Standing sentry along the National Mall are monuments and memorials to towering figures in American history. But generations after they cemented their legacies, something is tarnishing their image.
A black mass is spreading like a disease over the marble of Washington, D.C. Abraham Lincoln was the Great Emancipator, but so far, the National Park Service hasn’t been able to free the 16th president’s memorial from the slime.
“Between Tennessee and Ohio, right on the edge… you can see that real dark spot, and it’s starting to creep down a little bit,” Mike Litterst of the park service told CBS News’ Mark Albert.
The substance is actually biofilm, made up of a thousand different bacteria, mold and other species that adhere themselves to stone surfaces.