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Magnetite, Limestone & Charcoal

Jul 3rd, 2009 | By | Category: Features

The early Germans and Scots-Irish settlers who migrated to the Elizabethtown area stumbled upon an area rich in natural resources.  The fertile soils to the southeast of town, which supported a vast forest, derived from limestone bedrock.

The limestone itself became important for industry when outcrops of a dark, extremely hard rock were discovered to be magnetite, which contained as much as 60 percent iron ore.  The large deposits of magnetite found at Cornwall and at Silver Spring (today, Grubb Lake) when heated in a mixture with limestone and charcoal, produced molten iron.

To separate the magnetite from the rocks in which it was embedded, Peter Grubb started an iron furnace at Cornwall in 1739 beside the huge magnetite deposit.  The limestone needed as a flux to separate impurities, known as slag, from the ore was already quarried by local farmers to obtain lime for their fields so it was readily available.  Obtaining fuel to heat both the magnetite and limestone to melting temperatures was a problem.  Wood was plentiful but did not burn hot enough.

Roasting wood under controlled conditions, however, left almost pure carbon, charcoal, and blowing air into a charcoal fire produced a very hot flame.  Early farmers in Donegal Township who spent the winter months cutting trees to clear their lands could make extra money by making charcoal.  They leveled an area about 30 feet in diameter and stacked cut logs on end around a small central open space (chimney) until the stack was 20 feet wide at the base and 20 feet high.  When warm weather came and the logs had dried, the outside of the stack was covered with leaves and soil to seal out most air.  A fire was started in the center.  The mass was kept smoldering for 10 to 14 days with the amount of air allowed in the stack closely monitored.  If a flame occurred, the pile burned too intensely leaving ashes, not charcoal.  After the wood was reduced to charcoal, it was sold to the furnace.

Many men who did not own land were hired as woodcutters or colliers to “coal” the wood.  At the Cornwall Iron Plantation woodcutters were the most numerous workers.  Some of the men had families but many were hermits who lived in small cabins near the coaling site.  One collier who became a local legend was an African-American slave owned by the Grubbs named Governor Dick.  His cabin was at the foot of a hill named for him.  Today you can walk to the top of Governor Dick at Mt. Gretna and climb a tower to look out over Lebanon County.

The Cornwall forced air furnace was two stories high and workers charged the furnace by dumping cart loads of charcoal, limestone and iron ore down the furnace chimney.  A bellows, powered by a large water wheel was used to force air through the furnace.  Every day the roaring fire consumed all the charcoal that could be made from an acre of forest.  Molten iron was drawn from the bottom of the furnace about twice each day.

By 1750, Pennsylvania was the top iron producing colony for the English king, George II.  Pennsylvania was producing a seventh of the world’s supply of iron much to the dismay of people in our mother country, England.  Donegal Township farmers benefitted from close proximity to inexpensive iron.  Local farmers used plows that were made with wooden frames but the plow point that broke the soil and the moldboard that turned the soil were made of iron.  Both parts had to be replaced at regular intervals because the scraping action of the soil wore away the iron.  Additionally, blacksmiths made horseshoes, housewares and tools at reasonable prices.

In 1802 after the American Revolution, N.B. Grubb, an ironmaster, constructed the forced air Mount Vernon Furnace along the Conewago Creek in present West Donegal Township (between Zeager Road and the railroad).  Grubb owned substantial acreage in the vicinity of his furnace for making charcoal.  His need for fuel was so great that he also bought wood and charcoal shipped down the Susquehanna River.

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