Board Thread:Skyrim/@comment-121.216.112.47-20130902071354/@comment-7953253-20130906124702

Maybe some spells can only be made available after reaching a certain skill in a school of magic. You need to be around lvl 60 Alteration for Ash Shell and Ash Rune to be available, as they are Adept and Expert Alteration spells. As well as Poison Rune, which is Adept in Restoration.