Necromancy, Spellweaving, and Mysticism spells can be cast from scrolls. The scrolls replace the need for having the spell reagents or the spell in a spellbook (on you at the time of casting). You will still need the required mana to cast the spell.
Unlike Magery scrolls, they do not allow you to cast the spell at a lower required skill. Casting from Magery scrolls treat the spell as two circles lower than its level,
for casting chance (i.e. 8th Circle spells cast via scroll will be treated a 6th Circle spell, so a GM mage will have 100% success casting them from a scroll).
Stayin Alive,
BG