The Edinburgh Geologist
Issue no 38

The mud springs of Wootton Bassett, Wiltshire 

by Bill Baird

To mark the silver anniversary of the publication of The Edinburgh Geologist, Bill has agreed to write a further Strange Earth to continue the series.

The 'mud springs of Wootton Bassett' seems a fairly innocuous but interesting title, and forms part of the introduction to a paper in the Proceedings of the Geologist's Association. As reported in New Scientist, however,  the headline ran 'iridescent fossils rise up from volcano'. There are not many active volcanoes in Wiltshire, so perhaps we should investigate the matter a little further. The site of the mud springs is a small wood called Templar's Firs, near Wootton Bassett. It seems that these features were drawn to the attention of the then Nature Conservancy Council by Willie Stanton in 1974. Rather than being the result of volcanic activity, however, it is understood that the mud springs were formed by water under pressure finding its way to the surface at the site. In its journey to the surface, it passed through a layer of clay which forms a colloid suspension in water. Of added interest at this site is the presence of well-preserved ammonites, brought to the surface by the upwelling mud. These Jurassic fossils are typical of the Ampthill Clay and indicate a Mid to Late Oxfordian age.

The initial description of these mud springs was of three domed blisters some 10 m long by 5 m wide by 1 m high. There was a skin of vegetation containing a core of liquid mud which oozed from any fissure in the skin to a nearby brook called Hancock's Water. It is from Hancock's Water that most of the fine ammonites and other fossils have been collected. The technical explanation for the occurrence of the mud springs is that they are related to the local geology, in that they occupy sites in valley bottoms cut into the Ampthill Clay along synclinal axes. They seem to be driven by groundwater in the Coral Rag aquifer which crops out and is recharged beneath Wootton Bassett. From measurements taken in order to understand the mechanism of the springs, it seems that there are irregularly-shaped chambers underneath the mud domes which do not seem to be deeper than 20 m. It is probable, however, that there are further lateral and vertical fissures allowing movement of water and mud into these chambers.

The mud springs at Wootton Bassett have caused considerable interest amongst geologists and others. During recent site investigation, the British Geological Survey has provided support and assistance with seismic, stratigraphical, geochemical and hydrogeological input (Bristow et al., 2000). Fossil collectors have made available their collections for study to enable the stratigraphy of the source rock to be accurately defined. Further site searches in the general area have revealed similar springs near Greenham Common. Of course, no such site is free from the attentions of the well-meaning, if ill-advised, who wish to make it 'safe'. It was allegedly for this reason that approximately 100 tons of rubble were tipped into the most active spring in Wootton Bassett in 1990. The 100 tons of rubble disappeared without trace, except for the equivalent amount of mud which poured into Hancock's Water. This then had to be cleared from the brook by the long-suffering workmen of the local council.

It seems that, at present, activity is at a low level in the mud springs of Wootton Bassett. This is hardly surprising as they have been poked, jumped up and down on, dredged and sampled in various ways. However, what this site shows is how the mysteries of geology can occur on one's own door step. The mud springs of Wootton Bassett are a recognised part of the ancient town's social history, prompting a full-page write-up in the local guide Welcome to Wootton Bassett. They have also been the inspiration for some 50 papers in the literature and caused much argument and discussion amongst the scientific community.

Further reading:

Bristow, C.R. et al., 2000 in 'The lithostratigraphy, biostratigraphy and hydrogeological significance of the mud springs at Templar's Firs, Wootton Bassett, Wiltshire', Proceedings of the Geologists' Association, volume 111, pp. 231-245.

Bill Baird is well-known to Fellows, having been the author of many articles for this magazine, in particular the Strange Earth series, the first of which appeared in 1984. Bill was President of the Society towards the end of the last Millennium. 

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