It's on the ground floor (which is below ground level at the front) of a Victorian house. The dark brown and blue patches are bits of underlay rubber that have stuck to the floor.
Am I right in thinking that the thin rubbery surface on most of the floor is intended to seal against damp? And that its absence in places would explain a patch of mould on the carpet? It was under a chest of drawers.
The exposed parts don't *feel* damp.