Are you heating the oven with the stone in it, then letting it rise on the stone? That could account for the odd shape, but it still wouldn't make it dense. I still think the density is from not rising enough before baking.
Instead of heating the oven with the stone in it, you could try setting a pan of hot water in the bottom of the oven, beneath the stone, and closing the door. That would warm the oven, without overwarming the stone and give the dough some additional humidity so it would rise higher (and no need for slashing, if you don't want to). Once the dough is doubled, you can remove the pan of hot water or leave it in the oven while the bread bakes. It will give the bread a chewier crust. If you prefer a dryer crust, you'd need to take it out.