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Earth Science Conservation Review
| Slieve Croob | Down |
| Site number: | 569 | ||
| ESCC: | EO | ||
| Locality Type: | Inland exposure | Status: | ASSI |
| Grid Reference: | J31854535 Centroid | ||
| Google maps: | 54.33982,-5.97349 | ||
| County: | Down | Council area: | Newry, Mourne & Down District Council |
| Period: | Devonian, Silurian | ||
| Stages: | Lower Devonian | ||
| Lithostrat: | Newry Igneous Complex | ||
| Site Description | |
|---|---|
| Highlights: | |
In the area around the summit of Slieve Croob, numerous natural exposures of Silurian country rock have been subjected to contact metamorphism as a result of proximity to the Newry Igneous Complex. The country rocks affected were originally sedimentary greywackes and shales and have been transformed into hornfels and fused (or mobilized) sediment. | |
| Introduction: | |
The site is located at the northern margin of the late-Caledonian Newry Igneous Complex along part of its contact with Silurian country rock The site includes an area around the summit of Slieve Croob to the west and east of a communications facility. The first edition of the Banbridge (Sheet 48) one-inch to the mile geological map (Geological Survey of Ireland, 1871) indicates a zone of contact metamorphism in the area around the summit of Slieve Croob. There is a steep contact, dipping at up to 80°, between indurated country rock and granite. The zone of contact metamorphism is considerable, and is up to 1km wide. At Slieve Croob, the contact strikes north-northwest and is sub-parallel to bedding in the surrounding Silurian sediments. Bedding dip is variable but generally steep (45° to 80°). The predominance of two dip directions (to the northwest and the southeast) indicates the presence of folding. In the accompanying geological memoir (Egan, 1872) the nature of the metamorphism is discussed. Alteration of original sedimentary rocks to 'mica schist' is remarked upon and taken as clear evidence that the granite formed as a result of melting of the country rock. Reynolds (1934) described the nature of metamorphosed rocks in the contact zone in the vicinity of Slieve Croob; her map and descriptions indicate areas of hornfels and fused sediments which were later referred to as mobilized sediment (Reynolds 1936). | |
| Description: | |
The site covers an area around the summit of Slieve Croob to the west and east of the communications facility. Metamorphosed country rock is exposed in a series of crags west of the communications facility. To the east and southeast there are further exposures of metamorphosed country rock and granodiorite belonging to the northeast pluton. The approximate position of the contact can be determined at this site. The metamorphosed country rocks at this site are biotite-and cordierite hornfels and fused (mobilized) sediments. Some of the best examples of these rocks are observed to the west of Slieve Croob summit. The rocks are generally fine-grained and massive, weathering in an irregular manner giving rise to a furrowed appearance (Reynolds, 1934). Textures vary in detail from those resembling fine-grained biotite granite to what is essentially a hornfels rich in biotite. Original bedding is not obvious close to the contact but may be determinable elsewhere. These rocks contain cordierite; where this mineral has been weathered out the rock takes on a pitted appearance. A stretched and deformed lamprophyre dyke is located east of the communications facility within metamorphosed country rock. Such dykes are particularly associated with the northeastern end of the Newry Igneous Complex. This intrusion most likely belongs to the earlier of two series of lamprophyre dykes recognized by Reynolds (1931). | |
| Importance: | |
The Slieve Croob site is of national importance offering access to high quality outcrop of hornfels and fused (mobilized) sediments that together comprise the metamorphosed country rock. | |
| Interpretation: | |
At this site, heat generated from the northeast pluton of the Newry Igneous Complex (Meighan & Neeson, 1979) has contact metamorphosed sedimentary greywackes and shales forming a rock type known as hornfels. Metamorphism has occurred in a zone as much as 1km wide around the granodiorite. Close to the contact the sediments have been mobilized, intruded by melt and recrystallised giving rise to the fused (mobilized) sediment. Reynolds (1934) stated that the metamorphic rocks in the vicinity of Slieve Croob represent part of the roof of the northeast pluton. The lamprophyre dyke observed on Slieve Croob was most likely sheared and deformed by a regional deformation (Cameron, 1981) that also lead to some of the deformation seen within the granodiorites. | |
| Conclusions: | |
The Slieve Croob site is of national importance offering access to high quality outcrop of hornfels and fused (mobilized) sediments that together comprise the metamorphosed Silurian country rock. | |
| Notes: | |
For information and references on other sites within the Newry Igneous Complex see the following sites: Key Site 568 - Ardglass, Co Down Key Site 570 - Shannaghan Hill Key Site 571 - Ballymagreehan Quarry Key Site 572 - Rathfriland Key Site 573 - Gransha Key Site 574 - Aughnagon Quarry Key Site 575 - Goraghwood Quarry Key Site 576 - Newry By-pass Key Site 577 - Cam Lough Quarry Key Site 578 - Kearney Point Key Site 579 - Ballyhalbert Pier For general information and references on the Caledonian Igneous Complexes of N. Ireland, and for directions to other regional sites, see the following site: Key Site 595 - Introduction to the Caledonian Igneous Complexes of N. Ireland | |
| Keywords | |
|---|---|
| Minerals: | Biotite, Cordierite |
| Rocks: | Greywacke, Hornfels, Shale, Lamprophyre |
| Structures: | bedding, Caledonian, mobilisation |
| Relations: | Contact metamorphism |
| Access | |
|---|---|
| Management: | |
Access to the site is via a private road that services the communications facility. Permission will be needed to gain vehicular access to this road. There is however a pedestrian right of way. Vehicles can be left in a car park at [J30054525]; the main exposures are a 2km walk from this point. The site occupies an area of fenced mountainous farmland currently used for rough grazing of sheep. No exposure of interest occurs within the confines of the communications facility. There is an abundance of outcrop over an extensive area around Slieve Croob, there is therefore no need to restrict hammering or sampling at this site. The rocks of the Newry Igneous Complex are considered to be prospective for a number of minerals including base metals and gold. Licensed mineral exploration and production has previously been carried out in Counties Armagh and Down. The area which includes this site is likely to attract further exploration activity. | |
| Uses | |
| Uses: | Farmland; rough grazing for sheep. |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1871. 1:63,360 Geological Sheet 48 (Banbridge). (Dublin, Ordnance Survey for Geological Survey of Ireland). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 03 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Slieve Croob, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=569. Accessed on 2026-11-08. |
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