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

Inscription. (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. (Marker Number 3.)

Topics. This historical marker is listed in this topic list: Industry & Commerce.

Location. 39° 35.03′ N, 77° 26.065′ W. Marker is near Thurmont, Maryland, in Frederick County. Marker can be reached from Catoctin Furnace Road (Maryland Route 806) south of Kellys Store Road, on the right when traveling south. Touch for map. Marker is at or near this postal address: 12731 Catoctin Furnace Rd, Thurmont MD 21788, United States of America. Touch for directions.

Other nearby markers. At least 8 other markers are within walking distance of this marker. Raceway and Dam (about 300 feet away, measured in a direct line); Bowstring Arch Bridge (about 400 feet away); Second Growth Forest

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(about 500 feet away); Little Hunting Creek (about 600 feet away); Ruins of the Ironmaster’s House (about 600 feet away); Ironmaster's Mansion (about 700 feet away); Catoctin Furnace (approx. 0.2 miles away); Catoctin Iron Furnace (approx. 0.2 miles away). Touch for a list and map of all markers in Thurmont.

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 March 3, 2023. It was originally submitted on October 23, 2021, by Allen C. Browne of Silver Spring, Maryland. This page has been viewed 238 times since then and 13 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.