The opening section of this book is called Animals and we leap from sand hopper to winkle to prawn, understanding the complex interconnectedness of these underexamined lives, learning a new and perspective-altering fact on every page. Then, all of a sudden, there's a chapter on the pre-Socratic philosopher Heraclitus.

It's a segment of exquisite beauty, a bravura act of writing that seems not only to provide a model for the rest of this book, but changes the way you understand the whole dizzying Nicolson oeuvre. This is a writer who has moved from memoir to literary criticism to nature writing via The Mighty Dead, one of the best books on Homer ever written. In his chapter on Heraclitus, Nicolson reads a rock pool through the work of the great philosopher, bringing to the crucible of tidal life "a systemic understanding whose wholeness relies on its union of opposites". We begin to understand that the thread that links Nicolson's books is precisely this – a philosopher's wish to provide a way of comprehending the place of the individual in a vast and shifting world, the quest for a good life, the search for new answers to old questions. ...

The real journey of The Sea Is Not Made of Water occurs in its second and third parts, though. We come to recognise that the chapters on rock pools have only been a rehearsal, a study for what is to come. From the Lilliputian intimacy of the rock pool we spool out to chapters on the tides and the formation of rocks – vast in space and time, vertiginous in their scope and ambition. The last part of the book provides a history of the humans who inhabited this wild and rocky Scottish shore from pre-history to the present, with Nicolson applying the same sympathetic scientific curiosity to these lives that he gave to the winkles. "Life is tidal, full of loss and arrival, a thing that makes and ebbs," he writes at one point, and this is what we take away from the book – that we are all in rock pools, knitted within complex systems. We are part of nature, not separate from it.

Here's an idea: the best books are never only, or even mainly, about the subject they claim to be about. The novelist John Barth said something like this when asked what kept people turning pages. "The question 'Who am I?' is what ultimately motivates the reader," he said. The greatest literature – and this unique and terribly moving title is great literature indeed – reaches beyond itself to speak to us of the most profound and essential things. Spending time in Nicolson's rock pool will change your life and the way you view the lives of others.