Down To Earth

Jul 11, 2023 | Walk & Talk

geology map of the western weald

If you thought these articles were only of value to walkers, then think again. While researching this piece about geology it occurred to me that the subject might also be of interest to scrabble players. My companion on this walk and talk was local geologist Maurice Curry, and in order to ask some vaguely intelligent questions I had to do some homework. This meant learning my Miocene from Eocene and Cenozoic… to name just a few of the many technical terms. As a seasonal (Christmas) scrabble player, I immediately saw the value of adding these words to my vocabulary. Never again will I look down with dismay at a tile rack full of vowels and random consonants. Instead, the power and the glory will be all mine as I lay down ‘Cenozoic’, with the Z on a triple letter score. Well a girl can dream can’t she!

At school, history and geography were two discrete subjects and never the twain shall meet. However, in reality we know they fit together like hand in glove. This is particularly the case with geology. When the asteroid hit earth at the end of the Cretaceous period, not only were the dinosaurs wiped out, but the foundations of our chalk Downs were established. Geology is all about making connections between the historical timeline of our planet and the rocks and minerals under our feet.

Local Geology

As a walker who spends a fair bit of time looking at my feet, it is impossible not to notice the ever-changing geology underfoot. Furthermore, with Petersfield at the apex of the Western Weald it offers particularly rich pickings for both amateur and professional geologists alike. So, keen to learn more, Maurice and I set out on a walk from Queen Elizabeth Country Park back to Petersfield over the chalk downs, onto the Upper Greensand, over the Gault and down to the Hythe Beds of the Rother Valley. Over the length of our 5 mile walk we crossed at least 8 different geological strata (within the chalk alone there are 5 different types) and travelled through millions of years of history too.

Maurice was quick to point out that he is not a specialist in our local geology, having spent much of his career studying hydrocarbon-bearing rocks of one sort or another in Romania, Russia, the North Sea and Caspian basin. This actually put me at ease as I have also spent 20 years following my husband around similar locations and naturally picked up some jargon along the way.

Rock Formation

As we puffed our way up the chalky, white path, towards the ridge, outcrops of flint provided a convenient excuse for a break. How were they formed, I asked. While the question was obviously relevant in both time and place, I clearly wasn’t quite ready to process the answer, as what I initially heard was more scrabble words. Maurice was fortunately very patient, and with a little more probing I think I cracked it. For flint think silica rich skeletons of sponges and other microscopic organisms broken down to produce a gel which replaces the chalk, often  following old shrimp or other animal burrows, hence them occurring as nodules.

The climb also provided the perfect opportunity to discuss the processes that lifted up the Wealden Dome, of which the Downs are simply the remaining edge. Maurice explained that the Downs were the response of the distant Alpine orogeny; a phase of mountain building that began 65 million years ago which was responsible for the whole line of mountains from the Pyrennes in the west across to the Himalayas in the east. That certainly helps provide some perspective and makes you realise that geology transcends national boundaries. This is most evident with our burgeoning wine industry, which benefits from the same advantageous geology as France’s champagne region.

Down off the Chalk

After a short break in Buriton, observing the various locally derived stones used in nearby buildings, the pond that is fed by springs along the foot of the Downs (that arise due to a change in geology), we set off across the flat sandy fields of the Upper Greensand belt. 16th century writer Gervais Markham referred to the Greensand hills of our area as “hillish and sliding country”, which felt quite apt as we zig-zagged our way down the steep slope behind Nursted House to arrive on the Gault Clay at the bottom. Out walking you will often see evidence of landslides in the sandy areas around Petersfield. As an interesting aside, Maurice also mentioned that Nursted House has its own connection to geology, having been where Sir Roderick Impey Murchison, a famous 19thcentury geologist, met his future wife Charlotte Hugonin.

A Sticky End

I have to say that clay is a bit of a swear word in our house. I hate it with a passion, especially in winter. However, there is no escaping it as we are surrounded by variations of the stuff here in Petersfield. Relatively speaking, as a walker, I’m going to stick my neck out and say that the Gault is not as bad as the Wealden clay. That said, it’s all nasty sticky stuff when wet and bakes hard as iron in the summer. As a sign of my indifference to the stuff Maurice and I pretty much glossed over it. Instead, I asked if he had a favourite period in evolution. His answer was the Devonian during the Paleozoic era. This is associated with beautiful red sandstone formations that can be seen along the coast of Devon and Southwest Ireland.

muddy boots

With all our talk about the earth’s evolution, and it clearly being a dynamic process that is yet to run its course, it seemed logical to also touch on climate change. During our chat Maurice had mentioned a huge extinction event at the end of the Permian period (250 million years ago) bigger than the one that killed the dinosaurs. It also coincided with one of the largest volcanic events in the earth’s history which produced huge amounts of carbon dioxide and released methane stored in marine sediments. Together this led to 70-80% of all life on earth being wiped out. While a statistic like this gives you pause for thought, the study of geology also demonstrates our planet’s amazing ability to heal and rebuild. It is merely that we won’t be around to witness it. And on that happy note I’m off to play…win a game of scrabble!



To view more geological maps visit the British Geological Survey

Read how local geology is a factor in the formation of Dew Ponds along the South Downs

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