|Tievebulliagh, Co. Antrim, from the north-east; the old track below the hill ends at the gravel pit in the main scree.|
|Site Type: ||Crag, Crags|
|Site Status: ||ASSI|
|District: ||Moyle District Council|
|Grid Reference: ||D194268|
|Rock Age: ||Tertiary, Cretaceous (Eocene, Palaeocene, Santonian)|
|Rock Name: ||Antrim Lava Group, Interbasaltic Formation, Lower Basalt Formation, Ulster White Limestone Formation|
|Rock Type: ||Basalt, Dolerite, Porcellanite|
|Minerals: ||Anatase, Bytownite, Chamosite, Chlorite, Cordierite, Corundum, Cristoballite, Gibbsite, Halloysite, Hematite, Hercynite, Hypersthene, Ilmenite, Maghemite, Magnetite, Metahalloysite, Montmorillonite, Mullite, Olivine, Picotite, Plagioclase, Pseudobrookite,|
|Other interest: ||plug, Contact, Intrusion, laterite, A Neolithic quarry and stone axe factory site. 19th century chalk pits are also located on the site.|
Summary of site:
Tievebulliagh is nationally and internationally famous as the source of refined Neolithic stone axes manufactured from a rare and limited rock type created by unusual geological circumstances. Populations of Neolithic people established an axe factory here somewhere around 3,000 years ago and so prized were the axes that they were traded widely. Axes from Tievebulliagh, or the only other similar site, on Rathlin Island, have been found in Britain from the north of Scotland and the Outer Hebrides to Dorset and Kent on the south coast of England.
The geology of the area, 5 km west south west of Cushendall, has a foundation of ancient Dalradian metamorphic rocks, around 600 million years old, surmounted by the Cretaceous Ulster White Limestone Formation which is around 100 million years old. These limestones emerged from the sea at the end of the Cretaceous and were carved by erosion into a karst landscape. This surface was then buried, around 60 million years ago, by the explosive burst that created the Lower Basalts at the onset of over 5 million years, on and off, of volcanic activity. As the volcanoes and fissures became quiescent at the end of the first major phase of volcanicity, a zone of red-brown, lateritic soil, the Interbasaltic Bed, was formed by deep weathering of the surface of the Lower Basalts. Further eruptions followed creating the Upper Basalts and it was during this violent episode that the rocks seen on the east face of Tievebulliagh were formed.
At Tievebulliagh an inclined volcanic plug (the choked feeding pipe of a volcano) with a disc-like shape has cut through the Lower Basalts along a north/south line. This plug or sheet, inclined at 45 degrees to the east, forms the line of crags on the east side of the hill and the dolerite fill clings to the basalts along the cliff face, obscuring them. The outer 1 to 2 m of the plug are enriched with the mineral olivine and the Lower Basalt lavas alongside the plug are altered to a glassy rock for a distance of up to 8 m from the contact. The high degree of alteration of what were already high temperature rocks (over 1,000 degrees when they formed) gives some measure of the temperature and volume of searing molten rock passing through the vent on its way to the surface. The rock that was so highly valued by the Neolithic toolmakers is an isolated block, 8 by 1.7 m, of the Interbasaltic Bed that detached far up the vent at the top of the Lower Basalts and then slid and subsided down the vent wall through the molten dolerite to jam or settle at what is now the base level of the cliff, extending somewhat deeper where it is concealed by the upper scree slope. The laterite (lithomarge) has been transformed by the intense heat into a form of basalt called porcellanite, the original minerals changed into a new suite stable at the higher temperatures. The mineralogy of the porcellanite is described in record 535 (also Tievebulliagh). The porcellanite is an extremely tough rock capable of taking a keen edge and a high polish: unlike the commonly available flint it is not brittle and consequently appears to have been the ideal and preferred Neolithic material for shaping the axes employed in forest clearances.
This was the pioneer site for the intensive study of thermal metamorphism of the laterites of the Interbasaltic Bed, establishing the geological basis of the axe factory.
Over 10,000 axes of Antrim porcellanite are known, by far the largest number from an identified source so far proved in the British Isles. There is a rich collection of Tievebulliagh porcellanite artefacts in the collections of the Ulster Museum, some of them exquisite in form and texture.
This site is designated as an Area of Special Scientific Interest and its remoteness offers a high degree of protection. All evident artefacts have been removed over the years since its first identification in the 20th century. Porcellanite flakes still emerge from disturbance of grassed scree and there remains excellent research potential.