I don't know about thoreau specifically, but if you would like to read a crazy fiction book about the over soul, read 'factoring humanity' by Robert J. Sawyer. It's based on the Jungian oversoul idea, but very loosely. It also involves aliens, psychologists and a hypercube. Kinda sci-fi, but set only about 20 years from now.
Haha, Jung, synchroinmicity. Just read about that book 2 days ago in Mt. Lebanon public library... (Factoring Humanity)