Chimney is still hot from a fire i had 24 hours ago. Whats the big deal?

I had a large fire in my fireplace. (Too big for the fireplace). And after the fire and all the coals burned out i could still feel heat coming from the chimney. I went outside several times to check for signs of a chimney fire. Nothing. But its been 24 hours since the fire went out and my walls and chimney are still somewhat warm. I don't know where all that heat could be stored or coming from for such a long time. By the way, it's January in Michigan so its cold outside.