Rescuers have called off a dangerous mission to save a 67-year-old Boston entrepreneur who slipped from an icy trail into a White Mountain crevasse while hiking with his son in New Hampshire. A snow ranger was lowered 50 feet into the chasm, but couldn't get any further into the narrowing opening to reach Norman Priebatsch. Efforts were called off yesterday due to increasing treacherous conditions, and rescuers believe it's now too late to help. “We are presuming it to be a recovery mission at this point,” the ranger told local ABC affiliate WMUR. Priebatsch founded biochemical company Adeptrix and helped launch a project to determine if an iPhone app could help with tinnitus. His son, Seth, founded social game system SCVNGR. (More Norman Priebatsch stories.)