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Earth Science Conservation Review
| Ballymiscaw - site of local interest | Down |
| Site number: | 703 | ||
| Locality Type: | Road cutting, Stream section | Status: | local interest |
| Grid Reference: | J402754 Centroid | ||
| Google maps: | 54.60779,-5.83017 | ||
| County: | Down | Council area: | Belfast City Council |
| Period: | Ordovician | ||
| Stages: | Upper Ordovician | ||
| Lithostrat: | Gilnahirk Group | ||
| Site Description | |
|---|---|
| Highlights: | |
A stream section and adjacent road cutting at Ballymiscaw expose outcrops of the Upper Ordovician Gilnahirk Group. Although the rocks at this locality are palaeontologically barren, these strongly tectonised turbidites are similar to strata which occur along strike to the northeast and which only contain Ordovician graptolites. The section at Ballymiscaw is one of the few inland exposures of the Gilnahirk Group. | |
| Description: | |
The stream section and adjacent road cutting at Ballymiscaw exposes a section through the greywacke turbidites of the Gilnahirk Group. The Gilnahirk Group comprises the sequence of greywacke turbidites that lies northwest of the Castlereagh Fault. These rocks are similar in lithology and degree of deformation to the sequence assigned to the Ordovician northwest of the Orlock Bridge Fault further along strike to the northeast. Compared to rocks of the Strangford Group (Silurian), most of the turbidite units are thinner (0.15-0.5m thick), grading is less common and bottom structures less prominent. In places (e.g. J402 756), there are intercalations of coarse-grained sandstone beds up to 0.4m thick containing pebbles of vein quartz, pink granite and dark grey mudstone. These coarse-grained to pebbly beds are tentatively correlated with the pebbly Luke’s Point Member in the Ballymacormick Block on the north County Down coast. Argillaceous interbeds include blue-black slaty mudstones, grey siltstones and pale yellowish micaceous bands which probably represent volcanic ash-falls. The arenaceous turbidites commonly possess a fabric of domainal character which consists of platy micaceous minerals roughly aligned and wrapping lenses of only weakly aligned quartz and other rock fragments. Overall there appears to be a higher state of deformation in the Gilnahirk Group compared to the younger Silurian rocks in County Down and more of the matrix is very finely crystalline, perhaps as a result of the increased deformation and possibly increased metamorphic grade. | |
| Importance: | |
The site is of scientific significance because it provides the best exposure of the Gilnahirk Group within the Belfast area. The section displays some good sedimentary structures such as interbeds, intercalations, bottom structures and grading although the latter two are less common and prominent. | |
| Keywords | |
|---|---|
| Rocks: | Greywacke, Sandstone, Turbidite |
| Access | |
|---|---|
| Approach: | Stream section and adjacent road cutting just north of Parliament Buildings, Stormont. |
| Uses | |
| Educ. Level: | This site is of limited educational value. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Ballymiscaw - site of local interest, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=703. Accessed on 2026-11-05. |
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