This Island is Incredibly Small and doesnt have much at all, except the Breeding Centre for Red and Green! It can only accessed after you have beaten the Elite 4, got the National Dex and the Ruby Plate from Island 1:
What It also has is an Ice Cave in which HM07, Waterfall is found

Hover to get area

Here are the Pokémon you will find in the wild on Four Island:

In The Cave
	Zubat	Common Common
	Golbat	Rare Rare
	Swinub	Common Common
	Delibird	Rare
	Sneasel	Rare
	Shellder	Uncommon
	Staryu	Uncommon
	Seel	Common Common
	Dewgong	Rare Rare
	Lapras	Rare Rare
In The Water
	Psyduck	Common
	Slowpoke	Common
	Poliwag	Common Common
	Poliwhirl	Rare Rare
	Gyarados	Rare Rare
	Wooper	Common Common

Thats all on Four Island...Click Here for Five Island