Where are all the buried treasures on horse isle?

Pirate Treasure
You can find pirate treasure on any beach. You will see a faint "X" marked in the sand, just like in the movies! Stand on it, and dig. You will have a message pop up in the lower left chat box (where PMs, "Chat here" and buddy chat show up) saying how much you found.

NPC Treasure
By "NCP Treasure" I mean treasure on islands, other than pirate treasure. You can normally get hints to their locations by talking to NPCs (Non-Playing Characters; such as shop owners, residents etc). There are numerous buried treasures around the world.