I've seen this on Google Earth and wondered what it was. The line is the old Erie mainline at Brier Hill near Youngstown, OH. on the grounds of the old Jeanette blast furnace.
http://www.hfinster.de/StahlArt2/archive-Youngstown-BW-1281-17-24.05.1992-en.html
http://www.sweetjennylandcompany.com/jeanette_furnace.htm
There are a bunch of cement trucks parked close so that may be the reason for all this slag.