Floor Covering

[sys_daw]

When I bought a new house some years ago I remember that the downstairs floors were covered in a black substance, almost solid tar like. Does anyone know what this is and what its primary use is for? Also, in my current house, which is around 200 years old, I notice that the floor is cold. Is there anything I can put under the carpet/underlay to help prevent heat loss. This is for the ground floor and I believe that the floor is solid i.e. no floorboards.

Thanks