| Previous Site | Next Site |
Earth Science Conservation Review
| Crows Glen - site of local interest | Antrim |
| Site number: | 720 | ||
| Locality Type: | Stream section | Status: | local interest |
| Grid Reference: | J294768,J288769 End(s) of linear site | ||
| Google maps: | 54.62324,-5.99658 | ||
| County: | Antrim | Council area: | Belfast City Council |
| Period: | Tertiary, Cretaceous, Triassic | ||
| Stages: | Middle Triassic, Palaeocene, Upper Cretaceous | ||
| Lithostrat: | Belfast Marls Member, Collin Glen Formation, Collinwell Sands Member, Hibernian Greensands Formation, Island Magee Silts Member, Lower Basalt Formation, Mercia Mudstone Group, Port Calliagh Chalk Member, Ulster White Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
This section along the banks and stream bed of the Forth River at Crows Glen exposes sections through the Mercia Mudstone Group (Triassic), the Hibernian Greensand Formation and Ulster White Limestone Formation (Upper Cretaceous) and the Lower Basalt Formation (Lower Palaeogene). In addition the section is cut by up to eight basaltic dykes (Palaeogene) and contains exposures of a distinctive red boulder clay glacial deposit. | |
| Description: | |
The Collin Glen Formation of the Mercia Mudstone Group (Triassic) is exposed in the bed of the Forth River at Crows Glen [J294 768] where it is cut by eight fine-grained basaltic dykes (Palaeogene). The rocks comprise red and red/green variegated marls and mudstones. In the nearby abandoned brick pit [J291 760] up to 20m of these beds are exposed. At Crows Glen, a small isolated exposure of the Hibernian Greensand Formation (Upper Cretaceous), can be seen 41m upstream (west) of the highest exposure of the Mercia Mudstone Group. Here the Greensand is composed almost entirely of grains of glauconite. These beds belong to the lowest Belfast Marls Member. Some 27m upstream from this point, beneath a small waterfall, about 3m of pale brown and grey fine-grained sandstone and marls are visible. The rocks are nodular in places and carry fossil Serpula and Pectinid fragments. Belonging to the Island Magee Siltstones Member, these rocks are overlain by 1.2m of very coarse and gritty chalky glauconitic sandstones of the Collinwell Sands Member. These sandstones contain many reworked and phosphatised sandstone pebbles from the underlying Island Magee Siltstones Member indicating a period of erosion prior to the onset of Collinwell Sands Member sedimentation. Thallasinoides burrows up to 60cm deep are common in both members. The glauconitic sandstones of the Collinwell Sands Member lie directly below the Port Calliagh Chalk Member of the Ulster White Limestone Formation. Above this, four flows of the Lower Basalt Formation (Palaeocene) are exposed [J288 769]. Flow 1 (at the base) is a 10m thick flow of amygdaloidal basalt. Flow 2 is over 15m thick and is composed of massive medium-grained basalt. Flow 3 consists of 3.6m of slaggy vesicular basalt followed by 7m of massive dense blue basalt and 2m of slaggy vesicular basalt. Flow 4 consists of over 3m of coarse olivine basalt. Finally a distinctive red boulder clay, which developed on the Triassic marls and mudstones during the last Ice Age, can be seen. | |
| Importance: | |
The site has some scientific value as it exposes one of the best sections through the Mesozoic and Palaeogene rocks of the Belfast area. The site is 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 time 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. For third level students, it would also provide a good section at which to learn the techniques of graphic logging. | |
| Keywords | |
|---|---|
| Minerals: | Glauconite |
| Rocks: | Basalt, Glauconitic sandstone, Greensand, Limestone, Marl, Mudstone, Olivine Basalt, Sandstone |
| Fossil Groups: | Trace fossils |
| Structures: | amygdales, vesicles |
| Access | |
|---|---|
| Approach: | This site is a stream exposure above northwest Belfast. |
| Uses | |
| Educ. Level: | The site is of educational value to second and third level students. |
| Record type: | SLNCI Report | ||
| Entered by: | E M Porter | ||
| Last updated: | 09/10/03 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Crows Glen - site of local interest, County Antrim, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=720. Accessed on 2026-11-06. |
| Previous Site | Next Site |