p. 56 and 57) iron ore and iron strata below the Conglomerate ( = the Sharon Formation) as well as beds of iron in the rocks between the Conglomerate and the Blue Limestone. That would indicate iron sources at and below the level of the furnace. Orton (1884, p. 383) referred the kidney ore which had been mined in the Mahoning Valley to the Sharon shale, an informal shale unit above the sandstones and conglomerate of the Sharon Formation as used here. Indeed, the gray shale adjacent to the furnace, which is below the Massillon sandstone, contains ironstone concretions.
Galaida (1941, p. 13) indicated that the original ore used was kidney ore obtained from local outcrops, and that the supply of this ore was short-lived. Belfast, in an unpublished 1979 class report (“A geologic field guide of Mill Creek Park”) noted the presence of an iron ore mine on the east side of Lake Cohasset, below the dam on the downstream side of the dam.
Stop 6. Hopewell (Eaton) Furnace, Yellow Creek Park, Struthers, Ohio
The Hopewell Furnace, also known as the Eaton (also spelled Heaton) Furnace, is located in Yellow Creek Park in Struthers, Ohio (Stop 6 on Fig. 20). (The name Hopewell is the most used name for this furnace and is the name used on the historic marker in this park, but the name should not be confused with the older, even better-known Hopewell Furnace located in Berks County, Pennsylvania [see Walker, 1966, for a description of that furnace]). This Mill Creek MetroPark stretches from where Lowell-ville Road crosses Yellow Creek south to the northeast side of the dam which impounds Lake Hamilton. The furnace is built into the hillside, into an outcrop of the Massillon sandstone, just to the east of Lake Hamilton, in the southernmost section of Yellow Creek Park in Struthers, Ohio.
Hopewell Furnace (Fig. 28) is accessible via the park trail that extends southward from a parking area along Wetmore Avenue, an east-west–trending street which roughly bisects this north-south–trending park along Yellow Creek. There is a historic marker for the furnace by the parking area. When curves of the winding trail are taken into account, the distance between the parking area and the furnace approaches 1 mi (1.6 km). The trail is easiest to traverse in dry weather when the stream is low, as it is necessary to cross Yellow Creek at least two times along the path to the furnace. The trail to the furnace site is scenic, however, and of special interest to geologists.
Outcrops of medium- to dark-gray shale containing iron-rich beds and concretions can be seen along the stream en route to the furnace. The gray shale, rich in ironstone nodules, is an unnamed shale subjacent to the Massillon sandstone (Stephenson, 1933). The iron-rocks derived from these layers can also be seen as float. These iron-rich rocks can readily be identified by oxidized exterior layers which are red in color. These can be interpreted as kidney or something similar to kidney ore. These iron-rich layers and concretions, however, do not readily fizz in acid, presumably because they are leached of siderite sure to deep weathering. In his archaeological reports, White (1978, p. 392; 1996, p. 234) described the ore used here as being kidney or reniform ore “generally composed of concentric layers or shells made distinct by weathering” and exfoliation, and having a “deep red-brown color.” He also noted (White, 1980c, p. 57) that the ore was found in “pockets or layers and as float material in Yellow Creek” or “from beds of shale” (White, 1996, p. 234). Butler (1921, p174) stated that the “ore found along Yellow Creek” was used as the raw material. So it is reasonable to infer that the iron-rich layers and concretions in the gray shales exposed here are the source of the iron. These layers, however, are not among those shown in typical columns (e.g., fig. 2 in Slucher and Rice, 1994) of the Pottsville.
White did some analysis of ore at this furnace site, describing (White, 1982, p. 24) the kidney ore used here as having 39.8% iron. In other papers, he also described the locally collected kidney ore at Hopewell as having an “average iron content of 51.3%” (White, 1980b, p. 513; White, 1979, p. 8).
The contact between the shale and the overlying Massillon along Yellow Creek is interesting for a number of reasons. The shale contains sideritic concretions that presumably were the source of iron ore. Also, the rock just below and above the contact with the Massillon appears to preserve some soft- sediment deformation and evidence of penecontemporaneous faulting and slumping (Fig. 29). Alternatively, this faulting might be interpreted as being due to fracture-relief faulting as identified elsewhere by Ferguson (1967). The Massillon sandstone contains anastomosing layers of coal to at least 6 cm in thickness; at least some of these layers are coalified Pennsylvanian trees. The Mas-sillon also contains prominent sets of cross beds and channel-form structures.
The furnace is built into the hillside above the creek, into an outcrop of the Massillon sandstone, just beyond and uphill of a stone arched-bridge carrying a large pipe. This hillside construction (Figs. 30 and 31), a common construction element in blast furnaces in both Ohio and Pennsylvania, allowed for the delivery of ore, limestone, charcoal, and coal from above. This hillside feature is so ubiquitous in furnaces built before the invention of the skip hoist that they are often referred to as “bank” furnaces (White, 1979, p. 6). Additionally, this placement was often found in conjunction with elevation changes in water, which were essential to powering the mechanisms used before steam power to force the air blast into the furnace. An overshot waterwheel here was powered by the flow of Yellow Creek, aided by a high dam (Reese, 1929). The upper layer of material at the base of the furnace is composed of a large amount of slag. Most of the slag seen here, as well as that found during archaeological investigation of the site by White (1980a, p. 57), is a dense, glassy black-colored slag.
This furnace is frequently cited in Ohio geological, historical, and cultural literature (the furnace and the ore along Yellow Creek are mentioned in the introductory stanzas of the Bruce Springsteen song, “Youngstown”). It was probably constructed by 1802–1803 (White, 1978, 1996) or at least by 1804 (Butler, 1921, p. 174; Stout, 1944a, p. 28), although Upton (1910, p. 602) cites an 1807 construction date. The Hopewell Furnace has been accepted by some authors as the earliest blast furnace west of the Alleghenies (Upton, 1910, figure caption on p. 593, but also see p. 602; Melnick, 1976, p. 170; White, 1996 and other references; Deblasio, 2010, p. 75). This claim, however, conflicts with claims for earlier furnaces west of the Alleghenies (Swank, 1878, p. 49; Mathews, 1885, p. 177) in western Pennsylvania, or “over the Alleghenies” in western Pennsylvania (Bining, 1938, p. 61–64). White, the principal modern proponent of this claim, was familiar with iron furnaces in western Pennsylvania (see White, 1986), so these claims may rest on one’s interpretation of the boundaries of the Alleghenies. The first trans-Appalachian iron furnace in western Pennsylvania, the Alliance Furnace (blown-in in 1789) is located near the western boundary of the Allegheny Mountain Section as defined by the Pennsylvania Geological Survey physiographic map (reproduced in Shultz, 1999, p. 342; Briggs, 1999, p. 364; and elsewhere). If the Allegheny Mountain Section is taken as a benchmark, then the Alliance Furnace is indeed just west of the western boundary of that section in Fayette County. Based on this criterion, the Alliance is indeed the first west of the Alleghenies. However, the confusion over this boundary and the exact location of the Alliance Furnace in relation to the boundary contribute to this ongoing dilemma. It should be noted, however, that the historic marker for Hopewell Furnace in the park claims that the furnace was “one of the first west of the Allegheny Mountains,” not the first. The Hopewell Furnace has also been noted as the first industry in Ohio, but that claim ignores the Ohio gristmills and sawmills established before 1802. Gristmills and sawmills were the first industries (manufacturers) in eastern Ohio as well as in western Pennsylvania (Hazen, 1908, p. 114).
The Hopewell Furnace was well studied by Youngstown State University archaeologist John R. White (1937–2009), who published a series of articles describing aspects of the furnace, (e.g., White, 1977, 1978, 1980b, 1980c, 1982, 1996). It is important for its very early construction date and for its early use of coal as well as charcoal as fuel and as the first iron furnace in Ohio. White provided a series of maps and diagrams of the site (e.g., in White, 1978, and especially White, 1996, which contain photos of the site as recently excavated).
The Hopewell Furnace originally used the abundant forests surrounding the furnace to produce charcoal, which the furnace initially used exclusively as fuel (Butler, 1921, p. 174). Charcoal is a great fuel and with the availability of the virgin forests of Pennsylvania/Ohio, charcoal was originally readily available. White (1996, p. 240) estimated that this charcoal production would have used ~240–250 acres of hardwood timber per year for the Hopewell. As the timber around the furnace was rapidly being depleted, the owners attempted to supplement the charcoal fuel with locally available bituminous coal. According to White (1980a) the high sulfur content that the coal was adding to the iron, and the inability of the flux to effectively remove it, caused the furnace to be abandoned after it underwent a structural failure around 1808.
The furnace utilized water power directed by a headrace (White, fig. 1) originating at the site of the present dam. This present high dam, impounding Lake Hamilton, was built much later (1907) than the furnace.
Stop 7. Struthers Historical Society, Struthers, Ohio
The Struthers Historical Society Museum (Stop 7 on Fig. 20) is located in a historic (1884) house at 50 Terrace Street, Struthers, Ohio, within a few blocks of the northern side of Yellow Creek Park. The museum is open by appointment.
There is a mining car in the yard next to the museum building. The museum itself includes artifacts related to mining and iron manufacture in the area, including artifacts such as iron, ceramics, and bone excavated at the Hopewell Furnace under the supervision of John White. The museum also includes a bound set of the local newspaper and various reprints, photographs, and other items related to the furnace and the town of Struthers.
Ray Novotny, Gary Meiter, Robert Orr, Julie Pantelas, and other staff at Mahoning County MetroParks provided help, permission, or aid in the study materials in the park. Theresa Kalka, Hiram College, and Veronica Fusco, Oberlin College, helped to uncover the millstone in the stream at Mill Creek Park in 2009 and 2010. Kathleen Farago, Cleveland Heights/ University Heights Public Library, and Cleveland and Maple Heights High students Terryn Mathis and Marcus Jackson also helped in the field. Matt O’Mansky, Department of Sociology and Anthropology, Youngstown State University, made archaeological materials from the Mill Creek Furnace available, as well as files of John White; Marian Kutlesa, Struthers Historical Society, provided images and information on iron furnaces. Natalie Simon, McConnells Mill State Park, Tom Anderson, University of Pittsburgh, John Harper, Pennsylvania Geological Survey, Ernie Slucher, U.S. Geological Survey, Ann G. Harris, Youngstown State University, and David Saja, Doug Dunn, Wendy Wasman, and Evan Scott, Cleveland Museum of Natural History, provided additional help, references, and other aid. Kathleen Farago and Lars Benthien, Case Western Reserve University, proofread versions of the text. The manuscript was further improved by the formal reviews of Charles D. Hocken-smith, Frankfort, Kentucky, and Ann G. Harris.
Figures & Tables
From the Shield to the Sea
This volume features field guides and descriptions of eight of the geological field trips offered during the Joint Meeting of the Geological Society of America Northeastern and North-Central Sections held in Pittsburgh, Pennsylvania, in March 2011. From glaciers to gristmills, shales to slides, these timely and topical trips highlight the region's geology from eastern Ohio to the Central Appalachian Valley and Ridge and show how it has shaped the region—topographically, structurally, historically, industrially, and evolutionarily.
- building stone
- chemically precipitated rocks
- clastic rocks
- construction materials
- field trips
- igneous rocks
- iron ores
- Lawrence County Pennsylvania
- Mahoning County Ohio
- metal ores
- plutonic rocks
- road log
- sedimentary rocks
- United States
- iron furnaces
- McConnells Mill State Park
- Mill Creek Park
- grist mills
- Yellow Creek Park