After I wrote my first “photo prop” blog post about the piece of rock that I found in Egypt, I got to wondering about this black and white stone, and what it actually was.
When I was 13, my family and I travelled to England (en route to France where we lived for a while). While visiting my great-aunt, who lived in the little village of Storrington in Sussex, we went for a traipse on the South Downs. At that age, I don’t suppose I was thrilled with the prospect, but I found this special stone (the prop at the back, not the pendant at the front…), which has travelled from home to home with me ever since! Yes, I confess to being a bit of a hoarder of nature…
A quick email to my mum later, to find out where we would have been walking, (thank goodness for her memory..mine just doesn’t stretch to things like that!!) and a quick Google later, I can tell you that it is flint, surrounded by limestone chalk.
(Now, thanks to the South Downs National Park Authority and The Bournemouth University, comes the history lesson… do fast forward the boffin part if you’re not that into it!! :))
125 million years ago, the south east of England was a low-lying landscape covered by a large shallow freshwater lake with several rivers flowing into it. These rivers carried vast amounts of clay or mud, which started to build up in layers on the bed of the lake. The freshwater lake was home to massive prehistoric reptiles such as the Iguanadon and the Plesiosaurus. Eventually the clays reached a thickness of nearly 200 metres, forming the first layer known as the Weald Clay.
The land continued to sink until eventually the ocean broke in laying down massive layers of sand known as Lower Greensand. The sea gradually deepened and the waters became still. Under these conditions, a thick dark mud collected known as Gault Clay. After this period, there were strong underwater currents in the sea and the sandier sediments of the Upper Greensand were deposited.
97 million years ago, the sea began to lay down the chalk of the South Downs. Chalk is a white soft limestone, which has been formed from the skeletons of marine creatures deposited, squeezed and eventually fossilised on the sea-bed. This process continued for 20 million years and to a thickness of more than 300 metres. Chalk contains visible fossils of creatures that lived in the sea 90 million years ago, including ammonites, sea urchins and fish sponges.
Flint occurs naturally within the upper chalk. It may be found on or just under the surface as nodules or deep underground as horizontal seams. Flint is the only hard rock to be found on the Downs. Flint was formed from the skeletons of minute animals, such as radiolarians, that floated around in those ancient seas.
65 million years ago the ocean floor began to rise, the sea became shallower and the formation of chalk stopped. Deposits of clays, pebbles and sands were laid down.
20 million years ago, the South Downs were raised from the seabed, through the movement of the earth’s crust. The land masses or ‘tectonic plates’ of Africa and Europe moved towards each other and collided. The rocks were pushed up and created mountain ranges, including the Himalayas and the Alps. The south east of England was caught up in this ‘Alpine Storm’ and the ripples pushed the layers of rock upwards forming a vast extended dome of chalk. The neat layers of sands, clays and chalk, laid down over millions of years in fresh and salt water gradually hardened into rock.
Over millions of years, the landscape has gradually changed shape to form the South Downs as we know it today. The centre of the dome has been eroded. The soft chalk at the top of the dome gradually cracked and crumbled and the falling rain carried off these shattered pieces of chalk. This left an outer upstanding rim of chalk surrounding a lowland plain formed from older layers of clay and sandstone. The outer rim of chalk forms the uplands of the North and South Downs and the central plain is known as the Weald.
2 million years ago were The Ice Ages. Although the South East of England was not covered in ice, an intensely cold climate dominated this area. This meant that the rock and soil was frozen for most of the year. Summer rain and melt-water could not soak into the frozen chalk. So this water formed streams which carved out valleys on the Downs. The rapidly melting snow during the last ice age also carried rock and soil from the hillsides on to the floors of the valleys.
When the climate became warmer, the frozen ground eventually thawed and the water soaked into the little holes in the chalk, leaving the valleys dry. These dry valleys, known in Sussex as coombes, are V-shaped with steep sides. Patches of clay with flints can be found in places on top of the Downs. This is the remains of some clay that was once on top of the chalk that got mixed up with flints from the chalk.
Mining for deeply bedded flint seams of flint began in the Early Neolithic, around 4000 BC, the extraction pits surviving today as large crater-like hollows in the chalk. Early people on the Downs found that they could use the razor-sharp edges of flaked flint as a cutting tool. Flint mines therefore represent one of the oldest and most distinctive forms of archaeological monument recorded from the British Isles. Mines are clearly visible today as a series of impressive oval and circular depressions.
I like to try to imagine what life was like back then. Imagine people, six thousand years ago, mining flint for tools. Wonder if any of them were my relatives?
So, there it is, my little piece of history. I am awed when I think of it! Not only does it remind me of England, and my heritage there, but fancy holding something in my hand that has been around for 100 million years!!!