This amazing book is itself a little like a flint, a misshapen stone egg of the Sussex Downs. It resists the reader at first, coated in the calcite rind of the author’s slow, scholarly journey, missteps and all. But when you persist, breaking the book’s spine or, as it were, knapping the flinty nodule, you find treasure within.

Alexandra Harris quotes the painter Paul Nash writing in 1937: ‘If I broke all the shells of all my wild stones, I should find that precious yolk which is like precious stones, the black core of the flint.’ From Nash, it’s a hop and a skip to Henry Vaughan, the metaphysical poet who ‘understood his heart as a cold flint that must be violently struck if it were to kindle into divine light’. He called his cycle of religious poems Silex Scintillans – flashing or fiery flint.

Harris’s associative range is second to none, and here she focuses her powers within a 20-mile square. She strikes two stones together under Cocking Down, after a five- hour walk on Midsummer’s Day. ‘A mote of light is visible just for an instant, in the shade.’ In these parts, picking flints from the fields was historically a job of last resort; but the stones have also been, since Neolithic times, a resource. ‘I picked them from their sockets in the path,’ Harris writes, ‘and tapped – gently at first, then with conviction.’ The echoes come.

Storrington was her first home. In the controlled chaos of ‘ensemble class’ in the village hall, she

liked to tap the xylophone and hear its chimes answered by church bells from across the field… I was already conscious of turning from the brightly lit room, where someone was shaking maracas, to look out at the hills in the night. I think I was aware of something grand and inviolable out there, but I didn’t understand much about the land about me and wouldn’t have known what to ask.

Harris takes a quadrat of land, with Storrington near its centre, and examines it as a geographer would a sample. The roots don’t come away clean, but extend, marvellously entangled, through time and space. It becomes thrilling to see the deep layering, the ‘multiple dimensions of time and place that make up the apparently fixed scene of the present’. I gasped when the painter John Constable attends, at North Stoke, the excavation of an old bridge, which in fact turns out to be a vast and ancient canoe or long-boat 1,000 years old. His careful sketch is among many helpful illustrations.

The quadrat goes down to Chichester, where we see Pallant House being built and rebuilt for fussy customers and its lumpen stone ostriches arriving in 1713, definitely ‘works of imagination’. They predated the menagerie the Duke of Richmond kept at Goodwood. His moose, transported from Canada, was such an attraction that in 1768 Gilbert White travelled from Selborne to see it but found it had died the day before he arrived. Harris shares Eric Ravilious’s woodcut of the sad scene.

Past Littlehampton (where, in 1789, Charlotte Turner Smith wrote her sonnets on seeing graves washed into the sea), the quadrat’s easterly extreme lies at Tarring. There men, women and children in the lean 1820s and 1830s set out in search of opportunity in Canada, sending back letters full of notes on the qualities of the soil they found.

To the north, we never reach Horsham, where Harris went to school, but the richly storied earth reveals a wartime Polish camp at Petworth, French Resistance spies at Bignor, Elgar composing at Bedham and Laurie Lee and Lorna Wishart in 1940 lying on their backs in the woods watching planes at war. Aerial maps change the perspective. Famous names mingle with local characters, visitors, sages. Jomo Kenyatta hunts a fox as if it were a leopard; Zygmunt Krawczyk fishes in the lake at Petworth where Turner fished in the 1820s; Ivon Hitchens paints his Modernist pastorals at Lavington Common.

A chance conversation with a biographer reveals to Harris that Ford Madox Ford recuperated after the war at Storrington. She sleuths for his house, Red Ford. ‘The name, of course, delighted Ford. He always set store by omens: repeated dates, magnetic places.’ Could the large house built around an older core be it? ‘I checked the stream at the bottom of the garden. The water was bright rusty orange-red.’

To Ford, it resembled the ideal Sussex cottage of his imagination, with a ‘monthly rose’ on the wall – ‘I knew there was never a labourer’s cottage in Kent or Sussex without one’ – and a hawthorn boundary ‘20 feet high and quite solid, as a quickset should be’. He bathed in the spring under the oak tree where there was a ‘dipping hole’. Harris knows what Ford possibly did not: that in 1855 an elderly widow digging for that spring in high summer discovered in the loosened earth a large cache of Roman coins buried in the 4th century.

Harris is already well known as a stunningly knowledgeable and perceptive cultural historian. Her decision to scour this small patch for meaning is a refreshing and radical act in its way. She majestically reclaims local history, wiping the slur off provincialism. She breathes life into the scantest records of ordinary existences, even though this sometimes takes quite a lot of flint work and a char cloth to catch the ‘grain of fire’. But she commits to the project until the grassy tumps and hussocks speak.

William Blake’s vision of his left foot being entered by John Milton came to him at Bognor of all places. That Blake names Bognor and Felpham is surprising, and important, says Harris: ‘The effect is to invoke all those thousands of places that are personal to other people.’ She puts Blake in a Protestant, dissenting tradition that allowed God to be local. The man was ‘provocatively thinking on planetary, national and local scales at once’.

Constable collected sand and different kinds of earth from Fittleworth Common and brought home specimens to lay on his dressing table. Where other men might have kept their silver snuff boxes, Constable placed his collections of soil. ‘The range of colours from one small patch of ground amazed him.’ We see the world in a grain of sand here, eternity in an hour. This book is a flint very much worth cracking.