Ore Skip At the top of the Head Frame, over the silo, a space is hollowed-out for ore cars to dump their load before going back underground in search of copper. Related Similar Images ...based on the tags: headframes, heights, pulleys, sheet-metal, tracks... The roof could be vented when locomotives were running inside. Approaching the power station and its giant stack. The stack replaced four shorter stacks in the 1960s, helping with pollution in the downtown corridor. Tucked-into the side of the concentration mill… these machines were meant to crush underground rock into a fine dust for mineral extraction. A better look at the rails in the floor, installed to help move heavy equipment around the building. The mill is one of the tallest buildings in the city. It’s too bad that the cupola with its big skylights and flagpole were removed. I never knew that all those elementary school balance bar exercises were for a very serious purpose: not falling to one’s death in the event they uncover lost Chicago history. Grand Army, as seen from a Gilman Tram grade. Note the rails in the floor that guided cars to the coating line, the side of which is lined with the windows in the center of the image. National Mine and its rockhouse (?) as seen from Mammoth Hill. From this angle, I am fairly certain this was a crushing and sorting house. The bottom looks like it has two aerial tram doors as well.