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Beaumont Red Crag Outlier, BEAUMONT, Tendring District, TM180246, Notified Local Geological Site
Site name: Beaumont Red Crag Outlier
Grid reference: TM 180246
Summary of geological interest
Site of geological interest with potential for geological education. The high ground at Beaumont Hall is capped with an outlier of shelly Red Crag which is visible in rabbit burrows and on footpaths. The site is of also of importance in the history of geology. Any excavations in the area should be recorded. Site is private land and accessible only on public footpaths.
An isolated patch, or outlier, of Red Crag, about a quarter of a square mile in size, caps the top of the hill occupied by Beaumont Hall. It is one of the few fragments of a once continuous deposit of Red Crag across north Essex that has been almost entirely destroyed by erosion. The Red Crag in this part of Essex consists of loose sand with abundant fossil shells and the fossils of other marine animals that lived in the Red Crag Sea that existed about 2 million years ago.
The Red Crag at Beaumont was first brought to the attention of the scientific world by the well-known Essex geologist John Brown of Stanway, who obtained over 90 species of fossil shells from a pit near the south-eastern extremity of the outlier and privately published a list of them in 1846. At the end of the nineteenth century the amateur geologist Frederick Harmer (1835-1923) carried out a detailed study of the fossils of the Red Crag (see entry for Little Oakley) and re-opened Brown’s pit where he succeeded in finding more than 260 species. Most of these were characteristic of the Walton Red Crag but a few were Arctic species which were rare or absent at Walton, indicating that this outlier may be slightly younger than the Walton Crag. With the permission of the landowner Harmer also dug a hole near the south-western limit of the Beaumont outlier which revealed 5 or 6 feet of Red Crag resting on London Clay. With the help of a labourer 7 or 8 tons of Crag sand were sifted and from this several species were encountered that were not found at the previous pit. Harmer published a detailed account of his work at Beaumont and elsewhere in the Quarterly Journal of the Geological Society in 1900.
Shelly Red Crag was formerly exposed in the sides of the pond near the church and in other temporary excavations made as part of the running of Beaumont Hall Farm. Farm workers would often come across the typical Red Crag gastropod Neptunia contraria that is known as the ‘left-handed whelk’ because it spirals in the opposite direction to almost all other known gastropods. At Walton, the normal right-handed specimens also occur but at Beaumont these were apparently unknown to the farm labourers and Harmer reports that they had formulated a theory for this: ‘Before the flood, everything was left-handed’!
In 1900 the mineral content of the Red Crag at Beaumont was analysed by treating a 25 gram sample with concentrated hydrochloric acid. What remained was 50% quartz but the other 50% contained a rich assemblage of other minerals, some of which are familiar gemstones. Along with the more common rock-formng minerals such as feldspar and mica were rarer minerals such as zircon, rutile, kyanite, and ilmenite together with yellow crystals of corundum and green and blue grains of tourmaline. There were also tiny red garnets that were so plentiful that the heavy concentrate had a strong pinkish colour. Grains of topaz have also been found in the Red Crag although none were recorded from the Beaumont sample. The presence of such minerals in the Red Crag is evidence that these sands were derived from metamorphic rocks, probably from the erosion of the Scottish mountains, and may have been recycled several times over hundreds of millions of years before being deposited on the floor of the Red Crag Sea. As the Red Crag continues to be eroded, here and at Walton-on-the-Naze, these minerals will end up on to the floor of the North Sea – the next stage in a continuous ‘rock cycle’.
The former Red Crag exposures at Beaumont are no longer accessible but fossil shells can be seen in places scattered on arable fields, such as by the public footpath east of Beaumonthall Wood. Red Crag sand and shells can also often be seen thrown out of animal burrows in the ditch bank alongside the footpath west of Beaumont Hall.
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Reference: Brown 1846, Harmer 1900 (p.715-716 & 740-741).
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