Wisdom, as many another priceless thing, must be dug from the very bowels of the earth.” Girolamo Cardano


The plan is to walk each of the itineraries in Geologist’s Association Guide No. 68 (The Geology of London). Not slavishly but in the spirit, after a fashion.

Walk 1. Harefield, 13 November 2015

Bad news on the train out of Marylebone: “passengers are reminded there is nothing in this mortal life except inanity, emptiness, and dream-shadows.” As if I needed reminding. I just wanted to find something – anything not wholly shit. Which is not setting the bar very high, but it didn’t need to be. From Denham I picked up the South Bucks Way to Denham Lock, sheltering briefly from squally rain; then cut up the canal, soon crossing to a car wide track next to old gravel pits. At South Harefield I struck north uphill to the Anzac memorial. Soon I was at my first stop, Harefield Great Pit, a former chalk quarry filled with household rubbish and capped with clay which until recent times provided grazing for a dairy herd. It is now a feral expanse of bramble and grassland criss-crossed by unofficial footpaths, with wide views across the Colne valley to Northmoor Hill, where an inspection of a swallow hole and a chalk pit were the last items on my itinerary: after I had given a nod to the Marble & Granite center next to the canal where the blank slabs gave me chills but were probably destined for kitchens.

At Northmoor Hill Wood I was barked at by a dog. There were no swallows in the hole: they had either returned to Capistrano through the chalk or been scared off by helicopters landing next door on the last of the pre-Anglian proto-Thames deposits; or Denham Aerodrome as it is sometimes known.


Whilst in prison Girolamo Cardano – the renaissance scholar of choice for Chiltern train drivers – redrew his coat of arms, a black eagle with wings outspread upon a saffron field. He added the image of a swallow singing under the eaves of a barn.

It was dark by the time I caught the train back to London. I sat opposite a couple of schoolgirls who, prompted by the Dollis Hill station sign, talked for a while about how they liked the name “Dollis”, which reminded them of “Dorris” which sounded very old fashioned. I wondered why they didn’t have bags – until the penny dropped. Their homework was on their phones or in the cloud: why would they need to give themselves a sore shoulder? I nodded off for a bit secretly quite glad that post-diversionary gravels weren’t included in my first itinerary. Best to hold some excitements back against a rainy day.

Walk 2 Long Valley Wood, 19 November 2015

Plenty of rain today. But my enemy was the dark. It needn’t have been but I got lost in Croxley. By the time I got myself right, I had to run or finish in the dim. A brainwave: if I reversed the loop across fields from Stocker’s Lock, Rickmansworth, I could walk the bit I didn’t know first and finish on the canal in the dark. No one, I figured, could get lost on a towpath.

I located Long Valley Wood which was full of chalk pits but failed to bring to mind the 4,000 palaeolithic artefacts found there and mentioned in my guide. I liked the path though – which ran along the old quarry edge behind suburban gardens. Later it widened as it climbed through woodland with glimpses of the Metropolitan Line rattling through deep clefts.

The loop – via Hill End – was a goodun’. I stopped for tea in steeply sloping woods where bungalows hunker down in old chalk pits – in fact a whole estate has been shoehorned into Summerfield Lane Quarry. No sign of any dissolution pipes though – or any other type of dissolution – at least not in the dark.

Walk 3 – Pinner Chalk Mine, 25th November 2015

I had been to Montesole Playing Fields in Pinner before whilst walking the course of Grim’s Ditch, which once stretched six miles from Pinner to Stanmore; at least it may have done if a line is inferred from the “surviving sections”. I had no idea of the even more remarkable survival beneath the bitch in Pinner. Precious enough to risk life and limb clambering down a shaft on a wobbly mountaineering ladder, apparently. I wasn’t tempted I needn’t add – and even if I had been I didn’t have a key to the 2.5m spiked security fence or concrete manhole cover of Pinner’s last accessible chalk mine in woods next to Montesole allotments.

When the Pinner chalk was first worked is, according to Ken Kirkman who wrote the definitive guide to the mines, not known. Pliny wrote about Britons marling land with chalk dug from pits. There may have been mines in Pinner in the sixteenth century. The impressive galleries of the Dingles Mine – sometimes 6 or 7 metres high – can be dated exactly. Workers left their initials on the ceiling with a burning candle, and a date: 1840.

Other shafts may yet be found. Ken Kirkman, again:

“How would you know if you had a shaft at the bottom of your garden? Look for rain water or waste water pipes that do not go into the public system. Tamp the ground with a broom handle and listen for a duller response. Watch for a circle of frost that melts more quickly because it’s over the warmer air in a shaft.”

There is something even more precious than chalk here to a geologist – in situ puddingstone, a rare type of rock conglomerate formed during another period of global warming, 55 million years ago, and another message writ in carbon that we ignore, according to Bryan Lovell, a senior research fellow at Cambridge University and former President of the Geological Society, at our peril.

Professor & Mrs. Trudge

Years ago I read an article in Herfordshire Life about a lost trackway, marked with large puddingstones, from Grime’s Graves, a complex of prehistoric flint mines in Norfolk, to Stonehenge. The writer, Professor Rudge, of West Ham Municipal College, and his wife spent every weekend for three years looking for stones to confirm their theory. The research generated quite a bit of media interest at the time and was reported in Time Magazine in July 1952. When I began studying archaeology in the nineties I put such nonsense aside: filed it, along with with ley lines and King Arthur under “lost causes”. I’m still intolerant of folkloric whimsy: even when given a post modern spin.

But I find myself more and more drawn to the deep poetry of Professor Rudge’s search. Aren’t we all pilgrims on a lost highway? And there are worse ways to spend your weekends than wandering about the green lanes of Essex with your wife looking for 55 million year old beach material. Now Bryan Lovell’s research suggests puddingstones really were the answer all along – Professor Rudge was just asking the wrong question.


Pliny also wrote that young swallows’ eyes could regrow if plucked out and that precious gems are found in their crops. Perhaps science has always been equal parts hard boiled observation and wishful thinking.


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