Is it tar paper, the kind that roofs are covered with before shingles are applied?

What do you mean by "the walls behind it are black". What part of it is black and what is the nature of the wall material? This might be wood fiber board often called beaver or buffalo board. It would be dark brown but it sometimes had an asphalt saturated face when used on the exterior of a building.

Thanks for the replies! I did a google image search on Beaverboard, and it's definitely not that or tar paper.

The walls are plaster over wood lath. The black stuff is some kind of coating on the plaster. The black layer is then covered with this weird rough paper and painted. My husband thinks the black stuff is some kind of adhesive for the paper, but it's not like any adhesive I've ever seen. If you touch it, your finger comes away dirty (although, in this house, it might just BE dirt :) ).

It seems like it's original-- I can't detect any paint layers under the black stuff, all the paint appears to be on top of the paper. It's in every room except the kitchen, utility porch and bath, which have normal painted plaster and beadboard.

I'll try to post a picture at some point-- I'm apparently the last person on earth who doesn't own a digital camera...

They used to use black mastic to mount things like mirrors or Vitrolite, and it was also used for linoleum glue, but never thought they'd use it for wallpaper paste. It will have to be scraped off. Maybe the brown paper was put on the keep it from bleeding through. It's really hard to stain block asphalt mastic. If it does bleed on you, try a PVA primer.
Casey

Thanks, Casey. I appreciate the info. Sure was hoping to avoid more scraping, though...

Hello, I know exactly what you are talking about because I just found it in my house, which was built in the early 1950s. I am wondering if it is mastic? Did you ever find more info after your original post? I decided to remove wall paper in the bathroom. It's only one layer and underneath I found a layer of black on the original wall. It almost looks like todays version of very old chalkboard paint. It's the colour of carbon paper, if anyone remembers that. Black, but almost with a dark purple haze and now that it's been uncovered it's starting to peel a bit, which has me concerned. Because I don't know what it is, I'm not sure if I should mess with it further. Now I just have a mess in the bathroom unfortunately.

Also, I hope it's not mastic because they say much of that had asbestos mixed in it, which would be very bad to scrape off.

WHERE is this house?

Usually old wallpaper was just adhered with wheat paste - which is easily removed by steam heat or warm soapy water + scrub brush. Have you tried that yet- that might tell you if the black is glue or some kind of paint layer that the paper was glued over....?