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Earth Science Conservation Review
| Lissan Water | Londonderry |
| Site number: | 1203 | ||
| ESCC: | EO | ||
| Locality Type: | Stream section | Status: | local interest |
| Grid Reference: | H815809 Approximate | ||
| Google maps: | 54.67006,-6.73678 | ||
| County: | Londonderry | Council area: | Mid Ulster District Council |
| Period: | Triassic | ||
| Stages: | Scythian | ||
| Lithostrat: | Lissan Conglomerate Formation, Sherwood Sandstone Group | ||
| Site Description | |
|---|---|
| Highlights: | |
The exposures at Lissan Water are the best exposures of the Lissan Formation, the basal Triassic conglomerate succession. | |
| Introduction: | |
These Triassic rocks occur on the north bank of the Lissan Water, Co. Londonderry, ~2.25km NE of Cookstown. These sediments were mapped during the original survey (GSI, 1880) and assigned to the Triassic Bunter Pebble Beds and resurveyed (GSNI, 1983) when the Triassic age was confirmed. | |
| Description: | |
In the north bank of the Lissan Water, 500m SW of Derrycrummy House, 6m of breccia are poorly exposed. The breccia comprises angular and subangular fragments up to 15cm across of pink granite, schist, vein-quartz and sandstone in a matrix which appears to be largely weathered granite. The sandy matrix also occurs as lenses. | |
| Importance: | |
This is the best exposure of the Lissan Formation, the basal Triassic conglomerates and breccias of the Sherwood Sandstone Group. It gives evidence of exhumation of an igneous rock mass through time thus it is of local importance and should be conserved. | |
| Interpretation: | |
The Ballyloughan Borehole section showed that these breccias occur up to 300m above the bottom of the hole and the lowest beds seen there were conglomerates with rounded pebbles and cobbles up to 15cm across. The breccias exposed in the bore core, like those described above, are essentially granitic, with only subordinate schists, while the older conglomerates contain a wide variety of rocks, including quartzite, sandstone, mudstone, porphyry, tuff and jasper as well as relatively scarce granite. It seems that exhumation of the Slieve Gallion granodiorite from its cover of metamorphic rocks and, probably Devonian and Carboniferous sediments, was progressive through early Triassic times. | |
| Conclusions: | |
The Lissan Water site is the best exposure of the Lissan Formation, the basal Triassic conglomerates and breccias and provides details of sedimentary structures that allow the environments of deposition to be determined. | |
| Notes: | |
For information on other Triassic sites see Key Site 1197 - Brown's Bay, Island Magee Key Site 1198 - Cloghfin Port, Island Magee Key Site 1199 - Collin Glen Key Site 1200 - Scrabo Hill - Triassic Key Site 1201 - Milltown Key Site 1202 - Drapersfield Quarry Key Site 1204 - Curraghlane. For general information on the Triassic System in N. Ireland see Key Site 1192 - The Triassic System in N. Ireland - Introduction. | |
| Keywords | |
|---|---|
| Rocks: | Breccia, Conglomerate |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | Width: | Height: | 6 m | ||
| Depth: | Area: | ||||
| Access | |
|---|---|
| Approach: | 2.25km NE of Cookstown. Access to the site is through fields, with carparking at the ford on Claggan Lane. |
| Management: | |
The exposure is very overgrown and could usefully be cleaned up. | |
| Map(s): | GSNI (1983) 1:50,000 Geological Sheet 27 (Cookstown) GSI (1880) One inch:One mile Geological Sheet 27 (Cookstown). | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Lissan Water, County Londonderry, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1203. Accessed on 2026-11-06. |
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