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Earth Science Conservation Review
| Carrs Glen - site of local interest | Antrim |
| Site number: | 709 | ||
| Locality Type: | Stream section, Valley | Status: | local interest |
| Grid Reference: | J314787,J314792 End(s) of linear site | ||
| Google maps: | 54.63978,-5.96478 | ||
| County: | Antrim | Council area: | Belfast City Council |
| Period: | Tertiary, Cretaceous, Jurassic, Triassic | ||
| Stages: | Jurassic Undifferentiated, Palaeogene, Upper Cretaceous, Triassic Undifferentiated | ||
| Lithostrat: | Collin Glen Formation, Creggan Chalk Member, Hibernian Greensands Formation, Island Magee Silts Member, Mercia Mudstone Group, Penarth Group, Ulster White Limestone Formation, Waterloo Mudstone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
This section along a steep valley at Carrs Glen exposes a section through the Mercia Mudstone Group (Triassic), the Waterloo Mudstone Formation (Jurassic), the Hibernian Greensand Formation (Upper Cretaceous) and the Ulster White Limestone Formation (Upper Cretaceous). In addition, the section is cut by at least three basaltic dykes (Palaeogene) and one sill and also exposes a distinctive red boulder clay drift deposit. | |
| Description: | |
The site is located 800m north-northeast of the Horseshoe Bend on the Upper Crumlin Road, The exposure in the steep valley of Carrs Glen, between Cave Hill and Squire’s Hill, is sufficiently good for a section to be constructed through the Mesozoic rocks of the area. Horizontally bedded red marls with green bands up to 10cm thick and abundant green reduction spots and streaks, pass upwards into uniform marls of the Collin Glen Formation of the Mercia Mudstone Group (Triassic). These marls, overlain by shales of the Penarth Group (Upper Triassic), are baked by an overlying dolerite sill to a hard blocky mudstone. The sill is overlain by a small exposure of the Waterloo Mudstone Formation (Lower Jurassic) [J3140 7919]. Here, a hard, shelly limestone 15cm thick is overlain by medium grey mudstones which contain some brachiopod and ribbed ammonite remains, possibly of Caloceras type. The beds have a dip of 29° to the west and they are clearly affected by landslip movements. Carrs Glen provides one of the best sections through the Hibernian Greensand Formation (Upper Cretaceous) in south County Antrim. Here, calcareous buff coloured siltstones alternate with soft greyish silty marls and are part of the Island Magee Siltstones Member. Intra-Cretaceous erosion has removed the succeeding Collinwell Sands Member so that the overlying Ulster White Limestone Formation rests directly on the Island Magee Siltstones Member. Formerly, Carrs Glen provided one of the best natural sections through the Creggan Chalk Member though this is now largely obscured. The entire Mesozoic section at Carrs Glen is cut by three Palaeogene dykes one of which causes a waterfall high in the glen 1.1km north-northeast of the Horseshoe Bend. Finally the distinctive red boulder clay that was developed on top of the Triassic marls and mudstones has been cut into by the stream at Carrs Glen. | |
| Importance: | |
The site has some scientific value as it exposes one of the best sections through the Mesozoic rocks of the Belfast area. The site is also of educational value as it provides a section through varied sedimentary and igneous rocks that demonstrate the geological history of this area from the mid-Triassic times to the present. As such it would provide an ideal opportunity to learn about changing environmental conditions and, through the presence of numerous dykes, would provide a good place to demonstrate the cross-cutting relationships between sedimentary and intrusive igneous rocks in this area. The site also displays evidence of thermal metamorphism and helps demonstrate the discordant and concordant nature of dykes and sills respectively. For third level students, it would also provide a good section at which to learn the techniques of graphic logging. | |
| Notes: | |
There are three raths (early Christian era dwelling places) along the glen, which lies in a scenic location between Cave Hill and Squire’s Hill. While none of the raths lie within the proposed SLNCI, they lie along a walking route that passes through the proposed SLNCI and within the boundary of the Cave Hill Country Park. Carrs Glen lies within the boundary of the Cave Hill Country Park and is featured on several walking routes through the Park that are promoted by Belfast City Council. | |
| Keywords | |
|---|---|
| Rocks: | Basalt, Dolerite, Limestone, Marl, Mudstone, Sandstone, Shale, Siltstone |
| Fossil Groups: | Ammonite, Brachiopod |
| Access | |
|---|---|
| Approach: | This site is located 800m northeast of the Horseshoe Bend on the Upper Crumlin Road, Belfast. |
| Uses | |
| Educ. Level: | The site is of considerable educational value. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Carrs Glen - site of local interest, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=709. Accessed on 2026-11-06. |
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