how old is the house ? is the pine floor tounge and grove, or laid side by side? why install plywood just to put carpet over it? was the floor uneven? is it possible the pine is the subfloor,and the plywood the underlayment? try having a flooring contractor in your area look at it.,post this additional info ,maybe i can help.

The house was built in the 20's. Each board is side by side with a groove that in the side that fits into the next board. I can tell by looking at the edges in the basement.

I guess it would be considered subfloor since it is the last layer of flooring underneath the plywood. The floor seems very solid and I sanded a piece of it for testing. It looks quite nice.

Thanks for the help.

If you have a loose piece, or very clear pictures, you might try taking either to a local lumber supplier and asking them. Trying to identify a wood species over the web might be a little difficult. But you can always try posting a picture.

the floor is a sub floor and while it is possible to finish it ,it would be very soft and a lot of maintainace, if you want a hard wood floor check out a good do it yourself type floor, a great one is made by bruce hardwood its called coastal woodlands ,its very easy to install,as it is a floating floor (not glued down,but glued in the t/g and installed over pad.***** and home depot can order it for you.

carpetman,
If it is new white pine you are right that it will be soft, but in that time period, it was common to use heart pine for flooring. It is extremely hard and strong. It was often used directly over the joists. It took wear well enough to be chosen for installation in public buildings such as schools and courthouses. It is similar in appearance to clear vertical grain doug fir flooring you can buy now. rubbing, sanding, or cutting it can release a turpentine smell.

If it is heart pine in decent shape, it is a rare and valuable find. It will gum up sanding pads easily though from the pitch in the wood.

It comes from the long leafed Lobblolly pine and is not commercially available anymore. There are only about 100,000 acres in plantation growth in the country. Old growth virgin trees are long gone and so is their heart wood, except for salvage operations.