Sounds like regular cutback asphalt adhesive. Two problems...(1).it may contain asbestos. (2) it is removed with Jasco adhesive remover, or mineral spirits. Both are very nasty and would best be done using an air fed respirator, or at a minimum a VOC respirator mask. The mineral spirits are quite flammable, and great care would have to be used in doing a large area. NO PILOT LIGHTS going anywhere, massive fresh air ventilation using fans.