The head librarian can translate them very roughly for a suitable bribe. They turn out to be names, and very old records of causes of deaths (such as "blinded by fire in sky, fell in ravine", "mauled by unknown beast", "contracted infection, too contagious to retrieve") - perhaps deaths that happened on the surface, except as far as she's aware, none of them go to the surface, because it's all overtaken by Cwyld, right? How strange, how strange.