This is a book-within-a-book story of a man who goes back in time 80 million years, proving that his theory of time travel works yet living out his life absolutely isolated from human contact.
Sam Magruder lives in 2162. We first learn of his amazing adventure when slabs of stone from 80 million years ago are discovered to contain "universal Swahili" - the language of 2162 - chronicling Maguder's amazing time jump. He writes of how he figures out "when" he is, how he survives, and of his musings on his purpose now that he can't ever get back to his life in 2162.
This is a treasure of a book. I really enjoyed the descriptions of how he survived the first days, how he tried to make sense of what happened to him, and how he got through his life.
Surrounding the 8 slabs of Magruder's story is philosophical argument about his life and its meaning by the Universal Historian, the Common Man, the Pragmatist, the Ethnologist, and Pierre Precieux, discoverer of the slabs. Each represents a different philosophical viewpoint. One thing that was terribly amusing was that Magruder's discussion of his (lack of) sex life was eliminated from the general translation available to the general public, but kept, for scientific accuracy in the official text.
Surrounding the book-within-a-book, are an introduction by Arthur C. Clarke, an afterward by Stephen Jay Gould, and a memoir by Joan Simpson Burns, daughter of the author, George Gaylord Simpson. All are well thought out and interesting reads on their own.
This book was found after the author's death by his daughter. He was the preeminent paleontologist of the 20th century, and this book is, according to Clarke, Gould, and his daughter, unconsciously autobiographical and revelatory of his strengths and weaknesses.