This is a book primarily about the abundance of life in that had been preserved in fossils in the Burgess shale.
Gould writes about the people who spent hour after painstaking hour examining the samples, deciphering the forms and understanding the compressed fossils in this rock formation. In the second part of the book he writes about Walcott, administrator at the Smithsonian institute until he died, and his error in the analysis in the samples. He then considers the what if questions that evolution throws up, in the final part.
I found the writing style to be quite dry and technical. Understandable to a certain extent given the subject matter, but my feeling is with science writers is that they should make the subject that they are writing about come alive, and this book didn't do it for me. The part on Walcott was good, he was a man who had a lot of influence and authority in the scientific advances in America, but he suffered some fundamental flaws.
This was written 20 or so years ago now, and in its time would have been a seminal work; now it is still important, but understanding of the creatures in the Burgess shale are now better understood and technology can bring them to life in ways that Gould could have never of considered.