Basswood or Linden and Yellow Poplar were/are used in furniture making.
But looking at the underneath side of the seat, my guess is walnut.
Black Walnut is really not black, ya know, but it is named such because of the White Walnut or Butternut, which is also a beautiful wood.
Interesting fact about Black Walnut is that direct exposure to Sunlight will turn it blacker n’ blacker.
My favorite wood is Sumac, when paired with Black Walnut to make lamps, checker boards, etc. (see picture on my "Gaff Hook" posting.)