You can apparently get grand souls ( I think that's what they're called) from mamoths. The invisible chest I found also had a soul mace in it..if the enemy dies in 3 seconds it collects the soul.
Oh yeah, so I bought that horse from whiterun - after dropping a ton of things, weapons armour etc in Dawnstar to be able to fast travel - 3 minutes later I went down a steep hill on the road and the horse jumped...and died. Couldn't heal it.
UGH
LMAO
So, restarted from the save just after opening the chest and lo-and behold the trade caravan was at the entrance to Dawnstar so I was able to sell things instead of droppin...though the prices weren't great, it was all lowly stuff like great swords and junk. Then I bought steel armour and now I can't afford the blasted horse! That was about 4 hours of play lastnight...ugh.