The Snow Cap is a natural block that looks like it's made of Dirt with a layer of Snow on it.
This block can be found in Taigas, Tundras or Mountains.
When this block is placed outside a cold environment, and especially in hot environments, it will turn into a block of Dirt after a short while.
Wood Treasure Chests can spawn on these surface blocks during night-times in complete darkness (with nor artificial light nearby).
No Creatures are known to spawn directly on Snow Cap blocks during the day or night, but on blocks of Snow nearby, Blizzard Chizzards will often spawn during the day and Arctic Mirus at night.