I am actually not the person that did the work, Jamie did it and well; I just ran off with the rug that was in desperate need of repair…thereby exposing a section of the floor.

Hard to say what the wood is, it may be hard pine.  Originally coated with shellac, making restoration fairly straight-forward.  Shellac is suspended in alcohol (you can actually get shellac in flake form).  Clean it, then rub it down with denatured alcohol which re-amalgamates whatever shellac was left, then two coats of shellac with some areas needing three (heavy traffic, sun, water, or tape from a taped down rug).  No sanding required.

This photo is about as close as we come to a ‘before’ image: the floor on the right is not yet done, the light mark is a where a rug was taped down.  You can see the difference in the quality of the color/light.

The floor refinished.  The circle in the center is a floor outlet.  This picture is also a nice illustration of the standard tendency for old houses to be built less than straight: look at the wall, the plaster is not cracked, the ceiling height really is that different!