Also, its white surface bespeaks a geology that recycles the surface, rather than letting the meteorite impacts darken the surface. Tethys and Mimas show many small fault criss-crossing the surface. Possibly there was an upwelling of carbonaceous ice from the deep core of Iapetus. Uranus's quadruplets look nothing like each other, aside from the cratering that all bodies in the solar system have suffered. Oberon, the outermost, shows some evidence of crater-filling volcanism, but none for fissure eruptions or faulting.
Titania has the start of faulting and fissure eruptions, in addition to some crater-filling.
Umbriel shows no evidence at all for an active geology. Ariel has a planet-wide system of fissure eruptions and faults. Finally, we come to Triton. Using the pictures from the November Scientific American, I have noticed some features that could be caused by the moon's internal geological processes. The first, going from south to north, are the plumes covering the polar cap.