Jack Williamson "Terraforming Earth"
The only other Williamson solo fiction that I've read has been stuff from the 1940s/ early 50s, so it's been interesting to read this work, published in 2001 when he was just 93 years old.
In fact it's a series of five vignettes covering millions of years involving the same characters: initially bored, I became more involved as the book progressed. My main memory is of a forest of wonderful conscious singing trees (sadly only really featuring in one vignette). While Williamson is not the first to write of singing/musical trees, I thought these particularly well imagined.