Sarsens
At some time in this period, after maybe 5 million of years of erosion, there was some further deposition, producing the Reading beds, of sand and gravels. On some of the Chalk Downs there was a thin layer of sand and gravel that later became hardened by silica. This is thought to be due to evaporation of groundwater containing dissolved silica – the mean annual temperatures were higher than 20C for long periods. This hard layer was broken up during the tundra conditions that existed during parts of the last 2 million years, and all that were left were scattered blocks called Sarsens, for example near Ashdown House, West Oxfordshire.
Here and there in the parish you can see light brown stones which are very hard, for example on the corner by the White Hart, by the barn in Townsend, and outside Princes Manor Farm. These are sarsens, and have survived although all the chalk they formed on has long since disappeared. As evidence they have not been brought here, there are still examples to be seen in the hedges and fields. The photo shows the group outside Bishop’s Manor Farm Barn, Townsend.
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