Sometimes I found also a skillbook on a shelf in the catacombs beneath Aleroth (level -1, in chamber where you must summon a skeleton (Hostile) by lighting 5 candles).
But most of the time No skillbook.
I remeber I found there once a time a skillbook for "Hell Spikes".
That's not a special shelf. You can do that for EVERY SHELF IN THE GAME.
In fact, it my "Let's Play" (see link in signature) of the game, that's pretty much what I did. I maxed out a TON of Wizard's spells without ever investing one single point into them, and I did it with plenty of shelves to spare. I could have maxed out a few more spells, but they weren't that great, so I didn't want to bother. (Poison Cloud, Deadly Discs, Resurrect, Banish(?), Wizard's Sight) If there was a spellbook for it, I found it on a shelf.
