Led.

Speaking of libraries: A big open-stack academic or public library is no small pleasure to work in. You're, say, trying to do a piece on something in Nevada, and you go down to C Floor, deep in the earth, and out to what a miner would call a remote working face. You find 10995.497S just where the card catalog and the online computer thought it would be, but that is only the initial nick. The book you knew about has led you to others you did not know about. To the ceiling the shelves are loaded with books about Nevada. You pull them down, one at a time, and sit on the floor and look them over until you are sitting on a pile five feet high, at which point you are late home for dinner and you get up and walk away.

John McPhee