Spreading seas says:
Spreading Seas 1U
Enchantment Aura
Enchant land
When Spreading Seas enters the battlefield, draw a card.
Enchanted land is an Island.
So let's say I cast it on a forest. Can I now tap the forest for G or U mana, or do I now only able to tap if for U? Basically I am asking does the forst stay a forest and in addition is an island (Like a dual G/U land tropical island), or is it only an island now?