In Pencader Hundred, medium to low grade iron ore was mined from open pits on Iron Hill and Chestnut Hill beginning in the early 1700s, first under Sir William Keith, Lieutenant Governor of Pennsylvania's Three Lower Counties (Delaware). The ore, commonly a brown or nearly black oxide of iron, was dug by hand and transported for refining, while the region's chestnut trees supplied charcoal made by colliers because wood alone did not burn hot enough to melt iron from ore. Iron processing first used simple forges in which smiths repeatedly heated and hammered the metal to remove impurities, then advanced to bloomery forges and blast furnaces, including a bloomery along the Christina River and the substantial Principio Furnace near the Chesapeake Bay outside North East, Maryland, where oyster shells served as a flux. Four tons of ore traditionally produced one ton of iron, and the final product, pig iron, could then be hammered, rolled, or cast into goods such as weapons, pots, and nails. Mining and iron production here developed within a wider demand for iron created by the Great Northern War from 1700 to 1721, which pushed England to seek iron from its American colonies as Swedish exports declined. In 1723 John England began operating the successful Principio Furnace in Cecil County, Maryland, and in the same year Samuel James and investors built Abingdon Furnace near Chestnut Hill, though that operation failed for lack of an economical supply of flux and was sold at sheriff's sale in 1735. Pencader Hundred remained chiefly a mining district, with most ore sent elsewhere for refining and most refined iron exported through the nearby Chesapeake Bay, until iron operations continued under later proprietors and finally ceased by the turn of the 20th century under William McConaughey.