[thejeff]

You cannot use more gems in casting a spell than you have in the path of the spell.
You also cannot use more than one more than the gem cost of the spell.
I'd have to check the manual, but I believe it is confusing but not actually wrong.
There was a discussion here a while back that hashed this out. I went into that with the impression that you could use one gem to boost your level to be able to cast the spell, then more to reduce fatigue. I think the manual discusses all of these in separate places, leading to much of the confusion.