Is this on a slab or can you see from underneath what is supporting the hearth?

It's not a slab house.
In the basement, there is a huge peice of concrete "attached from the
wall to the basement ceiling at a minor angle"
It's hard to explain .....................

KIND OF like this angled red beam here - except in concrete :
http://www.bifold.com/assets/2.06.I2.gif