These are worlds of varying size and masses found beyond the snow line, but which have managed to develop thick atmospheres and a geologically dynamic surface. The atmospheres of these worlds are typically made of nitrogen and large quantities of methane, with other hydrocarbon elements as well. Depending on the dynamics of the world, a hydrocarbon or methane liquid cycle may also be present. Water is also present on these worlds, but because the planets are so cold, the water ice is literally as hard as granite, and indeed plays a similar role to rock on Gaian worlds.
The surface of the planet is composed of ice "bedrock", and on those worlds with liquid methane cycles, that ice can be eroded down into smaller rocks and pebbles, even sand. Cryovolcanism also typically occurs, with melted or semi-melted water from the warm interior welling up in much the same manner as molten magma. Life is always possible on such planets and moons, but because of the cold temperatures involved, such life would have a very low metabolism, and likely would rarely develop beyond the simplest of forms. Example Titan; Muuhome