 This is a center furnace. The road runs up the hill to Penn State University Park campus and the town of State College. But State College didn't even exist when the university was founded in 1855. The university was built up the hill from the iron furnace, and they've been making iron here since 1791. This is glass slag. This is what was left when they melted the ore to get the iron out and drained that away, and then this chilled and it froze to make the glass. Melting the ore took energy, and the energy came from charcoal, and the charcoal came from trees. The fire of furnace for a year took more than a half a square mile of trees. But the furnace was served by an independent community, and it had people in it who built houses and heated them in the winter and cooked, and that took wood too. Running a furnace and what was around it took a square mile of trees a year, and there were lots of furnaces and lots of forges like Valley Forge that turned the iron into useful things. The furnace closed in 1858. Production moved west to use better ores and to use coal as a fuel because the trees were gone. It was about the same time as peak whale oil and just before the first modern oil well up the road here in 1859. Today we have whales and we have trees because we burn fossil algae and fossil trees, oil and coal and natural gas.