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Earth Science Conservation Review
| Derryvree | Fermanagh |
| Site number: | 4 | File Number: | H33 |
| ESCC: | ED | ||
| Locality Type: | Lost, Roadside section | Status: | ESCR |
| Grid Reference: | H361390 Approximate | ||
| Google maps: | 54.29897,-7.44551 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Quaternary | ||
| Stages: | Pleistocene | ||
| Site Description | |
|---|---|
| Highlights: | |
The Derryvree site contains in situ freshwater organic horizons between two regional till bodies (Colhoun et al., 1972; McCabe, 1987). This is the only known site in Ireland where a finite 14C date has been obtained from organic detritus below a Late Midlandian till. The organic silts contain a flora and fauna of cold northern aspect and are dated to 30,500 ± 1170 B.P. (Birm. 166). The stratigraphic succession demonstrates an Early Midlandian glaciation, a phase of open tundra vegetation possibly with a periglacial climatic regime during the late Middle Midlandian (~30ka B.P.) and a Late Midlandian glaciation. The stratigraphy provides critical evidence for climatic oscillations during the Midlandian Cold Stage. | |
| Introduction: | |
Derryvree is situated in the south-western continuation of the Clogher Valley which is floored by Lower Carboniferous sandstones, shales and limestones. The site occurs at 55m to 65m O.D. on the main road between Maguiresbridge and Brookeborough, 3km northeast of Maguiresbridge. The site was exposed during road straightening in 1969 when a major cut revealed the stratigraphy of the Derryvree drumlin. The latter is heart-shaped comprising a basal platform of lower till overlain by an elongated (NE/SW), drumlin-forming till ridge. The sedimentary succession (lower till, organic silts, upper till) was described by Colhoun et al., (1972). The main conclusions reached were that lowland ice sheets developed during the Early and Late Midlandian and that extensive lowland ice sheets were absent in the Middle Midlandian. It is emphasised that the Derryvree organic series represents a phase of open Tundra conditions rather than a pollen- or beetle- based interstadial (McCabe, 1987). | |
| Description: | |
The cut through the drumlin trends from 50-230 deg. over a distance of 410m and is 5m to 8m in depth. Three main stratigraphical units were exposed: Derryvree Till: This till occurs at the base of the section and probably rests on black shales. It is massive, overcompacted with dispersed cobbles and pebbles which constitute 12% of the unit. The homogenised matrix (88%) is mainly fine sand and silt. Fabrics of pebble A-axes show strong preferred orientations between 295 and 340 deg. T. The coarse fraction consists mainly of Carboniferous limestone/sandstones (47%) and clasts derived from the O.R.S. (32%) to the north. Up to 11% of clasts have been transported 5km to 6km from the Silurian inlier at Lisbellaw to the north. Pockets of poorly-sorted, pebbly gravel overlie the till in the central part of the section. Derryvree Silts: Organic detrital silts directly overlie the unweathered top of the Derryvree Till. The silts are up to 3m thick and occur within two small basins in the undulating surface of the lower till unit. Along the main section the lamination of the silts parallels basinal margins, like a bedded drape over about 120m. In sections normal to the main exposure the upper part of the silts has been contorted and sheared into the overlying till. The dark-grey silts and fine sands are parallel-laminated and contain thin horizons (5mm to 15mm) of moss detritus. In all samples the pollen content was low and in a poor condition. A percentage pollen count (probably primary) showed Gramineae 76, Cyperaceae 13, Salix 4 (3 grains of herbacea-type), Betula 2, and some aquatic remains (eg. Potamogeton, Pediastrum and Bolryococcus. Long distance or derived pollen included Alnus, Betula, Corylus, Pinus, Picea and Ulmus in very low amounts. The moss remains were the most numerous fossils and formed a biological matrix which was in situ or almost so. Grasses, sedges and mosses were dominant in a landscape which supported a varied vegetation with a tundra aspect. The beetle evidence conjures up a picture of a sandy-bottomed pool, rich in plant detritus and surrounded dominantly by moss and associated plants, forming a treeless, muskeg environment. There also must have been higher and drier ground nearby which was not closely vegetated, to explain the beetles associated with Salix bushes and those which are markedly heliophilous. The floral and faunal assemblages are complimentary and indicate an arctic type climate. Of the 28 beetles identified, eight are now north-British or montane and another six occur only in more northern latitudes. The absence of weevils suggest an extremely harsh climatic regime. A sample of moss-rich detrital mud provided a radiocarbon age of 30,500 ± 1170 years B.P. (Birm. 166). This is the first 14C date in Ireland on organic deposits that are certainly overlain by thick, Late Midlandian till. Maguiresbridge Till: The upper, streamlined part of the drumlin is composed of a black-brown compact till which overlies the organic silts. It varies from 1m to 6m in thickness and shows a sharp contact with the underlying Derryvree Till along the flanks of the drumlin. Thrust structures associated with deposition of the Maguiresbridge Till penetrate the lower till in the northeastern part of the section. The clast composition of this till is similar to that of the Derryvree Till but it contains a greater percentage (60%) of Carboniferous detritus. Clast fabrics were variable (31° to 349°T). | |
| Importance: | |
The Derryvree site is important at local and national levels for similar reasons. These include - 1: It is the only site in Ireland where organic deposits, below thick Late Midlandian till, have been dated by 14C positively (30,500 ± 1170, Birm. 166). 2: The organic series contain a scientifically interesting flora and fauna. 3: The Derryvree Till represents an Early Midlanidan glaciation. Tills from this stratigraphic level are known only from three sites in the north of Ireland. 4: Only three sites in Ireland show this tripartite stratigraphic sequence. 5: The site demonstrates environmental conditions towards the end of the Middle Midlandian around 30.5ka B.P. 6: The floral assemblages are of outstanding phytogeographical importance in revealing for the first time something of the Irish flora of the last cold period but prior to the advance of the last ice sheet. | |
| Interpretation: | |
The homogenised aspect of the lower till together with strong fabrics, massive structure, presence of glacially-facetted clasts and absence of any stratification or flow structures suggest that it was deposited by basal ice processes. Borehole records to the north at Hollymount suggest it is part of a regional till sheet in this part of eastern Fermanagh (McCabe et al., 1978). Local erratic carriage and the occasional presence of igneous erratics indicate a southerly ice flow from centres of ice dispersion in County Tyrone (McCabe, 1987). The restricted beds of overlying poorly-sorted gravels probably represent washing of the till surface, though their precise significance is unclear. Regional stratigraphic comparisons indicate that the Derryvree Till is Early Midlandian in age. Available stratigraphic, biostratigraphic and erratic evidence from Aghnadarragh, Hollymount and Derryvree suggest this till unit represents a major expansion of lowland based ice masses in the north of Ireland during the Early Midlandian. A major hiatus or non-sequence is present between the Derryvree Till and the overlying fossiliferous Derryvree Silts. The in situ organic silts contain a flora and fauna of cold northern aspect which was treeless and muskeg in character with a rich moss flora. The Derryvree Silts provide unequivocal evidence of environmental conditions towards the end of the Middle Midlandian around 30ka B.P. They are regarded as a herb-biozone on the basis of their fossil content (Bowen et al., 1986). The stratigraphic evidence from the site suggests that no large ice sheets existed in lowland Ulster during the later part of the Middle Midlandian (McCabe et al., 1978). The overlying Maguiresbridge Till is subglacial in origin because it contains well-defined shear zones, shows a strong deformational contact with the lower till and forms a streamlined drape around older sediments. It is related to ice flow from the north and is part of the extensive drumlin fields of lowland Ulster. Stratigraphically this site was selected as the type site for drumlin-forming till in the north of Ireland (Mitchell et al., 1973). | |
| Conclusions: | |
The tripartite sequence represents critical parts of the last cold stage, and provides an insight into changing environmental conditions and climatic inference during that time. The Derryvree Till documents growth of a lowland ice sheet probably during the Early Midlandian. An hiatus occurs between this event and the organic rich Derryvree Silts which indicate that a herb-biozone and tundra climate occurred during the latter part of the Middle Midlandian. The upper till is drumlin forming (Maguiresbridge Till) and is late Midlandian in age. The Derryvree site is one of the most important Quaternary sites in Ireland from both stratigraphic and palaeobotanical viewpoints. | |
| Notes: | |
The original exposures suggest that the organic deposits are preserved as small basins in the lower till and are probably not laterally extensive. The road cut is now graded and stable. It is impossible to see any stratigraphic elements. | |
| Keywords | |
|---|---|
| Rocks: | Till |
| Fossil Groups: | Insects etc, Plant |
| Structures: | herb biozone |
| Relations: | Glacial deposit |
| Geomorph: | drumlin, subglacial, till |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | 410 m | Width: | Height: | ||
| Depth: | 5-8 m | Area: | |||
| Access | |
|---|---|
| Approach: | Derryvree is situated in the south-western continuation of the Clogher Valley. The site occurs on the main road between Maguiresbridge and Brookeborough, 3km northeast of Maguiresbridge. |
| Management: | |
At present it is difficult to envisage that the site will be reopened as the main road will not be widened again. Possibly if the slope began to slump, especially on the northern side of the cut, fresh samples could be recovered and re-examined for comparative purposes. It is important to note that the site was only originally open for a few days and very few samples were recovered. It is suggested that any future engineering work on the road cut should be notifiable and a fresh investigation of the deposit undertaken. | |
| Uses | |
| Uses: | The original site is located in a road cutting. Adjoining fields are used for grazing and silage. |
| References (5) | |||
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| Bowen, D.Q., Rose, J., McCabe, A.M. & Sutherland, D.G., 1986. Correlation of Quaternary glaciations in England, Ireland, Scotland and Wales. Quaternary Science Reviews, vol. 5, pp.299-340. | |||
| Colhoun, E.A., Dickson, J.H., McCabe, A.M. & Shotton, F.W., 1972. A Middle Midlandian freshwater series at Derryvree, Maguiresbridge, Co. Fermanagh, Northern Ireland. Proceedings of the Royal Society, London, vol. B180, pp.273-292. | |||
| McCabe, A.M., 1987. Quaternary deposits and glacial stratigraphy in Ireland. Quaternary Science Reviews, vol. 6, pp.259-299. | |||
| McCabe, A.M., Mitchell, G.F. & Shotton, F.W., 1978. An inter-till freshwater deposit at Hollymount, Maguiresbridge, Co. Fermanagh. Proceedings of the Royal Irish Academy, vol. 78, pp.77-89. | |||
| Mitchell, G.F., Penny, L.F., Shotton, F.W. & West, R.G., 1973. A correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, vol. 4, pp.1-99. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 27 (Upper Lough Erne). | ||
| Record type: | Environment Serv. GIS, ESCR report | ||
| Entered by: | Crowther, P.R. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Derryvree, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=4. Accessed on 2026-11-06. |
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