I've found my Mystery Abstract.
It is indeed a fallen tree. It looks as if some inexperienced woodsman attempted unsuccessfully to cut the tree down after it was dead but still standing. It eventually fell down of its own accord.
I went for a walk this afternoon in the nearby woods where I had seen ladyslippers in May. I was out for over an hour, following every trail that I might have gone on that day. I was about to give up, when I finally found it, about 6 feet from where I parked my car!
Here is the original "abstract," so you don't have to go looking for it, and below it is today's image, which I think shows the scene better.