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Earth Science Conservation Review
| Skeagh and Craigcluggan | Antrim |
| Site number: | 1189 | ||
| ESCC: | EO | ||
| Locality Type: | Crag, Crags | Status: | ESCR |
| Grid Reference: | D302062,D294081 Centroid, Not Entered | ||
| Google maps: | 54.88697,-5.97104 | ||
| County: | Antrim | Council area: | Mid & East Antrim Borough Council |
| Period: | Tertiary | ||
| Stages: | Eocene, Palaeocene | ||
| Lithostrat: | Antrim Lava Group, Upper Basalt Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
Occurrence of elongated olivine dolerite plugs of Tertiary age associated with olivine porphyritic Upper Basalts, possibly produced by coalescence of separate conduits along the line of a fissure eruption. | |
| Introduction: | |
The Craigcluggan and Skeagh plugs occur ~10km NW of Larne and are members of a group of elongated olivine dolerite plugs intruded into Upper Basalts in the east Antrim area. These and other examples have been recorded by Patterson and Swaine (1957), Walker (1959) and Lyle (1980). Lyle and Patton (1989) published details of petrography and geochemistry of the plugs and associated lavas. The field relationship of the lavas and plugs and their textural and geochemical similarities suggest the plugs acted as feeders for the lavas. See Fig. 1 from Lyle and Patton (1989) for the geological context of these and other plugs in east Antrim. | |
| Description: | |
A summary of the field relationships of the Craigcluggan plug was given by Patterson and Swaine (1957) who recorded a steeply plunging junction with the country rock, the formation of a topographic feature with an elongate plan and with a width much greater than the average dyke. (i) Petrography of the plugs and associated lavas The hill at Craigcluggan consists of olivine dolerite intruded into Upper Basalts and there is extensive outcrop of olivine- phyric basalts to the east of the summit. Southwards along the line of elongation of Craigcluggan are further outcrops of dolerite, the largest of which is Skeagh, ~2km to the SE (see Fig. 2 from Lyle & Patton, 1989). Skeagh is also olivine-phyric with outcrops of olivine-phyric basalts nearby. Walker (1959) noted that many of the more fine-grained and olivine-rich upper basalts such as are common on the higher ground of Antrim have a streaky flow-banding well shown on weathered surfaces, with bands ~1-2cm thick of slightly different grain size. The Upper Basalts around Craigcluggan and Skeagh commonly show this feature. Lyle and Patton (1989) published electron microprobe data which revealed the presence of a low-calcium pyroxene phase in addition to the Ca-rich augite phase previously recognized by optical microscopy. This 2-pyroxene assemblage confirms the essential tholeiitic nature of the Upper Basalts as indicated previously by their geochemistry (Lyle, 1980). | |
| Importance: | |
The plugs and associated lavas at Craigcluggan and Skeagh provide excellent examples of the elongate and aligned minor intrusions which occur throughout the Antrim Lava Group. The possibility of a feeder relationship existing between the plugs and lavas at these localities is important within the context of the Tertiary igneous province of NE Ireland. Given the scarcity of proven feeder relationships within the whole British/Irish Tertiary Volcanic Province the localities have a significance beyond N. Ireland. | |
| Interpretation: | |
A consensus exists among various workers that the alignment and elongation of plugs in the Lower and Upper Basalts of east Antrim are significant with respect to the origin of the lava plateau. Walker (1959) discusses the formation of elongated plug-like conduits along the line of the original fissure and considers the Craigcluggan plug with its elongated form to represent the final stage in the evolution of an elongated plug from the coalescence of smaller separate plugs. There is no doubt that Skeagh is of similar origin and the smaller occurrences of dolerite between the two main exposures are part of the same system. In addition to the field relationships and the textural similarities that exist, the geochemical data (Lyle & Patton, 1989), indicate a co-magmatic origin for the flow banded basalts and dolerites at Craigcluggan and Skeagh. There is also a clear olivine fractionation control over the differentiation of both groups. | |
| Conclusions: | |
The site provides one of the best examples in Antrim of the link between intrusive features and associated lavas, with clear field relationships and textural and geochemical similarities. | |
| Keywords | |
|---|---|
| Rocks: | Basalt, Dolerite, Olivine Basalt |
| Structures: | dyke, fissures, flow-banding, phenocrysts, plug |
| Relations: | Intrusion |
| Access | |
|---|---|
| Approach: | ~10km NW of Larne. |
| Management: | |
Both sites are relatively remote and little visited except by specialist research workers. There is no access other than by farmtrack from the adjacent Deerpark Road for Craigcluggan, and from the Glenview Road near Tory Bridge for Skeagh. Outcrop consists of relatively low crags and there is no perceived safety hazard. No maintenance is required. | |
| Uses | |
| Uses: | Both localities are used as rough pasture for sheep grazing. |
| References (4) | |||
|---|---|---|---|
| Lyle, P., 1980. A petrological and geochemical study of the Tertiary basaltic rocks of northeast Ireland. Irish Journal of Earth Sciences, vol. 2, pp.137-152. | |||
| Lyle, P. & Patton, D.J.S., 1989. The petrography and geochemistry of the Upper Basalt Formation of the Antrim Lava Group in northeast Ireland. Irish Journal of Earth Sciences, vol. 10, pp.33-41. | |||
| Patterson, E.M. & Swaine, D.J., 1957. The Tertiary dolerite plugs of northeast Ireland - a survey of their geology and geochemistry. Transactions of the Royal Society of Edinburgh: Earth Sciences, vol. 63, pp.317-331. | |||
| Walker, G.P.L., 1959. Some observations on the Antrim basalts and associated dolerite intrusions Proceedings of the Geologists Association of London, vol. 70, pp.179. | |||
| Map(s): | See 1:50,000 O.S. Sheet 9 (Ballymena, Larne). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Skeagh and Craigcluggan, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1189. Accessed on 2026-11-08. |
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