Sarsen Stones - Geology
Sarsen – a derivation of Saracen – stones, are blocks of hard sandstone – a sedimentary rock, which consists of quartz grains bonded together by a naturally formed siliceous cement. They were formed some 60-50 million years ago, when layers of silt and sand (mainly quartz), laid down as river or marine sediment, were saturated with silica-rich groundwater. Later on, possibly due to either acidification, or evaporation, of the groundwater, the silica precipitated out and filled the gaps between the grains of sand. This eventually acted liked a mineral glue (siliceous cement), sticking enormous numbers of sand grains together to form a layer of solid rock just below the water table. Subsequent ice and water action, broke this rock layer up into the boulders (Sarsen Stones) that we see today. The stones vary in texture and colour, depending upon grain size, surface erosion, and mineral impurities, e.g. small amounts of iron oxide can make them look darker, especially when wet. They are found across much of the United Kingdom, and vary widely in size and shape, the most famous Sarsen stones being those found at Stonehenge (together with Bluestones).
These stones are not however native to Eastern England, and there have been at least two theories postulated as to how they got to this part of the country. The first is carried along and deposited by glacial action during the last ice age, and the second is that they were deposited by the River Thames – which used to flow well to the North of its present course, entering the sea probably in the vicinity of what is now Clacton, but possibly even further North than this.
Some uses of Sarsen stones have been as boundary markers, protective stones for the corners of buildings, and even briefly as building materials – although they were found to attract too much damp for this purpose.
The Ingatestone Sarsen Stones.
There are several stones of various sizes in Ingatestone - a name derived from the Saxon version Ing-atte-stone (or the People at the stone), suggesting that perhaps the stones were already present when the Saxons settled there. It is also considered possible that from the number of stones, there may once have been a stone circle of some sort in the vicinity, of which these stones formed a part.
The two most prominent Sarsen stones stand on the footpath, either side (E and W) of Fryerning Road, where they form a tolerated obstruction - protected by a preservation order. There is however no indication of when, or how, they were placed in their present position.
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Q1. What are the approximate sizes of these two stones, and is the texture and appearance of both the same. If not, how do they differ, and can you suggest why this might be.
Q2. How long ago, and in what geological period were they formed.
Q3. Of what mineral are they principally made, and what is its basic chemical composition.
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