island
嶋 centers on an island, specifically a landmass surrounded by water, often with a mountainous or raised terrain.
嶋 is a variant form of 島, combining 山 (mountain) and 鳥 (bird). The bird component likely served as a phonetic element, while 山 reinforces the mountainous nature of many islands.
A mountain (山) rises from the sea, and a bird (鳥) perches on it: that isolated peak is an island.
For トウ, imagine a tall island mountain that looks like a toe sticking out of the water: toe -> トウ.