Near Thurmont in Frederick County, Maryland — The American Northeast (Mid-Atlantic)
Slag Heaps
Photographed by Allen C. Browne, October 21, 2021
1. Slag Heaps Marker
(The slag you see is an historic resource, Please, do not remove any of it.)
The mounds you see around you are the furnace's waste product slag. When iron ore, is superheated in the furnace and fluxed with limestone, the molton iron sinks and impurities rise. Skimmed and discarded, the slag hardens into a glassy or airy rock similar to volcanic glass or lava rock.
Slag was removed from the furnace about every six hours and allowed to run onto the ground to harden. The large pieces were later broken and loaded into wagons for removal. Slag disposal became such a problem that slag was used everywhere to fill holes and finally just piled in heaps near the furnace.
Erected by Catoctin Furnace Historical Society. (Marker Number 3.)
Topics. This historical marker is listed in this topic list: Industry & Commerce.
Location. This marker has been replaced by another marker nearby. It was located near 39° 35.03′ N, 77° 26.065′ W. Marker was near Thurmont, Maryland, in Frederick County. It could be reached from Catoctin Furnace Road (Maryland Route 806) south of Kellys Store Road, on the right when traveling south. Touch for map. Marker was at or near this postal address: 12731 Catoctin Furnace Rd, Thurmont MD 21788, United States of America. Touch for directions.
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Regionally, this marker was in the Washington Metropolitan Area and in Central Maryland. It was also in the American Mid-Atlantic. Globally, it was in the North Atlantic Region, North America, the Western Hemisphere, the Western World, and the Anglosphere. Historically, it found itself in what was once one of the original Thirteen Colonies and also the Antebellum South.
Other nearby markers. At least 8 other markers are within walking distance of this location: A Lost Pond (here, next to this marker); Waste Management (a few steps from this marker); Recreation For All (within shouting distance of this marker); The Bridge that Moved (about 300 feet away); A Fractured Landscape (about 400 feet away); Powered by Water (about 400 feet away); Destruction and Renewal (about 500 feet away); A Creek Rediscovered (about 600 feet away). Touch for a list and map of all markers in Thurmont.
Other markers no longer nearby. Raceway and Dam (was about 300 feet away, measured in a direct line but has been replaced with another marker now near it); Bowstring Arch Bridge (was about 400 feet away but has been replaced with another marker now near it); Second Growth Forest (was about 500 feet away but has been replaced with another marker now near it).
Photographed by Allen C. Browne, October 21, 2021
2. Slag Heaps Marker
Photographed by Allen C. Browne, October 21, 2021
3. Slag Heaps Marker
Photographed by Allen C. Browne, October 21, 2021
4. Slag
Credits. This page was last revised on May 18, 2026. It was originally submitted on October 23, 2021, by Allen C. Browne of Silver Spring, Maryland. This page has been viewed 722 times since then and 43 times this year. Photos: 1, 2, 3, 4. submitted on October 23, 2021, by Allen C. Browne of Silver Spring, Maryland. • Mark Hilton was the editor who published this page.
