Sarsens are scattered widely over the downs but they are most dramatic seen lying along the dry valleys leading to the river Kennet. The name sarsen may come from Anglo Saxon ‘sar sten’ a troublesome stone, or from ‘saracen ‘ meaning foreign or alien. Locally they are called grey wethers because, in the half-light, they are said to look like sheep. The name recalls a time when flocks were shepherded on the unfenced downs.
They are not old as rocks go but they are unusual. It is rare for rocks as young as this to get so hard. From about 65 million years ago the chalk sea bed gradually rose to become land and layers of alluvial sand and clay were deposited over it. Sarsens were formed within these layers about 50 million years ago. The climate then was warm and wet. Groundwater became saturated with dissolved silica. Variations in the acidity of the water caused the silica to crystalise between the sand grains , cementing patches within the deposits beneath the soil. Ancient, palm-like plants grew in the tropical conditions and sent roots into the still soft stone. Tubular root holes and fossilised root remnants can still be seen and show how quickly the stone hardened. If the deposits contained flints they too were incorporated into the sarsen. Occasionally a jumble of pebbles left by a flash flood long ago has been preserved in a “pudding” stone.
The traditional theory is that the concentration of sarsens in our valleys came about later, during two and a half million years of successive ice ages. Glaciation (the fully frozen area covered with glaciers and ice-sheets) extended almost to north Wiltshire. A little to the south, in this peri-glacial region, extremes of alternating frost and water saturation broke up the surface of the land. Slippage of waterlogged earth carried slabs of broken rock over the underlying permafrost into the valleys. Torrents of meltwater, on their way to the river Kennet, washed away surrounding silt and left the sarsens exposed. The valleys created this way are typically asymetric. The stream beds moved gradually towards the steeper slope leaving a gentler gradient on the other side.
A newer theory has it that most of the sarsens formed in situ, in valleys already existing, where the water table came close to the surface. The sandy deposits at the top of the water table were hardened by silica drawn up into them by capilliary action. During the ice ages these valleys were eroded into their present shape leaving the sarsens behind.
Before the mid 19th century sarsen deposits extended far beyond the remnant areas protected now. Stones filled the valley from Lockeridge to beyond Boreham Wood. From Piggledene they stretched up to Overton Down. They lay along Clatford Bottom and at Stanley Wood. In 1644 Symonds Diary of the Marches of the Royal Army records that “stones lie so thick as you may go upon them all the way.”
On the 15th of June 1668 Samuel Pepys passed by on his way from Bath to Marlborough. After admiring Avebury Circle he went on by way of Green Street, now a bridleway, across Overton Down and Fyfield Down.
“About a mile on it was prodigious to see how full the downes are of great stones and all along the valleys stones of considerable bigness most of them growing certainly out of the ground so …. thick as to cover the ground. Which makes me think the less of the wonder of Stonage for hence they might undoubtedly supply themselves with stones as well as those at Abebery.
Until recently folklore had it that sarsens grow and Pepys had an ear for a story.
All the valleys are protected now one way or another. The Valley of Stones lies in Fyfield Down National Nature Reserve which overlaps Avebury World Heritage Site on its west. It is also part of a larger Site of Special Scientific Interest. Rare lichens grow on the stones. One of them is a specialist, found only on the acid hard-rock of sarsens. Others are highland and maritime species, not unusual in themselves, but surprising here. The upper valley is capped by clay-with-flints, where gorse grows on the more acidic soil. Below Green Street this changes to undisturbed chalk grassland with its typical flora. Grazing schedules are managed to prevent the stones becoming overgrown and shading the lichens. Lighter grazing in summer allows the wild flowers to seed.
Piggledene and Lockeridge Dene have been owned by the National Trust since 1907. Many donations from the local community helped with the original purchases. Financial help was given again in 1997 to buy the hillside at Lockeridge. The National Trust site analysis includes, as one of the strengths of the property, a community sense of ownership. Both are managed to “maintain the ancient character of the sites” with their “boulder streams and scattered trees reminiscent of the wildwood”. Here too lichens are protected by careful grazing. No herbicides or pesticides are used. Trees are retained because they also support lichens and mosses. Dead wood is left to rot. Piggledene is another Site of Special Scientific Interest.
We each have a private, almost a secret, relationship with these places, made up of our own experiences, like watching buzzards riding the thermals or wondering at the beauty of banded snails or finding tiny moss pom-poms colonising root holes. The valleys lie open to the weather, under a wide sky, revealing the forces of nature that made them. The lives of the people who used their stones are written into the landscape. Some left their humble, functional work – paving setts, gateposts and cottage walls. Some, long ago, left their great ritual monuments at Avebury and Stonehenge. We time-travel here.
National Trust. Lockeridge Dene and Piggledene S.S.S.I. Statement of Significance.
Patrick Cashman. English Nature.
Isobel Geddes. Hidden Depths
Peter Fowler. Landscape Plotted and Pieced.