I'm there in game but I can't find it
Stone egde is Not in the cave at all you head down the waterfall head go south east in the direction to the bridge then follow the path until you see land.
The TM #Mega Pinsir is talking about is TM 79 Frost Breath
When your in the room with abomasnow and the karate guy slide on the ice to find a path which splits in 2. Stone edge is in one of the split paths. Hope I helped!
Go down the waterfall and there is a little ledge near the water where it is.