The author does a creditable job of creating an entertaining read, given the dearth of historical records and William Smith's largely unexceptional life. Alas (at least for narrative purposes), Smith wasn't one of those fascinating dilitantes of the 18th/19th century who managed to dabble in science, arts, literature, politics, and philosophy, all while managing an extravagent estate. Smith was obsessed with just one thing - geology/paleontology - but what he did, he did exceptionally well. His geologic map of the U.K. - the first geological map ever endeavored, remarkable accurate for its time - may not have changed the world on its own, but his theories on stratographic deposition - especially when combined with Darwin's insights into natural selection - definitely contributed to a continental shift (pun intended) in how future generations came to regard natural science.
Up until Smith's work at the beginning of the 19th century, it appears no one had bothered to question why the Earth beneath our feet seemed to be layed down in layers, why some of those layers contained coal while others didn't, nor why some of those layers seemed to contain fossils of sea life even though they were located far inland. Primarily this is because, at that time, people were busier trying (with uneven success) to fit observed facts into the Biblical account of Earth's genesis rather than visa versa.
Smith's work as a coal miner and drainage engineer placed him in the ideal position - geographically and historically - to start piecing together the puzzle that laid the foundation for a more scientific approach to geological time and Earth's origins.
All was not science and glory for Mr. Smith, however - partly due to the jealousy of rivals, partly due to bad luck, partly due - even the author admits - to Smith's own deficits. The man was an poor communicator, vain, spendthrift, and a terrible procrastinator, who also appears to have married unwisely and to have made a series of inexplicably reckless decisions that eventually led to disgrace and bankrupcy. Never fear - the story has a happy ending! Towards the end of his life Smith's reputation was salvaged and today the "Father of English Geology" occupies his rightful place in the pantheon of geology gods.
I agree that the story is a thin one, made even thinner by the fact that Smith appears to have been an inconsistent, unreliable journalist and there's a dearth of 3rd person accounts to corroborate or enrich Smith's sparse narrative. For instance, I'm still not sure whether his fascination with geology was merely the result of intellectual curiosity or more of an obsession/compulsion; I'm not clear whether he was socially adept or a social disaster(different anecdotes seem to come down on different sides); it's not clear to what extent Smith reconciled (or failed to reconcile) his findings with extant beliefs re. Earth's history; and Winchester's such a Smith fanboy that I can't shake the feeling he may have omitted information/analysis that would have shed a less favorable light on our reticent protagonist.
Having said that, I give Winchester props for making this story of geological exploration broad, engaging and accessible. If the author's portrait of Smith isn't quite complete, at least I gained interesting insights into British history, the geology of the U.K., the state of scientific discovery in the late 1700s/early 1800s, and debtor's prisons. His descriptions of geological phenomenon are simple and lucid (though a few more charts/graphs might have been useful). And if Winchester's heavy use of foreshadowing does sometimes confuse the chronology, at least it keeps you turning pages right up until the end. Perhaps not a great book, but I definitely don't regret the time I spent in Mr. Smith's company, and hope one day to be able to visit his great map at the headquarters of the Geological Society in London on the strength of this amiable tale.