Why US army and US marines in Iraq?

I know that the US has been in Iraq for a while and I've been wondering for a while... why would the US army and the US marines be deployed in Iraq? I mean seriously just one of the two is overkill since there are collition forces so why? and besides why the marines its not like its an island bordering the sea. Anyone know a GOOD reason they deployed both?

Because the Marines get the protection details, like Embassy duty, and things like that. They're kind of a jack of all trades, master of none kind of organization. No offense to the Marines, just that they're used pretty much everywhere, but unlike the other services don't have one "specialty" area.

Ah well that makes sense I guess although if they don't specialize in that type of combat why deploy them since they would cost a lot money just to keep them going ya know? No offense cause they do adapt and get the job done and thanks