Rain Forest

Rain forests were a lush biome, which existed in the game prior to the Adventure Update.

Description
Rainforests are very wet biomes with many trees, which have a 1 in 3 chance of being big, instead of 1 in 10 like all other biomes. They only generate oak trees, and have a large amount of tall grass and ferns. A biome is classified as a rainforest if the temperature is greater then 97% and the rainfall is more than 90%. This could be the biome with some of the most cliffs and hills, because the world generator reduces height variation at lower rainfalls.