I'm a sucker for personal-theme books.
By "personal-theme books", I mean "books that are a combination of memoir, philosophical investigation, and some factual content into a coherent whole, united by some thread." I've read several this year. Done well, these books tie together the small scale and the large, the personal and the abstract, in a way that sheds light on both.
In Underlands, the unifying thread is ... not history, exactly, but a sense of beginnings, of foundations. Nield weaves together his own family history in the south Wales mining areas with the history of those mines and the geology that produced them, throwing in some social history and some archaeology along the way. An old church is built of a particular rock because it's the only suitable building stone in the region; a layer of sediment goes from seabed, to hillside, to quarry, to abandoned; a mining disaster spares a young Ted Nield because his family has moved. Every is is founded on a succession of was.
It's a quirky book. Like most good "personal-theme" books, it's decidedly meditative in tone and digressive in substance. If you're looking for a straightforward fact-learning exercise, this isn't it. It's more of an invitation to ruminate. As a non-professional but habitual
For poetical geological writing, you can't not read John McPhee. The book that I kept thinking about while reading Underlands, however, is Steven Johnson's The Invention of Air, which--although less memoir-ish--can be read as an extended riff on the theme of "connectedness".