Apr 3, 2020

Objects of wonder in my garden


Sedgwick Museum Conservator, Sarah Wallace-Johnson, writes about working from home and using the opportunity to find fascinating things in nature in our own gardens.
Category: 2020
Posted by: Sarah

In our confinement during the Coronovirus crisis it might seem that we are cut off from the world and all its wonders. However, a trip into the garden can be very interesting and being forced into a more confined space can, perhaps, make us look in more detail at our outside spaces.  I will be writing blogs about my expeditions to the tiny wilderness outside my back door over the coming months. This week I am featuring Sarsen Stones (a Wiltshire dialect name), in my small Oxfordshire garden.

Sarsen StoneThese beautiful ginger, brown, sandstone rocks once covered much of Southern England in a continuous sheet or cap. They were laid down during the Cenozoic in the warm climates prevalent at that time. To the touch they have a smooth, almost glassy feel, this is because they became silicified (glass is made from silica) during their deposition turning them into a rock called a silcrete. The warm climate meant that water containing dissolved silica was drawn up through the sands evaporating on the surface leaving the silica to crystallise, cementing the sand together into the rocks we see today. If you look at the photographs you will see many holes all over the surface, these are left by the roots of plants that were growing on the land surface at the time. An amazing trace fossil, showing the soil surface of a once living environment. During the Ice Ages, glaciers ripped up the cap of silcrete and scattered them across the Downs of Southern England.

Sarsen StoneHumans have had a long association with these characteristic rocks. In Neolithic times great monuments were raised from massive Sarsen stones. Today we see these ancient monuments in our landscapes at sites such as Avebury and Stonehenge. In more recent times the rocks that were left on steeper ground became known as Greywethers as they look, from a distance, like flocks of sheep (a wether is a type of sheep) on the downs. Many of the smaller pieces are removed from fields as they damage agricultural equipment and have been used extensively for building stones.
It is amazing that a rock in my garden can tell such a story and take us to distant times and places when the world was a very different place.

Sarah Wallace-Johnson
Sedwick Museum Conservator