Archaeologists at a dig site in southwestern Pennsylvania have discovered a layer of the Earth's crust consisting entirely of Welcome Back, Kotter merchandise. 'The strata we have discovered, located approximately 15 feet beneath the surface, dates to the mid-1970s and consists of items ranging from posters of Sweathog leader Vinnie Barbarino to lunchboxes depicting Arnold Horshack,' head archaeologist Adrian Richelieu said. It is the largest such find since 1989, when archaeologists near Albuquerque, NM, discovered a 20-foot-thick layer of T.J. Hooker Trapper Keepers. 