We love the River Quaggy. We also love Blackheath pebbles, the smooth, black flinty rocks found in the river which reveal how the London area rose out of the sea came to be. QWAG members Paul Rainey and Pamela Zollicoffer explore a story as old as time – well, perhaps just 55 million years.
The mind-blowing story of the humble Blackheath pebbles in the River Quaggy starts with QWAG’s Secretary, Pamela, picking up a pebble during a QWAG event in the river, as Pamela recounts…
Finding black stones in the river
During my time in the River Quaggy removing invasive plants and plastic and other waste, I often noticed many beautiful, smooth, black rounded pebbles on the riverbed.
On one event I picked up one of the humble stones. It was truly a thing of beauty, glistening in the palm of my hand, reflecting light from its wet, black, slightly pitted but smooth surface. Its solid weight and size felt reassuring in my hand – like holding a paperweight. I put it in my rucksack and took it home.
At home, reflecting on the day, I found the stone in my pack and thought it must tell a story. I asked Paul Rainey, a geologist and fellow QWAG member, to tell me the story of how the pebbles had been formed and come to be in the Quaggy – see below.
I thought that this natural object from the river would interest people visiting QWAG stalls at public events and at our meetings. They might even like to have one of the pebbles as a memento of the river.
Coincidently, I heard of the death of Gary Dahl, an advertising copywriter, creative director and entrepreneur in the USA.
Dahl had been in a bar with friends who were complaining about the work involved in keeping a pet. The joking led to his idea of the perfect pet – a rock requiring no feeding, grooming, walking, taking to the vet or sadness when pets die.
Dahl wrote an instruction manual for ‘pet rocks’, placed smooth stones collected from a beach in Mexico in a box with straw and ventilation holes, and marketed it – and the 1970s Pet Rock fad was born, and Dahl made millions.
How the rocks were formed
For the story behind the pebbles, I turned to fellow QWAG member, Paul Rainey, who is a geologist, who takes up the story. Paul writes…
The black flint of the Blackheath pebbles was originally formed beneath the surface of the chalk, which at that time formed the bottom of the sea, about 87 million years ago.
The flint formed in layers, sausage shapes or boulders, with white ‘rinds’. More chalk, perhaps 100 metres thickness, formed over time. Eventually, what became the London area rose out of the sea exposing the chalk to erosion, sometimes by the sea and sometimes by large rivers, that removed most of that 100 metres of chalk.
The flint is much harder than the surrounding chalk and so is easily removed from it. It was thoroughly rolled around into well-rounded pebbles without rinds which were then deposited in offshore pebble banks. The Blackheath Pebble Beds were formed about 55 million years ago.
The surface markings on the pebbles are evidence of this process. The ‘chatter-marks’ on the surface of the pebbles shows how they repeatedly hit each other, perhaps jostled by the tides.
Over the next 15 million years this area was mainly under the sea and being buried by perhaps about 200 metres of sediment, including the London Clay. During the final 40 million years the area has mainly been land with the sediment slowly being removed.
Your own Quaggy rock
Contact QWAG if you’d like to buy one of pebbles. Each one has been carefully selected by Pamela from different stretches of the River Quaggy and comes in a small hessian sack with a certificate of authenticity signed by Paul.