Snorunt actually has two evolutions. It evolves into Glalie at level 42, and it can also evolve into Froslass if one uses a Dawn Stone on it. However, only female Snorunts can be evolved this way.
If one evolves into a Glalie, it retains its ice Pokémon type. If one uses the Dawn Stone and evolves a Froslass, the Pokémon's type changes to both ice and ghost. This allows the two evolutions to learn completely different moves as well as affecting the Pokémon's base stats in different ways. Glalie receives a bonus in all base stats by 30 points, whereas Froslass receives smaller bonuses in some, such as hit points, and defense, but receives a very large boost to speed in exchange.