The coup de grace to the old belief was given when Pickering and Douglass found that the dark areas were traversed by permanent lines. (scientificamerican.com)
Information that describes the specific hazards of cavern diving including: silting, line entanglement and breakage, disorientation from permanent lines and emergency situations unique to caverns. (dive-the-world.com)
Fact is, the New York ballot now hosts five permanent lines beyond the Republicans and Democrats. (nypost.com)