Underlayment on uneven wood floor

Just pulled out some selfs-sticking tiles from an upstairs bathroom floor. Found this beige compound underneath that it's kind of like a dried putty. Some of it came up with the tiles. Under that is what I'm guessing is carpet adhesive, then a very uneven wood floor. Anyone know what this stuff is called? Do I have to remove it, or can I buy some more of it to smooth it out? Ultimately I'd like to put sheet vinyl in. Tia

 

Got a picture?
Explain what you mean by uneven. and "wood" floor.
Wood could mean be a lot of things.
To do this right once the subfloor is cleaned up you going to have to go over it with 1/4 underlayment multiply plywood (no glue! ) making sure not to attach to the floor joist, no gaps' fastened every 4" on the edges for to 6 to 8" in the field.
Once laid any gaps or flaws are filled in and sanded once dry.
I use a narrow crown staple gun to do this job with it set to bump, should be able to nail a whole sheet in about 2 min.and no filling needed.

 

Thanks for the reply. After working in there some more, I think this stuff must be adhesive, as it is much stickier than the few patches of bare floor I uncovered. I think you're right and it's got to come out.
Wood refers to some sort of hardwood floor boards, laid directly over the floor joists. Uneven my means everything you could imagine. There are chunks missing, boards that butt together at different levels, and pronounced slopes. I would say the slope is about 1/2-3/4 inch across one doorway, for example. In cases like this, is it really practical to try and level it?
i have a photo, but can't figure out how to add it with my phone.

 

Floor needs to be flat, not level. Use wood filler to fill in the bad places, not gypsum based. Then put down the 1/4 " underlayment.

 

Thanks for the responses guys. The floor is not even close to flat OR level. I think the right way to do this is as the earlier poster described, with self-leveling compound, or to pull up the subfloor and shim the joists. However, I'm pressed for time and i suspect those solutions will lead to more problems - threshold issues, slc leaking into the floor boards, further movement of the floor, etc. I'm thinking about using shingles/roofing felt to shim new underlayment enough to get the floor to something closely resembling "smooth". I happen to have some laying around, and Dr. Google tells me some people do that. Has anyone on here tried it? Thanks again.