You can't assume anything. It may be shellac, but someone in the 1970s could have applied a layer of polyurethane or Bona Wood floor finish. Or it could be no finish at all.

Test the finish:
http://www.woodmagazine.com/materials-guide/finishes/what-finish-is-that-anyway/

Then look up the recommended cleaning method for that finish.

marita40:

For an inexpensive and harmless fix, I'd hit it with Scott's Liquid Gold.

Check out the link posted by lazygardens. If you don't find all the answers,follow up on Wood Magazine's online help.
I have subscribed for years and find their articials first rate.
Painting and refinishing is 90% prep and there are no wham bam short cuts to get good results.

Pictures please! :)

I'm not in the house yet jmc--that is, not closed yet--but will send photos soon!