Cobblestone in basement (strong damp smell)

[Matty0682]

I live in a 200 year old property with a basement. The basement floor is s combination of flagstone and cobblestone which have been sealed (not sure what with but is transparent, see first pic).

There was a smell of damp coming from beneath the basement stairs (the area was sealed off). I have exposed the area under the basement stairs. and there are more cobblestone but not sealed with anything.

What can I use to seal these cobblestone? At the moment I am using a dehumidifier and letting it breathe.

Or do I leave it as is? (I have removed as much soil as I can and washed them)

Thanks

[Conor]

How is the basement ventilated?

[Matty0682]

There is a window (always open) and a door leading in courtyard in the basement, so ventilation generally ok.