I started Lost to the Ages some time back. After supposedly finding the third shard I can't seem to find the forth. Nope, there's no map marker or anything! I've checked the Wiki and it seems the last one is supposedly in a place called "Raldbhar". But again, there's no map marker on my map at that location. Anyone know what's up?

Also, I say "supposedly finding the third shard" because I can only remember finding two, but my quest log says I've found three. The ones I remember finding are the one at Arkngthamz, and the second at Deep Folk Crossing. I can't remember going to Mzulft for the third. I also only have two shards in my inventory. Is this some kind of bug I've found?