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Earth Science Conservation Review
| Ballymacombs More | Londonderry |
| Site number: | 1250 | ||
| Locality Type: | Cutting, Field, Subcrop | Status: | ASSI |
| Grid Reference: | H985989 | ||
| Google maps: | 54.82866,-6.46729 | ||
| County: | Londonderry | Council area: | Mid Ulster District Council |
| Period: | Quaternary | ||
| Stages: | Holocene | ||
| Site Description | |
|---|---|
| Highlights: | |
Ballymacombs More is a small remnant of the once extensive diatomite deposits of the Lough Neagh and Lower Bann. Recording the environmental history of the area through part of the Holocene, the deposits are of importance to a number of research specialisms. | |
| Introduction: | |
The area is of special scientific interest because of its deposits of diatomite and associated materials. Diatomite consists of accumulated diatom frustules with differing amounts of clay, silt, sand and peat. Diatoms are microscopic aquatic plants, surrounded by a silica box, or frustule, of various shapes, depending on the species. The diatomite (also known as Kieselguhr or Bann clay) deposits in Northern Ireland were one of the most extensive freshwater diatomite sequences of post-glacial age in the world. | |
| Description: | |
Ballymacombs More is one of the most extensive remaining blocks of diatomite in Northern Ireland and the only substantial site with overlying peat. This more complete stratigraphy permits detailed environmental reconstructions to be made for the Lough Neagh and Lough Beg area and provides local information on habitat transition from open water through marginal swamp and carr woodland, to the development of raised bog peat. The idealised general sequence of deposits is as follows: basal sands (former lake or river bed) overlain by fen peats (initial colonisation phase following a fall in water level), diatomaceous peats and clays (periodic inundation), diatomite (gradually deepening water) and ombrogenous peats (raised bog). In places substantial wood peats are present indicating past wet carr woodlands. The diatomite shows a high percentage of non-planktonic species in the basal levels. Higher up the strati graphic column, planktonic species increase, indicating rising water levels. The basal sequence shows a pollen record consistent with a Boreal age (pre-7500 years BP) with high frequencies of Scots Pine Pinus sylvestris and Hazel/Bog Myrtle Corylus avellana/Myrica gale. The Boreal - Atlantic transition is indicated by the rise in Alder Alnus glutinosa, and this change to a wetter climate is associated with an increase of the planktonic diatom Aulacoseira subarctica. Diatomite formation had ceased by the Sub-Boreal period (5000 years BP). Coring has shown evidence of charcoal within the diatomaceous series, suggesting phases of human occupation. . The site is also of interest in the context of the development of Irish environmental studies being one of the localities where Professor Knud Jessen undertook pioneering work on stratigraphic coring and pollen analysis during the 1930's and 1940's. The diatomite is of international importance for biological, geological, hydrological and climatological reasons. Its archaeological significance is also considerable given its contemporaneous links with sites of early human settlement. This assemblage gives a record of past water levels in the Lough Neagh basin and of climatic change since the last period of Irish ice. These remaining sites are amongst the most important deposits of freshwater diatomite in the world and are unique when considered with the associated materials particularly archaeological. | |
| Importance: | |
The diatomite is of international importance for biological, geological, hydrological and climatological reasons. Its archaeological significance is also considerable, given its contemporaneous links with sites of early human settlement. This assemblage gives a record of past environmental conditions in the Lough Neagh basin, and of climatic change since the last period of Irish ice. These remaining sites are amongst the most important deposits of freshwater diatomite in the world, and are unique when considered with the associated materials. | |
| Interpretation: | |
The deposits were mainly formed between 8000 and 4500 years Before Present (BP) and are found in low lying land around the northern shore of Lough Neagh and in the Lower Bann valley. Although diatomite was formed in water and represents the extent of a former, larger Lough Neagh, the presence in the deposits of archaeological remains shows that many of these marginal areas were only seasonally inundated. | |
| Conclusions: | |
The diatomite deposits of the Lough Neagh and Lower Bann areas have mainly been lost through commercial extraction. The remaining locations are of considerable significance to a range of research specialisms as well as their association with a lost industry. | |
| Notes: | |
Diatomite, also known locally as Bann Clay, occurs in a deposit up to 0.9 m thick in the valley of the River Bann between Toome [H 990 907] and Portglenone [C 980 039]. It was deposited in freshwater lakes during early post-glacial times and consists of the microscopic siliceous skeletons of diatoms. When dry, it is a friable, white, chemically inert powder that can be used as a filler in paint, plastic and rubber manufacture, but also as an absorbent in animal litter, an abrasive for metal polish, an insulant, and as a filtration agent in the food and pharmaceutical industries. Diatomite was extracted manually on a small scale until the late 1960s but is no longer worked. (GSNI source) See also site reports for Culnafay (Record no. 1251) and Toome (Record no. 1252) and Introduction to the diatomite deposits of Northern Ireland (Record no. 1253) | |
| Keywords | |
|---|---|
| Minerals: | Diatomite |
| Rocks: | Diatomite |
| Fossil Groups: | Diatoms |
| Access | |
|---|---|
| Approach: | No public access. Approached from Newferry Road to south |
| Restrictions: | Private land |
| Management: | |
Permitted commercial peat extraction | |
| Development: | Permitted commercial peat extraction |
| Threats: | Activities that change the host environment or physically disturb the deposits. Land drainage, deep ploughing, afforestation , development. Ongoing permitted peat extraction continues on the site with a requirement that a minimum peat depth is left in situ at the end of the sites commercial working life. |
| Record type: | ESCR report | ||
| Entered by: | I J Enlander | ||
| Last updated: | 27 Mar 2019 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Ballymacombs More, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1250. Accessed on 2026-11-05. |
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