I really want to know how they got the swirled effect on top of this log cake. I was thinking modeling chocolate and then taking a tool and making the lines and then "painting" it with melted milk chocolate.. Other then this idea I am at a loss any help would be awesome!!! 

Maybe it's buttercream with cocoa dragged through it with a cake comb? 

I think it is buttercream with cocoa dragged through it too, but I am guessing a fork was used to pull it through the icing in a circle while rotating the turn table

Thank you all so much! This is the finished product!!! I ending up using white mopening chocolate and cocoa powder. The customer wanted chocolate buttercream :) sorry it's sideways 

Here's a better picture!