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Earth Science Conservation Review
| Cregagh Glen - site of local interest | Down |
| Site number: | 717 | ||
| Locality Type: | Inland exposure | Status: | local interest |
| Grid Reference: | J365709 End(s) of linear site | ||
| Google maps: | 54.56841,-5.88948 | ||
| County: | Down | Council area: | Belfast City Council |
| Period: | Ordovician | ||
| Stages: | Upper Ordovician | ||
| Lithostrat: | Gilnahirk Group | ||
| Site Description | |
|---|---|
| Highlights: | |
There is an extensive section of rocks visible in Cregagh Glen with exposures of almost 244m of strata belonging to the Gilnahirk Group (Upper Ordovician). Alternations of arenaceous and argillaceous beds of a predominantly grey colour but with purple, lilac and greenish coloration in places can be seen. | |
| Description: | |
An extensive section through rocks of the Gilnahirk Group (Upper Ordovician) is visible in Cregagh Glen where almost 244m of strata are exposed. Entering the glen from the Knockbreda Road, the first exposure, 174m south of the road, is 5.5m of purple greywackes, slightly shaly in places and dipping NNW at 80°. South of a gap in the section of about 0.75m, 0.6m of faulted shales are visible, then 15m of greywackes, thick-bedded towards the bottom and flaggy and shaly in the top 4.6m. The dip of these rocks varies from NNW at 70° to vertical. Southwards for about 73m, greywackes and shales alternate in almost equal proportions. At 375m south of the Knockbreda Road, hardened shales are exposed. These rocks are siliceous and slightly gritty in places and at least 19m thick. Despite a prolonged search, no fossils have been found. The next important group of beds consists of thick-bedded fine- to medium-grained greywackes with shaly partings, totalling 36m in thickness, which form the waterfall 410m south of the road. Another thick group of beds, 20m of hardened shales, is visible 520m upstream from the road. These shales, which are bluish grey and purple with some purple and green mottling, are twisted in places and are separated by a gap in exposure of 1.2m from 4m of closely similar shales. These in turn are separated by 1.5m of bluish grey and purple greywackes from another 1.2m of grey and purple shales. For another 183m southwards there are several exposures of greywackes and shales, mainly purple in colour and dipping 10° to 20° either side of vertical. | |
| Importance: | |
This area is of some scientific value as it is provides a well exposed section through the Upper Ordovician Gilnahirk Group. The section is of some educational value as it provides an easily accessible and extensive section through the Ordovician rocks of the area. It is also of value for third level students as it allows correlation with similar stream sections further west and some potential for demonstrating graphic logging techniques. | |
| Notes: | |
The upper (southernmost) section of the glen is a property of the National Trust. The glen is easily accessible and forms an established walking route in the area. The waymarked Ulster Way passes along the top (south) of the glen. | |
| Keywords | |
|---|---|
| Rocks: | Greywacke, Shale |
| Access | |
|---|---|
| Approach: | The site is a 700m section south off the Knockbreda Road. |
| Uses | |
| Educ. Level: | The site is of some educational value. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Cregagh Glen - site of local interest, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=717. Accessed on 2026-11-06. |
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