In the mid-19th century the Lehigh Valley became one of Pennsylvania's leading producers of cast iron and iron products. Most of the farmers in Lower Macungie took advantage of the need for iron ore. On the neat, hundred-acre farms that had been the sustenance of the population for so long, ore pits began to appear, and washeries were built to clean the limonite ore of its clay.
Ore was hauled from the mines to furnaces in Macungie, Alburtis and Emmaus, and to loading wharves along Indian Creek Road from which it was transported on the East Pennsylvania Railroad. This railroad line is now operated by Norfolk Southern.
Small densely wooded areas often mark the site of a former iron mine. Some mine holes and several limestone quarries are filled with water. Large surface clay deposits are common throughout the area; these were the settling ponds of the numerous washeries.
Lock Ridge Iron Company
The Lock Ridge Iron Company, now within the borough of Alburtis, was originally in Lower Macungie Township. Construction of one furnace began in 1867; a second was built in 1868. Merchant pig iron was produced here by one of the Lehigh Valley's dominant pig-iron producers, the Thomas Iron Company, until late 1921. Lehigh County maintains the remains of the furnace as one of its industrial heritage sites.
Rock crushers were erected at the massive slag dumps and much of the crushed slag was used as sub-base for the Northeast Extension of the Pennsylvania Turnpike in the mid-1950s. Slag from the Macungie Furnace, which had been stored west of Brookside Road at Indian Creek Road, was used for the macadam base Brookside Road when the state widened the road.