| Previous Site | Next Site |
Earth Science Conservation Review
| Torr Head - Dalradian | Antrim |
| Site number: | 34 | File Number: | D24 |
| ESCC: | EC | ||
| Locality Type: | Coastal section | Status: | ESCR |
| Grid Reference: | D234406 Centroid | ||
| Google maps: | 55.19751,-6.06208 | ||
| County: | Antrim | Council area: | Causeway Coast & Glens Borough Council |
| Period: | Precambrian | ||
| Lithostrat: | Altmore Formation, Middle Dalradian Group (Argyll), Owencam Formation, Runabay Head Formation, Torr Head Formation, Upper Dalradian Group (S Highland) | ||
| Site Description | |
|---|---|
| Highlights: | |
The Dalradian outcrop at Torr Head includes the best exposures of metamorphosed limestones in Northern Ireland. Within the 20 km thick Dalradian Supergroup of NW Britain and Ireland it has been found that considerable reliance can be placed on the correlation of distinctive, and frequently thin but widely distributed, sedimentary units. The boundary between the Argyll ('middle' Dalradian) and Southern Highland ('upper' Dalradian) groups is coincident with the top of a major limestone unit which probably correlates with the Torr Head (Limestone) Formation of NE Antrim. | |
| Introduction: | |
In Northern Ireland the outcrop of Dalradian metamorphic rocks, the oldest strata exposed in the Province, mainly occurs in two areas. Firstly, in Counties Londonderry and Tyrone, is the large expanse of the Sperrin Mountains which extend westwards into County Donegal, in the Republic of Ireland. Secondly, in the extreme north-east corner of Co. Antrim, isolated by some 50 km from the Sperrins, is a subsidiary tract of metamorphic rocks that appear from beneath the Cretaceous and Palaeocene (Tertiary) cover between Ballycastle and Cushendall. Between this area in Co. Antrim and the eastern margin of the Sperrins, basalt lavas of Palaeocene age are exposed at the surface. Geophysical surveys indicate however that in the subsurface, the younger Phanerozoic strata, in particular the basalts, conceal a NE-SW orientated ridge of basement (metamorphic) rocks that has probably existed as high ground since, at least, pre-Carboniferous times and affected the deposition and distribution of Carboniferous, Triassic, Cretaceous and Palaeocene rocks. Location: Torr Head lies in the extreme NE corner of Co. Antrim and represents one of many prominent headlands that characterise the coastal scenery of this part of Northern Ireland. Bibliographic Review: As early as 1816 Berger (p. 136-41) recognised the mica-slates, 'primitive limestone' and 'hornblende slate' of NE Antrim, and since then the structure, stratigraphy and metamorphic history of these rocks has been studied in considerable detail. Because of the geographical proximity of NE Antrim to Kintyre, in SW Scotland (a distance of only 21 km) most accounts noted the strong similarities in their stratigraphical sequences and concluded that the structure in Co. Antrim was a direct continuation of that in Kintyre and Cowall, the exposed rocks being inverted and thus forming part of the lower limb of the Cowall anticline. The publication by the Geological Survey of Northern Ireland, in the early 1960's, of One Inch to One Mile geological maps and of the geological memoir for the Ballycastle area (Wilson and Robbie, 1966), including Torr Head, identified seven lithological groups. The formal assignment of lithostratigraphical names to these various 'groups' was completed by Legg et al. (1985, Sheet 2) who recognised the presence of strata of both the Southern Highland and Argyll groups and located their boundary at the top of the Torr Head (Limestone) Formation. General Geology: In general the succession consists of psammitic and pelitic chlorite-albite schists with green beds occurring at many horizons although Wilson and Robbie (1966, p.19) described their thickest occurrences at Leckpatrick and Carnaneigh. Both of these horizons, and the intervening Loughan Bay Schists, were subsequently included by Legg et al. (1985) in the Runabay Head Formation. Without doubt the most important marker horizon in the Dalradian of NE Antrim is the Torr Head (Limestone) Formation. This has been equated with the Dungiven and Culdaff limestones in the Sperrin Mountains and Donegal respectively and with the Tayvallich and Lough Tay limestones of the Scottish Dalradian succession. As in all parts of the Dalradian outcrop in Northern Ireland the rocks have been subjected to a complex deformation history but in NE Antrim only attained a metamorphic grade in the green schist facies. Mineral assemblages in the schists are dominated by quartz, albite, muscovite and chlorite with minor biotite, garnet (mostly chloritised), hornblende and epidote. Albite schists are particularly common in the succession. Knill (in Wilson and Robbie, 1966) concluded that albite porphyroblasts grew statically in the more pelitic rocks between the D1 and D2 deformation phases, were subsequently rotated and further enlarged, under static conditions, and finally granulated. Regional metamorphic grade appears to increase from N to S in the area. Most geologists working in NE Antrim have concluded that the structure of the rocks there, is a direct continuation of that in SW Scotland at Kintyre and Cowall. The succession is thus assumed to be disposed in a major antiform downward-facing to the S and SE and aligned in a north-easterly direction. Occasional sedimentary structures demonstrating a younging direction appear to indicate that the succession is inverted and thus occupies a position on the lower limb of the nappe structure although such occurrences are uncommon. Two main deformation phases are recognised in NE Antrim. The primary phase consists of the first 3 fold phases, F1, F2 and F3 and their associated crenulation cleavages and lineations. No examples of F1 folds are known but the S1 cleavage is parallel to bedding and causes grain extension. Examples of F2 folds show them to tight to isoclinal. The development, style and orientation of F3 folds is variable, being upright in the N and flat-lying in the S. The second deformation phase occurred after the formation of the folds and associated schistosities and lineations, and is expressed as a major north-eastward plunging anticline, or broad dome, called the Altmore Anticline (Wilson and Robbie, 1966). The effect of this later deformation was to dome the early-formed, flat-lying anticlinal nappe and cause the downward-facing of the antiformal closure, to the SE. | |
| Description: | |
Approximately 2 km to the SW of the Torr Head area is part of the outcrop of the Phanerozoic cover rocks of Triassic (Sherwood Sandstone Group), Upper Cretaceous (Ulster White Limestone Formation or Chalk) and Palaeocene (early Tertiary - Lower Basalt Formation) age. These rocks are separated by an angular unconformity from the Dalradian metamorphic rocks which occur to the NE and are exposed in coastal section between Portadoon and SE of Leckpatrick. Only 4 of the 6 lithostratigraphical formations identified in the Dalradian of NE Antrim occur between Portadoon in the N and Leckpatrick in the S. These are the Owencam, Torr Head, Altmore and Runabay Head formations. Where original bedding can be recognised, strata are gently inclined to the NW and, based on sedimentary structures, appear to be inverted. Thus the stratigraphically oldest strata, the Owencam Formation (DBOF), crop out to the NW of Torr Head and are structurally underlain, to the SE, by progressively younger strata. The Owencam Formation consists primarily of psammitic quartz- schists with quartz-feldspar grits. Also included within the formation are several meta-dolerite intrusions, chlorite schists and two thin horizons of interbedded limestone and black phyllite. The best exposures and Type Locality of the Torr Head (Limestone) Formation occur at Torr Head where the limestone is closely associated with meta-dolerite 'intrusions'. Inland there are a few scattered limestone exposures mainly in the east-flowing stream located S of Torr and in streams about 500 m NW of Farranmacallan. The rock is generally a grey to black siliceous limestone, often slightly schistose with elongated quartz grains standing out on weathered surfaces. The black limestone exposed on the E side of Torr Head consists of an interlocking mosaic of coarsely crystalline lamellar calcite with minor amounts of angular quartz, chlorite and muscovite. Anhedral crystals of albite occur in the limestone exposed at Portnadig. Lenticular 'intrusive' bodies of meta-dolerite, often referred to as epidiorites are intimately associated with the limestone. In the coastal section between Escort Port and Portnadig, separate meta-igneous intrusions 10 m and 20 m thick occur in the limestone. The outcrop of the Altmore Formation occurs between the Torr Head Formation and the Altmore Fault. The rocks consist of dark and pale-coloured semi-pelitic and psammitic quartz-schists, with some biotite, and thin lenticles of dark pelitic schist. At the NE end of its outcrop the Altmore Formation is progressively attenuated by the Altmore Fault. S of the Altmore Fault is part of the outcrop of the Runabay Head Formation which consists of coarse psammitic and pelitic albite schists. It also includes the Leckpatrick Green Beds at the stratigraphic top and the Carnaneigh Green Beds at the stratigraphic base. The latter beds are typically chlorite- biotite schists with minor epidote while the former, which consist of dark green hornblende-biotite schists with some epidote and albite most closely resemble metadolerite intrusions. | |
| Conclusions: | |
The Dalradian metamorphic rocks of NE Antrim are superbly exposed at many coastal sections between Ballycastle and Cushendun. The area of Torr Head is particularly significant because of the good sections in the Torr Head (Limestone) Formation. This is considered to equate with the Tayvallich and Lough Tay limestones in Scotland and thus to provide a means of correlating these disparate sequences in northern Ireland and Scotland and to mark the position of the boundary between the Argyll and Southern Highland groups of the Dalradian Supergroup. | |
| Notes: | |
A small tourist interest is apparent. A well worn track leads to the disused RNLI Station at the summit of Torr Head, however the hand railings are in urgent need of repair. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Schist |
| Structures: | anticline, nappe |
| Access | |
|---|---|
| Approach: | Torr Head can be accessed via the coast road from Cushendun to Ballycastle. Parking facilities are available. |
| Uses | |
| Uses: | Land use practices are largely confined to pasturing of sheep. Grazing on the higher slopes is heavy, posing a possible threat to the habitat. |
| References (4) | |||
|---|---|---|---|
| Berger, J.F., 1816. On the Geological Features of the North-Eastern Counties of Ireland. With an introduction and remarks by W. Conybeare. Transactions of the Geological Society of London, vol. 1 numb. 3, pp.121-222. | |||
| Legg, I.C., Pyne, J.F., Nolan, C., McArdle, P., Flegg, A.M. & O'Connor, P.J., 1985. Mineral localities in the Dalradian and associated igneous rocks of County Donegal, Republic of Ireland, and of Northern Ireland. Reports of the Geological Survey of Ireland, numb. 85/3. | |||
| Wilson, H.E., 1972. Regional Geology of Northern Ireland. HMSO, Belfast. | |||
| Wilson, H.E. & Robbie, J.A., 1966. Geology of the country around Ballycastle. Memoirs of the Geological Survey Northern Ireland. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 5 (Ballycastle). | ||
| Record type: | Environment Serv. GIS, ESCR report | ||
| Entered by: | Crowther, P.R. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Torr Head - Dalradian, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=34. Accessed on 2026-11-07. |
| Previous Site | Next Site |