In a way both the mines and Skull Cavern have a floor look depending on the main monsters to be found on each floor. Only Skull Cavern has their main monster random (mummies/ghosts, bugs/slimes, and pepper rex) rather than a predetermined order. The layout of the floors in Skull Cavern vary a lot more than in the mine.
And when the floor look different from what you'd expect in the mine, you know it's either a slime infestation or a dungeon floor with skeletons and haunted skulls.