ITHACA, N.Y. - A 19-year-old Cornell student was killed after falling into a gorge, authorities said.     Scot Elwood, from New Albany, Ohio, fell into the Fall Creek Gorge shortly before 11 p.m. Thursday, according to Ithaca Police. Witnesses said he was walking with a friend and jumped over a fence, believing there would be a path below.     Ithaca Fire Department Lt. Willis Sheldon, who rappelled down the gorge to reach Elwood, told the Ithaca Journal that he was found lying on a ledge and had no pulse.     Elwood, a sophomore, was a member of the university wrestling team.