Earth Science Conservation Review
| Cashel Rock - Caledonide Igneous Complex | Tyrone |
| Site Type: | Crags |
| Site Status: | ASSI |
| Grid Reference: | H600808 |
| Google maps: | 54.67218,-7.06997 |
| Rocks | |
|---|---|
| Rock Age: | Ordovician |
| Rock Name: | Tyrone Volcanic Group, Laght Hill Tonalite |
| Rock Type: | Rhyolite, Tonalite |
| Interest | |
| Other interest: | Caledonian, lopolith |
Introduction:
Cashel Rock is a prominent hill in otherwise featureless country directly north of the main Omagh to Cookstown Road (A505). Access to the site is by walking northwards across moorland from Leaghan [2600 3810]. The tonalite at Cashel Rock forms part of the more extensive intrusion referred to as the Laght Hill Tonalite.
On Portlock's geological map of the area, (1843) the tonalite at Cashel Rock was not distinguished from the surrounding rocks which were described collectively as "metamorphic rocks of hornblendic type". However, in the accompanying text, "syenitic" rocks were noted at several localities including Cashel and nearby Formil. These rocks were clearly distinguishable from the green schists of the surrounding area, and were described as consisting primarily of hornblende, quartz and feldspar. Portlock remarked upon the "confused and imperfect crystallization" of this lithology but stopped short of acknowledging its origin as an intrusive granitoid.
On the first edition of the one-inch to the mile geological map (Sheet 26, (Draperstown)) (Geological Survey of Ireland, 1882) the rocks at Cashel Rock were not distinguished from the surrounding "Chloritic, Talcose & Micaceous Schists" and were loosely classified as being of "Lower Silurian age". In the accompanying memoir, Nolan (1884) described "Cashel Hill" as being composed mostly of "very peculiar rocks which show little schistose structure, and are usually massive having in many places the appearance of igneous rocks".
Hartley (1933) produced the first detailed lithological map and description of the central Tyrone Ordovician volcanic plutonic terrane. He classified the rocks at Cashel rock as "hybrid rocks" and aplogranite.
On the second (1:50,000 scale) edition of Sheet 26 (Draperstown) (Geological Survey of Northern Ireland, 1995), Cashel Rock was classified as tonalite and felsite and mapped as one of a series of a closely related elongated intrusions which includes the Laght Hill Tonalite and Crockyneill Summit.
Rocks at Cashel Rock form part of the Tyrone-Girvan Sub-Terrane of the Midland Valley Terrane (Bluck, 1992) and are broadly equivalent in age to the ophiolitic-volcanic associations at Girvan-Ballintrae (Scotland) and Clew Bay (County Mayo) (Hutton et al., 1985).
On Portlock's geological map of the area, (1843) the tonalite at Cashel Rock was not distinguished from the surrounding rocks which were described collectively as "metamorphic rocks of hornblendic type". However, in the accompanying text, "syenitic" rocks were noted at several localities including Cashel and nearby Formil. These rocks were clearly distinguishable from the green schists of the surrounding area, and were described as consisting primarily of hornblende, quartz and feldspar. Portlock remarked upon the "confused and imperfect crystallization" of this lithology but stopped short of acknowledging its origin as an intrusive granitoid.
On the first edition of the one-inch to the mile geological map (Sheet 26, (Draperstown)) (Geological Survey of Ireland, 1882) the rocks at Cashel Rock were not distinguished from the surrounding "Chloritic, Talcose & Micaceous Schists" and were loosely classified as being of "Lower Silurian age". In the accompanying memoir, Nolan (1884) described "Cashel Hill" as being composed mostly of "very peculiar rocks which show little schistose structure, and are usually massive having in many places the appearance of igneous rocks".
Hartley (1933) produced the first detailed lithological map and description of the central Tyrone Ordovician volcanic plutonic terrane. He classified the rocks at Cashel rock as "hybrid rocks" and aplogranite.
On the second (1:50,000 scale) edition of Sheet 26 (Draperstown) (Geological Survey of Northern Ireland, 1995), Cashel Rock was classified as tonalite and felsite and mapped as one of a series of a closely related elongated intrusions which includes the Laght Hill Tonalite and Crockyneill Summit.
Rocks at Cashel Rock form part of the Tyrone-Girvan Sub-Terrane of the Midland Valley Terrane (Bluck, 1992) and are broadly equivalent in age to the ophiolitic-volcanic associations at Girvan-Ballintrae (Scotland) and Clew Bay (County Mayo) (Hutton et al., 1985).
| Enlander, I., Dempster, M. & Doughty, P., 2024. Cashel Rock - Caledonide Igneous Complex, County Tyrone, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=589. Accessed on 2024-12-26 |
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