That's pretty much what both of ours looked like. I just dug all the rubble out from underneath and took a sledgehammer to them, then bricked up the hole left behind. Took far longer than it ought to have done.
I dug out the rest of the rubble last night, and removed the bricks of the constructional hearth. I plan on fitting a small joist between the chimney pillars, then two from that over to the existing floor.
That's pretty much what both of ours looked like. I just dug all the rubble out from underneath and took a sledgehammer to them, then bricked up the hole left behind. Took far longer than it ought to have done.
Caveat: I have little to no idea what I am doing.